Technical Journal 09 Papers 135 - 149
Welcome to the ninth edition of the Atkins Technical Journal which features papers covering a wide range of technologies but with many common themes. A great example of this comes from our asset management work where our Highways and Transportation business is leading the way in advising clients on maintaining availability of highway networks, while the paper on Skynet 5 shows we are doing the same in our Defence, Aerospace and Communications business for satellites.
Innovation and thought leadership is evident in all the papers; we have transferred learning from our Aerospace teams to our Bridge teams to produce Fibre Reinforced Polymer bridge prototypes and we have led the global sustainability debate in diverse areas such as the implementation of electric vehicles, environmentally acceptable waste disposal techniques and biomass combined heat and power technologies. We are constantly extending and improving current industry practices across all that we do, informing the next generation of codes of practice. The papers here present examples from such diverse areas as the treatment of water run-off from highways to the fatigue of stranded cables under vibration.
I hope you enjoy the selection of technical papers included in this edition. This ninth Journal, and all previous editions, are available on our external website. We have introduced an email subscription alert service and if you wish to fnd out more, please visit: www.atkinsglobal.com/en/about-us/our-publications/technical-journals;
Chris Hendy Network Chair for Bridge Engineering Chair of H&T Technical Leaders’ Group
Atkins
Technical Journal 9 Papers 135 - 149
Drainage 135 Adapting assessment of road drainage to the Water Framework Directive 05 136 Tram drainage 15
Environment & Sustainability 137 Winter Haven Chain of Lakes: conservation and restoration targets for sustainable and innovative watershed planning 25 138 Landflls vs. incinerators: identifcation and comparison of the hazards posed by the toxic emissions associated with the disposal of municipal solid waste in Puerto Rico 37 139 Powering ahead: how to put electric vehicles on Scotland’s roads 51
140 The feasibility of biomass CHP as an energy and CO2 source for commercial glasshouses 61
Highway Network Management 141 Performance management framework for managing agent contractors 81 142 The Area 6 MAC approach to planning & programme management 91
Structural Dynamics 143 Determination of minimum vessel wall thickness under design condition loadings 101 144 Innovative optical measurement technique for cable deformation analysis 113
Structures 145 Optimised design of an FRP bridge using aerospace technology for ultra-lightweight solutions 121 146 Reconstruction of drystone retaining walls using composite reinforced soil structures 127 147 Vehicle-induced vibration of a concrete flled steel tube arch bridge 135
Systems Engineering 148 A SPAR modelling platform case study: Skynet 5 143 149 How can CBTC improve the service on a saturated railway system? 149
Contents
3 4 135
Ian Dalgleish Adapting assessment of Environmental Scientist Water & Environment road drainage to the Water Atkins Framework Directive
Abstract
Mark Blackmore Atkins has accumulated a wealth of practical experience of investigating the Principal Consultant impacts to the water environment from highways and road run-off. Since Water & Environment 2009 we have been applying the guidance for this area using part of the Design Manual for Roads and Bridges (HD 45/09) and its associated water Atkins quality model Highways Agency Water Risk Assessment Tool (HAWRAT). This was developed by the Highways Agency (HA) with the Environment Agency (EA) to meet the European Water Framework Directive (WFD) requirements for discharges from highways. Using this WFD compliant approach to assessing the impacts of run-off on surface waters, Atkins has gained practical experience of refning feld data for use in HAWRAT and prioritising possible mitigation actions (or measures) on a scheme, catchment or even country scale. However, there are still ambiguities with obtaining and applying treatment effciencies for the potential mitigation measures. These are important as the selection of particular solutions (e.g. swales, balancing ponds and wetlands) has a fnancial impact on the scheme design and an absolute impact on water quality. In this paper the changes in the DMRB approach to treatment of road drainage driven by the WFD are considered and the process to reduce the impacts on the wider water environment is explored.
Introduction
The planning and construction of Not only is there a requirement for new and modifed road schemes the Highways Agency not knowingly have the potential to impact on to pollute the environment, but now surface waters, groundwater and with the WFD and associated River food risk. In most cases there would Basin Management Plans (RBMP) be a planning requirement for an prevention of diffuse pollution assessment to be completed for from highways may become a key highway new build or improvement component of reducing impacts from schemes. For water, this assessment catchment-wide activities on our has been guided by best practice environment. and transposed into methodology As long ago as May, 2004, the in the Design Manual for Roads Highways Agency identifed 5 key and Bridges (DMRB) European issues relating to implementation legislation in the form of the Water of the WFD that affect the water Framework Directive (WFD)1, adopted environment. These included: in 2000, has been incorporated (November, 2009) into the DMRB as • The identifcation of key 2 a new Standard HD 45/09 . This has pollutants and concentration Drainage changed the method of assessment, levels in highway run-off; requirement for data collection and • The impact of known soluble the type of data collected to assess highway run-off on the ecology of the impact of road development on receiving waters; the water environment.
5 • The accumulation and dispersal of requirement for assessing the existing suspended sediments in waters; The background of the baseline condition for comparison. If the existing condition is not • The fate of pollutants found in WFD accurately assessed there could be the unsaturated zone; The WFD is European legislation an issue with over-compensation or • The performance effcacy of that was enacted to deliver a better under-compensation with mitigation. different pollution treatment water environment and a consistent Under-compensation could systems. approach to water management have a detrimental effect on the environment and over-compensation The frst three issues have now been across European Community member could be questioned in terms of value addressed in part through research states. It requires planning on a long for money. leading to the new Standard and term basis, outlining a process to guidance contained in HD 45/09. be implemented over three 6 year Meeting good ecological planning cycles up to 2027. As such There is ongoing research by Water status Research Council (WRc) into the its national adoption is undertaken fourth issue. As yet, it has not been over a period of tens of years, long Prior to implementation of the WFD, possible to address the ffth issue. enough to plan large-scale changes. the EA used River Ecosystem targets It is a single, but large and complex and assessed compliance based on Ian Barker, Head of Water at the piece of legislation from which biological and chemical monitoring Environment Agency has reported the following key points can be results. Through the WFD there has “Rivers in England and Wales are at extracted, relevant to implementation been a requirement to consider more their healthiest for over a century. in the UK, with particular regard to parameters, particularly for biology, But there are still big challenges. highways assessment. which contribute to an ecological Pollution from felds and roads needs and a chemical classifcation for each 1. There is a requirement to to be tackled and the Environment body of water. The EA currently has prevent any deterioration of Agency has plans to revitalise 9,500 maps available on its website that water quality; miles of waterways between now show the existing and proposed 3 and 2015.” 2. There is a requirement to meet (2015) ecological objective of main This paper focuses solely on refning “good” ecological status; watercourses in the UK. For most Atkins’ method of assessment of 3. There is a requirement for rivers there will be a requirement to water quality and surface water, catchment scale management. meet “good” ecological status by although HD 45/09 covers the wider 2015.5 aspects of groundwater and food These three points will be dealt with below. The immediate impact of a risk too. Consideration will be made requirement to meet an objective of: No deterioration of “good” ecological status on the assessment method provided in HD • The background to the WFD; Taking the recent M25 DBFO 45/09, is that this objective should be contract4 as an example, it • The key technical points of the used for the majority of watercourses is common to fnd there is a current assessment measure (HD which within HD 45/09 would requirement, in contract, for no 45/09); now be assessed to have a “high” worsening of effect with regard to importance. • Issues relating to assessment of the water environment. In real terms, mitigation. at the time of planning there was a Determining the importance of Where appropriate, examples general trend for increasing traffc a water feature is part of a three are used giving experience of the in the National Traffc Forecasts and step method used to determine application of the new guidance. consequently the likelihood of higher the signifcance of effects of This includes work that Atkins has pollution loading in the future. If a road scheme on the water undertaken on the M25 Design this holds true for future traffc environment. The other two steps Build Finance and Operate (DBFO) forecasting and if contracts require include determining the magnitude widening scheme, A21 planning “no worsening of effects”, it could of impact of a scheme and then applications and Priority Outfall be argued that nearly every new fnally combining steps 1 and 2 to studies in the East of England and road scheme and most improvement provide a signifcance of effect. A across Wales. schemes will be required to include higher importance is likely to result mitigation, as without it there in greater signifcance of effects, would be deterioration in the quality most often adverse for a new of road run-off (or worsening of development. Taking this a step effect). Implicitly this also suggests a further, given that most watercourses
6 135 Adapting assessment of road drainage to the Water Framework Directive
will now have a high importance (previously many watercourses may have been medium or low), a relatively lower magnitude of impact (due to road design) will now lead to adverse signifcance of effects. If the designer were to submit the same road scheme plan post HD 45/09 (that had been submitted before) it is likely there will be a greater requirement for mitigation overall and fewer watercourses that require no mitigation. Catchment Scale The DMRB through HD 45/09 continues the processes developed in its predecessor, HA 216/06, in applying the WFD to assessment of road drainage. These processes can be applied in a strategic way by investigating drainage from entire Figure 1. Review of completed road scheme outfall mitigation on Thorney Bypass A47. road networks, thus considering the This would now be required to meet “Good” WFD standards. The reed lined ditch catchment scale effects of road run- seen in the background (behind access track) is one example of a treatment type not off. covered in HD 45/09 During the time that the DMRB HA Area 6 in the East of England. “real” impact of highway run-off on guidance was drafted, the WFD A typical method of approaching a local and catchment scale which required the production of River catchment assessment is to use will direct further mitigation. Basin Management Plans (RBMP) readily available road geometry data to consider, among other things, collected by local highways teams to Key developments of “catchment” effects of development. determine high and low catchment Each of the 10 regions of England points. Once these catchments are HD 45/09 published RBMPs in December 2009.6 determined a high level assessment As an annex to these plans there can be undertaken using the Key technical developments in the is an Annex C entitled “actions to principles of HD 45/09 to determine new HD 45/09 assessment include: deliver objectives”. For most regions, if a catchment is likely to fail to meet • A Memorandum of within these actions or “programme current water quality standards. Understanding (MoU) developed of measures” there is a requirement All catchments that pass can be with the EA; to improve discharge from highways. scoped out. All catchments with the In a few areas it is likely that potential to fail can then be further • The method becoming a Standard particular action will be taken on assessed using the HAWRAT tool (requiring Departures from existing road networks to improve to provide a prioritisation of most Standard in some instances where poor discharge quality. As there is a polluting outfalls in a catchment or mandatory requirements cannot deadline of 2015 for watercourses region. This information is shown as reasonably be met); to meet good ecological status the a layer within the Welsh Assembly • Development of the Highways HA and Welsh Government (WG) Drainage Data Management System Agency Water Risk Assessment have been undertaking outfall (WADDMS) and the Highways Tool (HAWRAT). prioritisation studies to consider Agency Drainage Data Management which outfalls on the highway One of the key benefts of HD System (HADDMS) databases Drainage 45/09 is that great effort has network are the worst performing available over the internet for been made to undertake relevant and which outfalls could be improved highways users to interrogate. to help meet these standards. research applicable to an assessment It is likely that this information methodology alongside the EA who Atkins has had key involvement, will be used at a high level for the were involved from the beginning. leading the priority outfall assessment Highways Agency to agree with the This process has culminated in a scheme across Wales and within Environment Agency on what is the refreshed MoU between the HA 7 and the EA.7 The MoU not only dilution calculations and the mass fuoranthene, again copper and zinc covers technical water information, balance contribution of heavy metals are taken as representative of the but information exchange. Indeed, from routine road run-off. This was group of deposited pollutants and in although there may be greater assessed against an Environmental the majority of cases will be used as requirement for scrutiny on highway Quality Standard (EQS) based upon the “critical” contaminant requiring schemes, in the long term, as the limits of concentration found in mitigation. In some instances RSTs process for information exchange the Freshwater Fish Directive8 for will be exceeded where AACT are not disseminates around the EA and dissolved copper and total zinc and in this case the HA still expects practice comes into line as agreed, (the two metals most commonly provision of mitigation. the MoU should aid consultants in associated with road drainage Historically mitigation has included more effcient assessment (with less pollution). Any breach of the a wide range of measures including cost in terms of data requests) of standards is deemed a failure. bypass separators, catch pits, environmental impact. The new assessment for chronic soakaways, planted ditches and A key component of Atkins’ work on pollution in the DMRB uses Annual ponds. These mitigation measures, improvements to the A21 widening Average Concentrations (AACT) which are considered in HA103/06, schemes has been consultation with taken from the WFD, again for could be considered to provide a the Environment Agency and Natural copper and zinc. HAWRAT estimates pollutant removal treatment effcacy. England. Most recently this has led to the annual concentrations of run- The effcacy of mitigation measures extended investigations of the impact off from the road surface based on for routine run-off pollution is of the scheme on groundwater via expected rainfall events and uses this applied to HAWRAT by means of monitoring highlighted in initial to estimate the impact on average a percentage fow or pollutant scoping studies. This additional concentrations in the watercourse. reduction factor. The application of monitoring is providing a solution Although the levels of zinc and mitigation with reference to spillage to the scheme that will not restrict dissolved copper are more stringent risk has to be applied via a spillage the groundwater supply to a in the new guidance, which may reduction factor related to Table 8.1 groundwater dependant SSSI. lead to a requirement for more of HD 45/09, built into a separate mitigation, the use of annual average worksheet within HAWRAT. This As HD 45/09 has been produced concentrations is less onerous for removal effcacy is also dependant on as a “Standard” (rather than an road outfalls. As road discharges are the proportion of catchment run- “assessment” or “advice”) there are not continuous discharges any short off the mitigation is treating. There now sections of the document that term impact can be offset during are a number of measures that are have to be met or would require a drier periods at most locations with not considered (in terms of effcacy) Departure obtained through the HA, regard to AACT. In addition to the within HA103/06. Within the recent if the defned mandatory contents of use of AACT to determine chronic M25 widening improvements Atkins the standard are not adhered to. The (or long term) pollution a new liaised with the Highways Agency key standards include: measure was developed to consider and Environment Agency to agree a • No new discharge will be allowed acute (short term) pollution. This treatment effcacy for a Downstream to any area in Source Protection measure better refects the nature Defender vortex separator for Zone 1 (SPZ1) without proving of road pollution often being in improving removal rates of total zinc there would be no effect to “fashy” loads, which are thought and sediment. groundwater and source of more generally to build up and be The fnal component of HAWRAT abstraction (for example there washed off in a “frst fush” effect. includes a consideration for the are numerous discharges to SPZ1 Consideration was made as to how ecological effects of sediment in around the M25 and where this short term pollution from roads the water environment. As early possible these were removed might affect organisms through as 1998 the importance of the during the recent widening empirical studies.9 environmental effects of sediment scheme); Thresholds developed to consider were documented within guidance,10 • Spillage risk from existing outfalls short term pollution are known however until the new Standard, no must not be increased. as Run-off Specifc Thresholds defnitive test had been produced (RSTs). The RSTs are based in part for highway assessment. Within the The development of HAWRAT is a upon consideration of Probable WFD there is an increased onus on key feature of HD 45/09. Prior to its Effect Levels (PEL) on ecology from not only assessment of sediment and development the methods that had sediment bound pollution. Although its effects on ecology, but also on been used to assess chronic pollution RSTs consider other pollutants such its effects on morphology of bodies from road discharge included simple as cadmium, total PAH, pyrene and of water. Within the DMRB a model
8 135 Adapting assessment of road drainage to the Water Framework Directive
has been developed considering of 1 in 17, signifcantly reducing the highway widening may physically sediment input from a highway sediment loading predictions. One restrict groundwater supply to a catchment area and the receiving possible solution to assessment of nearby designated conservation site, surface water. However, this only watercourse gradient could be to highlights that there are still potential considers the effect of sediment on consider the use of topographical impacts on the water environment ecology by estimating sediment build survey data and site photographs not directly covered by HAWRAT up, not the effect on morphology. to estimate gradient. On a number and other associated tests within HD The consideration of sediment within of sites investigated by Atkins, 45/09. HAWRAT is important enough that interpolation of topographical data As with its predecessor guidance, HD failure of this test alone would lead has compared favourably with feld 45/09 considers the impact of routine to minor adverse magnitudes of investigations. run-off from outfalls not necessarily impact on the water environment. just as an individual outfall but within The model considers the extent of a watercourse reach which respects sediment deposition and whether the whole catchment management the watercourse into which there driver of the WFD. It also guides the is discharge could be considered user to consider cumulative sediment “accumulating” (a model specifc impacts. The rules for aggregating term referring to the propensity of discharges differ slightly between sediment to gather at an outfall due routine run-off and sediment. For to, for example, low fows or gentle both assessments consideration gradients). needs to be made for each outfall There is little refned information individually as well as their combined about sediment loading and so effect. A combined assessment at present the extent of sediment should occur for discharges within accumulation is estimated and a 1km section of a watercourse for controlled by an arbitrary level set soluble run-off and within 100m by the HA. Through practice this is for sediment. Preference is given likely to be refned. With regard to to consideration of higher quality, the sediment test, the current default more ecologically diverse (and usually parameters (post HD 45/09) for the larger) watercourses downstream test are conservative and include: Figure 2. Measurement of river bed rather than the immediate receptor profle near Port Talbot, Wales leading of highway drainage which in many • A 1m wide watercourse; to refnement of gradient effecting sediment deposition in HAWRAT cases is often a small roadside or • A 1 in 1000 long slope agricultural ditch. watercourse gradient; Within HAWRAT there is also To reduce the need to repeat • A Roughness coeffcient - a consideration to account for environmental baseline assessments Manning’s “n” of 0.07 (very sensitivity of designated sites (i.e. the HA is beginning to record weedy, heavy timber). such as Sites of Special Scientifc previous assessments for stretches Interest, Special Protection Area of road subject to new development Initial evidence is that many or Special Area of Conservation). schemes on the Highways Agency discharges fail the sediment tests The threshold levels for failing Drainage Data Management System and, if so, HD 45/09 directs the user RSTs are halved (internally within (HADDMS).11 It is now a requirement to undertake a feld survey to obtain the model) if there is a designated of all schemes to submit electronic data that can be substituted for the site within close proximity, making versions of tests undertaken for the default settings. Initial indications, the test more onerous. Of course, water environment assessment to the from Atkins’ feldwork on the relevant information provided to HA. A21 project and in Wales are that experienced practitioners for the receiving watercourses generally have environmental assessment could “better” sediment accumulating
show that there would either be no Drainage conditions than proposed by effect or no connectivity with such a HAWRAT, as the default settings are designated site, potentially reducing very conservative. As an example the requirement for mitigation. recent measurements undertaken Conversely, in the example of in a watercourse in Wales, see discharge from the A21 proposed Figure 2, returned a gradient highway widening project, where
9 Planning for %Reduction: Inlet to Outlet Road Site/Treatment Devies Intial Second Total mitigation to meet the form of form of system requirements of the treatment treatment treatment Metals 15 11 24 Bypass oil separator/ WFD A34 surface fow wetland/wet PAHs -1 99 99 balancing pond TSS 37 73 83 The fnal key point of discussion regarding meeting the more Metals 7 7 ambitious standards of the WFD A34 Filter Drain PAHs 52 52 within the highway assessment TSS 38 38 method is consideration of Metals -7 41 30 Oil trap manhole/ mitigation. M4 PAHs -30 -26 sedimentation tank There has been advancement in the TSS -19 43 33 guidance of the DMRB with respect Metals 19 35 48 to identifying various treatment Full retention oil separator/ M40 PAHs 13 50 57 effcacies (i.e. percentage removal) wet balancing pond for soluble pollutants for different TSS -9 62 58 treatment methods in routine run-off Metals 27 39 56 Bypass oil separator/dry A417 PAHs 4 16 22 between 2000-2012. These have balancing pond included empirical studies undertaken TSS 56 -37 40 by the HA and EA, published in 2003.12 13 Further research was then Table 1. Source Table 3.2 HA 103/06 that summarises water treatment information to undertaken between 2002 and 2009 be used in assessment of highway impact on the water environment (with the HA and EA partnering existing HA treatment datasets15 to be applied to each road. Roads with WRc) that considered typical documented in the DMRB as will be required to include two pollutant loading within road run-off summarised in Table 1. or (if discharging to a sensitive alongside toxicity of substances to watercourse) even three levels of ecology. This research has led toward However, among practitioners the treatment as normal. Discharge to the consideration of a “treatment use of the data provided by the EA ground will be a preference. One train” approach to mitigation of and HA studies is regarded as not thing is clear; the use of SUDS or highway run-off, which involves more truly representative of actual effcacy vegetative treatment systems is likely than one type of treatment in series rates. For example, consideration to become more prominent within to provide better mitigation. This of 7% removal effcacy for flter development schemes associated type of approach is described further drains as shown in Table 3.2 of HA with the progression of the Flood and in the SUDS Manual.14 103/06, compared against 80-90% Water Management Act (FWMA).18 removal effcacy for flter drains as As part of the process of winning noted in CIRIA c60916 shows the Without clear guidance on the the tender for the M25 widening widespread difference and that effcacy of vegetative treatment in 2006 a “treatment train” was there is clear evidence that reporting systems one way of improving proposed linking greater treatment of treatment effciencies could be accuracy of assessment of the with greater areas of pollution and refned. Unfortunately neither HD potential of treatment measures is more sensitive water receptors. 45/09 nor the Sustainable Drainage through a written “departure” to the This included a combination of System Manual17 published in 2007 HA. Bespoke mitigation such as straw bypass interceptors, “downstream improved or updated understanding bales provided in agricultural areas defenders” and treatment ponds of treatment effciencies. (and shown in Figure 3) will provide to protect the most sensitive water levels of mitigation not addressed in receptors. The draft National Standards for HD 45/09. So far the approach of the SUDS were released in December The application of suggested Highways Agency via the DMRB has 201118 and are applicable to local pollutant removal effcacy rates for been to consider mitigation through authority roads, although not directly particular mitigation methods from vegetative treatment systems to applicable to highways. These more recent best practice manuals some extent, but there is also the standards do not provide improved such as CIRIA c609 were investigated potential for proprietary systems treatment effcacy estimates. but were found to be very variable to replicate natural drainage and However, there is a requirement for derived from very small datasets. This provide treatment. the number of treatment methods led to the dependence on already 10 135 Adapting assessment of road drainage to the Water Framework Directive
Within the M25 widening scheme supplier tests are required to ensure use of telemetry was incorporated a “departure” was submitted Atkins provides the best solution into the M25 design providing and approved by the HA to to our clients. This will ensure the remote alarms for oil in bypass use a Downstream Defender most appropriate treatment type separators and CCTV to monitor hydrodynamic19 separator, operating on Atkins’ future commissions for a outfalls. This ensures maintenance to remove sediment loading and range of different types of treatment. when required and a quick response sediment bound pollutants as In turn this will help Atkins improve to serious spillage risk. There is also part of the treatment system. its design beyond the guidance guidance given within the DMRB that Understanding of the processes currently existing in the DMRB. stipulates that mitigation be applied operating for this treatment should serious spillage risk endanger As part of the HD 45/09 assessment mechanism, combined with a protected site or protected process there is also consideration of laboratory testing presented by species. Here, consultation with the reduction of serious spillage risk. See the manufacturer (which had been appropriate people in environmental Table 2. undertaken prior to the project protection agencies is important. starting), allowed the drainage Through experience of working and environment teams to adopt Optimum risk System Reduction Factor with a planning authority on A40 a suggested 15% removal effcacy R (%) F improvements in Wales the proximity rate for sediment bound metals. Our Passive systems of particularly sensitive water, the judgement was required to consider Cleddau River, (the type that is operational fow rates that were Filter Drain 0.6 (40%) recognised by the ethos of the WFD) outside of the test data provided Grassed Ditch/Swale 0.6 (40%) with evidence of otter holts, was by the supplier. Our understanding Pond 0.5 (50%) enough to convince the authorities of the processes operating within wetland 0.5 (50%) to provide spillage risk mitigation this particular system led us to Infltration basin 0.6 (40%) even though the risk of occurrence propose that no removal of dissolved Sediment Trap 0.6 (40%) was very small and well outside the metals could be expected from this immediate requirements of the HD mitigation method which better Vegetated Ditch 0.7 (30%) 45/09. Given the clear direction of refected the true benefts of the Active Systems the WFD to protect ecology in water mitigation on the type of pollutants Penstock/valve 0.4 (60%) and using expert advice, our designs requiring assessment. Notched Weir 0.6 (40%) should practically consider the types Other Systems of ecology we are trying to protect Oil Separator 0.5 (50%) and whether mitigation measures in addition to those required by Table 2. Spillage risk reduction factors taken from HD 45/09 Table 8.1 the DMRB could best satisfy client requirements. The method in HD 45/09 to assess HD 45/09, as infuenced by the WFD, spillage risk uses measures from requires more emphasis on mitigation the road design and data on traffc and there may be more cases where density and make up to determine more than one stage of treatment the likelihood of a serious spillage will be required. Previously, under HA event happening. This is measured in 216/0620 the designer could use a the number of years, or return period referenced method in HA 103/06 to of an event. Again professional determine a required area of planting judgement needs to be applied to in a balancing/hybrid pond that was determine the value and effect of designed to completely treat (given Figure 3. Use of a straw bale (in rear mitigation. Using the methodology enough planting area) any polluting of channel) to flter water quality. No in HD 45/09, a reduction in spillage situation. guidance on treatment effcacy exists risk of 70% could be achieved by for similar methods of water quality Until HA 103/06 is updated and proposing the design of a vegetated Drainage treatment ditch. However, the performance of the HA provide further guidance this system for some pollutants such on treatment effciencies, there will An understanding of the key as milk could be questioned. There is be a need for designers to work pollutants that may impact the water also scope for using methods outside alongside manufacturers and apply environment combined with the the guidance of HD 45/09 to improve best practice guidance to show the physical treatment processes involved mitigation of serious spillage risk. The benefts and effciencies of treatment and greater information from measures to meet WFD standards. 11 Where vegetative treatment systems are considered in scheme design, Summary in addition to guidance within the DMRB (HA103/06), there will also The application of the WFD be a need to obtain and apply through relevant guidance has cross sector research information required highway engineers and on mitigation effcacy rates and environmental teams to consider best practice for operation. The catchment wide, ecological effects of requirement for this information highway run-off including sediment will be likely to increase with the discharge and compliance with a greater requirements for use of broader range of new water quality SUDS following the FWMA, being standards that refect the current applicable to both local authorities legal framework. and the Highways Agency. Although the current DMRB goes a In addition to the planning for long way to address the requirements mitigation a method to respond to of the WFD, there are still areas pollution incidents and to maintain that can be improved in future pollution treatment features should iterations. A better understanding be a standard provision with Atkins of the infuence of sediments and designed road schemes. At present the need to study the physical there is no requirement within HD changes to watercourses along with 45/09 to provide either a method effectiveness of mitigation are all for maintenance or a method for areas that will need to be addressed response to a pollution incident. in the near future. However, within the design of In considering how to meet the the M25 drainage scheme the standards, Atkins will be looking incorporation of alarms (within for opportunities to provide better bypass separators), CCTV and a treatment solutions for highways central management system for discharges which will allow new maintenance all added value to development to enhance our water providing a quick response to environment rather than impact pollution incidents should they occur. upon it. At present the existing An important consideration for driver for improvement of the effective application of treatment water environment has been led systems includes provision of by the Highways Agency, highways adequate maintenance plans and authorities, HD 45/09 and the Priority consideration of maintenance within Outfall Assessment programme. the design and consultation process. However, where urban run-off Historically drainage systems have from roads may be shown to be suffered a lack of maintenance contributing to failure of WFD sample in some regions and resources to points, there may be a driver through improve maintenance will continue River Basin Management Plans for to be stretched in the near future. further improvement of discharge Continued negotiation with the from our road network. Environment Agency, Internal Drainage Boards, local authorities and other interested parties will ensure access to mitigation features will not hinder the effectiveness of treatment measures.
12 135 Adapting assessment of road drainage to the Water Framework Directive
References
1. Water Framework Directive 2000/60/EC. 2. HD 45/09 Road Drainage and the Water Environment DMRB, Volume 11 Section 3 Part 10. 3. BBC 31/12/2010 http://www.bbc.co.uk/news/uk-england-12098028. 4. Schedule 23 2.1 (3) b M25 contract. 5. Environment Agency WFD River Classifcation maps http://maps.environment-agency.gov.uk/wiyby/ wiybyController?topic=wfd_rivers&layerGroups=default&lang=_e&ep=map&scale=3&x=456769.4583333337&y= 302349.6249999998#x=527956&y=386044&lg=1,7,8,9,5,6,&scale=1. 6. Final RBMP http://www.environment-agency.gov.uk/research/planning/33106.aspx. 7. Memorandum of Understanding between the Environment Agency and the Highways Agency http://www.ha-partnernet.org.uk/portal/server.pt/community/memorandum_of_understanding/717. 8. The EC Freshwater Fish Directive (2006/44/EC). 9. Johnson, I and Crabtree RW, 2007, Effects of soluble pollutants on the Ecology of receiving waters, WRc Plc, Report No. UC 7486/1, UK Highways Agency. 10. DMRB Vol 11 Section 3 Part 10 3.14-3.16. 11. HADDMS http://www.haddms.co.uk/. 12. HA 103/06 Table 3.2 DMRB Volume 4 Section 2 Part1. 13. The Long term monitoring of pollution from Highway Run off: Final Report R&D technical report, P2-038/TR1 Moy, F, Crabtree RW and Simms, T. 14. The SUDS manual c697, CIRIA, 2007, London. 15. Sustainable Drainage Systems. Hydraulic, Structural and water quality advice, C609, London, 2004 CIRIA 16. The Flood and Water Management Act (c29) April 2010. 17. The SUDS manual c697, CIRIA, 2007, London. 18. The Flood and Water Management Act (c29) April 2010. 19. Downstream Defender http://mx1.hydro-intl.com/stormwater/downstream.php. 20. HA216/06 Road drainage and the water environment, 2006, DMRB superseded November 2009. Drainage
13 14 Drainage 15
136 Drain Box in position Truck Drain Box Truck
Figure 1. Figure Modern of a similar style products used and good practice being are is being developed on the second generation of UK tram systems and multi-million pound in the recent and upgrade of the refurbishment Some examples Blackpool Tramway. used recently of drainage products at Fleetwood below, shown are City Centre ), Metrolink 2 (Figure 3) and Dublin LUAS (Figure renewals ). 4 (Figure shows an extract from an 1 shows an extract from Figure Edgar Allen catalogue c.1920, which clearly shows the two main elements of point drains and transverse drains.
used and are not discussed further used and are drainage Interesting in this paper. to the techniques to relearn relate rails are when groove urban realm, usually to be found, either on a section of highway or in segregated sometimes referred pedestrian areas, to as a trambahn, or on carriageways fully integrated with vehicular traffc, with the tram given priority at traffc lights and junctions. no are There new drainage techniques to be learned; of those only reapplication known to earlier drainage engineers. Introduction Introduction Atkins was appointed to work on the drainage designs for improvements Phase to the Manchester Metrolink 1 & 2 works and has been part of the Engineering Support Services for the GMPTE (now Transport Team Manchester – referred for Greater on). This here to as TfGM from commission was let to draw upon the drainage experience of the author, who had also worked on Nottingham (NET Line 1) and was Transit Express the principal drainage designer for the latest upgrade to the Blackpool These & Fleetwood Tramway. second generation tram systems had the same drainage problems had to solve as their forerunners Some of the tracks will overcome. be on former railway lines, so similar drainage techniques to Network Rail for ballasted track can be standards Tram drainage drainage Tram Abstract the 2010 being a century, than have been in use in the UK for more Trams frst electric trams - one of the very famous of Blackpool’s 125th anniversary frst in the UK. in the world and the followed Blackpool’s Many other cities closed most of these were of the 20th century, the middle example, but from in or buried under tarmac. However, down and the tracks ripped up for scrap Bury opened to passengers. The Metrolink Manchester’s April 1992, Greater by the Eccles line in July the frst to open, followed and Altrincham lines were 2000. planning, tram systems, Many other cities in the UK now have, or are Dublin LUAS in the Republic of Ireland. including Nottingham, Edinburgh, plus second generation for this This paper sets down the drainage requirements of these tram experiences on a number of UK trams, based on the author’s systems. John Wotherspoon Engineer Group Highways & Transportation Atkins outlet to cross drains under the track, • Exceptionally increase to similar to the pipework in the right 100m hand image. • For roads steeper than 2%, Little design advice is currently review the above criteria and available as to what can be perhaps allow greater spacing considered good practice. The most authoritative guidance is • Outlet orientation vertical given by the Offce of the Rail leaving the drainage unit, Regulator (ORR) document “Railway with minimum diameter Safety Publication 2, Guidance on 75mm tramways, November 2006”. Clause • Point drainage units on 119 states, “Grooved rails should Figure 2. shared running have suitable drainage provided at appropriate intervals and locations • Point or transverse drainage (e.g. areas of ponding, bottom of units if segregated gradients), and when laid in the • Slot at least 20mm wide by highway, connected to surface 150mm long water drainage systems. The drains should be capable of being easily • Slot smooth edged and cleaned to allow removal of sand chamfered and other debris. The provision of • An appropriately sized drainage slots should not render the silt trap (perhaps a road rail incapable of providing suffcient gully) should be sited at or support or guidance for trams. Note: downstream of the groove The effect of the presence of rail drains, to allow easy and grooves on highway drainage may be regular maintenance signifcant”. • Owners and operators should Thus the two aspects to be dealt with agree funding of adequate Figure 3. are spacing, what is “appropriate”, maintenance of drainage and maintenance, how should a features. feature be “easily cleaned”? These key lessons were During 2009, as part of the Metrolink reinforced by a tramway Asset Phase 3 implementation, a review Manager to emphasise: of these issues was undertaken by Atkins on behalf of GMPTE. The • The the geometry of, elements of good design that and relations between, were thought to be important are the various road and summarised below, from the three track surfaces need to be points of view of a tramway drainage understood to defne the designer, the Asset Manager requirement for transverse Figure 4. for GMPTE and for Stagecoach drainage as opposed to a Metrolink, which has operated the point drain on its own At Fleetwood, the existing track tram service and maintained the • Drainage is needed at the was drained using the Edgar Allen network since July 2007. bottom of a “valley” products from the 1920s or earlier. A replacement product for the point • Drainage is needed to protect drain was recommended by Atkins Elements considered ‘good any set of points at the to the contractor and this was practice’ bottom of a gradient adopted and can be seen on the The key points from a designer’s • Intermediate drainage is left of the three images above. The perspective are: needed on a gradient to choice was based on two of the key • Maximum spacing of groove catch detritus and prevent a elements developed as good practice, build up further downhill described in more detail below. In drains 60m for roads fatter particular, this product allowed for a than 2% • Careful specifcation of the 150mm groove length and a vertical 16 136 Tram drainage
It is clear that good practice is being Problems associated with tram four foot, shoulder, six foot developed, though guidelines are not drainage insuffciency are illustrated and cess profles to avoid defnitive. Products are still being by two Case Studies, “The effects of ponding. trialled and the effectiveness of these poor drainage on a tramway” and The key points from an operator/ assessed. Manufacturers producing “Diffculty of maintenance affecting maintainer perspective are: well used products include ACO, the performance of tramway Hauraton, Riecken, Hanning & Kahl operation”. These illustrate how • Groove slot machined and and Birco. An area currently being elements of the developing concepts large/wide enough to cope addressed by work in Fleetwood and of good practice in UK tramways with the odd leaf or other Dublin relates to the better cutting were put in place to improve detritus. Narrow short slots of the slots within the grooved the future maintainability of the no good rail. Over the last 20 years, this was Manchester Metrolink system, using • Good drainage in front of all improved from small, poorly cut existing maintenance operations to facing points grooves (Figure 5); to longer slots bring about necessary changes. • No boxes on curves – risk of drilled and cut, though still with rail fracture unintended irregularities to catch Case Study 1 - The debris (Figure 6); to a slot milled in • Drainage solution should the rail, producing an even slot with effects of poor drainage have the necessary volume/ no irregularities (Figure 7). on a tramway capacity within the point or transverse drain such Introduction that anything greater than a shower does not cause it A major interchange between bus, to back up or require it to Park & Ride and Metrolink was be cleaned out every week constructed at Shudehill in 2002, because of sludge build up just a 5 minute walk from the within. Ideally a good clean Arndale Centre and located next to at start of autumn and again The Printworks, a state of the art in the spring with perhaps entertainment complex located in the attention during winter heart of Manchester City Centre with as required should be the a range of restaurants, bars and clubs frequency that should be alongside a cinema and gym. This aimed for Figure 5. valuable additional asset to GMPTE was a retroft to the existing City • Access to the drainage box Centre tram link joining Victoria and is easy i.e. easy removal of Piccadilly Main Line stations, which the lid, and large enough had opened ten years previously in such that it can be cleaned, 1992. ideally by mechanised means (gully sucker) to speed up the The problem maintenance process Three issues combined to make the • One size/type does not ft trackslab beneath the rails subside. all; the appropriate drainage First, the track was level; secondly, solution must be put in a signifcant catchment of tram place dependant on the Figure 6. and highway drainage fell towards location and the objective, this fat area; and thirdly, the block be it groove or switch tip paving between the platforms proved drainage, point or transverse not robust enough to shed all this drainage, segregated or non- water to the drainage channels and
segregated, traffcked or non- prevent water percolating through Drainage traffcked locations to the trackslab formation. Plate 1-1 (Figure 8) shows severe degradation • The ideal spacing depends on of the track and the surrounding circumstances at each groove surfaces. The trackslab had sunk drain location. in places, giving rise to uneven ride Figure 7. quality through the tramstop. This
17 failure had occurred in less than 8 years use of the new tramstop. The City Centre track had already been scheduled for entire renewal in 2009, so the opportunity was taken to investigate the problem thoroughly and propose a more robust solution. Plates 1-2 (Figure 9) and 1-3 (Figure 10) show how cores were taken of the existing trackslab. These led to the conclusion that the trackslab had failed to the extent that this would require total replacement. In addition, surveys were made of the catchments contributing surface water to the tramstop area. Drainage survey This was a simple visual survey of the area, assessing the position of existing road gullies, falls on the highways and tramway towards the Figure 8. Plate 1-1: Shudehill tramstop in Manchester, showing distressed tracks and tramstop and consideration of the surfacing highway drainage as it would have been prior to construction of the tramway. It was determined that Shudehill itself, several hundred metres of tramway and the tramstop itself all contributed surface water runoff, which congregated on the fat track area between the platforms. The tram movements and water led to failure of the block paving and generated sand and silt at ground level that blocked the linear drainage channels at the foot of the platform walls. This led to more water being retained in the tramstop area and the cycle of degradation continued. A study of As Built records demonstrated that adequate outfalls had been provided for the tramstop drainage, connecting to public combined sewers, but highway drainage on Shudehill had Figure 9. Plate 1-2: Ground investigation set up not been installed upstream of the tramway. The tramway created a Maintenance Improvements new pathway for the highway runoff, rather than the water continuing on Regular maintenance of the drainage Drainage to the formation was to gullies downstream of the route systems at the tramstop was not installed, the complete trackslab of the tramway, which would have considered a priority, leading to total was replaced and drainage of the happened pre Metrolink. failure of the linear drainage system. grooved rail was introduced. The Highway drainage maintenance was existing outfalls from the tramstop effective, but only of gullies already drainage were utilised, but additional installed. chambers and rodding points were included on the formation drainage,
18 136 Tram drainage
Figure 10. Plate 1-3: Recovery of cores Figure 12. Plate 1-5: … and at tramstop
replacement took place. The fnal improvement, not driven by the drainage needs, was the change of fnished surface between and around the new grooved rails, from conventionally laid block paving on a sand bed to exposed aggregate concrete. This choice, driven by experience of the failure of the surfacing at Shudehill and other locations also reduced substantially the likelihood of further drainage failures. The work was completed between April and November 2009, when the cross city tramway was closed for renewal, and it is anticipated that such a renewal will not be necessary again for perhaps another 20 years. It was also recommended that Manchester City Council should install additional gullies on Shudehill to catch more of Figure 11. Plate 1-4: Groove drainage upstream of Shudehill … the highway runoff before it reached to allow better maintenance facilities channels at the foot of the platform the tramway. for the future. As well as improving walls and rodding accesses. Though
the foundations for the trackslab, the it would have been preferable to Conclusions Drainage formation drains provided outfalls for increase the size of the channels, other drainage features introduced this proved impossible due to other Detailing of drainage features at at the tramstop. This included tramway infrastructure, namely initial design can have implications transverse drains as shown in plates communication and power ducting, on the life of transport infrastructure. 1-4 (Figure 11) and 1-5 (Figure 12), being located immediately below In the case of a tramway, it is a replacement of the linear drainage the channels. Thus like for like well known that rails wear out, particularly when sharp radii are 19 necessary to negotiate an existing city street layout. A need to renew the rails after a seventeen year life was not considered by Metrolink as unreasonable, but for the trackslab to have needed replacement as well can be considered an avoidable expense. Drainage failures were not the whole cause of the problem, but were certainly a contributing factor. Drainage improvements were introduced throughout the City Centre as part of the latest track renewals at locations identifed as problematic. Surface fnishes also changed, to improve the Manchester streetscape. A combination of these features is shown in Plate 1-6 (Figure 13), on Mosley Street, outside the City Art Gallery. The general area is shown as Plate 1-7 (Figure 14).
Figure 13. Plate 1-6: Groove drainage at Mosley Street Case Study 2 - Diffculty of maintenance affecting the performance of tramway operation
Introduction Metrolink carries nearly 20 million passengers every year, on three lines from Altrincham, Bury and Eccles into Manchester city centre. The Bury and Altrincham lines opened in 1992 and the Eccles line in 2000, creating a network of 37 stops covering 37 km (23 miles), served by a feet of 32 trams. By 2012 four new lines will nearly double the size of the tram network with 20 miles of new track and 27 new stops. The new lines Figure 14. Plate 1-7: …by the City Art Gallery will go to Oldham and Rochdale, drainage feature used could not be light shower of rain produces a Chorlton, Droylsden and Media readily maintained. This allowed signifcant fow of water in the City. At Media City, an existing track water from the road to the north grooves, which fows through the crossover on the Eccles line needs to of the Broadway tramstop to fow tramstop, collecting grit all the be brought into continuous use to down the rail grooves. Water that time, then discharges close to the allow the trams to access the new falls on the four foot (between the points mechanism which forms the stop. rails) and the six foot (between the crossover. The build up of grit and The problem tracks) fows along the groove until debris makes the operation of the the groove is full before it overfows points unreliable. Though drainage of the grooved to the roadway surface and fows rail had been introduced for the Plates 2-1 (Figure 15) to 2-4 (Figure to the kerbline to be collected by Eccles extension of Metrolink, the 16) illustrate the elements of the the highway drains. So, a relatively
20 136 Tram drainage
Figure 15. Plate 2-1: New Media City Figure 17. Plate 2-4: The points Figure 19. Plate 2-5: A light summer extension mechanism storm
Figure 16. Plate 2-2: Broadway stop, no Figure 18. Plate 2-3: The crossover Figure 20. Plate 2-6: The effect! groove drainage problem; the new track to Media To clean these, traffc management City under construction; the existing would be needed to run traffc Broadway tramstop, some 200m on the six foot. This can only be long with no groove drainage; the achieved during a night time closure crossover to be brought into constant of the lane. On a site inspection service; and the points mechanism to review the problem described, it adjacent to the grooved rail end. A was observed that most of the slots light summer storm of about ffteen and the boxes below appeared to minutes duration flled the groove be silted up, which suggested that and brought silt down to the points maintenance is problematic. This mechanism. The build up of debris is clearly not an easily maintained can be seen adjacent to the rail. feature. Figure 22. Plate 2-8: … extending for a kilometre This is illustrated above in Plates 2-5 (Figure 19) & 2-6 (Figure 20). Asset management Maintenance GMPTE has appointed an asset The road leading to Broadway manager to assist the processes as tramstop (South Langworthy Road) necessary. Day to day operation and has a wide six foot (the space maintenance are the responsibility of between the two tram tracks) the Operating Company, at the time marked as a ghost island with of writing Stagecoach Metrolink. The pedestrian refuges. It is a busy urban maintainer used its term contractor to inspect one of these features in
road, as can be seen in Plates 2-7 Drainage (Figure 21) and 2-8 (Figure 22). detail. First the sewer was surveyed Figure 21. Plate 2-7: Groove drainage and a 150mm connection was The groove rail point drains can be upstream of Broadway seen within the four foot (the space located, this being constructed as between the two rails of a single part of the sewer diversion works for tram track). The tops of these are the tram. Then, using an endoscope secured by two Allen screws and it was shown that the track drainage there is a 50mm horizontal outlet. box has a 50mm corrugated pipe on 21 its outlet. This pipe is approx 400mm in length and then connects into the 150mm plastic drainage pipe which then runs into the 525mm main sewer. The box lifted was on the cess rail (nearer the kerbline) and thus it can reasonably be assumed that the 150mm pipe spans the four foot. Improvements An improvement to the drainage was Figure 23. Plate 2-9: Groove drainage proposed. The style of groove drain upstream of Broadway box used for the Metrolink Eccles extension is no longer favoured, with an irregular cut in the groove and only a 50mm horizontal outlet for water and silt. A point drain product, shown in Plate 2-10 (Figure 24), had recently been installed in Fleetwood, Figure 27. Plate 2-13: Transverse drain as part of the Blackpool and Fleetwood Tramway Improvements, with a well machined slot and a 100mm vertical outlet. It was recommended that one or more of the existing groove drains on South Figure 24. Plate 2-10: … and at Langworthy Road should be changed Fleetwood for a more easily maintained feature. Other improvements recommended were for a variety of transverse track crossings by several manufacturers, to give the opportunity to trial products, regularly used in Europe, for the frst time in the UK. Within the tramstop area and in other areas of segregated tramways Figure 28. Plate 2-14: … details of running on grooved rails, it is more undertrack drain usual to use a transverse drain. Figure 25. Plate 2-11: Transverse drain in Two manufacturers’ products These recommendations were a traffcked area were recommended for trial at left with TfGM, who would have the Broadway tramstop. One of to determine an appropriate these is heavy duty and is claimed procurement strategy for the works by the manufacturer as suitable and assess the timing so that the for use in shared carriageway as works would complement the well as on segregated areas. This frst of the new Metrolink Phase 3 manufacturer also offers a lighter extensions opened, to Media City in duty ‘hinged’ product that is more September 2010. TfGM determined easily opened. Examples of these that it would be impractical to are shown in Plates 2-11 (Figure 25) replace any of the defective point & 2-12 (Figure 26), both of which drains on South Langworthy Road, have vertical 100mm outlets through but two transverse installations were the trackslab to a bend and outfall completed, a narrower one at the pipe below. An alternative, with a inbound end and a wider one at horizontal pipe beneath the track, the outbound end of the Broadway was also considered for trial (Plates tramstop area. These were both Figure 26. Plate 2-12: … and a 2-13 (Figure 27) & 2-14 (Figure 28)). supplied by the frst of the two segregated track manufacturers suggested by Atkins. 22 136 Tram drainage
These were photographed in August 2012 after they had been operating Conclusions for twelve months and were observed to be successful. The tram From this case study, specifc to service to Media City service operates tram drainage but of interest to as a shuttle during the daytime; every all drainage construction, the other tram terminating at Media elements of the need for designing City, the others travelling to Eccles, with maintenance in mind are well but in the evenings and at weekends illustrated. It is not easy to predict all trams run via Media City. Thus, how the future needs of a transport Figure 31. Plate 2-17: The points able to system will change. In this case, an the formerly unreliable points are function well now operating on a daily basis and operational feature (the crossover) are no longer a maintenance issue. will change from occasional to hourly The completed installations are use. The cost of failure of the asset illustrated below in Plates 2-15 to (the points) will be on the operational 2-18 (Figures 29-32). Atkins offered effciency of the tram system. the client an understanding of the Inbound trams would be unable to nature of the problem, a range of call at the highly prestigious Media options to provide a solution and City tramstop. As this will be the support for TfGM to procure this heart of the BBC, the ensuing poor based on knowledge of the various publicity could, literally, be broadcast manufacturers’ products and contact far and wide! Thus the failure of a details for pricing and supply. Figure 32. with clean trackbed simple drainage feature, or the poor downstream of drains choice of a product for reasons of economy, expedience or availability, Stakeholder engagement has far reaching conclusions. Tramways are being delivered using Design & Build forms of contract. Extensions or improvements to existing systems in the UK and the complete creation of a new system have been commonplace for the last 20 years. The owners of the assets created will generally be a local Figure 29. Plate 2-15: Wide transverse authority or a Passenger Transport drain Outbound … Executive. This body will have a long term responsibility for maintenance, such as the 125 years that Blackpool Borough Council and its preceding bodies have been successfully running a tram system in Blackpool and Fleetwood. The operator may change, perhaps as further extensions are added. TfGM is working with its third operator since it opened in 1992. Designers for Figure 30. Plate 2-16: … and narrow the drainage of trams can work for Inbound any of the above stakeholders. The parameters for the design cannot be
too prescriptive and each stakeholder Drainage can have a slightly different emphasis on the outcome of the design. All parties need to engage in these issues from preliminary design through to construction.
23 Acknowledgements
Thanks to my colleague, Chris Potter, for providing his constructive review of the script. Constructive comments from Matthew Hack, the Asset Manager for Transport for Greater Manchester (TfGM) on a draft of this paper are gratefully acknowledged, as is the permission of TfGM to publish the two case studies. These were initially prepared as part of the CIRIA RP941 draft report published in 2012 “Transport infrastructure drainage: condition appraisal and remedial treatment” and CIRIA’s inspiration for this paper is recognised.
24 Environment & Sustainability 25 137 ). The 3 Development of Conservation and for Sustainable Restoration Targets Management Resource Water further Targets) (or Resource develops the concepts presented Resource in the Sustainable Water a Management Plan by presenting model for identifying conservation for the target areas and restoration watershed. functions, which in turn contribute water to fooding, soil erosion, (and water supply) pollution, uses of and loss of recreational waters. Integrating ecosystem benefts or services into land use become planning has only recently part of a sustainable planning (Collins et al. 2007 approach ). 2 ) and is presented here. A GIS button tool was here. ) and is presented 1 The Sustainability Plan outlines an for managing watershed approach on existing that relies resources thereby natural infrastructure, costs to the public and reducing multiple benefts with providing water water quality, to respect and natural food protection, supply, systems. Impervious urban land uses and conversion of wetlands to developed land uses degrade watershed developed to automate scenarios of various combinations and rankings of developed to automate scenarios of water) and subsequently functions (e.g. surface and ground water resource the watershed. These targets targets in identify conservation and restoration conceptual design projects a mechanism for selecting locations for provide between for trade-offs and feasibility studies, identifying opportunities ecosystem services, benefts, quantifying loss of development and resource to guide a context targets provide and mitigating for that loss. The resource incentives for and develop development regulations, land use ordinances, water resources. protecting to planning and conservation is critical restoration for future Identifying areas targets restoration watershed. Conservation and in the Peace Creek efforts may be that potential projects based on available watershed-level data so are maps. Once targets become to each other and displayed as ranked relative based on site- can be selected specifc projects part of the planning process, consistent with the can be directed specifc feasibility criteria and development and conservation targets. restoration Animated and pdf versions of the Plan can be obtained at: http://northamerica.atkinsglobal.com/WHSP Introduction Introduction The Winter Haven City Commission the Sustainable Water approved Management Plan in Resource 2010, establishing a new direction for managing water resources in Winter Haven and the Peace (Atkins 2010 Watershed Creek Winter Haven Chain of Lakes: Chain of Winter Haven and restoration conservation and for sustainable targets planning watershed innovative Abstract targets in the Peace and restoration A model for identifying conservation Water to the Sustainable watershed was developed in response Creek City of Winter Management Plan completed for the Resource Haven, Florida (Singleton 2011 Pam Latham Principal Technical Professional & Environment Water Atkins North America Tom Singleton Tom Vice President & Environment Water Atkins North America The purpose of the project was to develop conservation and restoration targets that can be used to support future land use decisions in the City of Winter Haven and surrounding Peace Creek watershed. To accomplish this, available data were screened for relevance and scale appropriateness and a Geographic Information System (GIS) platform was used to create GIS layers that represent fve water resource functions: surface water quantity, surface water quality, groundwater quantity, groundwater quality, and habitat. Data intercepts representing the links between resource functions (e.g. surface water quantity) and benefts (e.g. water supply) were used to develop the resource function layers (Figure 1). Analysis of pre-developed (or un-impacted) Figure 1. Example of integration of data layers used to evaluate resources and develop conditions of resources provided the resource conservation and restoration targets basis for target areas: those with the least (or no) difference with respect recharge is a water resource function • A GIS button was developed to undeveloped (e.g. circa 1940s) and a measureable attribute (i.e. that allowed the user to evaluate conditions are referred to here as recharge potential), that translates changes in resource functions in conservation targets, while areas that to resource benefts, including water various combinations (e.g. with exhibit greater changes are referred supply, water quality, fsh and wildlife and without habitat data) habitat, etc. The approach relied on to as restoration targets. • Data were integrated to provide four primary components (outlined composite water resource data The product is a map of water below). resource management “target layers • Conservation and restoration areas”, represented by water • Locally-specifc data were added targets were developed at a scale resource data layers, in the to the watershed-scale data consistent with that of available, watershed. In addition to spatial to refne areas for which more relevant data. For example, land extent of targets, this study specifc data were available. documented an estimated loss of cover data are available for the 20,815 acre-feet of surface water entire watershed and illustrate Ninety-six available data sources storage loss since the 1940s as a differences between the more were reviewed for data relevant to result of the loss of wetlands and developed northern and less resource functions and benefts. reduced lake levels. developed southern watershed Available data that were insuffcient in areal extent to cover the • Data were acquired for these watershed, characterized by limited analyses and, in later steps, were Methods or no relationship to evaluating the ranked as a means of evaluating resource beneft, or unquantifable, the landscape, both temporally Five resource functions were defned were excluded from further analyses. (historic vs. existing) and spatially to characterize the hydrologic and Fifteen individual data layers were (across the watershed). This ecological character of the Peace subsequently retained to characterize precludes the use of data that Creek watershed: groundwater the resource function layers. quantity, groundwater quality, are not available for the entire surface water quantity, surface water watershed Data were frst evaluated for relevance to particular resource quality, and habitat. A resource • Data were ranked as a means of function, such as surface water, benefts matrix (Table 1) summarizes scoring and comparing data that groundwater, or habitat (surface the links between the resource have different units of measure functions (GIS layers) and resource and groundwater were further benefts. For example, groundwater segregated into surface water quality
26 137 Winter Haven Chain of Lakes: conservation and restoration targets for sustainable and innovative watershed planning
and quantity and groundwater Water Resource Benefts (Targets) quality and quantity). Some data Data Attribute Water Resource Recreation/ (defned below Water Water Flood Fish and were then combined with a second Functions Cultural table) Supply Quality Protection Wildlife data layer to produce the appropriate Resources data feld for analysis. For example, Groundwater land use was used in combination Potentiometric Storage x x x with recharge data to identify high surface vs. low recharge areas. Integrated Discharge (to NA x x x x (or composite) data layers for a surface water) resource function were developed Recharge Recharge x x x x from the individual data layers by Hydraulic Soils x x x summing and averaging data for conductivity each location across the watershed, Quality RCRA, SWAA thereby integrating GIS data layers into a composite resource function Surface Water (e.g. surface water quality) data Nutrient layer. The composite layer is the transport/ Impairment x x mediation equivalent of the resource function Sediment NA x x x layer (Figure 1). For example, the stabilization habitat function is a composite of Water levels listed species data, habitat type, Storage (natural x x x x x land use, and adjacent land use, and wetlands also addresses connectivity among Discharge (to habitats that typically refect streams surface and Recharge* x x x x x and wetlands. The process of data ground water) compilation, evaluation integration Water transport Connectivity* x x x x into GIS, and ranking and evaluation Quality Impairment throughout the watershed is Habitat summarized in Figure 2. The more Climate NA x x detailed data and ranking process are regulation outlined in Table 2. Nutrient NA x x x In the same way that non-parametric assimilation statistics rely on ranked data when Groundwater Groundwater* x x x x conventional parametric analyses mediation are inappropriate, data were Surface water Surface water* x x x ranked as a means of allowing mediation comparisons across resources with Soil formation Soils* x x x x different characteristics and units of Connectivity SHCA x x x x x measure. Altered conditions were Effect on assigned a value = “-5” (representing other resource FLUCFCS x x x x x Environment & Sustainability restoration), while relatively pristine functions** conditions were assigned a value = *Data layers included under a previous resource function. FLUCFCS = Florida Land Use Cover and “+5” (representing conservation) Forms Classifcation System, used in combination with other resource function data layers as a with respect to a particular resource measure of urbanization impacts. NA=not function (e.g. surface water storage). Table 1. Resource beneft function matrix: indicates relationships between resource Values of “0” were assigned to functions and benefts (x indicates relationship) data if a restoration or conservation condition could not be established. infltration soils were identifed for for surface water quantity and 2 for Therefore, areas in which the restoration. groundwater quantity). A location for which averaged ranks among the potentiometric surface has declined Final composite water resource fve resource function layers indicated were ranked “-5” while areas where data layers and the water resource relatively pristine water quality it has not declined were ranked management target areas were conditions, unaltered groundwater “+5”. Similarly, undeveloped high based on scenarios in which various and surface water conditions, and and moderate infltration soils would resource function layers were “natural” fsh and wildlife habitat be considered conservation potential, assigned different priorities (e.g. 1 while developed high and moderate also represented a location with 27 Figure 2. General approach to developing conceptual conservation and restoration resource targets
a high conservation potential. In wetland that still has storage but historical and current wetlands and contrast, a location in which all has been impacted by agricultural lakes, including wetlands associated these resources are altered would be practices for decades. Therefore, with water conveyances such as assigned a high value for potential this resource function represents streams and creeks, foodplain restoration. potentially recoverable water wetlands, isolated wetlands, and storage in the case of restoration National Wetlands Inventory (NWI) Although the process described here targets and opportunities for water wetlands (which include seasonally was carried out for all fve water storage management in the case of inundated wetlands). Federal resource functions, a single example conservation targets. Connectivity Emergency Management Agency (surface water quantity) is presented is diffcult to measure, but is (FEMA) foodplains are designated to illustrate the development of a important when considering the for food risk and insurance purposes potential water resource target. historic surface water connections. (based on the one percent annual While connectivity is not measured food occurrence or “100-year Surface water quantity for surface water, it can be foodplain”) and are not, therefore, superimposed on the targets map to included in the analysis. In the Peace The surface water quantity resource examine its infuence. Connectivity is Creek watershed, however, historic function represents the change a measure of habitat, however, and wetlands closely follow the FEMA in surface water storage between is typically consistent with surface 100 year foodplain. historic (1940s) and current water connections. conditions. Restoration is a measure Data layers used to develop the of lost water storage, but not the The areal extent of the surface surface water quantity resource overall quality of, for example, a water quantity data layer includes function layer are listed and
28 137 Winter Haven Chain of Lakes: conservation and restoration targets for sustainable and innovative watershed planning
Data Additions/ Rank Value Combinations
Resource Data Layers Data Fields Function -5 0 5 2009 Land Use 2008 Potentiometric Surface Watershed Delineation
Developed/ Undeveloped/ Undeveloped/ Floridan recharge x Recharge Recharge Recharge 1 Recharge > 10 > 10 to 10 Pre-development Groundwater potentiometric Quantity x Change Change = 0 NA Change <> 0 surface Developed/ Undeveloped/ Soils x Infltration C, D, B/D A, B A, B Source Water Groundwater Inside Outside Assessment 500-ft Buffer NA Quality 500-ft buffer 500-ft buffer Areas (SWA) Resource Conservation Groundwater Inside Outside 500-ft Buffer NA and Recovery Quality 500-ft buffer 500-ft buffer Act Facilities Gain /No Historical land Loss of x PRE_FLUCFCS Change in use (wetlands) Surface Water Storage Quantity Storage 2009 land use FLUCFCSCODE 2. PROMPT: Choose data layer to combine 2. PROMPT: 5. PROMPT: Weigh Resource function layer Resource Weigh 5. PROMPT: Ridge/valley Developed/ Insuffcient Undeveloped/ x x Impacted Rank parameters in chosen data feld 4. PROMPT: lakes Impacted data Not Impacted Scenario Conservation/ Restoration Target Product: Signifcant Surface Water Priority NA 0 Priority 1 - 7 1. PROMPT: Choose data layers for each water resource function Choose data layers for each water resource 1. PROMPT: surface water Quantity 3. PROMPT: Choose data feld to be used for ranking each set 3. PROMPT: Water quality Insuffcient x Impaired Impaired Not Impaired status data Strategic Habitat Conservation Priority NA NA Priority 1 - 5 Areas (SHCA) Historical land Habitat Cypress, Sand PRE_FLUCFCS NA NA use Pine Residential, Cypress, 2009 land use FLUCFCSCODE NA Tree Crops Pine Flatwoods
Table 2. Data layer compilation, ranking, and mapping for conservation and restoration targets development (left to right) described in Table 3 and rankings are Data Layer Description Source, Date listed in Table 4. The process of data Historic land use against which to Atkins, as developed for Peace River Historic Land Use selection, ranking, and application is measure changes in land use Cumulative Impacts Study Environment & Sustainability summarized in Table 5. For example, Current land use for comparison Current Land Use SWFWMD 20096 the change in surface water storage with historic land use was calculated from a comparison of Depth and duration of natural hydrologic conditions (hydroperiods communities to evaluate changes Hydrology Duever et al. 19867 - see below) under historic and in surface water storage between current land use/land use using current and historic land use. GIS and follows the approach used Table 3. Data representing surface water quantity resource functions for the Natural Systems Model the South Florida Water Management Attribute Used in Ranking Rank District uses to model pre-drainage Change in surface water storage conditions in the Everglades (SFWMD 20104) and refned as presented Loss/gain in hydroperiod -5 for the Collier County Watershed No change in hydroperiod 5 Management Plan (Atkins 20105). Table 4. Ranking scale used to assign priority for the surface water quantity resource function
29 Hydrology scoring is the functional Historic Wetland and Lakes Land Cover value of a land parcel based on the Land Cover Cypress Freshwater Mesic Swamp Lakes Total persistence of historical hydrologic Class Swamp Marsh Hammock Forest reference conditions. Hydroperiods Agriculture -90 -91 0 -344 -101 -626 are estimated based on the typical range of depth (inches) and duration Cypress 0 0 0 -39 -2 -41 Freshwater (days) of inundation of the vegetation 555 0 0 -936 -4,156 -4,537 community. No change from historic Marsh conditions would result in a score of Current Golf Course -60 -37 0 -258 -62 -417 “+5”, while total loss of hydrology Land Mesic Flatwood -136 -128 0 -108 -20 -392 Use/ (e.g. a cell dominated by a historic Mesic Land -331 -37 0 -517 -77 -962 condition wetland or open water Cover Hammock body but which now experiences no Pasture & Bare -2,742 -1,189 0 -5,811 -319 -10,061 inundation) would result in a score Ground of “-5”. The hydrology score was Swamp Forest 936 39 0 0 -187 788 applied on a 750 feet x 750 feet cell Urban -618 -421 0 -1,915 -1,460 -4,414 basis. Lakes 859 839 0 930 0 2,628 The hydrology score for a cell/parcel Wet Prairie -497 -291 0 -1,782 -211 -2,781 is based on the ratio of the existing Total -2,124 -1,315 0 -10,780 -6,596 -20,815 depth and duration in comparison to the historic condition, adjusted to a Table 5. Calculated changes in surface water storage from historic to current land use/ scale of “-5” to “+5”. For instance, land cover conditions (acre-feet) a site that historically had an average the groundwater dependence of A total of 2,124 acre-feet (Table hydroperiod of six months and an the ridge lakes and the changes 4) of historic water storage in average inundation of 12 inches, but in these lakes as a consequence cypress swamp has been lost due which currently is inundated for only of the declining aquifer. The valley to conversion to many different two months at an average depth lakes have a greater surface water land uses (e.g. 90 acre-feet of of four inches (i.e. the site currently infuence, which is also refected in storage to agriculture, 60 acre- experiences one-third of the depth the more elongate shapes compared feet to golf course, 618 acre-feet and duration of the historic condition with the round ridge lakes. to urban development). Similarly, for that site), would have a hydrology 6,596 acre-feet of former lake/open score of “-1.67”. More simply, a The shift from native uplands to water storage have been converted cypress swamp that was converted urban development represents a to other land covers/uses (e.g. 101 to an urban land use would be change in surface water storage in acre-feet of historic lakes converted represented by a loss of storage and the watershed, although the urban to agriculture). Overall, this indicates have a rank of “-5”, while a cypress areas actually had greater storage. an estimated 20,815 acre-feet of swamp that retained its hydrology Consequently, urban areas that surface water storage have been would have a rank of “+5”. were formerly native uplands were lost, primarily due to a conversion assigned a value of “0” to avoid Surface water quantity restoration of wetlands and lakes to developed the appearance that “restoration” and conservation targets are mapped (urban, agriculture, and golf courses) was recommended solely based on in Figure 3 (the footprint of a land uses (Table 5). These losses a gain in surface water storage. In locally proposed road, the Central were due primarily to loss in forested addition to mapping the changes Polk Parkway, is displayed in maps wetlands (cypress swamp and swamp in surface water from historic to throughout this document as for forest, 12,904 acre-feet) and open current conditions, the loss of reference). The most conspicuous water/lakes (6,596 acre-feet). storage represented by the changes feature is the pattern of ridge lakes was calculated. For example, a In terms of restoration opportunities, (along the Winter Haven Ridge) conversion from wetlands such as some of the conversions may designated as predominantly cypress swamp and wet prairie to represent opportunities to regain restoration (brown) lakes and the agriculture and urban land uses water storage. For example, a total of “valley” lakes (on the adjacent, represents a particular loss of surface 10,061 acre-feet of former wetlands lower, Polk Upland) designated as water storage that may be restored, and open water were lost due to predominantly conservation (green) although restoration of agricultural conversions to pasture and bare lakes. This is consistent with the lands is more likely than restoration ground (Table 5) and represent a result of previous studies of the of urban lands. loss of the same amount of storage Winter Haven Lakes that point to
30 137 Winter Haven Chain of Lakes: conservation and restoration targets for sustainable and innovative watershed planning
Conservation and restoration resource target scenarios
The fve individual resource function layers (groundwater quality, groundwater quantity, surface water quality, surface water quantity, and habitat) were merged to generate a conservation and restoration resource target map that identifes areas for restoration or conservation, based on a comparison of historic and existing conditions (e.g. historic and existing water storage) or the presence/ absence of historical attributes (e.g. permeable land surface). The fve resource layers were, metaphorically speaking, “stacked” together, and the data in each of the fve layers were averaged together for each pixel location across all fve resource layers (refer back to Figure 2) to produce a single map. Conservation and restoration resource targets have been developed at a scale appropriate to the available data. Because the land use regulatory system operates at different political and legal scales than the natural scales of ecosystems (Arnold 20078), however, individual projects developed as part of future efforts will have to be examined at the appropriate scale. The GIS button tool was developed Figure 3. Composite surface water quantity resource function layer to automate scenario development that may be seen as a restoration of the differences in water depths. of the resource target map (outlined Environment & Sustainability opportunity. Although changes in lake levels previously in Figure 1). Using have not been evaluated for many the tool, different scenarios are Numerous lakes are mapped as lakes, a previous study (Atkins 2009) developed by assigning different restoration (brown) due to storage documented an average decline of weights to resource function layers loss, while some are mapped as 5 feet in lake levels in the Winter (Figure 4). A scenario would be conservation (green) due to gains. Haven Chain of Lakes. Although data based on the relative importance of Losses and gains are based on are available that estimate 1850s each resource function layer and the comparisons between historic and land cover using 1927 soils maps, the footprint of the proposed project existing land use cover (i.e. areal soils maps are not pre-development and the current or future land use, extent of lakes) and typical changes and differences between the 1927 i.e. the user could examine the total in depth associated with changes and 1940s land cover maps appear impact of a proposed project on the in land use. For example, a loss of negligible. Consequently, the existing fve resource layers combined and/ 10 acres of a lake due to a change historic (circa 1940s) and current or one or more layers at a time. from open water to urban would (2009) data are considered the best If the surface water quality and be a greater loss than a shift to a data available for this project. quantity functions were considered marsh or forested wetland because adequate for a particular purpose,
31 such as evaluating potential National groundwater quantity resource areas greater than 20 acres in size Pollutant Discharge Elimination function layers had the most (100 percent of the target areas are System (NPDES) permitting, the comprehensive data of the fve retained in the project GIS layers other layers could be omitted. One resource function layers and are to ensure data integrity). The color example is presented here. of particular interest at both state scheme was changed to include the and local levels. To further focus two different resource layers in this An alternate scenario, Scenario 1, on restoration and conservation case (blue for surface water and can be generated if more importance targets with higher priority, the green for groundwater). These two to the surface water quantity 30th percentile for groundwater data layers were combined and are resource function layer is preferred target areas and 100 percent of mapped in Figure 6 and illustrate when compared to the other the potential surface water storage the concentration of groundwater resource function layers. Assigning were retained for displaying water targets in the northern portion of the surface water quantity layer a resource data layers and targets. In the watershed and surface water weight of “3” results in a scenario addition, “noise” was removed from targets in the southern portion of the in which surface water quantity has the fnal map by omitting contiguous watershed. three times more infuence than the other four resource function layers (Figure 5). Similar to Scenario 1, the restoration targets are predominantly in the heavily developed City of Winter Haven. However, weighting the surface water quantity resource function more than the other resource layers results in a shift to include many more of the green conservation areas (e.g. in the northern portion of the watershed).
Figure 4. Scenario 1: example of GIS button tool for surface water quantity weight=“3” and remaining resource function layers are assigned weight = ”1”
Composite water resource data layers and resource targets
Combining resource function layers into composite data maps provides a means of identifying areas with restoration and conservation Figure 5. Scenario 2: conservation and restoration resource target map when surface potential with respect to more water quantity weight = “3” and remaining resource function layers have weights =”1” than one layer. Surface water and
32 137 Winter Haven Chain of Lakes: conservation and restoration targets for sustainable and innovative watershed planning Environment & Sustainability
Figure 6. Composite water resource data layers for the Peace Creek Watershed 33 In some cases, discrepancies were conservation projects can be located focus restoration efforts on only noted in the water resource data appropriately throughout the restorable (non-urban) areas, or map/model due to false historic watershed, while development can any combination of these efforts. wetland signatures. In one case, be directed in a way that is consistent Estimates of loss of water storage land use/land cover data classify a with the restoration and conservation were consistent with previous lake (Lake Lulu) as restoration and targets. patterns identifed for water quantity conservation. The conservation and refect differences in ridge Local governments face challenges designation is a result of the (Winter Haven Ridge) and valley (Polk to using land use planning to protect persistence of the wetland forest Uplands) geology that dominate the water resources and associated despite lower water levels, i.e., the watershed. Water storage restoration community benefts. Therefore, wetland tree species are long-lived targets included predominantly the to the extent that restoration and and will persist for years and the ridge lakes in the Southern Chain conservation of priority locations area therefore exhibits no change of Lakes, while lakes identifed for cannot be accomplished through from historic to current. Similarly, a conservation included mostly valley land planning and other non- piece of property identifed as wet lakes in the Northern and Interior structural controls, engineering prairie because of a “wet” signature Chain of Lakes (consistent with and other structural controls is in pasture, but the wetland results of the recently completed will need to be identifed. These signature remains and the property is study of the Interior Chain of controls are less effective and more designated as potential conservation. Lakes). Another practical option costly to implement than non- To address these issues, project- is restoration of storage that can structural controls and, therefore, specifc data/studies can be used be recovered without impacting local governments should consider to make cosmetic revisions without adjacent land owners. In contrast, leveraging its land planning altering the raw data. areas of water storage that remain authorities, including using incentives unchanged (or with little change) to protect water resources, to are identifed as conservation targets Conclusions: water the greatest extent possible. The and include Lakes Hamilton, Henry, City of Winter Haven may choose resource targets Haines, Rochelle, and Smart in the to implement monitoring and Northern Chain of Lakes. Conservation and resource targets other feedback mechanisms for provide a mechanism for the City of adaptive management of water The resource targets developed for Winter Haven to select locations for resources. Identifying the resource this project provide a model for conceptual projects and feasibility targets allows the implementation revising the City’s ordinances and studies, identify opportunities for of strategies to examine specifc developing incentives to protect trade-offs between development projects, options for land use water resources in the watershed. and ecosystem benefts, quantify a planning, and private sector concepts These mechanisms will be developed loss of services, and mitigate for that such as mitigation banking and as part of the next step in carrying loss. For example, opportunities to regional stormwater ponds. Some out the Sustainability Plan. This mitigate for impacts to groundwater communities have established goals report presents the resource targets elsewhere in the watershed can that target tree canopy increases in that can be used to evaluate, direct, be readily identifed. The resource recognition of air and water benefts, and support land use decisions targets provide a context for land use while others have imposed regulatory that contribute to sustainability in measures to guide revisions to land jurisdiction over land use to prevent the entire watershed, including the use ordinances and development development because the costs portion of the watershed that forms regulations and to develop incentives associated with land use regulation the Sapphire Necklace, which was for protecting water resources. and land acquisition were less than the focus of the Sustainability Plan. the costs of building additional water The resource targets are presented Identifcation of areas for future treatment facilities that would be as conservation and restoration maps restoration and conservation is even necessary if the development was that provide the watershed context in more important from a planning permitted. which to focus and develop a range perspective. The resource targets of water management alternatives. The City of Winter Haven may, as developed for the Peace Creek These alternatives, as well as the another example, choose to restore watershed provide locations for rules, ordinances, and other planning a portion of an estimated 20,815 restoration and conservation in mechanisms to implement them, will acres of surface water storage lost the watershed, based on available be accomplished as part of future to conversions to other land uses watershed-level data. Once these planning and design charrettes with (primarily urban and agriculture). targets become part of the planning City staff. process, specifc restoration and Or, stakeholders may choose to
34 137 Winter Haven Chain of Lakes: conservation and restoration targets for sustainable and innovative watershed planning
Acknowledgements
The Atkins project team included Tom Singleton, Pam Latham, Ph.D., Katherine Anamisis, Emily Keenan, and Leslie Gowdish, Ph.D. Special acknowledgement to Mike Britt, P.E., Director, Natural Resources Division, City of Winter Haven, who conceived of the original sustainability plan. Also, thanks to Jackie Cooper, Atkins, who provided valuable editing assistance.
References
1. Singleton, T.J. 2011. Sustainable Water Resource Management Plan. Atkins Technical Journal 6, paper 92: 99-109. 2. Atkins. 2009. Sustainable Water Resource Management: A Conceptual Plan for the Peace Creek Watershed and the City of Winter Haven, Florida. Final Report to the City of Winter Haven. 3. Collins, S.L., S.R.Carpenter, S.M/ Swinton, D.E. Orenstein, D.L. Childers, T.L. Gragson, N.B. Grimm, J.M. Grove, S.L Harlan, J.P. Kaye, A.K. Knapp, G.P. Kofnas, J.J. Magnuson, W.H. McDowell, J.M Melack, L.A. Ogden, G.P. Robertson, M.D. Smith, and A.C. Whitmer. 2010. An integrated conceptual framework for long-term social– ecological research. Ecological Society of America: Frontiers in Ecology and the Environment. DOI:10.1890/100068. 4. SFWMD. 2011. Natural System Model. http://www.sfwmd.gov/portal/page/portal/xweb%20-%20release%202/ natural%20system%20model. 5. Atkins. 2010. Collier County Watershed Management Plan. Final Report to Collier County. 6. SWFWMD (Southwest Florida Water Management District). 2009. Land use data. Available from website. http:// www.swfwmd.state.f.us/data/gis/layer_library/?search=fuccs. 7. Duever, J.J., J.E. Carlson, J.F. Meeder, L.C. Duever, L.H. Gunderson, L.A. Riopelle, T.R. Alexander, R.L. Myers, and D.P. Spangler. 1986. The Big cypress National Preserve, National Audobon society Research Report No. 8. New York. 455 p. 8. Arnold, C.A. 2007. The Structure of the Land Use Regulatory System in the United States. Journal of Land Use and Environmental Law 22(2): 441. Environment & Sustainability
35 36 Environment & Sustainability 37 138 Figure 1. Location map Figure Introduction Introduction 9,860 tons of Approximately municipal solid wastes (MSW) are generated in Puerto Rico (the Island, ) every day (ADSPR, 1 see Figure 2003). 15.3% of Approximately segregated this mass is presently (ADSPR, 2008). The for recycling 8,351 tons per day (tpd) remaining in landflls. During is disposed-off the 100 or so years since we became society (Life, 1955; a throw-away 2001), as cited in Rathje & Murphy, in Puerto Rico has the MSW stream 2,000 acres approximately in resulted meters) of opened (8,093,745 square or closed landflls (ADSPR, 2003), for an average rate of twenty new acres (404,687 m2) of landfll per year. Seven out the nineteen (36.8%) sites listed as the most polluted in (2011) are Puerto Rico by the USEPA former landflls. 2 for See Figure the location of the 31 landflls still in operation in 2007. Abstract and incinerators were Air Pollutants (HAPs) emitted by landflls Hazardous Rico (PR) landfll’s quantifed one Puerto The USEPA estimated and compared. extrapolated were results 3.02, and those emissions using LandGEM Version Emission The USEPA land-flled municipal solid waste (MSW) stream. for PR’s the incineration emissions from utilized to estimate HAP Factors (1995) were per year (tpy) of that PR landflls emitted 106.2 tons Results are of this MSW. 26 HAPs during 2008: known Organic Compounds, eight are Volatile All are (17.1 carcinogens possible or potential (11.4 tpy) and seven are carcinogens tpy). Incinerators would emit 394.2 tpy of eight HAPs: 98.8% would be (0.6 tpy) and one is a acid (389.5 tpy), fve known carcinogens hydrochloric fve using data from also estimated (0.1 tpy). HAPs were potential carcinogen operating incinerators (range: average: 493.3 tpy), the 39.4 - 1,245.8 tpy, (13.3 carcinogens worst performer would emit fewer known/possible/potential tpy) than landflls do (28.5 tpy). Landflls vs. incinerators: vs. incinerators: Landflls and comparison identifcation by the posed of the hazards with associated toxic emissions solid of municipal the disposal Rico waste in Puerto Francisco J. Pérez Francisco J. Pérez Aguiló Senior Scientist/ Manager Project Figure 3 illustrates two Island landflls. Landflls and incinerators pose hazards to public health and the environment, but which one poses fewer hazards? This study investigates the toxic emissions for existing, modern incinerators, and compares them with the toxic emissions presently emitted from landflls in the Island. Figure 2. Location of Puerto Rico Landflls Sanitary landflls
The sanitary landfll is the most widely utilized disposal method for solid wastes (UNEP, 2002) and is the least expensive alternative when land is not in short supply. Landflls generate no visible emissions, except during fre events, and require very little manpower and equipment. However, MSW buried in a landfll remains there for hundreds or thousands of years (Rathje & Murphy, 2001). The following are notable exceptions:
1. Methane (CH4) and Carbon
Dioxide (CO2) will result from the biological decomposition of the organic matter, according to the following formula:
Organic substances + microbial
activity = heat + CH4 + CO2 + contaminants
This “landfll gas” will invisibly ventilate out of crevices, the landfll surface, or a system designed for this purpose Figure 3. Examples of Puerto Rico Landflls (Elías-Castells, 2005). CH4 and
CO2 are important greenhouse MSW has been deposited in the biochemical reactions that gasses; however, CO2 is the landfll, and its generation occur within landflls, and they removed from the atmosphere continues for decades or even are emitted to the atmosphere by photosynthetic organisms hundreds of years (E.A., 1997; in the landfll gas stream (Elias- (algae and plants), whereas CH4 ATSDR, 2001; Ferry, 2002; Castells, 2005). Table 1 shows is not, and is a greenhouse gas USEPA, 1998c, 2002 and 2005a; the typical landfll contaminants. 21 times more potent than CO2 Durmusoglu, Yavuz & Tuncay, These gasses range in impact (USEPA, 1998c and 2005b). 2005). from nuisance odors to toxicity The methane fraction of this (USEPA, 1999; Chian & DeWalle, 2. Volatile and semi-volatile gases “landfll gas” is sometimes used 1979). as fuel (USEPA; 1998b, 2002). can be present in the MSW Landfll gas generation peaks stream deposited in landflls. 3. The liquids deposited in the approximately 30 years after These are also formed during landfll will fnd their way to the 38 138 Landfills vs. incinerators: identification and comparison of the hazards posed by the toxic emissions associated with the disposal of municipal solid waste in Puerto Rico
landfll bottom. Precipitation will percolate through the layers of MSW deposited, fuelling microbial as well as chemical decomposition of the MSW. Liquids moving within the landfll dissolve organic and inorganic contaminants. Landfll leachate is normally toxic (Jones-Lee, 1993; Elías-Castells, 2005), has a high biochemical Figure 4. Landfll Schematic oxygen demand, a low pH, and is contaminated with heavy metals and soluble organic Pollutant ppmv Pollutant ppmv 1,1,1-Trichloroethane (methyl Dichlorodifuoromethane 15.7 species (Elias-Castells, 2005). 0.48 chloroform)a The modern practice is to collect Dichlorofuoromethane 2.62 1,1,2,2-Tetrachloroethanea 1.11 it throughout the bottom of the Dichloromethane (methylene 14.30 1,1-Dichloroethane (ethylidene chloride)a landfll and re-apply it at the top 2.35 dichloride)a with or without some treatment. Dimethyl sulfde (methyl 7.82 1,1-Dichloroethene (vinylidene sulfde) Even when a bottom liner is 0.20 chloride)a present, there is always seepage Ethane 889.0 1,2-Dichloroethane (ethylene through seams or cracks (USEPA, 0.41 Ethanol 27.20 2001). This impact decreases dichloride)a Ethyl mercaptan (ethanethiol) 2.28 once an impermeable cap is 1,2-Dichloropropane (propylene a 0.18 placed over a landfll during its dichloride) Ethylbenzenea 4.61 proper closure, but it is present 2-Propanol (isopropyl alcohol) 50.10 Fluorotrichloromethane 0.76 during its entire active life. Acetone 7.01 Hexanea 6.57 Landfll closures under current Acrylonitrilea 6.33 Hydrogen sulfde 35.5 regulations require at least three Benzene 1.91 Mercury (total)a,d 0.000292 monitoring wells to determine Bromodichloromethane 3.13 Methyl ethyl ketonea 7.09 whether landfll leachate Butane 5.03 Methyl isobutyl ketonea 1.87 contamination is migrating outside Carbon disulfdea 0.58 Methyl mercaptan 2.49 the site, a fnal grading to divert Carbon monoxideb 141.0 Non-Methane Organic runoff away, a gas collection and 595.0 a Compound (as hexane) recovery system, and a fnal capping Carbon tetrachloride 0.004 to keep precipitation off the buried Carbonyl sulfdea 0.49 Pentane 3.29 a Perchloroethylene waste. The duration required of Chlorobenzene 0.25 3.73 (tetrachloroethylene)a these measures, indicative of their Chlorodifuoromethane 1.3 impact, can be as short as 30 years Propane 11.10 Chloroethane (ethyl chloride)a 1.25 and as long as 100 years. t-1,2-dichloroethene 2.84 Environment & Sustainability Chloroforma 0.03 Trichloroethylene Chloromethane 1.21 2.82 (trichloroethene)a Dichlorobenzenec 0.21 Vinyl chloridea 7.34 Table 1. Typical contaminants of landfll Xylenesa 12.10 gas (USEPA 1995)
USEPA NOTES: This is not an all-inclusive list of potential landfll gas constituents, only those for which test data were available at multiple sites. a Hazardous Air Pollutant listed in Title III of the 1990 Clean Air Act Amendments. b Carbon monoxide is not a typical constituent of LFG, but does exist in instances involving landfll (underground) combustion. Therefore, this default value should be used with caution. Of 18 sites where CO was measured, only 2 showed detectable levels of CO. c Source tests did not indicate whether this compound was the para- or ortho- isomer. The para-isomer is a Title III-listed HAP. d No data were available to speciate total Hg into the elemental and organic forms. ppmv = parts per million based on volume of landfll gas. 39 Incinerators as Emissions Control Technology Pollutant Uncontrolled Emissions Spray Drier/ Fabric Filter Emissions alternative (kg/Mg) (kg/Mg) Arsenicb 0.00214 0.0000212 The controlled burning of MSW was b developed to reduce the volume Cadmium 0.00545 0.0000136 of MSW to be disposed, convert CDD/CDFc 0.000000835 0.0000000331
the caloric output into energy, and CO2 985 * recover materials that survive the COd 0.232 * process: Cromiumb 0.00449 0.0000150
b Organic substances + O2 = heat + HCl 3.20 0.106 CO2 + H2O + contaminants Mercuryb 0.0028 0.0011 The USEPA (1995) has compiled a list Nickelb 0.00393 0.0000258 of typical emissions that come out NOxd 1.83 * of the smokestack for the various Leadb 0.107 0.000131 types of incinerators under different scenarios of emissions control, see Particulate a 12.6 0.0311 Table 2. Mater SO 1.73 0.277 The more effcient the combustion 2 process, fewer contaminants are Table 2. Typical Emissions for incinerators with and without emissions control generated (Elias-Castells, 2005). USEPA NOTES: However, heavy metals and the un- CO2 emitted from incinerators may not increase total atmospheric CO2 because emissions may be combusted organic substances that offset by the uptake of CO by regrowing biomass. remain in the ash residues, including 2 Emission factors should be used for estimating long-term, not short-term emission levels. This those formed during incomplete particularly applies to pollutants measured with a continuous emission monitoring system (e.g.,
combustion can make incinerator ash SO2). disposal a problem (USEPA, 1998a). kg/Mg = kg of emissions per Megagram (1,000,000 grams or 1.0 metric tons) of solid waste These “incinerator solid wastes” combusted. occupy a small fraction of the volume * = Same as “uncontrolled” for these pollutants. of the original MSW, reducing the a PM = Filterable particulate matter, as measured with EPA Reference Method 5. required landfll capacity needs by b Hazardous air pollutants listed in the Clean Air Act. 85% (Renova, 2000). Signifcantly c CDD/CDF = total tetra- through octa-chlorinated dibenzo-p-dioxin/chlorinated dibenzofurans. reducing the volume of the material 2,3,7,8-tetrachlorodibenzo-p-dioxin, and dibenzofurans are hazardous air pollutants listed in 1990 to be disposed in landflls signifcantly Clean Air Act. d reduces the disposal problem. Control of NOx and CO is not tied to traditional acid gas/PM control devices. e Calculated assuming a dry carbon content of 26.8% for feed refuse. Just like the decomposers in the biosphere, incinerators return energy results in leachable levels below and materials for anthropogenic allowable concentrations (USEPA, Not in my backyard (human) consumption (Husar, 1994): 1996). The technology to turn ash Energy (approximate rate of 0.029 residues into stable cement-like A basic comparison between megawatts per ton of MSW), steam, substances (Keck and Seitz, 2002; these technologies indicates that construction aggregate (91.6 kg/ Buckley and Pfughoeft-Hassett, the incinerators fare much better ton of MSW), ferrous (38.1 kg/ton of 2006) has found many constructive than landflls in the following MSW) and non-ferrous (3.6 kg/ton) applications (NYT, 1919, USDOE, categories: Emission of greenhouse metals (Renova, 2000), as illustrated 2000; USDOT, 2000). At a minimum, gasses (Solano et al., 2002; USEPA, in Figure 5? these stabilization technologies allow 2006a), discharge of toxic leachate the solid residue to be disposed in (Jones-Lee, 1993; USEPA, 1996; Modern incinerator technologies landflls with minimal potential for USDOE, 2000; USDOT, 2000; include the processing of the fy- generation of toxic leachate and Keck and Seitz, 2002; Buckley and ash to trap the contaminants it occupying a small fraction of the Pfughoeft-Hassett, 2006), duration contains and make them unavailable landfll space when compared with of the impact (Elias-Castells, 2005), to the environment. For instance, the original MSW. materials recovered (landflls have incinerator ash containing 7.5% lead none), power generation (USEPA, and 0.2% cadmium, encapsulated 2006a), jobs creation (USDOT, 2000; in a sulphur polymer with additives 40 138 Landfills vs. incinerators: identification and comparison of the hazards posed by the toxic emissions associated with the disposal of municipal solid waste in Puerto Rico
RWB, 2001; CEPA, 2003) and land 7.7% to Fly Ash consumption (Renova, 2000). Public Landfill perception, however, is an area Tipping PRF to where incinerators fare far worse Floor Boilers 95% Boiler 1000ton 86% Sold than landflls, even though landflls MSW Ferrous also suffer from the not in my back 99% to 75MW of yard (NIMBY) syndrome (ANL, 1994; Enters Metal Process Shredders Electricity McCarthy, 2004). Recovery 14% used The most consistent argument in in-house opposition to the incinerators is their toxic emissions (McCarthy, 2004). Ferrous Earlier versions of the incinerator Metals Overall Bottom Ash 12% sparked this reputation: Incomplete 2.0% To Energy: 76.6% Recovered: 13.7% combustion, inappropriate or non- 0.7% Bulky and Landfilled: 9.6% existent emissions controls, and hazardous objects Non- other factors yielded large quantities Boiler Ferrous Ferrous of toxic contaminants in their AggregateTM 0.4% 2.1% atmospheric emissions (NYT, 1919; 9.8% USEPA, 1995 and 1998a). Many Figure 5. Incinerator schematic for a 910 tpd facility of the reports attacking incinerator emissions refer to the Harrisburg, Pennsylvania Incinerator, which began operations in 1972 (USEPA, 1985) and emitted at least two orders of magnitude more dioxins than the average U.S. incinerator of its time (USEPA, 1997a). Others refer to the Columbus, Ohio Incinerator, which operated between 1983 and 1994, during which time it emitted a full one third of the dioxin emissions in the U.S. (Lorber et al., 1998). Do modern incinerators contaminate as much? And, how do their emissions compare
The Experiment Figure 6. Example of a 2,700 tpd incinerator
The Arecibo landfll was used as the impact of the holiday MSW Emissions from all Puerto Rico MSW Environment & Sustainability a sample of the Hazardous Air stream and other fuctuations. incinerated = Results for incinerator Y X 8,301 tpd Pollutants (HAP) emissions generated The HAPs, those listed in Subchapter tpd MSW from the disposal of MSW in Puerto I, Part A, § 7412 of the U.S. Clean incinerator Y Rico landflls. It serves the sixth Air Act, were quantifed for the largest municipality in the Island hypothetical emissions of MSW Landfll HAP emissions data are and receives its fourth largest waste management in Puerto Rico using not so readily available. Until stream. A study by the ADSPR incinerators. HAP emissions data recently (USEPA, 1997b) there (2003) reported the weight in tons (waste processed and emissions) from was no requirement for landfll per year (tpy) and volume of MSW fve incinerators were also obtained gas monitoring. Even the 1997 disposed in all 31 Island landflls for from existing United States facilities regulation, which imposed gas one week each during 2003, and the through available U.S. Environmental monitoring to active landflls, was waste composition at 12 selected Protection Agency (EPA) databases. limited to the largest 5% of landflls landflls and two transfer stations. The emissions data obtained from (greater than 2.5 million metric ton Some stations, including the Arecibo these incinerators were scaled for capacity). Therefore, existing data landfll, were re-sampled to measure 8,301 tpd, in accordance with the needed to compare toxic releases following equation: from landflls are limited. However, 41 the USEPA has compiled a list of tpd deposited in Puerto Rico landflls simple reason: The amount of a toxic Emission Factors, which consist of daily, were extrapolated by this study substance is always the numerator averages of the available data of for the entire Island through the in the risk factors, such as dose (mg/ acceptable quality, obtained from following equation: Kg or milligrams of contaminant per hundreds of actual test results kilogram of body mass) or exposure Emissions Estimate for all MSW performed on actual emission (mg/m3, milligrams of contaminant deposited in Puerto Rico landflls = sources, and are representative of per air volume). Take away the mass LandGEM Results, Arecibo Landfll long-term averages for each type of of the contaminant and the risk X 8,301 tpd facility (USEPA, 1995 and 2008). goes to zero. Increase the mass of a 541 tpd contaminant available for exposure This study utilized the USEPA’s Landfll The results from the previous and the risk increases accordingly. Gas Emissions Model (LandGEM, exercise, namely the landfll gas Version 3.02) (USEPA, 2005a), emissions estimate, were used to prepared for the Arecibo Landfll Results: landfll estimate the toxic contaminants by the USEPA Region 2. The data emitted to the atmosphere from emissions in Puerto Rico collected by the USEPA (2009) in landflls in Puerto Rico using the support of their emissions model Emission Factors compiled by the There are 46 non-methane organic of the Arecibo Landfll covered a USEPA (1995). In the case of landfll contaminants in landfll gas, of which total of 33 years, from 1973, the emissions, these are expressed as 26 belong to the HAP category. A year it opened, through 2006. The a ratio of a pollutant emitted per total of 106.2 tpy of HAPS were LandGEM estimates emission rates volume of landfll gas (i.e. mg/m3). emitted at ground level from open for all landfll gases, including: and closed landflls throughout the methane, carbon dioxide, non- To estimate emissions of non- Island in 2008, including 248,686 tpy methane organic compounds, methane organic contaminants from of carbon dioxide and 90,637 tpy of and individual air pollutants, and landflls, the following equation is methane, for a total of 2,152,063 tpy is based on the following frst- used by LandGEM: of greenhouse gas CO2-equivalents; order decomposition rate equation 6 (USEPA, 2005b). Table 3 shows the QP = 1.82 Q CH4 + C p (1x10 ) to quantify emissions from the resulting emissions for the sample decomposition of MSW in landflls: where: and for the Island. Q = Emission rate of pollutant P, m3/ n 1 P Of the 26 HAPs in Puerto Rico landfll M i -kt yr QCH = KL e ij gas, seven are known carcinogens 4 ∑ ∑ 0 10 t=1 j=0.1 3 (Vinyl Chloride with 5.2 tpy, QCH4 = CH 4 generation rate, m /yr, Acrylonitrile with 3.8 tpy, Benzene Where: from LandGEM results (above) with 1.7 tpy, Ethylene Dichloride with CP = Concentration of P in landfll gas QCH4 = annual methane generation in 0.5 tpy, Propylene Dichloride with the year of the calculation (m3/year) (Emission Factor, ppmv) 0.2 tpy, Chloroform with 0.04 tpy, i = 1 year time increment 1.82 = Multiplication factor, assumes Carbon tetrachloride with 0.007 tpy, that approximately 55% of landfll and Ethylene dibromide with 0.002 n = (year of the calculation) - (initial tpy) and a further seven are possible gas is CH4 and 45% is CO2, N2, and year of waste acceptance) other constituents carcinogens or potential occupational carcinogens (Tetrachloroethylene with j = 0.1 year time increment The Emission Factors (USEPA, 1995) 6.9 tpy, Trichloroethylene with 4.2 -1 for MWCs were used to estimate the k = methane generation rate (year ) tpy, Ethylidene Dichloride with 2.7 Island’s emissions if all MSW land- tpy, 1,1,2,2-Tetrachloroethane with Lo = potential methane generation flled in Puerto Rico were processed 2.1 tpy, Methyl chloride with 0.7 tpy, capacity in cubic meters per mega- with incinerators. gram (m3/Mg) of MSW. 1,4-Dichlorobenzene(p) with 0.3 tpy, and Vinylidene Chloride with 0.2 Mi = mass of waste accepted in the Mass of toxics as a tpy), for a total of 11.4 tpy of known ith year in Mg surrogate for risk carcinogenic HAP emissions and th 17.1 tpy of potentially or possible tij = age of the i section of waste mass Mi accepted in the ith year The mass of HAPs emitted should occupational carcinogenic HAP (decimal years, e.g., 3.2 years) be a strong indication of the overall emission. risk that landflls and incinerators The results obtained for the Arecibo With the exception of a minute pose. Mass is the most important Landfll, which accepts an average amount (0.001 tpy) of mercury, factor in risk assessment for one of 541 tpd, or 6.5% of the 8,301 most of the 106.15 tpy of HAPs
42 138 Landfills vs. incinerators: identification and comparison of the hazards posed by the toxic emissions associated with the disposal of municipal solid waste in Puerto Rico
in landfll gas consist of volatile Arecibo CAS Number Chemical Name Puerto Rico organic compounds (VOCs), some Landfll halogenated, with a heavier-than- 74-82-8 Methane 6,430 90,637 air vapour (mean vapour density = 124-38-9 Carbon Dioxide 17,643 248,686 3.8, range = 1.7 – 6.5). Their high 79-34-5 1,1,2,2-Tetrachloroethane 0.1 2.1 density keeps these contaminants close to the ground, available to 106-46-7 1,4-Dichlorobenzene(p) 0.02 0.3 human receptors and the food 107-13-1 Acrylonitrile 0.3 3.8 chain. VOCs also participate of the 71-43-2 Benzene 0.1 1.7 atmospheric photochemical reactions 75-15-0 Carbon disulfde 0.04 0.5 and contribute signifcantly to the 56-23-5 Carbon tetrachloride 0.0005 0.007 formation of ground-level ozone and smog (Elias-Castells, 2005). 463-58-1 Carbonyl sulfde 0.02 0.3 108-90-7 Chlorobenzene 0.02 0.3 Results: incinerator 67-66-3 Chloroform 0.003 0.04 emissions 100-41-4 Ethyl benzene 0.4 5.5 75-00-3 Ethyl chloride (Chloroethane) 0.07 0.9 Should the fve incinerators sampled 106-93-4 Ethylene dibromide (Dibromoethane) 0.0002 0.002 process all of the Island’s MSW, they 107-06-2 Ethylene dichloride (1,2-Dichloroethane) 0.03 0.5 would generate anywhere from 39.4 75-34-3 Ethylidene dichloride 0.2 2.7 to 1,245.8 tpy of HAPs, with an 110-54-3 Hexane 0.5 6.4 average of 493.3 tpy, see Figure 7. 7439-97-6 Mercury Compounds 0.00005 0.0007 The single largest HAP present in 74-87-3 Methyl chloride (Chloromethane) 0.05 0.7 the emissions of the fve incinerators 71-55-6 Methyl chloroform 0.05 0.7 evaluated is hydrochloric acid, which contributed anywhere from 99.0% 78-93-3 Methyl ethyl ketone (2-Butanone) 0.4 5.8 to 99.8% of the HAP mass, with 108-10-1 Methyl isobutyl ketone (Hexone) 0.2 2.2 an average of 99.3%. Lead is the 78-87-5 Propylene dichloride 0.02 0.2 next most important component 127-18-4 Tetrachloroethylene (Perchloroethylene) 0.5 6.9 of the incinerator HAP emissions, 108-88-3 Toluene 2.9 40.6 comprising an average of 0.038%, 79-01-6 Trichloroethylene 0.3 4.2 with mass ranging from 0.04 to 13.07 tpy (average = 2.73). Mercury 75-01-4 Vinyl chloride 0.4 5.2 compounds followed in order 75-35-4 Vinylidene chloride 0.02 0.2 of concentration, comprising an 1330-20-7 Xylenes (isomers and mixture) 1.0 14.4 average of 0.054% of the emissions Total HAP emissions: 7.5 106.2 for all fve incinerators. Mercury emission estimates using the various Table 3. Landfll gas and hazardous air pollutant (HAP) estimates for the Arecibo Landfll and for Puerto Rico based upon the 2008 MSW deposit rate incinerators as models would range Environment & Sustainability from 0.009 to 1.1 (average = 0.3) tpy. Cadmium is the fourth most All emissions figures in tons per year (tpy). Significant digits were removed for clarity. important component of the HAP emissions, comprising an average of 0.011%, with a mass ranging from 0.00 to 0.24 (average = 0.06) tpy. Another estimate of HAP emissions from incinerators was obtained from the USEPA’s Emissions Factors (USEPA, 1995 and 2003), which Figure 7. Comparison (in tpy) of HAP emissions in Puerto Rico: Landflls v. incinerators provide fve technology scenarios: No emissions controls, electrostatic precipitators, spray dryer/electrostatic precipitator, duct sorbent injection/ fabric flter, and spray dryer/fabric
43 flter. Each set of emissions control are trapped, forming a “cake” in 0.05 tpy (0.013%), and dioxins & technologies has its strengths and the surface of the fabric flters, furans with 0.0001 tpy (0.00003%). its weaknesses (Elias-Castells, 2005), which further provides fltering and These are the only HAPs listed in the and may be installed in series for adsorption (Elias-Castells, 2005; Emissions Factors (USEPA, 1995) for additional removal of contaminants. and USEPA, 1998a, b, 2008). Spray incinerators. dryer/fabric flter is also the most The spray dryer/fabric flter Out of the eight HAPs that would frequently used emissions control technology was selected mainly due be emitted by incinerators, fve are technology for incinerators in the to the simplicity and effectiveness known carcinogens (Lead with 0.5 United States (USEPA, 2003). of this process: Water or partially tpy, Arsenic with 0.08 tpy, Chromium treated wastewater (for re-use) Total HAP emissions estimate using with 0.06 tpy, Cadmium with 0.005 is sprayed into the emissions, the Emissions Factors was 394.3 tpy. tpy, and Dioxins & Furans with often with additives such as lime The single largest HAP present in the 0.0001tpy) and one is a potential
(CaCO3) or caustic soda (NaOH) for emissions, based on this national occupational carcinogen (Nickel with pH adjustment and contaminant average is, again, hydrochloric 0.09 tpy), for a total of 0.6 tpy of adsorption. The spray lowers the acid. It comprised 98.8% of the known carcinogen emissions and emissions temperature to below the HAP mass (389.5 tpy), followed by 0.09 tpy of potentially carcinogenic temperature of formation for dioxins Mercury with 4.0 tpy (1.03%), Lead emission. and other organic pollutants (Lorber with 0.5 tpy (0.038%), Nickel with Incinerator emissions are discharged et. al., 1998; USEPA, 1997a, 1998a, 0.09 tpy (0.024%), Arsenic with through a smokestack designed to and 2006b). As water evaporates to 0.08 tpy (0.020%), Chromium with the height necessary to ensure that steam, the solids that are left behind 0.06 tpy (0.014%), Cadmium with emissions do not result in excessive
Emission MWC-A MWC-B MWC-C MWC-D MWC-E Factors tpy Received 2008 100,375 602,250 281,780 220,825 102,930 for MSW w/Spray MWC - PR MSW 2.7% 16.4% 7.7% 6.0% 2.8% Drier/Fabric Emissions Multiplier 36.61 6.10 13.04 16.64 35.70 Filter MWC PR MWC PR MWC PR MWC PR MWC PR Hydrochloric acid 20.6 754.1 41.6 253.8 3.0 39.1 74.0 1,231.4 4.6 `64.6 389.5 Lead Compounds 0.001 0.04 0.03 0.2 0.02 0.3 0.8 13.1 0.003 0.1 0.5 Hexachlorobenzene 0.2 7.4 Mercury Compounds 0.005 0.2 0.05 0.3 0.001 0.01 0.07 1.1 0.0003 0.009 4.0 Cadmium Compounds 0.001 0.03 0.002 0.01 0.0008 0.01 0.01 0.2 0.05 Manganese Compounds 0.004 0.1 Polycylic Organic Matter 0.003 0.1 Formaldehyde 0.0002 0.007 Arsenio Compounds 0.0000002 0.000006 0.0009 0.005 0.08 1,3-Butadiene 0.00002 0.0007 Benzene 0.000020 0.0007 Beryllium Compounds 0.00006 0.0004 Dioxins & Furans 0.0000002 0.000006 0.000004 0.0001 0.0001 Naphthalene 0.000002 0.00008 Nickel Compounds 0.0000004 0.00002 0.09 Chromium Compounds 0.00000001 0.0000004 0.06 Total 20.8 761.9 41.7 254.3 3.0 39.4 74.9 1,245.8 4.6 164.9 394.3
Table 4. HAP Emissions from Incinerators: Sampled Incinerators, and USEPA’s Emission factors. Extrapolated for all MSW Landflled in Puerto rico in 2008 All Emissions and MSW fgures in tons peryear. Emission factors in kilograms per megagram of MSW. Estimates based upon the estimated 3,674,611 tpy MSW land-flled in the island (see Table 1). Decimal places rediced to the frst non-zero to illustrate order of magnitude. Calculations with all signifcant fgures. MSW= Municipal Solid Waste, MWC = Municipal Waste Combustor or incinerator, PR = Puerto Rico
44 138 Landfills vs. incinerators: identification and comparison of the hazards posed by the toxic emissions associated with the disposal of municipal solid waste in Puerto Rico
concentrations of air pollutants in the emissions (105.4 tpy) consist MWC-C. If its combustion and immediate vicinity of the source as of a blend of organic solvents emissions-control technologies a result of atmospheric downwash, and degreasers, four of which were utilized in the management eddies, and wakes which may be are known carcinogens, and six of all MSW presently land-flled created by the source itself, nearby of which are possible/potential in Puerto Rico, incinerators would structures or nearby terrain obstacles. carcinogens emit 37% fewer (67 tpy) HAP Contaminants remain suspended as emissions than landflls presently • Incinerators would emit 18 particles in the emissions, and are do (106.2 tpy), see Figure 7 times fewer known carcinogen deposit by gravitational settling over HAPs than landflls do; 0.6 tpy • The proportion of Hydrochloric time. for incinerators v. 11.4 tpy for Acid (HCl) to the total HAP landflls, or 10.8 fewer tpy than emissions was consistent between Assessment conclusion Puerto Rico’s present method of the estimates from the USEPA solid waste disposal, see Figure Emissions Factors (98.8% HCl) Unless otherwise specifed below, 8. This fnding would contradict and the estimates from the fve the following conclusions draw the general knowledge that incinerators sampled (range = upon the USEPA’s Emission Factors incinerator emissions are worse 98.8% to 99.8% HCl). HCl estimate and not from the individual than landflls deserves particular consideration. incinerators sampled. The former is Acute effects stem from its • Incinerators would emit 190 representative of long-term average corrosivity to the eyes, skin, and times fewer possible carcinogen emissions from all incinerators in the mucous membranes. Drinking it or potential occupational United States. causes corrosion of the mucous carcinogenic HAPs than landflls membranes, esophagus, and • The community that hosts a do; 0.09 tpy for incinerators v. stomach, with nausea, vomiting, landfll has the long-term liability 17.1 tpy for landflls, or 17.0 and diarrhea. However, HCl of the underground storage fewer tpy than Puerto Rico’s “is a natural physiological fuid of slowly decomposing refuse present method of solid waste present as a dilute solution in the with the ensuing emissions disposal (greenhouse gasses and non- stomachs of humans” (Manahan, methane organic compounds, • Actual operating facilities can 1994, p. 679). HCL is a mineral including HAPs) and leachate achieve far greater reductions of acid with unlimited solubility discharges to the ground and HAP emissions than the national in water, which reacts readily groundwater. Once an incinerator US averages in the Emission with carbonates (CO32-) in soil is shut down its impacts cease Factors. That is the case of dissolving them, resulting mainly • Landfll emissions occur at ground level, where they are close to the human population, cattle and other links to exposure pathways, increasing the potential exposure to the HAP emissions.
Incinerator emissions are required Environment & Sustainability to be at a height that minimizes concentrations of air pollutants in the immediate vicinity of the source and that maximize Figure 8. Comparison (in tpy) of known carcinogenic HAP emissions in Puerto Rico: Landflls v. incinerators dispersion of potential pollutants • Incinerators would emit 3.7 times more HAPs than landflls; 394.3 tpy for incinerators v. 106.2 tpy for landflls (presently), or 288.1 additional tpy than Puerto Rico’s present method of solid waste disposal. However, 98.8% of the HAPs in incinerator emissions consist of Hydrochloric Acid. In Figure 9. Comparison (in tpy) of potential/possible carcinogenic HAP emissions in contrast 99.2% of the landfll Puerto Rico: Landflls v. incinerators
45 in calcium chloride (CaCl2), cancer mortality rates (Torres-Cintr n Although it is impractical to discuss potassium chloride (KCl) or et al., 2010). here the health effects of all sodium chloride (NaCl); carbon contaminants emitted by landflls Cancer is the second leading cause dioxide and water, in accordance or incinerators, one that deserves of death in Puerto Rico after heart with the following equations particular consideration is Vinyl disease, and accounted for 16.6% (from Kolthoff, Sandell, Meehan Chloride (VC). 5.2 tpy of it are of all deaths in 2004 (Torres-Cintr n, and Buckenstein; 1969, p. 1101): emitted in Puerto Rico’s landfll gas et al., 2010). Out of 8,953 deaths
(see Table 3, Table 4). VC is a due to all causes in 2004, of which CaCO + 2HCl CaCl + CO + H O 3 2 2 2 known human carcinogen by the 1,515 deaths were due to cancer,
inhalation route of exposure, and breast cancer leads with 209 deaths, K CO + 2HCl 2KCl + CO + H O 2 3 2 2 by analogy, through the oral route followed by liver/hepatic cancer with
of exposure; and a likely human 191 deaths (Ortiz-Ortiz et al., 2010). Na CO + 2HCl 2NaCl + CO + H O 2 3 2 2 carcinogen by the dermal route. A Many of the contaminants from
1-in-10,000 increase in the risk of both landflls and incinerators have Calcium chloride is commonly cancer is expected for continuous the liver or kidneys as target organs. used as an electrolyte in sports lifetime exposure to 23 µg/m3 of VC However, there are no incinerators in drinks. Potassium chloride is during adulthood (USEPA, 2010). operation in Puerto Rico to date, but consumed as a sodium-free there are approximately 2,000 acres substitute for table salt (sodium Kielhorn, Melber and Wahnschaffe of open and closed landflls emitting chloride) (2000) conducted a study of MSW these gases. landflls, and found up to 200 • The combined emissions of mg/m3 of VC in landfll gas up The results of this research project carcinogens and possible to 10 mg/L and in groundwater are but the tip of the iceberg: or potential occupational contaminated with landfll leachate. though they lack smokestacks, carcinogens would also be much These investigators combined municipal solid waste landflls emit lower if all of the MSW presently relevant epidemiologic studies copious amounts of hazardous air land-flled in Puerto Rico were from several European countries, pollutants at ground level, including processed using MWC-C (0.8 tpy) and documented an excess (45 tons of carcinogens per year—even instead of Puerto Rico’s present times the average) of liver cancer in some where the effects are latent method of solid waste disposal populations near landflls, primarily for decades. Landfll emissions of (28.5 tpy): 27.7 tpy (97% fewer). due to angiosarcoma, the type of these gases peak once the waste See Figure 10 cancer associated with VC. These sits in them for about 30 years, • Actual operating facilities can investigators, as well as the USEPA and continue emitting them for emit far more HAPs than the (2000), demonstrate a statistically a century. They consume land USEPA (1995) averages. If the signifcant elevated risk of liver at a ferocious rate for an island combustion and emissions-control cancer, primarily angiosarcomas setting, contaminating land and the technology used by MWC-D were in the liver, from exposure to groundwater beneath it. They are utilized in the management of VC. The average latency for liver also one of the largest anthropogenic all MSW presently land-flled in angiosarcoma due to VC is 22 years sources of atmospheric methane, Puerto Rico, incinerators would (Kielhorn et al., 2000), yet it has been a greenhouse gas 21 times more
emit 1,073% more (1,140 tpy) documented to be as long as 51 potent than CO2. Incinerators, on HAP emissions than landflls years (Bolt, 2009). 28% of the most the other hand, reduce by up to 85% presently do (106.2 tpy). See contaminated sites in Puerto Rico are the volume of solid waste that must Figure 7 located in municipalities with high be disposed of, producing power and • Even the worst performer in terms of total HAP emissions, out of the incinerators sampled, MWC-D, would emit approximately one half of the carcinogenic and possible or potential carcinogenic HAPs (13.3 tpy) than landflls presently do (28.5 tpy). See Figure 10.
Discussion Figure 10. Comparison (in tpy) of known potential/possible carcinogenic HAP emissions in Puerto Rico: Landflls v. incinerators 46 138 Landfills vs. incinerators: identification and comparison of the hazards posed by the toxic emissions associated with the disposal of municipal solid waste in Puerto Rico
steam even from the mayonnaise left in a jar and its label, and recovering References the glass and steel cap once 1,000ºC of thermal oxidation has stripped 1. ADSPR (2003). Final report: Waste characterization study. Prepared by the rest. Incinerator impact lasts Wehran P.R., Inc. & Shaw EMCON/OWT, Inc. while they operate and when 2. ADSPR (2008). Dynamic plan for the management of solid waste in properly designed and operated, Puerto Rico. Autoridad de Desperdicios S lidos de Puerto Rico. MP generate far fewer HAPs—especially Engineers of Puerto Rico, P.S.C. carcinogens—than landflls. 3. ANL (1994) Trash, ash and the phoenix: Waste-to-energy facilities after the Supreme Court decision of May 2, 1994. Argonne National Laboratory, Washington, D.C. http://www.osti.gov/bridge/product.biblio. jsp?osti_id=100237. 4. ATSDR (2001). Landfll gas primer: An overview for environmental health professionals. U. S. Department of Health and Human Services, Agency for Toxic Substance Substances and Disease Registry, Public Health Service, U.S. Department of Health and Human Services, Division of Health Assessment and Consultation. 5. Bolt, H.M. (2009). Case report: Extremely long latency time of hepatic angiosarcoma in a vinyl chloride autoclave worker. Experimental and Clinical Sciences Journal 8, 30-34. 6. Buckley, T. & Pfughoeft-Hassett, D.F. (2006). Review of Florida regulations, standards and practices related to the use of coal combustion products. Final report. Prepared for USEPA and USDoE 2006-EERC-04- 03. 7. CEPA (2003). Diversion is good for the economy: Highlights from two independent studies on the economic impacts of diversion in California. California Environmental Protection Agency, Integrated Waste Management Board. March, 2003. 8. Chian, E.S.K. & DeWalle, F.B. (1979). Effect of moisture regimes and temperature on MSW stabilization. Proceedings of the Fifth Annual Research Symposium, MSW: Land Disposal. EPA-600/9-79-023, 32-40. 9. Durmusoglu, E., Yavuz, M. and Tuncay, K. (2005). Landfll settlement with decomposition and gas generation. Journal of Environmental Engineering 131(7) 783-784. 10. EA (1997). A quick reference guide: Estimating potential methane
production, recovery and use from waste. Environment Australia. ISBN 0 Environment & Sustainability 642 19463 7. 11. Elias-Castells, X. (Ed.), (2005). Tratamiento y Valorizaci n Energética de Residuos. Madrid: Fundaci n Universitaria Iberoamericana/Ediciones Díaz de Santos. 12. Ferry, S. (2002). Landfll perimeter gas control. MSW Management 12(5). http://www.mswmanagement.com/july-august-2002/landfll-perimeter- gas.aspx. 13. Husar, R.B. (1994). Ecosystem and the biosphere: Metaphors for human- induced material fows. In: R. U. Ayres & Simonis, U. E. (Eds.), Industrial Metabolism: Restructuring for Sustainable Development. Tokyo: United Nations University Press. http://capita.wustl.edu/ME449-07/Reports/ Ecosystem_Biosphere.pdf.
47 14. Jones-Lee, A. & Lee, F. (1993). Groundwater pollution by municipal landflls: Leachate composition, detection and water quality signifcance. Sardinia ‘93IV International Landfll Symposiums. Margherita di Pula, Italy. October 11-15, 1993. 15. Keck, K.N. & Seitz, R.R. (2002) Potential for subsidence at the low-level radioactive waste disposal area. Idaho National Engineering and Environmental Laboratory, Prepared for the U.S. Department of Energy. 16. Kielhorn, J., Melber, U. & Wahnschaffe, C. (2000). Vinyl chloride: still a cause for concern. Environmental Health Perspectives 108(7) 579–588. 17. Lorber, M., Pinsky, P., Gehring, P., Braverman, C., Winters, D. & Sovocool, W. (1998). Relationship between dioxins in soil, air, ash and emissions from a municipal solid waste incinerator emitting large amounts of dioxin. Chemosphere 37(9-12), 2173-2197. 18. Manahan, S.E. (1994). Environmental Chemistry 6th ed. Boca Raton: CRC Press. 19. McCarthy, T.M.. (2004). Waste incineration and the community. Waste Management World Sept-Oct 2004 London: James & James (Science Publishers). http://www.seas.columbia.edu/earth/wtert/sofos/McCarthy_WTE_ experience.pdf. 20. Ortiz-Ortiz, K.J., Pérez-Irizarry, J., Marín-Centeno, H., Ortiz, A.P., Torres-Berrios, N., Torres-Cintr n, M.,…Figueroa- Vallés, N.R. (2010). Productivity loss in Puerto Rico’s labor market due to cancer mortality. Puerto Rico Health Science Journal 29(3) 241- 249. 21. NYT (1919). Favor refuse incinerator: Merchants’ Association is opposed to present dumping system. The New York Times Editorial. http://query.nytimes.com/mem/archive-free/pdf?res=F10F1EF9395C1B728DDDA80A94DC40 5B898DF1D3. 22. Rathje, W. and C. Murphy (2001). Rubbish! The archaeology of garbage. New York: Harper Collins Publishers. 23. Renova (2000). Siting consultation application, Volume 2: Environmental impact report. May, 2000. 24. RWB (2001). Economic impacts of recycling in Iowa. R.W. Beck, Inc. for the Iowa Department of Natural Resources. 25. Solano, E., R.D. Dumas, K.W. Harrison, S.R. Ranjithan, M.A. Barlaz, and E.D. Brill (2002). Life-cycle-based solid waste management II: Illustrative applications. Journal of Environmental Engineering (October, 2002) 993-1005. DOI: 10.1061/(ASCE)0733-9372(2002)128:10(993). 26. Themelis, N.J, Kim, Y.H. & Brady, M.H. (2002). Energy recovery from New York City municipal solid wastes. Waste Management and Research Vol. 20(3) 223-233. 27. Torres-Cintr n, M., Ortiz, A.P., Pérez-Irizarry, J., Soto-Salgado, M., Figueroa-Vallés, N.R., De La Torre-Feliciano, T., Suárez-Pérez, E. (2010) Incidence and mortality of the leading cancer types in Puerto Rico: 1987-2004. Puerto Rico Health Science Journal 29(3), 317-329. 28. UNEP (2002). Landfll still a necessary and effective practice. United Nations Environment Programme, Division of Technology, Industry, and Economics. 29. USDOE (2000). A comparison of gasifcation and incineration of hazardous wastes fnal report. U.S. Department of Energy, National Energy Technology Laboratory. DCN 99.803931.02. 30. USDOT (2000). Recycled materials in European highway environments: Uses, technologies, and policies. International Technology Exchange Program, U.S. Department of Transportation, Federal Highway Administration. FHWA-PL-00-025. 31. USEPA (1985). Summary report on corrosivity studies in co-incineration of sewage sludge and solid waste. EPA 600 S2-85 099. 32. USEPA (1995) Compilation of air pollutant emission factors – Volume 1: Stationary point and area sources (AP- 42 Fifth Edition). January, 1995. Section 2.4 MSW Landfll updated November, 1998. Section 2.1 Refuse Combustion updated October, 1996. 33. USEPA (1996) Stabilization/solidifcation processes for mixed waste. EPA 402-R-96-014. 34. USEPA (1997a). Locating and estimating air emissions from sources of dioxins and furans. EPA-454/R-97-003.
48 138 Landfills vs. incinerators: identification and comparison of the hazards posed by the toxic emissions associated with the disposal of municipal solid waste in Puerto Rico
35. USEPA (1997b). Approval and promulgation of State air quality plans for designated facilities and pollutants, New Mexico; control of landfll gas emissions from existing municipal solid waste landflls; correction for same, Louisiana. Federal Register Vol. 62, No. 203, October 21, 1997. 36. USEPA (1998a). The inventory of sources of dioxin in the United States. April 1998. This document is for review purposes only, and carries a disclaimer that it does not represent Agency policy. USEPA600/P-98/002Aa. 37. USEPA (1998b). Inventory of U.S. geenhouse gas emissions and sinks: 1990-1996. USEPA236-R-98-006. 38. USEPA (1998c). Greenhouse gas emissions from management of selected materials in MSW. USEPA 530-R-98- 013. 39. USEPA (1999). 1990 emissions inventory of forty potential section 112(k) pollutants, supporting data for EPA’s section 112(k) regulatory strategy: Final report. 40. USEPA (2000). Toxicological review of vinyl chloride (CAS No. 75-01-4) in support of summary information on the Integrated Risk Information System. EPA/635R-00/004. 41. USEPA (2001). RCRA fnancial assurance for closure and post-Closure. Offce of Inspector General, USEPA. Report No. 2001-P-007. 42. USEPA (2002). MSW in the United States: 2000 facts and fgures. EPA530-R-02-001. 43. USEPA (2003). Emission factor documentation for AP-42 section 2.1: Refuse combustion. 44. USEPA (2005a). LandGEM landfll gas emissions model, Version 3.02. EPA-600/R-05/047. 45. USEPA (2005b). Metrics for expressing greenhouse gas emissions: Carbon equivalents and carbon dioxide equivalents. EPA420-F-05-002. 46. USEPA (2006a). Solid waste management and greenhouse gasses: A life-cycle assessment of emissions and sinks, 3rd Edition. EPA530-R-02-006. 47. USEPA (2006b). An inventory of sources and environmental release of dioxin-like compounds in the United States for the years 1987, 1995, and 2000. EPA/600/P-03/002F. 48. USEPA (2008). Background information document for updating AP-42 Section 2.4 for estimating emissions from MSW landflls. EPA/600/R-08-116. 49. USEPA (2009). LandGEM landfll gas emissions model, Version 3.02. for the Arecibo Landfll. USEPA, Caribbean Environmental Protection Division (CEPD), USEPA, Region 2. 50. USEPA (2010). Health Effects Notebook for Hazardous Air Pollutants. http://www.epa.gov/airtoxics/hlthef/ hapindex.html. 51. USEPA (2011). List of RCRA and NPL sites. http://www.epa.gov/region2/cleanup/sites/prtoc_sitename.html. Environment & Sustainability
49 50 Environment & Sustainability 51
139 – Powered by Parallel Hybrid – Powered or diesel a conventional petrol braking engine with regenerative the technology that captures energy generated under braking. This energy is converted into electricity which is usually used to power the vehicle at low speeds or boost the engine to improve The Toyota fuel economy. and Lexus Prius and the Toyota Hybrid SUVs use Parallel Hybrid technology entirely Series Hybrid – Powered by an electric engine but with a small conventional engine used to keep the vehicle battery charged. E-REV, Ampera The Vauxhall
and used to inform WWF Scotland’s and used to inform WWF Scotland’s Electric vehicles of electric 4 types currently are There vehicle (EV) on the market: • • address these and, with the right address policies in place, could put Scotland in of a revolution at the forefront transport. road 1 . To 4 . 2 . 3 The Scottish Government has committed to establishing a mature market for low carbon cars by 2020, and an electric vehicle charging in Scottish cities infrastructure It provides a brief description of the different types of electric vehicles and types of electric vehicles a brief description of the different It provides vehicle use in Scotland. It electric identifes and ranks the barriers to greater could be used to address which then describes the range of policy measures for the Scottish Government,these barriers and identifes the top priorities It concludes by discussing of the public sector. local authorities and the rest developments in Scotland. recent of the Institute Trust, the Energy Savings The study involved input from of lithium- largest independent supplier Advanced Motorists, Axeon (Europe’s Arup, One North East, ion battery systems), Scottish and Southern Energy, ITS UK, Cenex and Dundee City Council. by was reviewed The fnal report and Axeon. Allied Vehicles, Scottish Power, Introduction Introduction The Climate Change (Scotland) Act a legally binding 2009 introduced target of at least an 80% reduction gas emissions across in greenhouse all sectors of the Scottish economy by with 1990 levels). 2050 (compared this target to be met, the for In order Scottish Government has recognised the need for ‘almost complete transport decarbonisation of road by by 2050 with signifcant progress wholesale adoption 2030 through of electric cars and vans (EVs), and signifcant decarbonisation of rail by 2050’ Powering ahead: how to put ahead: how Powering vehicles on Scotland’s electric roads Abstract by Atkins, Electric prepared on the fndings of a report This paper reports Driving the change (April 2011) Vehicles: recent report, Powering Ahead: how to put electric cars on Scotland’s roads roads on Scotland’s Powering Ahead: how to put electric cars report, recent (Dec 2011) achieve this transformation, the Scottish Government and local Scotland need to authorities across sizeable are there Although act now. barriers to the mass use of electric cars, the Scottish Government has many of the necessary powers to Jane Robinson Managing Consultant Highways & Transportation Atkins with a 50 mile electric range, is which includes full maintenance The research has identifed that expected to go on sale in the UK and servicing, but excludes many of the identifed barriers are in 2012; and is currently on sale electricity costs. equally applicable to private, public as the Chevrolet Volt in the US and corporate feets. However, there are a number of differences worth • Plug-in Hybrid – Capable Barriers to electric highlighting: of running on a rechargeable vehicle uptake battery or a conventional petrol • Local authority feets are or diesel engine. Although there Barriers to EV uptake can be expected to be least affected by are currently very few real world viewed as those limiting demand the identifed barriers, due to examples of PHEVs, they are the from consumers and those relating a need to show leadership by subject of increasing attention to supply in terms of availability demonstrating support for the by car manufacturers, with of vehicles and supporting technology required to meet CO2 Toyota, Ford, General Motors, infrastructure. These barriers are reduction targets. Company car Volkswagen and Hyundai all of varying scale and importance, users are expected to be most developing models. The Toyota and demand different levels of affected due to the high mileage Prius PHEV, with a 12.5 mile government response. they typically undertake and a electric range, has been leased general preference for larger, high to public organisations, police A summary of the main barriers to EV performing models and businesses since 2007 and is uptake, and their relative importance, • High purchase price could expected to be on general sale in is presented in Table 1. The list be expected to be less of a 2012 refects views from key stakeholders and experts, and evidence from an concern in the context of public • Battery Electric – Electric extensive literature review. and corporate feets given the engine only, powered by a strong buying powers of the rechargeable battery pack. To Three barriers emerge as being organisations concerned and a date, pure EVs have been have highly signifcant: high purchase greater appreciation of whole been limited to demonstration cost, limited range, and lack of life costs. However, public models, after market conversions, suffcient charging infrastructure. sector feet managers have and quadricycles such as the Other signifcant barriers relate to reported that they are unlikely G-Wiz which are mass and uncertainty regarding resale value to buy EVs for their feets unless power limited and are subject to and limited supply of vehicles. different regulations. However, a number of high quality EVs Barrier Overall ranking have been publicly launched in High purchase price Very high signifcance the UK in 2011 and 2012. Most Limited range of EVs and range anxiety issues Very high signifcance are small family cars (e.g. the Lack of recharging infrastructure and issues relating to Very high signifcance Mitsubishi-iMiev, the Nissan implementation and operation of infrastructure Leaf, the Peugeot iON/Citroën Uncertainty about future resale values, due to uncertainty High signifcance CZero, and the Tata Indica Vista about the life expectancy of the battery EV) or micro cars (e.g. the Smart Limited supply of EVs High signifcance Fourtwo electric drive). Their Lack of public awareness and knowledge about EVs High signifcance maximum range on one battery charge typically varies from 80 Limited performance and limited choice of vehicles High signifcance to 110 miles. The time taken to Aversion to new technology High signifcance fully charge the battery varies Weak image association High signifcance from 6 to 8 hours, although Limited value placed on environmental benefts by High signifcance batteries can be recharged to consumers 80% capacity in 30 minutes. The Uncertainty about future energy costs High signifcance Mitsubishi i-Miev and the Nissan Leaf are retailing at £23,990 and Limited environmental benefts associated with current Moderate signifcance models £25,990 respectively5 (after a £5,000 Plug-in Car Grant from Lack of support network (e.g. garages with appropriate Moderate signifcance skills and equipment) the Government6); while Peugeot iON/Citroën CZero is being Lack of engineering skills Moderate signifcance offered on a four-year, 40,000 Table 1. Ranking of barriers to EV uptake mile lease for £416 per month,
52 139 Powering ahead: how to put electric vehicles on Scotland’s roads
incentivised to do so by the Place is prioritising work in Denmark Market model for charging Government, because the overall because of the tax incentives for EVs, infrastructure in the Netherlands13 cost is currently seen as being and, in the US, Ford has identifed In the Netherlands, EnergieNed, the Dutch uncompetitive7 the 25 most electric vehicle-ready organisation for energy producers, traders cities and is now working with them and suppliers, and Netbeheer Nederland, • The limited range of EVs and to deliver its Focus electric car and the Dutch organization of grid operators, commissioned a study to design the market lack of recharging infrastructure 10 other models . model for EV recharging infrastructure. is likely to be less of a concern Within the preferred market model, the for corporate utility and public charging point operator is responsible sector feets where daily mileage Policy instruments for for operating the recharging point, for is predictable and less than the settlement, and for granting access to the overcoming barriers to recharging station. The electricity provider maximum range of a single electric vehicle uptake in turn is (as in the telecommunications battery charge, and where industry) responsible for the customer. The provider has a contract with the customer infrastructure can be provided A range of potential policy measures in a depot to allow overnight offering full access to recharging spots, and is available, which can be categorised is responsible for cost settlement with both charging. Scheduling tools may into six generic types (see Table 2). the customer and the operator. be required to manage charging, and the electricity supply Measures combine ‘sticks’ to All measures are considered to be may need to be upgraded, as discourage purchase of conventional realistic proposals for encouraging historically, many premises were internal combustion engine vehicles, EV uptake. However, a minority built with limited provision of and ‘carrots’ to encourage electric relate to matters which are currently power for the building and car vehicle uptake. It is assumed reserved to the UK Parliament, and park. that strong incentives will be require the Scottish Government to needed throughout the period lobby for change at a UK level or The collective impact of the barriers to 2020. Technology aversion is request additional devolved powers identifed in Table 1 and the scale of generally a barrier to uptake of new in order to make changes in Scotland the challenge is summed up by the technologies until market penetration alone. fact that by the summer of 2011 only has reached at least 15%, suggesting 2,500 of the 28 million cars in the the need for strong incentives until UK were electric, just 0.008% of the 2020 and beyond. feet8. Although there are already far more EV models available now, and Many of the measures identifed are more to come, their share of new either already being implemented car sales must increase to be close elsewhere in the world (e.g. to 20% by 2020. Although this is a scrappage scheme in Italy; Peugeot’s signifcant acceleration, it is backed ‘Mu’ initiative in France – see below), by car manufacturers leading the EV are the subject of previous research charge. For instance, GM, maker of and evidence (e.g work place parking the Volt, has said that “by the end of levy), or refect initial intentions the decade, 20% of all car sales will of the Scottish Government (e.g. 9 be electric” . proposed target of 100% of the Environment & Sustainability public sector feet be alternatively The scale of transformation required powered by 202011). is signifcant and will require targeted intervention by both national and Peugeot’s ‘Mu’ initiative12 local government to kick start the The scheme allows users to exchange credits market and establish the right (or ‘points’) for hire of a range of vehicles regulatory framework to protect and accessories (including scooters, bikes, consumers and ensure EVs ft with roof boxes and child seats) available from Peugeot dealerships. Following trials in within a sustainable transport future. a number of French cities, and in Berlin, Car manufacturers are already Milan and Madrid, it launched in the UK carefully targeting the roll out of in 2010 at two dealerships in London and EVs to those countries and cities Bristol. Users pay a membership fee of £10. Purchasers of the Peugeot iOn electric car that have taken the steps needed will automatically become members of Mu to support the shift to this new and are then expected to receive credits that transport technology. For instance, can be used to rent vehicles through Mu the battery swap company, Better meaning they have full access to a range of transport modes.
53 Action for Action for A - Infrastructure and support services measures Scottish local gov Gov A1 - EV Infrastructure Strategy for Scotland (as part of a broader EV Strategy and Action Plan for Scotland, see F4). x A2 - Government action to agree technical standards, specifcations and regulations for recharging infrastructure x A3 - Government action to agree market model for recharging infrastructure x A4 - Funding for publicly accessible recharging points x x A5 – Incentives for workplace recharging infrastructure x x A6 - Support for home recharging infrastructure x x A7 - Planning guidance on the provision of recharging bays and infrastructure x x A8 - Building regulations relating to the provision of recharging infrastructure in new buildings x A9 - Battery swap feasibility study x x A10 - Induction recharging research x A11 - Qualifcations for garage mechanics and quality insurance scheme for garages servicing, undertaking MOTs, and x repairing EVs A12 - Working Group to address the electricity generation and distribution requirements for EVs x B - Alternative ownership models B1 - Car club schemes x x B2 - Other ownership models x x C - Fiscal measures and subsidies – vehicle purchase incentives C1 - Grants for purchasing new EVs x C2 - Scrappage scheme designed to increase sales of EVs x C3 - Grants for purchasing second hand EVs x C4 - Registration tax (increase ‘frst year rates’) x C5 - Registration tax feebate scheme x C6 - Tax credits x C7 - Enhanced capital allowances x D - Fiscal measures and pricing policies to reduce running costs D1 - Road pricing (congestion charging schemes, low emissions zones, road tolling) x x D2 - Workplace Parking Levy x x D3 - On-street parking charge policies x x D4 - Vehicle Excise Duty x D5 - Fuel tax x D6 - Company car tax x E - Awareness, information and training measures E1 - Demonstration projects x x E2 – Provide opportunities for consumers to test drive EVs x x E3 - Customer information about EVs and where to charge them x x E4 - Public promotion campaigns x x E5 - Eco-driving training x x F - Other Government leadership measures F1 - Public sector procurement of low carbon vehicles for own feet x x F2 - Government research x x F3 - Funding to convert specifc vehicles to electric platforms x F4 - A high profle EV Strategy and Action Plan for Scotland, setting out a clear vision supported by targets or milestones x F5 - Mandate specifying proportion of EV sales by major manufacturers x F6 - Government action to encourage private sector to convert to EVs x x F7 - Lobbying to increase the EU target for the emissions-intensity of new cars and vans x
Table 2. Summary of measures considered
54 139 Powering ahead: how to put electric vehicles on Scotland’s roads
Figure 1. Tesla Model S full-sized electric four-door sedan, produced by Tesla Motors. On show in Santa Monica, California (Nov 2012)
score highly as effective measures in are unlikely to be effective measures Assessment of potential their own right, because they address in their own right. They should be measures the ‘very high signifcance’ barriers seen as secondary, support measures relating to ‘range anxiety’ and ‘lack which will be important in growing A high level assessment of the of infrastructure’. These measures the EV market, once barriers relating identifed measures was undertaken need to be prioritised frst. to ‘high purchase price’, ‘range anxiety’, and ‘lack of infrastructure’ against a range of criteria Fiscal measures and pricing policies have been addressed. This does (effectiveness, impact on wider policy relating to running costs (Type
not mean that there is not a case Environment & Sustainability areas including sustainable transport D) provide an indirect means of for implementing or continuing to and social inclusion, deliverability, addressing the ‘high purchase implement some of them now, as public acceptability and affordability) price’ barrier, providing consumers part of a strategy to shift mindsets, to identify ‘priority areas’ for action. are willing to offset some of the but it needs to be recognised that purchase price against long term The assessment indicates that there these measures on their own will not running cost savings. While there is a hierarchy of measures in terms of achieve signifcant uptake of electric is some evidence that fuel price effectiveness. vehicles. increases (for example) have resulted Alternative ownership models (Type in a shift towards more fuel effcient Similarly some measures categorised B) and fscal measures and subsidies cars, there is also evidence that as other Government leadership relating to the purchase price of private consumers tend to heavily measures (Type F), tend not to vehicles (Type C) are most effective discount future running cost when address the ‘very high signifcance because they directly address deciding which car to purchase (Arup barriers’ directly, and are unlikely to the ‘high purchase price’ barrier, and Cenex, 2008)14. be effective measures in their own identifed as being of ‘very high right. signifcance’. Infrastructure measures Measures relating to awareness, and support services (Type A) also information and training (Type E)
55 No. Measures to increase uptake of electric vehicles Priority measures 1 Publish a high profle EV Strategy and Action Plan for Scotland, setting out a clear vision supported by targets for 2020 and beyond. This should be supported by an EV Infrastructure Strategy for Scotland, for the provision and roll out of appropriate The assessment process described recharging infrastructure, and describing how drivers will use the infrastructure. above was used to prioritise the 2 Work with relevant stakeholders in Scotland, the rest of the UK, and across Europe, measures into three groups – top to set technical standards, specifcations and regulations for implementing recharging priorities, secondary priorities, and infrastructure. tertiary priorities. 3 Commission a review of market models for recharging infrastructure in Scotland and implement the recommendations of the review. This would involve taking into account The top priorities are those measures the UK Plug-In Infrastructure Strategy15, working with energy providers, electricity which have been identifed as being retailers, EV manufacturers, private infrastructure providers and the public sector, to most effective in addressing the ‘very ensure consistent and appropriate pricing and payment approaches. high signifcance’ barriers relating to 4 Scottish Government and local authorities provide funding for publicly accessible ‘high purchase cost’, ‘limited range recharging points. of EVs’, and ‘lack of recharging 5 Encourage manufacturers to offer alternative ownership models to consumers in infrastructure’. These measures need Scotland by promoting Scotland as an attractive market for manufacturers, and engaging to be implemented as a matter of with manufacturers to understand and infuence their decisions about where to focus their sales strategy. Scottish Government or other public sector bodies work with urgency, if the target of 300,000 EVs manufacturers to ‘trial’ alternative ownership models amongst employees or as part of on Scotland’s roads by 2020 is to the vehicle procurement process, and publicise benefts. be met. They include infrastructure 6 Scottish Government provides a £10,000 subsidy* for the frst 25,000 EVs sold in and support measures, alternative Scotland (as recommended by the UK CCC), to ‘kickstart’ early uptake of EVs, £5,000 for ownership models, vehicle purchase the second 25,000 EVs in Scotland, and reducing for subsequent 25,000 EV milestones. incentives, and other Government *£5,000 assumed to come from the UK Plug-In Grant for the frst EVs in Scotland. leadership measures (procurement policies and lobbying to increase the 7 Scottish Government introduces a scrappage scheme to encourage consumers to EU target for the emissions intensity purchase EVs, with subsidies reducing as EV uptake increases. of new cars and vans produced by 8 Scottish Government provides grants for purchasing secondhand EVs from specifed manufacturers. dealers with subsidies reducing as EV uptake increases. Secondary priorities are those 9 National and local government work together to incentivise businesses to install measures that have been shown to recharging points. This would involve engaging directly with the largest businesses with be most effective at addressing the employee car parks to highlight the benefts of encouraging use of EVs rather than conventional vehicles; by providing free advice; and by providing match funding to ‘high signifcance barriers’. These ‘innovator’ and ‘early adopter’ businesses wishing to install recharging points in existing measures will be important in driving parking spaces. These measures would be most effective if linked to exemption from a EV uptake across the ‘early adopter Workplace Parking Levy. market’, and will need to follow the 10 Publish advice for residents on home recharging and guidance for electricians on the implementation of the top priority type of facilities needed (including issues to be considered in communal parking areas). Local authorities to disseminate information. measures. 11 Publish national planning guidance on the provision of recharging bays and infrastructure Tertiary priorities are those measures as part of a parking strategy which supports wider sustainable transport objectives. which may be needed to expand EV 12 Update building regulations to set out minimum requirements regarding the provision of uptake to the mass market, or are electrical infrastructure and recharging points in all new buildings. areas where Government action may 13 Set up a Working Group co-chaired by the Transport and Energy Ministers of be required if the private sector does stakeholders from the energy and transport sectors and including consumer groups, not succeed in addressing barriers tasked with addressing the electricity generation and distribution requirements for EVs. identifed as being of ‘moderate 14 Local authorities work with existing car club operators to introduce EVs into feets and signifcance’. introduce EV-based car clubs in other cities. 15 Scottish Government, local authorities and other public sector organisations support The top priorities identifed through an earlier than average switch to low carbon emissions vehicles for public sector feet the assessment process are presented vehicles (cars and vans) through procurement policies (e.g. extending funding for the in Table 3. They represent a Low Carbon Vehicle Procurement Support Scheme); and a 2020 target for 100% of powerful package of measures, and public sector feets to be electric, where appropriate. if successfully implemented would 16 Scottish Government should lobby the EU to tighten the EU target for the emissions ensure that Scotland is well placed to intensity of new cars and vans produced by manufacturers. decarbonise road transport, reduce Table 3. Priority measures designed to tackle the most signifcant barriers and increase dependency on oil, maintain good electric vehicle uptake in Scotland mobility levels, and grow the Scottish economy.
56 139 Powering ahead: how to put electric vehicles on Scotland’s roads
Figure 2. Tesla Model S full-sized electric four-door sedan, produced by Tesla Motors. On show in Santa Monica, California (Nov 2012)
The overall propriety is to put in Scotland and WWF Scotland, and priorities and actions to advance place an EV Strategy and Action aims to establish Scotland as an EV wholesale adoption of EVs Plan for Scotland to provide clarity pioneer, maximising the economic, • EV Readiness Initiative: work to on policy priorities, describe support environmental and social benefts establish a portfolio of projects mechanisms, defne the intended of EVs as an integral part of a to advance EV adoption and market model, identify R&D support sustainable transport system and a implement the recommendations Environment & Sustainability and set out the route map for an smart energy grid. of the roadmap. established charging infrastructure A key focus is the delivery of three (Measure 1). By engaging a range of stakeholders key activities, which will commence in this process, E-cosse will create Signifcant progress has been made from April 2012: shared commitments across on this front since the publication • Establishment of an EV Strategy government and industry. The of the Atkins and WWF Reports. Board: a high-level forum of initiative has been established On 28 March 2012, Keith Brown leaders from government and with the support of experts from MSP, Minister for Transport and industry to promote policies and a number of leading organisations Infrastructure, announced a new programmes that advance EV which will continue to play a crucial collaboration between government, adoption and maximise economic role. These include: Allied Vehicles, industry, WWF Scotland and opportunities for Scotland Axeon, Dundee City Council, EVAS, other key stakeholders to advance IBI Group, Nissan, Scottish Power, wholesale adoption of electric • Preparation of an EV Roadmap: Serco, Siemens and SSE. vehicles (EVs) in Scotland16,17. expert stakeholders will work with E-cosse (www.e-cosse.net) has Transport Scotland to develop been jointly initiated by Transport a shared vision and set future
57 Other organisations will also be encouraged to join this initiative and Acknowledgment provide support in realising the full potential of EVs to contribute to the The paper was presented at the 8th annual Scottish Transport Applications economic, environmental and social and Research (STAR) Conference, 16 May 2012. transformation of Scotland. Notes Summary and 1. Atkins (2011) Electric Vehicles: Driving the change. The full report conclusions provides detailed descriptions of each barrier and its relative impact on the public, corporate and private car feets before setting out detailed The Climate Change (Scotland) Act policy analysis of the most effective policy measures to overcome these 2009 requires the almost complete and increase the uptake of EVs. The full report can be found at http:// decarbonisation of the transport scotland.wwf.org.uk/what_we_do/tackling_climate_change/electric_ sector. This means that alongside vehicles/ a massive shift in investment away from roads and towards active 2. WWF Scotland (2011) Powering Ahead: how to put electric cars on travel, public transport and smarter Scotland’s roads. See assets.wwf.org.uk/downloads/powering_ahead_ measures18, Scotland must replace web.pdf its fossil fuelled cars with low 3. Scottish Government (2009) Meeting Scotland’s Statutory Climate carbon vehicles. In order to achieve Change Target this, the embryonic electric vehicle market needs to be supported and 4. See http://ww.scotland.gov.uk/Resource/Doc/346760/0115345.pdf encouraged by effective government 5. www.mitsubishi-cars.co.uk; www.nissan.co.uk interventions. This paper presents a powerful package of measures 6. See http://www.dft.gov.uk/pgr/sustainable/olev/grant1/ that, if adopted by national and 7. Based on feedback provided at a seminar for vehicle feet managers, local government, would ensure jointly hosted by the 2020 Climate Group and Transport Scotland, Scotland is at the forefront of the EV to discuss the practicality of adoption of low carbon vehicles at feet revolution. operational level While the scale of the challenge is 8. See http://www.racfoundation.org/media-centre/98375 signifcant, electric vehicles offer an exciting and substantial opportunity 9. See http://www.thisismoney.co.uk/money/markets/article-2023141/ to decarbonise road transport in General-Motors-forecasts-4m-electric-vehicles-year-built-2020.html Nick Scotland, reduce dependency on oil, Reilly, boss of Vauxhall Opel said,“I believe that by the end of the decade maintain good mobility levels, and 20% of all car sales will be electric.” grow the Scottish economy. 10. See http://green.autoblog.com/2011/04/21/ford-25-most-electric-vehicle- readycities/ 11. See http://www.scotland.gov.uk/Resource/Doc/277292/0083254.pdf 12. See www.mu.peugeot.co.uk 13. See http://www.accenture.com/nl-en/Pages/insight-changing-game-plug- inelectric-vehicle-pilots.aspx for full report from Accenture. 14. Arup and Cenex (2008) Investigation into the Scope for the Transport Sector to Switch to Electric Vehicles and Plugin Hybrid Vehicles 15. See http://www.dft.gov.uk/publications/plug-in-vehicle-infrastructure- strategy 16. The EVent: Powering Scotland through Electric Vehicle Technology, Scotsman Conferences in association with Jewel & Esk College, Edinburgh, 28 March 2012 17. See http://assets.wwf.org.uk/downloads/microsoft_word___e_cosse___ stakeholder_briefng___march_2012.pdf
58 139 Powering ahead: how to put electric vehicles on Scotland’s roads
18. Smarter Travel Choices measures include: school and workplace travel plans that encourage the use of ‘greener’ transport modes like walking, cycling and buses, personalised travel planning, promotion of walking, cycling and public transport, car clubs and car sharing schemes, tele-working, teleconferencing and home shopping. Environment & Sustainability
59 60 Environment & Sustainability 61 140 2 . Commonly, heat . Commonly, 5 2 2 . Electrical energy is used 4 2 gas-fred boilers (where available) boilers (where gas-fred for pumps, supplementary crop for pumps, supplementary crop systems, lighting and environmental whilst CO is often utilised to enrich the glasshouse atmosphere and the glasshouse atmosphere yield crop increase and CO supplied by natural are For commercial glasshouses, heat For commercial is the majority energy requirement, and is used to maintain internal within specifed limits temperatures facilitate optimal growth to in order up to 12 months of for regimes on the specifc depending the year, contexts use represents a signifcant fnancial use represents relatively where especially burden, low cost fossil fuels (such as natural available and where not gas) are higher cost fuels such as kerosene required. fuel oil or grid electricity are 2 . In the 1 e . In fnancial 2 3 2 /year, resulting in annual resulting /year, 2 . Intensive horticulture is . Intensive horticulture 2 2 2 within the modelling tool to carry out multi-parametric techno-economic within the modelling tool to carry out The impacts of both presented. are analyses for various operational scenarios mechanisms upon economic support capital grant and generation tariff-based variations in feedstock fuel investigated, along with those of feasibility are prices. Net CO CHP the implementation of biomass accruing from reductions commercial glasshouses glasshouses commercial CO emissions for the sector in excess very energy intensive; combined energy consumption values for UK glasshouse operations can exceed 600 kW h/m of 2 million tonnes indicate that feasibility is very sensitive to the relationship between specifc to the relationship indicate that feasibility is very sensitive their match with glasshouse temporal biomass CHP power:heat ratios and along with economic factors profles, electrical and thermal energy demand support. Withsuch as specifc levels of capital and tariff-based the utilisation biomass CHP offers available fnancial support mechanisms, of currently CO economically viable signifcant for realising signifcant promise emission the UK as a case study, energy and COthe UK as a case study, demands of candidate glasshouse terms, for a sector characterised by of small businesses a preponderance operating within the context of rising energy prices, this intensive energy UK, the horticulture sector has a UK, the horticulture value of over £2bn and accounts 12% of agricultural for around output are also assessed. Finally, technical options, marginal costs and sale tariffs tariffs technical options, marginal costs and sale also assessed. Finally, are for CO for specifc scenarios. The results evaluated and supply are recovery installations on an hourly basis are established using both measured and using both measured established installations on an hourly basis are for and thermal generation profles benchmark datasets. Modelled electrical biomass CHP systems of rated available small-scale a number of commercially outputs of 0.1–5 MW of their application also derived, and the results are component of the EU’s agricultural component of the EU’s land areas with signifcant sector, occupied by glasshouse operations. In the Netherlands and Spain alone, Ha and 50,000 Ha 10,000 around dedicated currently are respectively to glasshouse operations Introduction Introduction is a key Intensive horticulture The feasibility of biomass CHP of biomass The feasibility and COas an energy for source Abstract been developed to examine the A techno-economic modelling tool has and power (CHP) technologies to provide feasibility of biomass combined heat the energy and CO Using horticultural glasshouses. demands of commercial reductions in this sector. in this sector. reductions Loughborough University Loughborough Dr. Paul Rowley Paul Dr. Senior Lecturer for Renewable Centre Energy Systems Technology Oliver Moreton Senior Engineer Energy Atkins whilst natural gas-fred combined using the UK as a case study. Specifc and simulation studies have been heat and power (CHP) with fue gas objectives of the work include (a) to carried out in the UK in order to catalyst cleaning can also be utilised develop a methodology to assess and model energy consumption profles to additionally provide electricity, model glasshouse demand profles and propose specifc energy demand 4,10,12 heat and CO2. Due to the daytime for electricity, heat and CO2 along reduction scenarios . Glasshouse
requirement for CO2, in specifc with associated CO2 emissions; (b) structures typically comprise a cases, hot water thermal storage can to carry out discounted cash fow single layer of 3mm thick glass set
be used to overcome the mismatch net present value (NPV) and CO2 in an aluminium framework, and between night-time heat and reduction analyses for candidate the majority of heat loss occurs
day-time CO2 demands, although biomass CHP technologies and via conduction and ventilation this is not commonly utilised in glasshouse applications and (c) to mechanisms13. Conduction losses 6,7 the UK context .With commercial assess the potential of CO2 recovery depend on the glasshouse material glasshouse operators coming under from biomass CHP and evaluate conductivity (defned by elemental increased pressure to reduce both associated cost scenarios. U-values), whilst ventilation losses
operational costs and CO2 emissions, depend on the age, type and biomass CHP (with CO recovery condition of the glasshouse along 2 Model development where viable) offers a potential with the nature of any active means to achieve these goals, and methodology ventilation system9. A previous especially where grants or enhanced heuristic modelling study, validated tariffs for small-scale renewable A numerical cashfow model against measured fuel use data14 electricity and heat generation was developed using the Excel has quantifed glass house heat loss, are available. A number of small- spreadsheet environment in order and this is the basis for the current to assess the economic performance scale (0.1–5MWe) biomass CHP fabric heat loss model, given by the technology platforms are currently of the candidate BCHP platforms, following equation: at or near commercial status. In using both system and demand data Equation 1 addition to capital and operational as inputs. Assessment of economic viability was carried out using a costs, biomass CHP viability depends Qf = UA(t - t ) - K largely on operational effciency, net present value (NPV) simulation t i o analysis for each platform (see thermal/electrical energy generation Qf characteristics and site-specifc Section Economic analysis below). where t is the rate of heat loss [W], energy demand profles7a. However, The model allows the operation U is the thermal transmittance of the there has been very little recent of the system to be adjusted hour material, also known as the U-value research focussed upon the techno- by hour and allows many different [W m-2 K-1], A is the elemental area scenarios to be evaluated. Although 2 economic analysis of biomass [m ] and ti and to are the internal and CHP technologies in practical only a specifc UK glasshouse external temperatures respectively applications8,9b, whilst one study has application was considered in this [ oC] and K is the net short wave been carried out for biomass heat- study, the model allows demand radiation [W/m2]. K may be inferred only applications in a glasshouse profles for any particular case to by using sol–air temperature values context10. Thus, as biomass CHP be analysed if suitable data are given by the following equation: available. Likewise, other base technologies mature towards wider Equation 2 commercial availability, the need case assumptions may be adjusted depending on the specifc context in for evaluation of applications of the a . I - ∆Q which the model is applied. ir technology within specifc sectors tsol-air = t o ( ho ) such as glasshouse horticulture Heat demand analysis becomes more pressing in order to where a is the solar radiation inform and educate stakeholders The protected crops sector currently absortivity of a surface [-], I is the about the realistic potential of the accounts for around a quarter of the global solar irradiance [W/m2] and direct energy use in UK agriculture, technology. ∆Qir is the extra infrared radiation and this is primarily for heating and due to difference between the Within this context, the aim of humidity control11. Heat is required external air temperature and the the present work is to develop a to temporally maintain crop-specifc apparent sky temperature [W/m2]. In model suitable for multi-parametric temperature regimes within the practice, solar radiation estimates can techno-economic analysis of various internal glasshouse environment, be made based on meteorological biomass CHP platforms as a source and typical set points range from observations, and sol–air temperature of electricity, heat and CO for 2 16C to 25C depending upon crop reference datasets are available for commercial glasshouse applications, requirements. Previous empirical applications such as this15.
62 140 The feasibility of biomass CHP as an energy and CO2 source for commercial glasshouses
The effective U-value of the Electricity demand depends on the type of crop, the rate glasshouse material also depends of photosynthesis and the ventilation Electricity is primarily required to on incident wind speed16, and this rate. To determine the hourly operate pumps, fans and ancillary relationship is given below by the glasshouse CO demand the supply equipment which control the 2 following equation: rate of CO kg/h/ha and associated internal glasshouse environment, 2 light intensity for the user’s specifc Equation 3 whilst lighting is also often used to growing strategy is specifed as aid continued crop growth during U = U + 0.6336w model input variables, together with v c periods of low lux levels. For the a daily solar radiation profle for where U is the elemental U-value purposes of this study, electricity v each month. For the purposes of this including wind effects, U is the consumption data were obtained c study, the maximum CO demand constant U-value of the material from a number of commercial 2 was set at a typical value of 250 and w the wind speed [m s-1]. To glasshouse operators, and this was kg/h/Ha4 and proportionally reduced determine the heat losses due to used to model an hourly demand when radiation levels fall below 400 ventilation, a value for the glasshouse profle to represent a typical W/m2. air change rate, expressed as air day in each month per square changes per hour (ACH) is needed. meter. Validation of modelled The ability to use biomass CHP This depends on the type and data was subsequently carried exhaust gases as a source of condition of the glasshouse and the out via correlation with published crop-growth promoting CO2 can incident wind speed9. Roof vents benchmark data for UK glasshouse potentially add economic benefts 3 are also used to actively control the energy consumption . Modelled data to a scheme provided CO2 sales internal temperature during sunny for both heat and electricity demand revenue offset the increased capital days and thus the air change rate will were then used as a reference and costs. However, as biomass exhaust change as the vent position is varied. linearly scaled according to specifc gas contaminants signifcantly Equation 4 gives the ventilation heat glasshouse foor area parameters. exceed permitted levels (Table loss rate. Such an approach is consistent with 1), feedstock fuel quality control combined with primary (pre- Equation 4 current accepted methodologies for assessing building energy combustion) or secondary (post Q consumption using benchmark combustion) gas treatment is v = 0.33NV(t - t ) t i o data3a, and is suitable for use in required. In the current study, the Q heuristic modelling approaches. maximum additional capital cost of where v is the heat loss due to t CO2 recovery equipment acceptable ventilation, N the air change rate per Statutory Biomass whilst maintaining at least the hour and V the glasshouse volume limit (ppm) corresponding base-case NPV for 3 [m ]. The total heat loss rate from Sulphur <0.2 8–29 each platform was modelled in order dioxide [SO ] the glasshouse can be calculated by x to assess the feasibility of specifc combining the fabric and ventilation Ethylene 0.2–0.4 4–11 primary or secondary gas treatment [C H ] heat loss components as shown in 2 4 proposals. the following equation: Carbon monoxide 1–5 109–1746 For exhaust gases to be suitable for Equation 5
[CO] glasshouse applications, it must meet Environment & Sustainability Q Q Q Nitrogen strict purity requirements. As can T = f + V 12–34 86–180 t t t oxide [NOx ] be seen from Table 1, untreated biomass combustion gases are not Table 1. Glasshouse exhaust gas appropriate for direct injection into For modelling purposes, contamination limits and typical solid a greenhouse atmosphere7. Under material U-values and measured biomass fuel content6,19 meteorological data for the England complete combustion 1 MWh of Midlands were used to calculate CO demand and supply energy provided by cellulose biomass 2 would typically produce 308 kg CO , total hourly annual heat demand, modelling 2 and subsequently an average daily whilst natural gas produces 184 Carbon dioxide (CO ) is required for demand profle was generated for 2 kg CO2. Therefore biomass has the plant photosynthesis, and increased each month. Validation was carried potential to provide a greater rate CO concentrations of typically out via comparison with metered 2 of CO2 per MWh at a competitive 1000 vppm within the glasshouse energy demand data from glasshouse cost provided gas purifcation can be atmosphere can lead to improved operators along with published carried out economically. crop productivity and fruit yields4,17,18. benchmark datasets3. The rate of CO2 supply required
63 Biomass CHP system modelling turbine system, but the working the investment results in a rate of fuid has a much lower boiling point return greater than the minimum To model the technical and and can therefore achieve higher rate d, and in the absence of economic performance of a number effciencies in smaller systems. alternatives this would be a proftable of current commercial biomass investment. However, when the NPV CHP systems, data were obtained Direct solid biomass combustion with is negative, the investment would from both published sources and air turbine (Sol-AT) not give a return at the minimum manufacturers for systems with Solid biomass is combusted directly rate d, and indicates a non-proftable an electrical power output of and used to heat air via a heat investment. To assess candidate 0.1–5MW 20,21. System descriptions, e exchanger. The heated air is then biomass CHP feasibilities, temporal identifer codes and performance expanded through a turbine which is glasshouse energy and CO demand data are given below and in Table 2 used to generate electricity. profles along with CHP performance 2, together with equipment cost, and capital/operational cost data feedstock and energy price data Combined cycle biomass gasifcation were used to carry out the NPV obtained from communications with CHP (Gas-CCST) analyses for the candidate systems. individual manufacturers of each Combined cycle biomass gasifcation The model allows for the selection technology platform and system CHP is a development of standard of glasshouse size, commodity and integrators, along with reference to biomass gasifcation technology, fnancial costs and CHP operating published sources from the EU and together with an internal combustion regime making the model fexible for US and communications with utility (IC) engine. The exhaust gases pass all glasshouse applications and future companies [10,21a–e]. through a heat recovery steam use. For the purpose of this study a Solid biomass gasifer with internal generator, and the steam is then 40,000 m2 glasshouse is considered. combustion engine (Gas-IC) used to generate further electricity. An initial ‘base case’ economic Potential benefts include improved analysis was carried out, and a Solid dry biomass is converted into electrical effciency and enhanced subsequent multi-parametric analysis a combustible gas by heating in combustion of CO components. was achieved by investigating the a reduced oxygen environment. effects of varying fuel price, capital The gas is then cleaned to remove Economic analysis grants and CO costs. The effects particulates and other contaminants 2 Assessment of economic viability was of enhanced generation tariffs was before it is combusted in a modifed carried out using a discounted cash also investigated, in light of current or specifcally designed spark ignition fow net present value (NPV) analysis schemes such as the UK renewable engine. As for other biomass CHP for each scenario. NPV is a measure electricity feed in tariffs (FITs) and platforms, heat can be recovered that expresses the initial capital renewable heat incentives (RHI). from the gas generation plant, from investment and all subsequent cash Finally, the economics of recovering the engine and the engine exhaust fows arising from avoided electricity CO from biomass CHP and the plant. 2 costs and sales of exported energy minimum CO2 sale price required Liquid biomass-fuelled compression (and CO2 where relevant) as an to maintain viability were analysed. ignition engine (Liq-IC) equivalent amount at time zero. This Table 3 shows the base case approach is particularly appropriate parameters used in the study10,21a–j. Virgin vegetable oil or processed when the cash fows associated with It should be noted that base case used cooking oil is combusted in a project vary over time, as is the net electricity export prices include a modifed compression ignition case with a biomass CHP investment. generation benefts available in the engine. Fuel prices are generally The net present value of a cash fow UK renewable energy generation, higher compared to solid biomass at time t is given by: including Renewable Obligation and more susceptible to price Certifcates (ROCs) and Climate variations. However, capital costs are Equation 6 Change Levy Exemption Certifcates typically lower due to the lack of a n A (LECs). dedicated fuel processing sub-system. NPV = t ∑ (1+d)t t=0 In common with other EU states, Direct solid biomass combustion with to access the fnancial incentives ORC (Sol-ORC) where At is the project’s cash fow (revenues minus costs) in time t, available to CHP in the UK the Organic Rankine Cycle (ORC) with t taking values from year 0 to scheme must meet quality criteria platforms use solid dry biomass fuel year n and d is the discount rate (an as set down in the EU CHP which is combusted directly and used interest rate used to calculate the Cogeneration Directive and the UK to evaporate a secondary organic present value of future cash fows). CHP Quality Assurance Scheme fuid which drives a small turbine. 22 When the calculated NPV is positive, (CHPQA) . The quality score is ORC is similar to a traditional steam dependent on the electrical effciency 64 140 The feasibility of biomass CHP as an energy and CO2 source for commercial glasshouses
Electrical Thermal Electrical Overall Aprox Specifc Power:heat Name Description output output effciency effciency installed cost ratio (MWe ) (MWth ) (%) (%) cost (£) (£/kWe ) Woodchip fuelled Gas-IC downdraft gasifer with IC 1.00 1.26 23 58 4.4:6.3 4.90 4900 engine Vegetable oil fuelled IC Liq-IC 0.40 0.30 40 85 4:3 0.15 370 engine. Woodchip direct Sol-ORC 1.25 4.00 19 90 1.2:4 5.02 3960 combustion ORC Woodchip combined cycle Gas-CCST gasifcation IC and steam 4.00 2.00 40 61 2:1 16.5 4020 turbine Woodchip direct Sol-AT 0.1 0.2 21 83 2:5 0.52 4770 combustion air turbine Table 2. Biomass CHP system details. Economic data are shown in GBP (£). At the time of writing, exchange rates for 1GBP were 1.60USD and 1.18Euros respectively and the useful heat generated from Parameter Base case value the scheme on an annual basis. CHP Solid biomass heating value (HHV) 19 GJ/tonne performance is optimised in cases when a relatively constant heat Solid biomass moisture content 10% demand is present throughout the Solid biomass heating cost 50£/ODT year; the plant can then be sized Liquid biofuel heating value 37 GJ/tonne according to this demand and the Liquid biofuel heating cost 500£/tonne CHP operated continuously. However, Availability 90% glasshouse heat demand is seasonal Average electricity base load net export price 145£/MW h and CHP system fexibility is an important consideration. Compared Average electricity peak load net export price 150£/MW h to natural gas fuelled technology, Electricity onsite sale price 55£/MW h solid biomass-fuelled CHP has lower Electricity import price 68£/MW h operational fexibility, and therefore Gas import price 17.4£/MW h any modelling approach needs Heat sale price 20£/MW h to take into account the different Glasshouse CO sale price 65£/tonne operating regimes and system sizing 2 needed to maximise returns. Where Waste disposal £10/tonne benefcial generation tariffs are the Project period 15 Years key driver for biomass CHP, this Infation rate (RPI) 3% Environment & Sustainability partly decouples proftability from Discount rate 10% the export electricity price alone. Loan interest rate 9% For thermal energy supply, solid fuel biomass CHP for glasshouse Table 3. Base case modelling assumptions applications needs to be sized to somewhat from those pertaining meet the base load heat demand, Results and discussion and therefore minimise any surplus to other scenarios. For example, heat and maintain good quality feedstock prices may be higher or The results for energy and CO2 lower depending on specifc market CHP status under the UK CHPQA demand and supply analyses scheme. Liquid fuel CHP has much conditions at a particular time, along with an economic modelling and may be infuenced by many greater fexibility in terms of system appraisal are presented below. It modulation and is comparable to variables of too complex a nature for should be noted at the outset that inclusion in a heuristic model of this natural gas fuelled CHP in terms of these results pertain to a UK specifc fexibility. This enables liquid fuel CHP type. However, the scenario-based scenario in which the model’s results presented here give a useful to operate in either base load or peak baseline assumptions (especially in load mode or indeed any profle in indication of the feasibility of BCHP terms of plant costs, energy tariffs technologies in other contexts, which between. and feedstock prices) may differ 65 can be explored in more detail via the CO2 demand detailed application of the software CO requirements increase during which is available from the authors. 2 daylight hours and reach a peak Heat and electricity demand around midday. During the growing
analysis season, CO2 demand correlates with crop growth rates and is greater Electricity, heat and CO demands for 2 in the summer months due to the 2 the 40,000 m base case glasshouse higher solar irradiance and longer are shown in Figure 1. For the daylight hours. CO2 is commonly base case scenario, modelled space provided by natural gas-fred boilers, heating winter power demand peaks and in some cases can be utilised Figure 2. Base case economic analysis 2 at 148 W/m , and is generally higher at concentrations of typically 1000 during day time due to the higher vppm, together with heat storage, to Effect of capital grants internal temperature requirements increase the combined effciency of Various capital and generation-based for optimal crop growth compared CO and heat production6. As natural incentives exist across the EU for CHP to night time. Monthly heat energy 2 gas is one of the cleanest fossil fuels, and renewable energy equipment23. consumption ranges from 21 kW the CO produced is suitable for In the UK, the Government’s h/m2 in the summer to 84 kW h/ 2 directly supplying the glasshouse3. Enhanced Capital Allowance m2 in winter. The calculated annual Alternatively, bottled CO can scheme enables businesses to claim heat demand of 625 kW h/m2 is 2 also be used for direct glasshouse 100% frst year allowance against consistent with accepted benchmarks enrichment, offering high gas purity tax for investments in equipment for glasshouses in the UK3. For and operational fexibility7, but this that meets specifc energy-saving the baseline analysis, the cost of incurs an extra gross cost of typically criteria, including good quality CHP. supplying heat loads via a gas-fred £100/tonne CO . Therefore, using current (2010) UK boiler operating at 90% nominal 2 corporate tax rates, the analysis was effciency was calculated. Economic analysis repeated assuming a 25% effective Electricity demand profles were An initial discounted cash fow capital grant is available, and the modelled using half hourly simulation analysis was carried out results are shown in Figure 3. In this glasshouse electricity consumption using typical current UK market base case, assuming base-case variable data over a 2 year period to create case parameters shown in Table 3. costs, all systems are proftable typical daily profles for each month. The simulation results are shown in (showing a positive NPV) up to a Electrical demand varies from a Figure 2, and indicate that feasibility specifc number of modules installed, minimum of 0.5 W/m2 in the winter for all systems is related to the extent after which point excess wasted to a maximum of 2.5 W/m2 in to which glasshouse electrical and heat generation rapidly reduces the summer, owing to the added thermal energy requirements match viability. Improved proftability is
operation of CO2 forwarding fans. the generation capabilities of each especially marked for systems with The annual electricity demand was candidate biomass CHP system. higher specifc capital cost due to calculated to be 13.5 kW h/m2. For the 40,000m2 glasshouse base the proportionally greater reduction Again, this is consistent with industry case, reductions in NPV as BCHP in up-front investment for these benchmark data3. module numbers (and therefore systems. electrical and thermal energy rated outputs) increase are due to relatively low CHP overall electrical: thermal generation ratios, resulting in increasing amounts of excess heat being generated for which no value is received. Base case proftability is marginal or poor for all systems except the liquid fuelled IC-based system, the viability of which is largely due to the lower equipment 2 Figure 1. 40,000m Glasshouse monthly capital cost compared to other Figure 3. Base case economic electricity, heat and CO demands 2 platforms. performance including 25% capital grant
66 140 The feasibility of biomass CHP as an energy and CO2 source for commercial glasshouses
Effect of enhanced electrical increase NPVs for all candidate power to heat ratios (resulting in generation tariff biomass CHP technologies, especially higher revenues from sales of high- for those systems with relatively value electrical energy) were found A number of EU states currently offer low electrical:thermal effciencies. to be the least sensitive to fuel price enhanced generation based tariffs Furthermore, the availability of a increases. Fuel price sensitivity was for renewable electricity generation, thermal generation incentive of this then investigated assuming enhanced including Germany and Spain24,25. level would also help offset fuel heat generation tariffs of £10 and Although biomass CHP is currently price sensitivity, and help reduce £15 respectively are available. In excluded from UK feed-in tariff risks associated with volatility in this case, greater benefts accrue (FIT) support, the technology was biomass CHP feedstock fuel prices. for those systems with relatively low originally included in proposals for Therefore, when combined with power to heat ratios. The maximum the scheme with a proposed tariff of other risk mitigation measures fuel prices that return a positive NPV £140/MW h for combined generation (including the implementation of are shown in Table 5. and export26. Therefore, given the UK secure long-term supply contracts government’s ongoing programme Site CO reductions within a mature supply chain or the 2 of periodic reviews of the FIT scheme development of vertically integrated For the base case scenario, the and eligible technologies, a sensitivity corporate or cooperative ‘risk/reward’ energy consumption for a 40,000m2 analysis was carried out to investigate structures which include feedstock glasshouse with heat provided by potential benefts of a FIT for biomass suppliers), the heat generation tariff- natural gas boilers and grid-derived CHP operators, and evaluate tariff based subsidies can be regarded as electricity results in annual CO rates required to maintain proftability 2 invaluable. emissions of approximately 6660 (a positive NPV). The results are tonnes, based upon current CO shown in Table 4. As is the case for 2 emission indices for natural gas and capital grants, specifc factors such grid-derived electricity respectively. as electrical:thermal effciency and Against this benchmark, and in specifc capital cost for each platform light of current and forthcoming EU have a strong impact on proftability carbon reduction commitments and and minimum required FIT levels. compliance targets, CO emission Furthermore, the range of FITs 2 reductions for each candidate required to maintain a positive NPV biomass CHP system were calculated, for the various technologies under and the results are shown in Figure consideration show that banding of 5. For the 40,000m2 base case, FITs for different sub-technologies Figure 4. NPV sensitivity to level of heat although CO reductions increase (such as combustion and gasifcation) 2 generation tariff with the number of biomass CHP may be benefcial at a policy level. modules (and hence renewable Effect of enhanced thermal Fuel price sensitivity energy capacity) installed, in an generation tariff Analysis of the effects of variations operational setting, CO2 reductions must also be considered in light of The UK Government’s renewable in fuel price on NPV for the base economic performance. Without heat generation incentive (RHI) case scenario show that systems
capital grants or enhanced Environment & Sustainability scheme offers thermal generation- with higher electrical effciencies and based support for biomass system operators at proposed rates System Gas-IC Liq-IC Sol-ORC Gas-CCST Sol-AT ranging from £10 to £79 per MWh Tariff (£/MW h) 147 120 117 135 148 depending on system scale. In order to assess the potential value of RHI Table 4. Gross generation tariff required for positive NPV incentives, sensitivity analyses were carried out for all candidate systems, System Base case HGT@£10/MW h HGT@£15/MW h and the results are shown in Figure Gas-IC £46 £59 £65 4. It is evident that a signifcant Liq-IC £598 £628 £643 positive effect on the NPV for all systems accrues for an RHI level as Sol-ORC £51 £83 £90 low as £5/MW h. The systems that Gas-CCST £65 £71 £74 beneft most by the RHI are those Sol-AT £50 £65 £72 that have lower electrical power to heat ratios, and an RHI value in Table 5. Maximum fuel price for positive NPV with two heat generation tariffs (HGT) £/ the range of £10–15/MW h would MW hth 67 generation tariffs, the analysis of flters/cyclones or via scrubbing for other contexts. Although care
indicates that a 45–60% CO2 saving using a fne water spray to intercept should be taken when utilising input can be achieved using gasifcation the particles26b. data derived from current or future and liquid fuelled IC platforms empirical case studies, these data respectively while maintaining a would nevertheless represent an marginally positive NPV, whilst the invaluable validation resource. availability of fnancial incentives Specifc input parameters such as up to levels currently available or equipment and fuel costs, energy sale proposed within the EU17,18 improves and purchase tariffs, biomass heating both fnancial and CO reduction 2 value and equipment performance viability for all candidate platforms. effciencies can vary signifcantly both temporally and geographically. Future trajectories for biomass feedstock prices and availabilities Figure 6. Effects on NPV due to variation are by nature highly uncertain. in glasshouse CO sale price with CO 2 2 Fuel supply risk (in terms of both recovery equipment investment at £1,000 k/MW contracting price uncertainties e and production variation) is a key The role of energy storage issue when projecting the results of studies of this type. Given Due to the demand mismatch the lack of a mature fuel supply between heat, electricity and CO 2 chain, together with the range of Figure 5. Effect of system type and generation, thermal stores (including alternative feedstock uses (such as aquifer buffers) offer the potential to number of modules on glasshouse CO2 the paper or furniture industries) if reduction store excess heat generated during prices in alternative markets exceed CO and electricity production, as is 2 viable biomass fuel prices, feedstock 27 Glasshouse CO2 recovery currently utilised in the Netherlands . could be sold to these alternative With an assumed glasshouse However, within the UK context, uses, resulting in an unviable BCHP CO sale price of £35/tonne, The glasshouse heat storage is much less plant. However, this barrier is not 2 commonly utilised, and numerous analysis shows that for CO2 recovery insurmountable if measures such as capital costs up to £1m/MWe, all commercial and technical barriers the use of appropriate long-term systems exhibit an increase in NPV. need to be overcome prior to its supply contracts are implemented. Subsequently, the sensitivity of the widescale implementation in the Furthermore, as the global biomass UK28. Therefore, in the current work, CO2 sale price was investigated fuel feedstock supply chain matures assuming a fxed gas recovery capital the economic viability of energy (largely driven by the high-volume cost of £1m/MWe. The results are storage technology was not analysed and low-cost requirements of the shown in Figure 6, and indicate as a means for utilising wasted heat largescale co-fring community) this all systems exhibit proftability for generated as a result of energy and may act to mitigate upward pressure CO2 mismatch. However, this is the CO2 sale prices ranged from £5 on future feedstock prices. In specifc to £35/tonne depending on the focus of current ongoing effort, and terms, a recent study by the US Dept. specifc biomass CHP platform under an analysis of the potential viability of of Energy21i projected availability consideration. thermal storage will be the subject of of biomass feedstock up to 2030 future work. based on three candidate fuel prices, It is beyond the scope of this study namely $20, $40, and $80 (£13, £26 to evaluate specifc technical routes Financial sensitivities and £52 respectively) per dry tonne for CO recovery. However, a 2 It should be noted that care in for forest biomass and $40, $50, and previous study26a posited a polyolefn transferring the results of the current $60 per dry tonne for agricultural membrane gas absorption process study to other contexts should be biomass. This study indicated that in for the capture of carbon dioxide taken. Given the lack of validated the case of the USA, forest resources from fue gases and subsequent data on the performance of BCHP are available over a wider price range delivery to greenhouses at practical systems in glasshouse applications than agricultural resources, with cost. In specifc biomass applications (and indeed on the performance increasing quantities at higher prices, it may be necessary to precede such of small scale BCHP installations whilst the resource potential does not a process by techniques to reduce in general), the results represent increase signifcantly over time given particulate emissions in the exhaust indicative, rather than defnitive, the standing inventory nature of the gas. This can be achieved via the use fnancial and energy performance
68 140 The feasibility of biomass CHP as an energy and CO2 source for commercial glasshouses
resource and how it is managed. optimal base-case analysis shows that Given these issues, any future users approximately 45% of annual heat Glossary of the modelling tool should take demand, 90% of electricity demand ACH: air changes per hour care in verifying the accuracy of input and a 45–60% reduction in site CO2 data. To address uncertainties in such emissions is achievable. CHP: combined heat and power parameters, future development of The analysis also suggests that the the model would beneft from the EU: European union availability of a 25% capital grant application of probabilistic methods, can result in project proftability, due FIT: feed-in tariff such as Monte Carlo modelling or to offsetting relatively high capital Bayesian network approaches, and IC: internal combustion costs for biomass CHP technology. work to this effect by the research An enhanced thermal energy NPV: net present value team is ongoing29. generation tariff at a minimum price ORC: organic rankine cycle of £10/MW h provides signifcant UK: United Kingdom Conclusions beneft to biomass CHP viability by improving overall project proftability IC: internal combustion A modelling tool has been developed and reducing sensitivity to fuel that facilitates the feasibility price increases, whilst an enhanced assessment of biomass CHP options electrical generation tariff of for commercial glasshouse operators approximately £140/MW h provides world-wide. By varying input increased forward economic visibility. parameters including local climactic It should be noted that these support data, energy/CO2 consumption levels are consistent with those profles and tariffs, and biomass currently being implemented in a CHP cost and performance data, number of EU states and beyond. proftability assessments can be Generation-based subsidies are best carried out on a location and placed to contribute to reduced application-specifc basis in light of project risk if guaranteed over the time and location-specifc cost and long term, and are index-linked energy tariff data along with any to infation. When combined with available support subsidies. additional strategies designed to help For the UK case study presented mitigate fuel price volatility such as in this paper, the use of specifc long-term feedstock price contracting techno-economic input parameters or project ‘joint-venture’ vehicles shows that careful selection of the that include feedstock suppliers, type and scale of BCHP platform overall project risk can be reduced for a specifc glasshouse application signifcantly. is critical in order to realise project Although biomass CHP exhaust gases proftability. The majority of solid are not directly compatible for use BCHP technologies are currently
in glasshouses, it may be feasible Environment & Sustainability characterised by relatively high capital to utilise these for CO2 enrichment costs, and whilst liquid biofuel IC- purposes with further treatment. By based systems exhibits relatively low realising CO2 values of around £35/ capital cost (and hence the shortest tonne (either via direct sale on site payback periods for the base case of via carbon trading mechanisms) cost assumptions used in this study) an additional investment of up to £1 this technology is also the most m/MWe for CO2 recovery equipment sensitive to fuel price fuctuations is feasible. Therefore, glasshouse such as pertains at the current time. CO2 demand provides a potential For the case study illustrated in this opportunity for the development of work, sizing of the biomass CHP biomass gasifcation CHP with pre system to meet the average summer CO2 recovery, and warrants further heat demand and electrical base investigation. load provides the most favourable techno-economic solution. For a typical 40,000m2 glasshouse, the 69 Acknowledgement
This paper was previously published in Applied Energy 96 (2012) 339–346, March 2012.
References
1. Aznar-Sánchez JA, Galdeano-G mez E. Territory cluster and competitiveness of intensive horticulture in Almería (Spain). Open Geogr J 2011;4:103–14. 2. National Farmers. Union report – why horticulture matters; 2008.
a. Wood SR, Rowley PN. A techno-economic analysis of small-scale biomassfuelled, combined heat and power for community housing. Biomass Bioenergy 2011;35:3849–58;
b. Bram S, DeRuyck J, Lavric D. Using biomass: a system perturbation analysis. Appl Energy 2009;86(2):194– 201. 10. Chau J et al. Techno-economic analysis of wood BM boilers for the greenhouse industry. Appl Energy 2009;86:364–71. 11. Adams S, Langton A. Energy management in protected cropping: manipulation of glasshouse temperature. DEFRA factsheet 06/09; 2009.
70 140 The feasibility of biomass CHP as an energy and CO2 source for commercial glasshouses
18. Improving the energy effciency of protected cropping in winter through the use of low intensity, long-day lighting. DEFRA project report HH3603SPC. Department for Environment Food and Rural Affairs, UK; December 2003. p.13–4. 19. Schwab E. Technologies for syngas purifcation. BASF presentation for IEA task 33 meeting; May 2009. slide 6. 20. Dong L, Liu H, Riffat S. Development of small-scale and micro-scale biomassfuelled CHP systems – a literature review. Appl Therm Eng 2009;29:2119–26. 21. Forestry Commission Biomass Energy Centre information sheet no. 4: combined heat and power.
22. Directive 2004/8/EC of the European Parliament on the promotion of cogeneration based on a useful heat demand Environment & Sustainability in the internal energy market and amending Directive 92/42/EEC. 23. Westner G, Madlener R. The beneft of regional diversifcation of cogeneration investments in Europe: a mean– variance portfolio analysis. Energy Policy 2010;38:7911–20. 24. Klein A, Pfuger B, Held A, Ragwitz M, Resch G. Evaluation of different feed-in tariff design options: Best practice paper for the international feed-in cooperation, 2nd ed. Berlin (Germany): BMU; 2008. http://www.feed- incooperation. org/wDefault_7/wDefault_7/download-fles/research/best_practice_paper_2nd_edition_fnal.pdf> [accessed 01.11.10]. 25. del Río Gonzalez P. Ten years of renewable electricity policies in Spain: an analysis of successive feed-in tariff reforms. Energy Policy 2008;36:2917–29. 26. Consultation on Renewable Electricity Financial Incentives 2009, DECC, July 2009, pp.83 [cost ref p1] Department of Trade & Industry. Impact of banding the Renewables Obligation – Costs of electricity production. April 2007. URN 07/948.;
71 a. Feron PHM, Jansen AE. The production of carbon dioxide from fue gas by membrane gas absorption. Energy Convers Manage 1997;38:S93–8; b. Karellas S, Karl J, Kakaras E. An innovative biomass gasifcation process and its coupling with micro turbine and fuel cell system. Energy 2008;33:284–91. 27. Pietola K, Lansink AO. Modelling energy saving technology choices in Dutch glasshouse horticulture. Econ Sustain Energy Agric: Econ Environ 2003;24:41–55. 28. Plackett C. ’Green’ glasshouse technologies not yet a realistic option. Horticulture Week; 10 April, 2008.
72 140 The feasibility of biomass CHP as an energy and CO2 source for commercial glasshouses
Appendix Glass Internal Temperature Set-point The glasshouse internal temperature set point is changed throughout the Technical considerations day, a typical set point temperature profle for tomatoes is given in Table Heat Demand 2 For tomato crops the temperature is dropped towards the end of the Glasshouse Air Change Rate day around sunset to encourage fruit Typical air change rates with roof size. The fgures in Table 2 have been vents closed are giving in the Table 1. used in the heat demand model. Figure 3. Monthly Heat Demand, 40,000m2 Glasshouse Glass Construction ACH Relative Time Hrs Temperature °C New construction 0.75 to 1 Sunrise -2Hrs 16 Electricity Demand Old construction, good Sunrise 18 Electricity demand profles 1.0 to 2.0 maintenance Sunrise + 2Hrs 20 Old construction, poor 2.0 to 4.0 Other daylight Hrs 23 maintenance Sunset -4Hrs 21 Table 1. Natural Air Changes Per Hour1 Sunset 15 Glasshouse Heating System2 Sunset +4Hrs 17 Due to the demand mismatch Table 2. Glasshouse Internal Temperature Set Point10 between heat and CO2 generation, glasshouses use large water tanks Natural Gas Heating Costs often referred to as buffers to store Figure 4. Hourly Electrical Demand W/m2 the heat generated during CO2 production. The heat storage tank Boiler effciency was developed in the Netherlands Gas p/therm η=80% η=85% η=90% in the 1980’s for glasshouse 20 8.53 8.03 7.58 applications. The buffer systems can 30 12.80 12.04 11.37 be open or closed; the closed buffer 40 17.06 16.06 15.17 system was designed to assist CO2 production only compared to the 50 21.33 20.07 18.96 more modern open buffer system 60 25.59 24.09 22.75 which can also be used for energy 70 29.86 28.10 26.54 management. With an open buffer Table 3. Cost to Produce 1MWh of Heat system it is possible to load and Figure 5. Monthly Electricity Demand, form Natural Gas 2 unload the buffer at the same time; 40,000m glasshouse this is achieved through the control Heat Demand Profles
CO Demand Environment & Sustainability of pumps with variable speed drives. 2 A mixing valve at the boiler or CHP Photosynthesis ensures that the return temperature Photosynthesis is a chemical process and hence fow temperature for a that uses the suns energy to convert given temperature lift meets the CO and water into energy such correct requirement. The temperature 2 as glucose. The overall chemical gradient within the buffer is reaction for glucose synthesis via measured to determine the current photosynthesis is shown below: amount of heat storage. An overview of a typical open buffer system is 6C02 + 6H2O + Light Energy 2 shown in Figure1. Figure 2. Hourly Heat Demand W/m for C6 H 12 O 6 + 6O 2 Each Month The rate of CO2 demand by the glasshouse crop increases with increasing PAR, and also increases
with increasing CO2 in the glasshouse atmosphere. Air temperature, Figure 1. Glasshouse Open Buffer System 73 relative humidity and water stress cleaned using Selective Catalytic
also contribute to the rate of CO2 Reduction (SCR) with a reducing demand. The concentration of agent such as Urea to reduce the
CO2 within the glasshouse will NOx levels and Oxidation Catalyst to also depend on the natural and reduce any unburnt hydrocarbons forced ventilation. In a well sealed i.e. Carbon Monoxide and Ethylene.
glasshouse CO2 concentration Ethylene is phytotoxic and CO is toxic can drop below outside ambient to humans.4 A typical natural gas 1 levels Without CO2 enrichment, CHP arrangement with exhaust gas ventilation can help increase the cleaning for glasshouses is shown Figure 7. Monthly CO Demand, CO concentration closer to ambient 2 in Figure 8. The use of a catalyst is 2 2 levels but at the cost of losing heat. 40,000m Glasshouse possible due to minimal variations With CO enrichment, the CO in the natural gas quality and low 2 2 Sources of CO will be diluted with the outside 2 particulate emissions. The use of atmosphere when the glasshouse Each MWh of gas burned directly the condenser on the CHP as well vents are opened to help control produces a proportionate amount of as reducing the moisture of the CO . Under complete combustion, the temperature. A lower CO2 2 exhaust gas helps to increase the methane (the main component of 3 concentration is maintained when concentration of CO2/Nm allowing natural gas) produces CO , water and 3 venting is being used to cool the 2 a higher concentration of CO2/Nm glasshouse. Table 4 below shows heat as shown below:4 to enter the glasshouse compared to
the estimated rate of CO2 required CO2 being supplied by boilers. CH4+ 2O2 CO2+ 2H2O + Heat to maintain set CO2 levels in the glasshouse. These fgures assume One MWh of natural gas burned
high light level conditions and will produce 184kg of CO2 based on minimal air changes. This will of the gross calorifc value (obtained course vary depending on the from DEFRA June 2009 conversion glasshouse ACH, light intensity, type factors3). Moisture needs to be of crop and growing strategy. removed from the exhaust gas as it Figure 8. Typical Arrangement of Natural can cause mould and fungus. Gas Fired CHP with Exhaust Gas Cleaning
CO2 level (ppm) CO2 Supply Rate Cost of CO2 Produced from Natural 500 70 to 90 Kg/Ha/Hr Gas Biomass combustion 900 170 to 190 Kg/Ha/Hr The typical cost (excluding equipment 1,300 250 to 350 Kg/Ha/Hr cost) per tonne of CO produced by The combustion of biomass takes 2 place in three stages, Drying (0 to Table 4. Rate of CO Required to boilers with natural gas burners is 2 200°C), Pyrolysis (200 to 400°C) and Maintain Set CO Levels1 shown in Table 5. 2 Oxidation (400 to 1000°C). Gas p/therm Gas £/MWh CO £/tonne CO2 Demand Profles 2 The complete combustion of biomass
20 6.82 37.17 with a chemical composition Cx H yO z 5 30 10.24 55.76 and oxygen is shown below; 40 13.65 74.34 50 17.06 92.93 Cx H y O z +(x + y/4 - z) O2 60 20.47 111.52 xCO2+ y/2 H2O+ Energy 70 23.88 130.11
Table 5. Cost of CO Production Using 2 Biomass mainly contains cellulose, Boilers with Natural Gas Burners hemi cellulose and lignin. Taking cellulose as a component on its own, Figure 6. Glasshouse Open Buffer System Natural Gas CHP the complete combustion would be Natural gas can also be combusted represented as follows: 4 in a reciprocating engine to form C H O + 6O 6CO +5H O+Heat part of a CHP plant, although the 6 10 5 2 2 2 exhaust gas produced by the engine It can be seen that under complete is not suitable for direct supply combustion this reaction produces to the glasshouse. It must frst be water, carbon dioxide and heat.
74 140 The feasibility of biomass CHP as an energy and CO2 source for commercial glasshouses
If cellulose has an energy value of The net produce of air gasifcation is System 2 - Biofuel (vegetable oil) 19GJ/t, using the atomic weights of found to be7 using compression ignition engine by each component, Living Power C6 H 10 O 5 + O 2
162 + 192 264 + 90 + Heat Cx H z + C n H m O y + CO + H2 + Heat Virgin vegetable oil or processed used cooking oil can be combusted Under complete combustion 1MWh Typically the gas produced will in a modifed compression ignition of energy provided by cellulose contain a mixture of different engine. The fuel price is higher would produce 308kg CO . Per components and this will depend 2 compared to biomass and more MWh of energy released biomass on the feedstock and gasifer used. susceptible to price variations, will provide a higher volume of CO For heat and power generation 2 however capital costs are lower compared to natural gas. Under the gas produced is then used in a compared to biomass systems. Heat real conditions however, complete spark ignition engine. The typical can be recovered from engine jacket combustion does not occur, slightly basic exhaust gas emission data was water, oil cooler, intercooler and higher concentrations of CO and obtained from an operational plant in 2 exhaust. other elements will be produced Austria and is shown in Table 7. depending on the actual fuel composition and combustion. Basic Component Concentration emission data was also obtained NOx ppm 372 from an compression ignition engine CO ppm 2920 operating on Soya oil, this data is shown in Table 6. Table 7. Exhaust Gas Composition from Engine Operating on Syngas @ 5% Figure 10. Biofuel CHP using 8 Contamination Concentration Oxygen Compression Ignition Engine Sulphur Dioxide [SO ] 153 ppm x This shows that the emissions levels System 3 - Direct Biomass Hydrocarbons [C H ] unknown x y as they stand would be unsuitable combustion with ORC by Turboden Carbon Monoxide [CO] 873 ppm for glasshouse applications. Other Solid biomass is combusted directly Nitrogen Oxide [NO ] 1913 ppm unburnt hydrocarbons would also x need investigating. and used to heat a secondary organic Particulates 5.3 mg/m3 fuid and drive a small turbine. This Table 6. Emissions from Compression Conversion Technologies is called the Organic Rankine Cycle 6 and is similar to a traditional steam Engine Operating on Soya Oil System 1 - Biomass Gasifer with IC turbine system, but the working engine by Alfagy / Enercarb Biomass Gasifcation fuid has a much lower boiler point Solid dry biomass is converted in and can therefore achieve higher Gasifcation is a thermal process to a combustible gas by heating effciencies in smaller systems. of converting dry solid fuels into in a reduced oxygen environment. gaseous ones under partial oxidation Gasifers can take many different conditions. The combustible gas shapes and forms. The gas needs to produced is referred to as producer be cleaned to remove particulates or synthesis gas (syngas) depending
and other contaminants before Environment & Sustainability on the oxidiser used e.g. oxygen it is combusted in a modifed or or steam. Gasifcation has certain specifcally designed spark ignition advantages that cannot be achieved engine. Heat can be recovered through direct combustion of the from the gas produced and from material, the main advantage being the engine jacket water, oil cooler, Figure 11. Biofuel CHP using Direct that the gas can be used in an intercooler and exhaust. Combustion with ORC internal combustion engine to then produce electricity and heat. Gasifers System 4 - Combined cycle biomass come in many different shapes gasifcation CHP by Babcock & and forms, each with their own Wilcox Volund advantages and disadvantages for The combined cycle biomass particular applications. gasifcation CHP is a further Air gasifcation can be expressed in improvement on the standard three stages; gasifcation with IC engine and is specifcally being developed by Oxidisation Pyrolysis Gasifcation Figure 9. Biomass CHP, Gasifer with IC engine one manufacturer. The benefts 75 are improved electrical effciency to reduce the particulate emissions Triad % Share 95 % and improved combustion of CO in the exhaust gas, this can be via a Waste Disposal £10/Tonne components. The tar that has to wet or dry process. The dry process be scrubbed out from the gas still involve the use of flters / cyclones, Project Period 15 Years contains energy and is separated and these can be in the form of bag Infation Rate (RPI) 3 % burnt with at a high stoichiometric flters or electrostatic flters and in Discount Rate 10 % temperature in the exhaust gas of the the wet process the exhaust gas is Loan interest rate 9 % IC engine, this ensures that excess scrubbed using a fne water spray CO from the IC engine is burnt out. to intercept the particles. Scrubbing Table 9. Baseload Modelling assumptions The exhaust gas then passes through also has the advantage of SO and x Gas and Power prices obtained a heat recovery steam generator, the NO particle removal but there is the x from www.heren.com/ on the 6th steam is then used to drive a steam added expense of water treatment. August 2009. ROC price obtained generator to generate electricity Deactivation of SCR can be caused from E-ROC website www.eroc. providing the combined cycle. The by blinding over of the catalyst co.uk, price correct on 7th July 2009. minimum plant size is 4MWe. The e.g. by particulate emissions, pore Biofuel referred to in the report is expected exhaust emission data is condensation and poisoning.10 Vegetable oil (Soya oil). The Biofuel shown in Table 8. Biomass Gasifcation cost was obtained from Living Power and M.W. Beer in August Component Concentration Water Gas Shift chemical reaction: 2009, the price had increased to NOx mg/Nm3 250 CO+H2O CO2+ H2 £525 in September 09 indicating SO2 mg/Nm3 10 the variations that can occur in CO mg/Nm3 150 Economic vegetable oil. Biomass referred to TOC mg/Nm3 30 in the report is woodchip, prices considerations were obtained from Manco Energy Table 8. Exhaust Gas Composition From and AHS Energy in August 2009. It 9 Combined Cycle Gasifcation CHP Modelling assumptions should be noted that vegetable oil is traded as a commodity and can vary System 5 - Direct Biomass Base Case on a daily basis. Biomass and Biofuel combustion with Externally Fired Air Parameter Value supply will also be subject to the Turbine by Talbots Solid Biomass Heating 19 GJ/Tonne site location and the supply should Solid biomass is combusted directly Value be investigated before a project is and used to heat air via a heat Solid Biomass Heating Cost £50/ODT developed. exchanger, the heated air is then Liquid Biofuel Heating 37 GJ/Tonne expanded through a turbine which is Value Loan Rate Sensitivity used to generate electricity. Liquid Biofuel Heating Cost £500/Tonne Using the modelling assumptions Availability 90% with no capital grant, the sensitivity Electricity Base load Export of the NPV was tested by adjusting 45 £/MWh Price the loan interest rate between 0 to Electricity Peak load Export 15%. The results are shown in fgure 50 £/MWh Price 13. System 2 has the least sensitivity, Electricity Onsite Sale Price 55 £/MWh still being able to maintain a positive Electricity Import Price 60 £/MWh NPV at a loan interest rate of 15%. Systems 1,3 & 5 have very similar Gas Price 47p/Therm sensitivity to loan interest rate and Heat Sale Price 20 £/MWh the NPV becomes negative when Glasshouse CO Sale Price 35 £/Tonne 2 the loan interest rate approaches CCL Electricity 4.70 £/MWh the range 7 to 11%. System 4 can Figure 12. Biofuel CHP using direct achieve a positive NPV up to a loan combustion with Externally Fired Air CCL Gas 1.64 £/MWh interest rate of 13%. Turbine RO 3.60 £/MWh ROC 53 £/MWh Method of Possible Biomass / LEC 4.70 £/MWh Biofuel CHP CO2 Recovery Triad 22 £/kWh Biomass & Biofuel Combustion ROC % Share 95 % Secondary techniques can be used LEC % Share 95 %
76 140 The feasibility of biomass CHP as an energy and CO2 source for commercial glasshouses
CHP status attracting 2 ROCs/ currently have a value of £4.70/MWh MWh. A further example of using and can be sold into the market. 16 modules of system 2 operating a peak profle in the summer is Renewable Obligation shown in Figure 15. In the winter The Renewable obligation is a this closely matches the winter mechanism in the UK market to heat demand meaning there is less encourage the use of renewable shortfall heat that has to be supplied electricity generation and was from boilers. updated in April 2009. Depending on the technology type, each MWh Figure 13. Sensitivity to Loan Interest of renewable electricity generated Rate will obtain a number of Renewable Obligation Certifcates (ROCs). Operating regime with System These ROCs have a value and can 2 (Biofuel) then be sold into the market and As Biofuel CHP has much greater / or used to meet the owners own fexibility compared to biomass CHP, renewable obligations. The value of it can be operated at base or peak ROCs can be obtained at www.eroc. load. An analysis was performed co.uk. Commercial users of electricity to look at the effects of installing a currently have to pay a Renewables 2 higher MWe system but operating Figure 15. 40,000m Glasshouse Obligation (RO) on electricity they use a peak profle in the summer and Demand and Generation from 16x from a non renewable source. The System 2 (Biofuel) Modules. Operating a baseload profle in the winter to rate is currently £3.60/MWh which is a Peak Profle in Months 5 to 9 and better match the heat demand and used to support the ROC mechanism. Baseload all Other Months. Heat Good quality Biomass / Biofuel CHP maintain good quality CHP. Figure Generation is Better Matched to Heat as defned by the UK CHPQA scheme 14 shows the typical glasshouse Demand demands and the generation from will obtain 2 ROC’s for each MWh ten system 2 modules operating a CHPQA generated, if a scheme fails to be peak profle in months 5 to 9 and a good quality due to excess heat not A CHP scheme must obtain a Quality baseload profle in all other months. being used, 1.5 ROC’s per MWh Index (QI) score above 100 under generated will be obtained. Full the UK CHP Quality Assurance details of the Renewables Obligation scheme to maximise the beneft Order 2009 can be found at www. from Levy Exemption Certifcates and opsi.gov.uk, the direct link is http:// Renewable Obligation Certifcates. www.opsi.gov.uk/si/si2009/pdf/ The CHPQA scheme in the UK has uksi_20090785_en.pdf. been operating since 2001. The QI score calculation is based on the electrical effciency of the CHP and its useful heat output, therefore to Environment & Sustainability maximise the QI score there must Figure 14. 40,000m2 Glasshouse be a use of the heat generated. Demand and Generation from 10x The QI calculations depend on System 2 (Biofuel) Modules. Operating the technology and size of system a Peak Profle in Months 5 to 9 and installed. The formulas are readily Baseload all Other Months available in the CHPQA guidance notes at www.chpqa.com. Operating base load on an annual basis, this system would only attract A Climate Change Levy (CCL) is 1.5 RCOs/MWh due to a large charged on all fossil fuels in the UK amount of heat that would be such as natural gas and electricity. dumped in the summer months. CCL on electricity is currently £4.70/ However, if the operating regime is MWh. Good Quality CHP has the changed to a peak profle in months beneft of being CCL exempt and a 5 to 9, the heat generated matches Levy Exemption Certifcate (LEC) is the demand much better and will obtained for every MWh generated continue to maintain good quality from good quality CHP. LEC’s 77 Bibliography
The following papers, guides and studies have all been consulted throughout the project and provide useful information relevant to various aspects of biomass fuelled CHP. 1. D.L Critten and B.J. Bailey, “A review of greenhouse engineering developments during the 1990s”, Agricultural and Forestry Meteorology, Vol. 122, 2002, pp. 1-22. 2. K. Popovski, “Factors Infuencing Greenhouse Heating and Geothermal Heating Systems”, Geothermics, Vol 17, No1, 1988, pp. 173-189. 3. Otto Fr sig Nielsen, “Climate Computer algorithms for Peak Shaving of Greenhouse heating demand”, Computers and Electronics in Agriculture, Vol. 13, 1995, pp. 315-335. 4. S.N Wass and I.A Barrie, “Application of a Model for Calculating Glasshouse Energy Requirements”, Energy in Agriculture, Vol. 3, 1984, pp. 99-108. 5. T.O’Flaherty & R.Cochran, “Determination of glasshouse heat requirements from temperature and wind records”, Symposium on Greenhouse Design and Environment, Vol. 46, pp. 33-54. 6. B. Ozkana, A. Kurklub and H. Akcaoza, “An input–output energy analysis in greenhouse vegetable production:a case study for Antalya region of Turkey”, Biomass and Bioenergy, Vol. 26, 2004, pp. 89 – 95. 7. G. Houter, “Simulation of CO2 consumption, heat demand and crop production of greenhouse tomato at different CO2 strategies”, CO2 in Protected Cultivation, Vol. 268, 1990, pp. 157-163. 8. J.G Hare, B. Norton and S.D. Probert, “Design of greenhouses: Thermal Aspects”, Applied Energy, Vol. 18, 1984, pp. 49-82. 9. D.W. Hand, J.D. Postlethwaite and M.A. Hannah, “Carbon dioxide generation from low-sulphur kerosene”, J.agric. Engng Res., Vol. 20, 1975, pp. 89-97. 10. S. Karellas, J.Karl and E.Kakaras, “An innovative biomass gasifcation process and its coupling with micro turbine and fuel cell systems”, Energy, Vol. 33, 2008, pp. 284 291. 11. A.A. Rentizelas, I.P. Tatsiopoulos and A. Tolis, “An optimization model for multi-biomass tri-generation energy supply”, Biomass and Bioenergy, Vol. 33, 2009, pp. 223-233. 12. S. N. Uddin and L. Barreto, “Biomass-fred cogeneration systems with CO2 capture and storage”, Renewable Energy, Vol. 32, 2007, pp. 1006-1019. 13. A. Marbe and S.Harvey, “Opportunities for integration of biofuel gasifers in natural-gas combined heat-and- power plants in district-heating systems”, Applied Energy, Vol. 83, 2006, pp.723-748. 14. A. Marbe, S.Harvey and T.Berntsson, “Technical, environmental and economic analysis of co-fring of gasifed biofuel in a natural gas combined cycle (NGCC) combined heat and power (CHP) plant”, Energy, Vol. 31, 2006, pp. 1614-1631. 15. M. Lapuerta et al, “Diesel emissions from biofuels derived from Spanish potential vegetable oils”, Fuel, Vol. 84, 2005, 773-780. 16. A. Kurklu, “Energy storage applications in greenhouses by means of phase change materials (PCMs) : a review”, Renewable Energy, Vol. 13, No. 1, 1998, pp. 89-103. 17. Hugo H. Rogers, G. Brett Runion & Sagar V. Krupa, “Plant Responses to Atmospheric CO2 Enrichment with Emphasis on Roots and the Rhizosphere, Environmental Pollution, Vol. 83, 1994, PP. 155-189. 18. D. P. Aikman, “A Procedure for Optimizing Carbon Dioxide Enrichment of a Glasshouse Tomato Crop”, J.agric. Engng Res., Vol. 63, 1996, pp. 171-184. 19. I. Keppo and T. Savola, “Economic appraisal of small biofuel fred CHP plants”, Energy Conversion and Management, Vol. 48, 2007, 1212-1221. 20. J. Chau et al, “Techno-economic analysis of wood biomass boilers for the greenhouse industry”, Applied Energy, Vol. 86, 2009, pp. 364-371.
78 140 The feasibility of biomass CHP as an energy and CO2 source for commercial glasshouses
21. R. T. Besford et al, “The Greenhouse Effect: Acclimation of Tomato Plants Growing in High CO2, Photosynthesis and Ribulose-1, 5-Bisphosphate Carboxylase Protein”, Journal of Experimental Botany, Vol. 41, 1990, pp. 925-931. 22. E. Nederhoff, “Open and Closed Buffer Systems for Heat Storage”, The Grower, Vol.59, 2004, pp.41-42. 23. J.Worley, “Greenhouses, Heating, Cooling and Ventilation”, The University of Georgia, Bulletin 792, 2009, pp.1- 10. 24. Dr. P. “Tans Mauna Loa CO2 annual mean data”, NOAA/ESRL, www.esrl.noaa.gov/gmd/ccgg/ trends/. 25. “Energy Benchmarks and Saving Measures for Protected Greenhouse Horticulture in the UK”, The Carbon Trust, ECG091, pp.8. 26. T.J Blom et al, “Carbon Dioxide in Greenhouses”, OMAF, ISSN 1198-712X, 2002. 27. S.V Loo et and J.Koppejan, “The Handbook of Biomass Combustion & Co-fring”, EarthScan, 2007, pp. 308- 310,334. 28. E. Schwab, “Technologies for Syngas Purifcation”, BASF Presentation for IEA Task 33 Meeting, May 2009, Slide 6. 29. T.Elsenbruch, “Latest Developments in the Use of Wood Gas in Gas Engines” GE Jenbacher Presentation at IDGTE Toronto, June 2008, Slide 33. 30. M. Kasper, “Syngas Conditioning by Lurgi Rectisol”, Lurgi Rectisol Presentation for IEA Task 33 Meeting, May 2009, Slide 19. 31. “Consultation on Renewable Electricity Financial Incentives 2009”, DECC, July 2009, pp.83. 32. Defra’s greenhouse gas (GHG) conversion factors for company reporting @ http://www.defra.gov.uk/environment/ business/reporting/conversion-factors.htm. 33. S.Wood & P.Rowley, “The Feasibility of Small-Scale, Biomass-Fuelled Combined Heat and Power for Community Housing”, CREST. 34. http://www.biomassenergycentre.org.uk. 35. http://www.gastechnology.org. 36. http://www.gasnet.uk.net. 37. https://www.chpqa.com. 38. http://www.crophouse.co.nz.
Companies Contacted
The following companies have been contacted during the project and I am grateful for any information provided. 1. Zero Point Clean Tec, USA Environment & Sustainability 2. AFC Energy, UK 3. Clarke Energy, UK 4. PRM Energy, USA 5. Joule Power, UK 6. Biomass CHP, UK 7. Mawera, UK 8. Living Power, UK 9. Baltic Energy Group, Denmark 10. Babcock & Wilcox V lund, Denmark 11. Advanced Plasma Power, UK 12. Looije Agro Technics, Netherlands
79 13. Schmitt Enertec, Germany 14. Steuler Analgenbau, Germany 15. Wight Salads.
Appendix References
1. J.Worley, “Greenhouses, Heating, Cooling and Ventilation”, The University of Georgia, Bulletin 792, 2009, pp.1- 10. 2. E. Nederhoff, “Open and Closed Buffer Systems for Heat Storage”, The Grower, Vol.59, 2004, pp.41-42. 3. DEFRA Conversion Factors http://www.defra.gov.uk/environment/business/reporting/conversion-factors.htm. 4. J. Chau et al, “Techno-economic analysis of wood biomass boilers for the greenhouse industry”, Applied Energy, Vol. 86, 2009, pp. 364-371. 5. A.V. Bridgwater, “Renewable Fuels and Chemicals by Thermal Processing of Biomass”, Chemical Engineering Journal, Vol 91, 2003, pp87-102. 6. Provided verbally by Living Power Ltd. 7. M.A. Azam et al, “Construction of a Downdraft Biomass Gasifer”, Journal of Mechanical Engineering, Vol ME37, 2007, pp.71-73. 8. Holzgas Gussing – Exhaust Gas and Pollutant Emissions from GE Jenbacher 620 – Provided by Clarke Energy. 9. Babcock & Wilcox V lund gasifcation information sheet provided by Baltic Energy Group. 10. V Loo et and J.Koppejan, “The Handbook of Biomass Combustion & Co-fring”, EarthScan, 2007, pp. 308- 310,334. 11. Provided verbally by Wight Salads Ltd.
80 Highway Network Management 81 141 Performance management The performance of the MACs is managed by the Highways Agency teams following a their area through cycle of ‘plan, improvement standard to do, check, act’ using measures identify levels of performance and enable benchmarking as a means of in operational driving improvement measures These performance delivery. in the motivating success set out are toolkit (MST) developed specifcally south west and west midlands. Each operational region is further broken is further broken operational region are of which there down into areas, 12 in total. Highway maintenance in each of these and improvement by a managing is managed areas agent contractor (MAC) under contract to the Highways Agency. England’s motorways and all-purpose England’s at over £87 Valued trunk roads. billion, the network carries one-third in England and traffc of all road traffc of all heavy freight two-thirds (www.highways.gov.uk). Although the scope of the Highways Agency is national, the country is divided into seven operational eastern,regions: east midlands, north east, north west, south east, Introduction Introduction Background The Highways Agency, an executive The Highways Agency, agency of the UK Department for responsible is the body Transport, for the operation, maintenance and of the strategic road improvement network in England on behalf of the The of State for Transport. Secretary Performance management management Performance for managing framework agent contractors Abstract framework for managing This paper describes a performance management network. Highways Agency trunk road agent contractors working on the UK which links the hierarchy of the framework is a performance At the core managing agent contractors with the operational activities carried out by the is weighted The hierarchy Agency. key business outcomes of the Highways to be accurately elements importance of hierarchy to allow the relative is everything and to avoid the default position whereby represented, utilises performance fags to equally important. The framework considered based on red, performance at higher levels in the hierarchy, visually represent The the hierarchy. assigned at the lowest level in scores amber and green show the detail behind a performance performance fags have the ability to amber a proportion of the fag will be green, a proportion whereby score, assigned and weightings depending on the frequency red and the remainder to reduce In an effort hierarchy. to the lower contributing levels in the scoring guidance document has been subjectivity in performance scoring, a management and in support of the framework. The performance prepared cycle akin to the is carried out on a monthly process continual improvement main benefts of cycle of ‘plan, do, check, act’. The improvement standard allowing thereby subjectivity, include reduced implementing this process visibility, contractors, increased comparability between managing agent decision making and auditability dialogue, targeted evidence-based increased in the and effciency effectiveness All of the above will help to drive improved delivery of managing agent contracts. strategic road network is made up of strategic road Richard Arrowsmith Arrowsmith Richard Planning and Performance Group Manager Highways Agency Seosamh B. Costello Senior Lecturer, Department of Civil and Environmental Engineering The University of Auckland James E. Powell & Efficiency Performance Manager Highways & transportation Atkins Simon R. Nuttall Managing Consultant Management Consultants Atkins for maintenance contracts (Highways Finally, taking sub-lever 1.2.1 as an Agency, 2009a), commonly referred Performance example, three aspects contribute to as the Toolkit. management to it, namely 1.2.1.a Programming schemes, 1.2.1.b Delivering schemes A number of the performance framework and 1.2.1.c Monitoring scheme indicators in the Toolkit are informed outcomes. by area performance indicators Performance hierarchy (APIs), as defned in the Area The descriptions and reference Performance Indicator Handbook At the core of the MAC performance numbers for each of the levers, (Highways Agency, 2007), and other management framework is a sub-levers and aspects have been suggested measures. Although the performance hierarchy which shows obtained from the latest version Toolkit has the potential to be a how the operational activities of a of the Toolkit. Full descriptions of genuinely powerful means by which MAC align with the key business the aspects are also available in the to evaluate MAC performance outcomes of the Highways Agency. Toolkit, abbreviated versions being against the Highways Agency’s key The structure of the hierarchy is used in the performance hierarchy business outcomes, the vast majority demonstrated schematically in due to space limitations. of the evidence in support of the Figure 1. The outcomes sit at the The fully developed performance performance indicators is agreed top of the hierarchy, a number of hierarchy for MACs, in the form of locally between the MACs and the levers contribute to each outcome, a a performance hierarchy poster, is Highways Agency area teams. In number of sub-levers contribute to included as supplementary data with addition, the performance score each lever and, fnally, a number of the online version of this paper. allocated to each performance aspects contribute to each sub-lever. indicator, commonly referred to as Performance scoring The Highways Agency’s key business an MST score, is by local agreement outcomes form the top tier of the The scoring of performance in the based on the evidence provided. This hierarchy as listed MAC performance management introduces a considerable degree framework is conducted at aspect of subjectivity into the process (a) network best value level, this being the lowest level of and reduces the opportunity for (b) operational safety standardisation in the Toolkit. Every comparison between MACs. aspect receives a red, amber or green (c) reduce congestion The national performance unit (NPU), score, hereafter referred to as a RAG part of the central division of the (d) high-quality customer service score, depending on performance. Highways Agency’s network delivery Where no data have been submitted (e) respect the environment. and development directorate (NDD), a fourth option is available, which recognised the need for a nationally The full hierarchy for the reduce is represented by the colour white. consistent approach to performance congestion outcome is demonstrated This ensures that failure to submit management. They also recognised in Figure 2, as an example. In this performance data is clearly evident the need for a performance case, three levers contribute to the and prevents erroneous assumptions management framework to monitor reduce congestion outcome, namely being made about missing data. performance and drive improvement (a) 1.2 Reduce congestion centrally. To meet this need the Scoring guidance MAC performance management (b) 1.3 Improve management of In an effort to reduce the subjectivity framework was developed. incidents in performance scoring, as well This paper describes the newly (c) 2.1 Increase availability on as the variability in locally agreed developed MAC performance network. evidence provided in support of the performance scores, a management framework in detail, Focusing on lever 1.2 it can be seen including the performance hierarchy scoring guidance document has that two sub-levers contribute to it, been prepared in support of the and performance scoring, and namely outlines the MAC performance framework (Highways Agency, 2010). management framework cycle (a) 1.2.1 Develop & implement The guidance document provides undertaken by the stakeholders on a programme of congestion easing detailed scoring guidance for each monthly basis. schemes and every aspect, grouped by (b) 1.2.2 Develop & implement outcome. The scoring guidance effective strategies & plans that also details what MACs need to reduce congestion. demonstrate to justify their scores and lists the associated evidence that needs to be provided. 82 141 Performance management framework for managing agent contractors
The guidance is aimed at MACs Weighting the performance The sum of the weightings directly and area teams to enable them to hierarchy below any element of the hierarchy agree on consistent, evidence-based equates to 100%. Hence, all the performance scores across all aspects All the outcomes, levers, sub- levers contributing to an outcome of the MAC contracts. Scoring MAC levers and aspects within the sum to 100%, all the sub-levers performance consistently will enable performance hierarchy are weighted contributing to a lever sum to compliance to be demonstrated and to allow the relative importance of 100% and, fnally, all the aspects improvement effort to be focused hierarchy elements to be accurately contributing to a sub-lever sum to where it is needed. Scoring should represented. Their inclusion also 100%. This is clearly demonstrated be conducted and agreed based avoids the default position whereby in Figure 3, using example upon the specifc guidance outlined everything is considered equally weightings, whereby sub-lever 1.2.1 in each section but in general green important. Consequently, the is weighted at 65% and sub-lever represents contract compliance weightings have the potential to be 1.2.2 is weighted at 35%. Both sub- against an aspect whereas amber a powerful tool to direct Highways levers contribute to the 1.2 reduce and red signify that improvement is Agency priorities through the congestion lever and the sum of needed. The general principles of the MAC performance management their weightings equates to 100%. RAG scoring guidance are detailed in framework. Similarly, the sum of the aspect Table 1 and a detailed example for a The weightings were initially weightings contributing to each of specifc aspect is provided in Table 2. set using the expertise of the the two sub-levers equates to 100%. It is intended that the guidance will area teams and NPU, and were These weightings are integral to the be further developed and improved subsequently reviewed by the NDD reporting and visual representation over time as current thinking moves director. However, as with the of performance at outcome, lever forward, priorities change and the scoring guidance, it is intended that and sub-lever level, whereby the RAG Highways Agency’s understanding the weightings are adjusted and scores at aspect level are propagated of the MAC contracts and their calibrated over time in response to up the hierarchy in the form of impact on the fve strategic outcomes improved intelligence and changing performance fags. develops. priorities. Highway Network Management
Figure 1. Schematic of performance hierarchy 83 Performance fags Performance at outcome, lever and sub-lever level in the hierarchy is represented in the form of performance fags, instead of averaging the performance score and displaying the resulting red or amber or green score. An example performance fag at sub-lever level is shown in Figure 4 using the example weightings for the aspects contributing to sub-lever 1.2.2 obtained from Figure 3. The performance fag at sub-lever level is a weighted summary of the aspects which contribute to it. In this case the percentage of red, amber, green and white included in the fag is a simple summation of the contributing aspect weightings for each colour, resulting in a performance fag with 45% green,15% amber and 40% red. The 45% green is Figure 2. Hierarchy for reduce congestion outcome obtained from the summation of the weightings for aspect 1.2.2.a (30%) and aspect 1.2.2.b (15%). The 15% amber is obtained from aspect 1.2.2.c (15%) and the 40% red is obtained from aspect 1.2.2.d (40%). The performance fag contains no white as performance information was provided for all the aspects contributing to sub-level 1.2.2. The percentage of each colour included in a performance fag can therefore be calculated by Equation 1 whereby the percentage of any colour in the sub-lever performance fag is a summation of all the aspects that were assigned that colour RAG score. Figure 3. Weighting the performance hierarchy Equation 1 n %colour = aspect weightings sub-lever ∑ colour 1 The propagation of scores from sub- lever to lever level and from lever to outcome level is slightly more complex. In this case, each of the lower performance fags will have a weighting assigned to it which represents its contribution to the element, and therefore performance fag, above it. In addition, each lower level fag will consist of varying Figure 4. Example performance fag for sub-lever 1.2.2 84 141 Performance management framework for managing agent contractors
Green Amber Red Targets for any relevant measures are being Some targets are not being met but plans are Targets are not being met met in place to address issues
Evidence is present There are some issues with the evidence items There are major issues with the evidence items against the aspect against the aspect Processes are under control Some non-conformities may be present but do Non-conformities are present which have a major not have a major impact on the service impact on the service Contractual requirements are being met Some contractual requirements are not being Contractual requirements are not being met, which met but this does not have a major impact on has a major impact on the service No non-conformances are present in the service relevant processes
Table 1. General principles of RAG score
Aspect evidence/measures Scoring of performance should Ref. Aspect include considerationof the Green Amber Red following typical evidence/ measures 1.1.6.c Comprehensive Demonstrate: Process in place and Process in place No process in place submissions jointly agreed for for the submission for the submission prepared for all Approvals, including technical the submission and and approval of and approval of approvals and approval, TTROs, price approval of all approvals all approvals and all approvals and departures from submissions, are comprehensive and departures from departures from departures from standards standards standards but joint standards agreement needed Departures from standards are Comprehensive, Approvals and Approvals and being adequately identifed accurate submissions departures from departures from have been made standards have been standards are not for all appropriate submitted but further always identifed and approvals prior to work information has been approvals are not progressing requested by the being sought approving authority Submissions are accurate, Work is progressing complete and submitted within before a departure timescales agreed with the has been agreed service provider Where innovative solutions have been proposed, effciency savings are claimed Potentials for departure are discussed with the approval authority in advance of the
submission Highway Network Management WebDAS has been used for all departures No work progresses until departure has been agreed Evidence: Agreed process for submission of approvals and departures WebDAS records Minutes of meetings Internal audits
Table 2. General principles of RAG score
85 percentages of red, amber, green and A performance fag, therefore, has therefore provide a transparent view white. The proportion of each colour the ability to show the detail behind of performance at lower levels and in the higher-level fag is therefore a performance score. For example, a prevent important issues against the sum of the products of the fag which is part green and part red specifc aspects being lost. weightings and percentages. Again, indicates that there are some areas of the resulting sum of the weightings good performance and some areas Contractual MST scores contributing to any particular of poor performance in the element The Toolkit requires MST scores to performance fag equates to 100%. being looked at. be assigned to each performance indicator (sub-lever level) according An example performance fag at lever Without the use of fags the to the guidelines set out in Table 3. level is shown in Figure 5, using the performance at outcome, lever and It is a contractual requirement that example weightings obtained from sub-lever level in the hierarchy would MACs agree such scores with the Figure 3. In this case, the resulting be reported as either red or amber Highways Agency area performance performance fag is 39% green, 28% or green. In such a scenario the manager on a monthly or quarterly amber, 14% red and 19% white. detail behind the score is lost. For basis depending on the measure. These are calculated from Equation example, amber at sub-lever level 2 below, in which percentage of each could indicate that all the aspects Although not part of the MAC colour in the lever fag is calculated contributing to that sub-lever are performance management from the sum of the product of the amber or that half the aspects are framework per se, the MST scores contributing sublever weightings and red and half are green. Clearly, are calculated for reporting purposes. the percentage of the same colour these two scenarios are signifcantly The MST scores are calculated in the corresponding sub-lever fags, different from a performance automatically according to a pre- divided by 100. perspective, but this information is defned rule set based on the RAG lost as performance is propagated scores assigned at aspect level and Equation 2 up the hierarchy. Performance fags the weightings assigned to them.
%colourlever = n (sub-lever weighting X % coloursub-lever ) ∑ 100 1 The 39% green is calculated by multiplying the weighting for sub- lever 1.2.1 (65%) by the percentage of green in the sub-lever 1.2.1 fag (35%) summed with the product of the weighting for sub-lever 1.2.2 (35%) by the percentage of green in the sub-lever 1.2.2 fag (45%), all divided by 100. The example Figure 5. Example performance fag for lever 1.2 calculation for green is clearly demonstrated in Figure 5. Although Score Satisfaction Requirement not shown for clarity, the percentage 10 Totally satisfed All aspects completed to entire satisfaction. of the other colours on the lever 1.2 performance fag is calculated similarly. 8 Highly satisfed Most aspects to entire satisfaction but some Finally, the outcome level aspects were only nearly satisfactory performance fags are similarly 6 Just satisfed A few aspects to entire satisfaction but some calculated, as detailed in Equation 3 aspects were only nearly satisfactory and some unsatisfactory below. 5 Neither satisfed nor dissatisfed Neutral performance Equation 3 4 Slightly dissatisfed Most aspects just unsatisfactory 2 Very dissatisfed Most aspects unsatisfactory but one or two were %colouroutcome = just satisfactory n 0 Totally dissatisfed All aspects unsatisfactory (lever weighting X % colourlever ) ∑ 100 1 Table 3. MST scoring guidance
86 141 Performance management framework for managing agent contractors
Step 2: scoring agreement is the central repository for the Performance cycle performance scores and associated Agreement on the scoring is reached comments from all 12 areas. monthly between the MACs and The performance management and Historical performance scores and the Highways Agency area teams. continual improvement process can comments are also retained in the The self-scored data entry sheet be seen as a monthly cycle, split into database. six steps, as demonstrated in Figure is tabled at the meeting and the 6. Each of these steps is outlined performance score for every aspect Producing the performance reports below. is discussed and agreed, along with The NPU is also responsible for the associated comments. This producing the performance reports Step 1: scoring and evidence has the valuable additional feature gathering and sending them back to the of encouraging a dialogue about area teams and MACs within the Scoring performance performance between the Highways agreed timescales. The scoring Agency and MACs, not just to focus propagation and development of The frst stage in the monthly on the immediate scores but to look performance cycle is the selfscoring performance fags are carried out in at what needs improving in the the MAC performance management of performance by the MACs and future. the gathering of associated evidence framework software. to justify their score. The scoring To aid speedy agreement and The reports are focused on providing of performance is conducted at approval of the performance scores information relevant to identifying aspect level only and all relevant the MAC performance manager problem areas and improving issues aspects should be scored. Based should provide the evidence to justify that exist, either at a local area level on the scoring guidance, each the self scores. The area performance or centrally. Typical categories of aspect is given a RAG score or, if no manager needs to approve all reports that can be produced within performance data are provided, then performance scores and associated the bespoke software include the the no data option is chosen. comments. following items. To assist with this process, a template Step 3: send area data entry (a) Area performance reports: data entry sheet has been provided sheet to NPU detailing performance fags at to all MACs. The data entry sheet Following the scoring agreement outcome, lever and sub-lever contains a list of all aspects grouped meeting and by the agreed date each level for any one area for any by outcome to mirror the layout of month the data entry sheet for each one month the scoring guidance document. area is emailed to the NPU. (b) Area performance comparison For each aspect, the data entry sheet The email is sent by the area reports: detailing performance includes a dropdown list with red, performance manager or a suitable fags at outcome, lever and amber, green and no data options deputy to the NPU, thereby signing sub-lever level for any number and an associated comments box. off the performance scores for that of areas for any one month. An Comments are required for all month. Data entry sheets received example screenshot is included aspects to explain the reasoning from any other source are not in Figure 7 at the outcome level Highway Network Management behind the allocated score. These deemed to be signed off and are not for fve hypothetical areas using should be instructive and allow the entered into the database. a dummy dataset reader to understand why a particular (c) Area performance trend reports: score was given and what actions Step 4: scores compiled and detailing performance fags at are required to improve the score, if reports produced outcome, lever and sub-lever possible, for next time. The NPU is responsible for compiling level for any one area over any Evidence gathering the performance scores centrally, number of months producing the performance reports To help justify their self scores, (d) Highest weighted red and and circulating to the area teams and the MACs should ensure that all amber reports: detailing the top MACs. associated evidence is in place in 10 highest weighted red advance of the scoring agreement Importing the data entry sheets and amber aspects. An example meeting with the Highways Agency Following receipt of the data screenshot is included in in step 2. The scoring guidance entry sheets from the areas Figure 8 for the highest details what MACs need to the NPU imports them into the weighted red report. demonstrate to justify their scores MAC performance management and lists the associated evidence that framework database. The database needs to be provided. 87 Figure 6. Performance management and continual improvement cycle
Figure 7. Screenshot of example area performance comparison report
88 141 Performance management framework for managing agent contractors
Responsibilities
Responsibility for performance management and continual improvement lies primarily with the NDD and the MACs. The regions and areas are responsible for managing the performance of the MACs and driving continual improvement. NDD Central is responsible for managing the MAC performance management framework process, Figure 8. Screenshot of example highest weighted red report including continual improvement Step 5: review reports and 2009b) under the performance of the process itself. However, all determine improvement audit framework (previously participants in the process have a collective responsibility to ensure actions Network Operations Audit of Contract Compliance (NOACC)). performance reporting is not just for The area team and MACs determine In particular, it comes under the reporting sake but is done to inform targeted improvement actions measure performance and continual improvement actions. informed by the performance improvement enablers in the MAC reports, with particular reference to audit matrix. Timetable for the highest weighted red and amber reports. The MACs then develop The process will also be subject to implementation action plans to incorporate those supplementary audits and reviews by improvement actions. the NPU to ensure that the process The MAC performance management itself is being applied properly across framework was trialled in three Step 6: implement the business. In addition, area teams areas during the fnal quarter of the improvement actions will perform their own reviews and 2009/2010 fnancial year and was rolled out to all 12 areas during the The MACs implement the checks on evidence presented by the 2010/2011 fnancial year. This was improvement actions as incorporated MACs in support of the performance done on a phased basis with four in the action plans. scores. areas adopting the new framework Timetable Change control in each of the frst three fnancial quarters. This phased approach The performance management and Based on feedback and further allowed feedback from the previous continual improvement process is research, the MAC performance quarter to be incorporated into the carried out monthly. However, step management framework will itself next phase of the rollout, thereby 6: implement improvement actions be subject to continual improvement. ensuring continual improvement Highway Network Management overlaps with steps 1 to 5 of any Changes will be centrally controlled during these critical early stages. number of future monthly cycles by the NPU to maintain consistency depending on the scale and required and comparability. Discussion and conclusion duration of the improvement actions. It is proposed to use the performance The performance management and measurement advisory group (PMAG) Audit and review activities span the continual improvement process – a consultative body – as the forum whole performance cycle, and feed described herein provides the to provide feedback to the NPU on directly into continual improvements Highways Agency with a monthly the process. There will be a formal of the process itself. ‘health check’ of MAC performance change control panel in the NPU in delivering their contractual who will assess the impact of any requirements. Critically, it makes no Audit, review and proposed changes and, having taken change to any existing contractual appropriate advice, decide whether change control requirement to report MST scores to implement the changes. but instead complements the process Audit and review Any changes will then be by providing clear scoring guidance The whole process is subject to the incorporated into the next planned where only limited guidance existed audit requirements for maintenance release of the MAC performance previously. contracts (Highways Agency, management framework.
89 The main benefts of implementing this process include the following: Acknowledgements
(a) reduced subjectivity of scoring This paper was previously published in Proceedings of the ICE - Transport, performance Volume 165, Issue 4, November 2012, pages 277-288. (b) comparability of performance The authors wish to acknowledge the support provided by the Highways across areas Agency and Atkins, in the frst instance, but also Aone+ (Halcrow, Colas and (c) increased visibility of Costain) and Enterprise Mouchel for their valuable contribution during the performance initial trials. (d) increased dialogue on Further information on the MAC performance management framework can performance and improvement be obtained from Atkins Highway Asset Management Group in Birmingham. actions (e) evidence-based decision making References targeting improvement actions 1. Highways Agency (2007) Area Performance Indicator Handbook, Issue (f) auditability of performance. 05, Rev 01. Highways Agency, London, UK. All of the above will help to drive 2. Highways Agency (2009a) Motivating Success: A Toolkit for Performance improved effectiveness and effciency Measurement – Maintenance, version 1.05. Highways Agency, London, in the delivery of MAC contracts. UK. 3. Highways Agency (2009b) NOACC Audit Requirements for Maintenance Further work Contracts, version 6.12. Highways Agency, London, UK.
The performance management 4. Highways Agency (2010) MAC Performance Management Framework – framework described in this paper Scoring Guidance, version 2.0. Highways Agency, London, UK. is a starting point from which to build and improve. Regular reviews of the framework are planned in order to capture lessons learnt and support continual improvement of the process. It should be noted that, in developing the framework, no attempt was made to assess the effectiveness or applicability of the existing performance measures. However, research is planned to review the existing performance measures, now that a working framework is in place. Future versions of the framework will be released as progress is made in this area and experience is gained from implementation of the new process. It is also intended to develop a web-based interface for the scoring, approval and reporting of performance. This would allow instant feedback on MAC performance, thereby making the process more effcient and reducing the time taken for the priority improvements to be identifed.
90 Highway Network Management 91 142 Re-structuring the organisation and offce layout to improve to improve layout Re-structuring the organisation and offce communication and fow of information; solution a planning and programming Development and implementation of community; of best practise within the MAC which is at the forefront our organisation. throughout focus culture Embedding a programme
The Area 6 MAC approach approach 6 MAC The Area and programme to planning management Introduction to 6 team has transformed its approach This paper outlines how Atkins MAC the business forward to drive management in order planning and programme delivery for the Highways contractual performance and service and improve Agency. of key areas and the three was required It explains why a change of approach change implemented which were: • • • performance and relationship Finally it highlights some of the fnancial, the new approach, Agency derived from benefts for Atkins and the Highways continuous improvement. of innovation, LEAN working and planned areas Steve Dickinson Schemes Manager Highways & Transportation Atkins Kevin Balaam Manager Programme Highways & Transportation Atkins • Restructuring the teams to Working in an integrated fashion Why was a new improve communication and they are coordinated by the Project approach to planning information fow; Management team to deliver the work in a planned and programmed • Creating a core Project and programme approach. To improve and facilitate Management team with ‘cradle to communication fow the offce layout management required? grave’ overview and ownership; was re-designed around the core Atkins performs both a Managing • Building a planning and Project Management team. Agent and Contractor role on the programming solution which MAC 6 contract. The organisational would drive the business forward; Planning and programme structure established at start of solution • Supporting the change through contract and roles within that streamlining the Quality Processes It is a contractual requirement that structure were different from the and supporting documentation the Service Provider submits to the typical consultancy design and with clarity to Contractual Highways Agency for acceptance contract administration role Atkins compliance and requirements; an Annual Plan for the Forward usually undertakes. As the contract Programme of works before the matured and the team increased • Leading and embedding a start of each fnancial year. The its understanding and knowledge, programme focussed culture Highways Agency submission it became evident that a number throughout the team through format is that of a fnancial forecast of signifcant changes in approach visual management initiatives, spreadsheet uploaded onto the were required in order to improve training, software investment Highways Agency fnancial system contract performance, consistent (and supporting licences) and (SfM). To populate this forecast it is service delivery, and commercial benchmarking. necessary to prepare a programme performance. The key issues for the funded Forward Programme identifed were: Implementing the of schemes. Previously, this was • Overly complicated quality change in approach done at high level on an Excel processes which in some cases spreadsheet platform and in some instances supported on Microsoft led to non-conformance and Restructuring the team unwieldy corrective actions; Project. There was no requirement to The principle changes to the maintain this basic programme and • An organisation structure organisation structure occurred in it was largely the responsibility of built around the above quality the Schemes and Commercial teams. Team Leaders in the Schemes Team processes which operated in A core Project Management team to apply their experience to manage silo working with ‘packages’ of supported by a MAC 6 Programme resources and deliver the Forward work handed from team to team Manager was created in the Schemes Programme. Whilst the team never and no clear ‘cradle to grave’ team with direct communication failed to deliver for the Highways ownership across the scheme lines to the Highways Agency Project Agency, it was recognised that there delivery process; Sponsors. Working closely with was no clear central platform which • A change in Highways Agency the wider team, Project Managers pulled together detailed scheme funding strategies with shorter undertake no design activities but programmes and key milestones, term maintenance agenda and are responsible for programme resource availability and utilisation, a drive to deliver more for less and fnancial monitoring/reporting revenue and cost, critical path and whilst requiring the Service throughout the project lifespan. linkage of projects. They ensure design, commercial Provider to be fexible and reactive Led by the Schemes Manager and construction teams maintain to budget changes. and coordinated by the MAC 6 programme and meet budgets and Programme Manager, it was decided manage contractual approvals and to build and develop a detailed Change management hold points. strategy Forward Programme for all schemes The Schemes commercial (Quantity and lump sum (operational) activities The Senior Management team Surveyors), design and construction utilising Asta Powerproject Enterprise developed a prioritised and teams were re-built under key software. managers to deliver as a single programmed change management As a starting point, it was necessary team, those stages of scheme strategy across the business to be to de-construct the relevant Quality delivery previously split into implemented over a six month period Processes and build up programme separate parts of the business. which focussed on: templates for all scheme types and
92 142 The Area 6 MAC approach to planning & programme management
Figure 1. Example of Level 2 programme design activities for a typical scheme values, incorporating not only design • Determine which schemes have Operations team and assign and target costing activities, but all weather susceptible activities estimated costs; contractual timescales, hold points, or have specifc programme • Logic link the programme approvals, key milestones etc. Each constraints in relation to when or and develop a critical path to template is built on two levels. Level how the works are undertaken; ensure prioritised delivery and 1, programme milestones and main • Determine programme for understanding of key milestones. scheme development activities, scheme development and delivery and Level 2, all detailed design This was carried out for all work and ensuring 100% utilisation of and project management activities activities undertaken in Schemes,
available resource pool across the Highway Network Management between milestones on Level 1. With Network and Operations teams. fnancial year within the MAC close involvement from design team team Application of the programme leaders, lead engineers, commercial and construction managers, each • Check and challenge resource to deliver the service activity on the Level 2 programme demand in the programme and The Programme Manager maintains was assigned a duration and generic re-profle over/under utilisation and oversees the Forward resource effort. The resource was of generic resource types as Programme in Asta Powerproject assigned a cost and the template appropriate; Enterprise. Its utilisation and programme duration and costs, • Determine external resource accessibility have broadened over the reality checked and adjusted/ requirements and specialist past 6 months by obtaining multi rationalised against out-turn sub-contracted design or access licences across the business actualised schemes of similar scope investigation/survey works and enabling the Project Managers to and complexity. assign an estimated cost to those update scheme programmes daily The next stage was to assign the activities as appropriate; and for the Schemes Manager and relevant programme template to other key managers to view the • Determine works identifed for every scheme in the confrmed programme to any level of detail. delivery through the MAC 6 Forward Programme and undertake supply chain or through Atkins the following exercise; 93 Figure 2. Example of Level 1 Milestone Metrics data (Baseline vs Actual)
The programme is used to plan and contractual processes and risk the Operations programme and manage resources and prioritise mitigation meetings and appropriate actualising progress on lump sum workload across the teams. For outcomes. This brings full visibility activities in the programme to fully schemes delivered by the service for the Highways Agency Project understand cost and value within the provider, 9 key milestones have been Sponsor and assists in prioritising business. The operations programme identifed at Level 1 programme. their workload and understanding of is used to prioritise resource effort in These are used to drive weekly, the scheme status. the six depots across the Area. monthly, quarterly priorities and Design Team Leaders and Lead The Schemes Manager has full resource effort. Additionally, they Engineers utilise the programme visibility of the Forward Programme facilitate integrated working with the to plan and manage the design delivery overview. By monitoring Highways Agency Project Sponsors team workload and effort. Bespoke the Level 1 milestone progress on a to mitigate any delays, identify reporting views by team or individual weekly basis, higher level reporting opportunities and understand using ‘code libraries’ of design to the Highways Agency Service potential risks to the programme activities from Asta, can be created. Manager and Atkins Contract delivery. By tracking and monitoring progress Director can be accurately made with Project Managers closely monitor and within their teams, Lead Engineers a current and actualised position update progress on their assigned are able to inform the Project ascertained at any given time. This is scheme programmes on a weekly Managers on forecast spend profles used to inform strategy and potential basis. Because the programme is and factors which may impact the additional spend opportunities resource and cost loaded, the Project programme. This informs planning with the Highways Agency Service Managers can ascertain an indication and risk mitigation discussions and Manager. of spend versus progress which is actions with the Highways Agency used to inform monthly fnancial Project Sponsors. reporting and checks against actual An Operations Programmer has been costs captured from Atkins fnancial appointed to assist the Programme systems. Risks to programme delivery Manager and focus on maintaining can be jointly managed applying 94 142 The Area 6 MAC approach to planning & programme management
Figure 3. Example of Design Team view (Top Level Summary showing concurrent progression of schemes)
Developing visual • Construction team planning and plan team priorities, targets management from the and programming boards for and issues. This is fed back programme mobilisation and construction through the Design Team Leaders activities which are used to plan and relevant Project managers When fully built and populated, supervision resource deployment, • Operations team develop Asta Powerproject Enterprise can be effcient utilisation of the supply visual management from the utilised to produce bespoke reports chain eg, linking up schemes programme in each of the six at any level of detail built into the in the surfacing programme depots to enable the Depot programme. The Schemes Manager to minimise demobilisation of
Agents to improve forward Highway Network Management developed a planning and progress blacktop gangs and plant; visual management area which is planning and help facilitate updated daily and is used to monitor • Commercial team target cost discussions and engagement with the high level priority and actions tracker which is used to manage the operatives on the Lump Sum required to deliver the programme. the milestones within the process activities programme. for preparing, submitting and The Programme Manager produces Training and support quarterly, monthly and weekly approving target cost estimates reports from Asta and updates for Provider Works. It is also used The Programme Manager was the visual management boards by the Managing QS to balance key to developing the Asta appropriately. The Schemes manager workload within the QS team, Powerproject Enterprise planning utilises the boards in discussion and facilitate meetings and progress and programming solution. meeting with senior managers and discussions with the Project Technical support and training were Project Managers in planning and Managers and set weekly and engaged from Asta plc to increase managing the portfolio in a proactive monthly priorities and accelerate knowledge of the software and its potential for broader way. • The roads and structures design application across the business. As teams develop a common visual Visual management has broadened the MAC 6 expert user and local management tracker to facilitate across the team driven by the Asta champion, the Programme Manager weekly team meetings to discuss programme to include: produced a User Guide for Project 95 Managers and rolled out a series of communication, the environment 1-2-1 on the job training sessions. As was created. Benefts to the experience and competency grew, To develop the culture it was Highways Agency training was gradually widened necessary to include every member across the team and resilience added of the team from trainee technician The development of the planning by creating an Assistant Project to Schemes and Commercial and programme approach by the Manager post with responsibilities Manager in ensuring they Atkins MAC 6 team has delivered which included an overview role for understood their contribution to multiple benefts for the Highways assisting the Project Management delivering the Providers Programme Agency: team to ensure the Provider for the Highways Agency and the Programme was always up to date • Contractual compliance: importance of taking full ownership on Asta. The most competent IT through visibility on the detailed for the role and work they undertake. literate junior staff were encouraged programme both parties have The Schemes Manager undertook to learn Asta and assist in updating a clearer understanding of workshops with the wider team, key and understanding the programme contractual timescales, application managers and individuals to embed and functionality. of the contract in respect the strategic change of approach of change control and risk A Programme driven culture and help individuals understand the management; changes in roles and responsibilities. A key part of the Senior Wide engagement in building the • Highways Agency Project Management Team change Annual Plan was encouraged and Sponsors are far more involved management strategy, was to create facilitated to create ownership and throughout scheme development an environment and culture of understanding. Visual management and have developed and matured programme ownership and delivery. serves not only to plan and prioritise their understanding of the end By identifying and implementing within the teams, but to create a to end process through monthly the right structure, right tools, right culture of meeting targets that are progress discussion and ad hoc people in key roles, and changing openly agreed and monitored. ‘business as usual’ meetings the offce layout to encourage centred around the programme and activities;
Figure 4. Example of Operational Depot programme view (Ardliegh Depot) 96 142 The Area 6 MAC approach to planning & programme management
Figure 5. Example of HA Project Sponsor - outstanding key tasks view/report
• Area Performance Indicators combining common design • Better working relationships (API): time and cost predictability tasks, meetings, site visits etc, between Atkins and the Highways targets have all been ‘green’ for across schemes being developed Agency Area team centred on 18 months; concurrently within the design an agreed Annual Plan and teams Provider Programme with a desire • Highways Agency Performance to work collaboratively and in Management Framework (PMFv8) • Increased confdence in Atkins’ an integrated manner to jointly for MAC and ASC contract ability to plan, manage and deliver. – all aspects for measuring deliver the Forward Programme performance on delivery of and Lump Sum activities Highway Network Management Forward Programme have been ‘green’ for 12 months; • Cost savings and effciencies in road space utilisation by identifying opportunities for combining traffc management into single sites or programmes and reducing target cost for individual schemes; • Potential for the Highways Agency to re-invest effciency savings into the network; • Key information for stakeholders quickly produced from Asta
• Effciency savings on cost Figure 6. Stakeholder view- Example of forward works programme within county of reimbursable activities by Suffolk for Suffolk CC
97 The benefts to Atkins
For Atkins many of the benefts are common in respect of strong consistent performance measures, improved working relationships etc. Other benefts include: • Clearer visibility to plan and manage resources effectively; • Confdence in quarterly business reporting to the board of directors and ability to deliver business targets; • Improved fnancial forecasting Figure 7. 2012/13 Q1 review showing average variance to baseline Annual Plan accuracy and checks on actualised (working days) at key Level 1 programme milestones costs; Powerproject Enterprise is recognised • Early preparation of weather • Improved performance and client as best practice in the MAC/ASC susceptible schemes enables feedback in respect of fnancial community. more effcient and risk mitigated reporting; delivery. Application of LEAN principles and • Improved commercial identifcation of effciencies include: performance by maximising Continuous • Single source of monitoring the revenue potential through being improvement initiatives in a position to discuss, prepare entire Providers Programme with functionality to bespoke reporting early designs or deliver additional The following is currently being work for the Highways Agency; to any level of detail in a simple and quick operation; undertaken or is planned for in the • Ability to benchmark performance current fnancial year: • Creation of report templates across the key milestones by parts • Quarterly detailed analysis of key of the business, teams, individuals from the programme to generate monthly data for incorporation programme milestones (forecast and discuss improvement plans versus actual) to assess outturn and adjustments to timescales etc; into PMF, API, Monthly Business Report and quarterly Business performance at key scheme • Signifcant increase in staff Reporting which reduces development and delivery stages morale, motivation and general duplication and time consuming and where improvements and feeling of being far more in data analysis; effort should be focussed; control of the programme at all • Building the draft Annual times; • Identifcation of concurrent working potential and effciency Plan framework for 2013/14 • Individuals understand their saving on design activities such as by reviewing resources and role and how they contribute to combined site inspection, TRIPS programme templates against delivering the service and business meetings, TTRO applications etc. outturn costs and duration; targets. It is estimated that there could • Adopting the same planning and be 15% effciency saving to the programming approach from Innovations and LEAN client of cost reimbursable design the start of the Atkins/Skanska activities during the current JV ASC Area 2 contract with The programming and planning fnancial year; potential to implement across solution implemented in MAC 6 is • Forward planning resource other Local Authority commissions an innovation over the conventional utilisation to maximise and Atkins Operational Services programming approach and has been productivity and work closely with contracts; expanded to include every activity the Highways Agency Area team undertaken in delivering the service • Developing visual management to take advantage of potential for initiatives across the business for the Highways Agency. The level early preparation of schemes; of detail and development built into following the Schemes team the Providers Programme using Asta approach and sharing across
98 142 The Area 6 MAC approach to planning & programme management
Operational Services with an initial focus in Area 2 ASC • Capturing outturn performance data for programme and costs and feeding into the 2013/14 Continuous value management process and bid submission to increase accuracy and confdence in budget allocations at funding. Highway Network Management
99 100 Structural Dynamics 101 143 Component stress Component stress Principal stress Density z p m l b z F m σ in vertical direction Force σ Mass of vessel PPSm Local primary membrane stress S Primary bending stress P intensity Allowable stress g difference Stress t Internal design pressure R Acceleration due to gravity ∆P thickness pressure Tentative ρ Internal radius of vessel in internal Increase pressure h W Height of fuid in the vessel acceleration Vertical Nomenclature Nomenclature P General primary membrane stress Determination of minimum of minimum Determination thickness under vessel wall loadings design condition Abstract vessels for nuclear a series of pressure During the concept design phase of vessel sizing minimum was developed to provide application, an approach under dynamic loading conditions. Calculations had been undertaken to thickness using ASME III Subsection determine an initial tentative vessel wall of mechanical loading was undertaken. NB, however only a limited assessment for extending the structural This paper outlines a static analysis approach loadings. These vessel shell to include design condition analysis of a pressure external and piping reactions include dynamic loading, support reactions minimum wall on the required which can have a signifcant infuence thickness. rules and assumptions that can be This paper is limited to outlining generic The method vessels. concept design of pressure applied to the preliminary within the design team. It to aid knowledge sharing was originally captured and rather an interpretation an exact methodology but does not prescribe application of the design code. a better defned vessel The aim is to provide analyses for fnite element stress geometry upon which to base the detailed both design and service conditions. beneft of this approach The perceived design changes being made will be a lower likelihood of major is that there during the detailed design phase. Simon Ratcliffe Engineer & Defence, Aerospace Communications Atkins condition loadings. Secondary Introduction Scope stresses in the shell and stresses in the mounting features and vessel ASME III NB rules for tentative The methods for calculation outlined attachments themselves are not pressure thickness and reinforcement here assume that the vessel is considered as part of this work. requirements for openings enable classifed as Class 1 and assessed only a very limited initial vessel sizing against stress intensity limits in the to be undertaken. This assessment American Society of Mechanical Assumptions is based on design pressure and Engineers Boiler and Pressure Vessel design temperature alone. Design Design Code Section 3 (ASME III) The assumptions stated below mechanical loads, such as those Division 1 Subsection NB1. The vessel are considered common to most resulting from shock or seismic is cylindrical in shape and contains cylindrical vessels and relevant to the effects also require a preliminary a working fuid (See Figure 1). It approach described in this paper. assessment. These dynamic loadings is a prerequisite that analyses to Additional specifc assumptions for can have a signifcant infuence on determine the dynamic response of individual vessels may be required the required minimum wall thickness. the pressure vessel on its support when the methods outlined here are structure have been undertaken put into practice: This paper describes a methodology in order to determine the actual for determining the minimum wall a) The vessel is assumed to be full equipment acceleration that is to be thickness requirement for pressure of the working fuid – this used in the structural analysis. vessels subject to high external removes the effects of ‘sloshing’ dynamic loading. Such loading can The calculation uses a static analysis fuid within the vessel; arise potentially on pressure vessels based on the load cases in Roark’s b) The vessel centre of gravity is at used in nuclear plant, the offshore Formulas for Stress and Strain2 its geometric centre; industry and in some military and is intended to be conservative c) The vessel is cylindrical and applications due to earthquake, blast by nature. Local stresses in the features spherical heads; and external impact. shell associated with nozzles and the mounting features are to be d) The vessel length is much The methodology extends the calculated in accordance with greater than the radius; structural analysis of ASME Class 1 methods contained in Annex G of pressure vessels to include all design e) Dynamic loading input can be PD 5500-20093. Alternative open condition loadings comprising the interpreted as an equivalent literature calculation methods shall combination of design pressure static load acting at the vessel be used if the mounting geometry and temperature, dynamic loading, centre of gravity expressed in is not suitable to be modelled using support reactions and external piping terms of gravitational References 2 and 3. reactions on nozzles. The approach acceleration (g); uses well documented hand This report is limited to outlining f) Vertical (z axis) and horizontal calculation techniques to determine generic rules and assumptions that (x and y axes) dynamic minimum wall thicknesses and nozzle can be applied to ASME Class 1 loadings are considered to be reinforcement requirements. vessels for calculating minimum acting independently of each thickness requirements. It does not The aim of this approach is to provide other and in isolation; prescribe an exact methodology for an improved defned vessel geometry specifc vessels but rather a general g) The vessel can be assumed to upon which to base the detailed approach. The guidance given here be symmetrical about the fnite element stress analyses for both is intended to be used to assist in vertical axis and the greater of design and service condition loadings the hand calculation and assessment the two horizontal dynamic at the detailed design phase. The of stresses and minimum wall loads (x and y axes) will be used perceived beneft of the approach thicknesses due to design condition as the bounding load case described in this paper is that there loadings. alongside the vertical dynamic will be a much lower likelihood of load; major design changes being required Only general primary membrane, to be made to the vessel during the primary bending and local primary h) The total stress at each location detail phase, which if they occur membrane stresses in the shell of will be assessed by summing can have adverse cost and timescale the vessel will be included in the the contributions from each implications on the project. assessment. Compliance with loading condition irrespective primary stress limits ensures that the of its sign. This is a conservative wall thicknesses are adequate to assumption and may be open prevent gross yielding under design to review should it result in
102 143 Determination of minimum vessel wall thickness under design condition loadings
excessively large wall Vessel Part/Region Load Case thicknesses; Vessel shell (remote from Internal pressure plus dynamic i) The allowable stress intensity discontinuities) loading (Sm) is evaluated at the design Vessel heads (remote from Internal pressure plus dynamic temperature of the vessel. discontinuities) loading Internal pressure plus dynamic Vessel shell local to nozzles loading plus external loading from pipe work Internal pressure plus dynamic Vessel shell local to mounting points loading plus external loading from pipe work Table 1. Summary of vessel regions being considered and the applicable load cases
Maximum Allowable Stress Stress Category Intensity
Pm Sm
Pl 1.5 Sm P + P m b 1.5 Sm PI + Pb 0.6Sm average primary shear stress across section Pure Shear 0.8Sm maximum primary shear stress across section in torsion Figure 1. Sketch Of Generic Cylindrical Vessel Table 2. Limits of stress intensity from ASME III Figure NB-3221-1 and NB-3227.2 Calculation sequence • repeat calculation if necessary General approach with an increased wall thickness The outline of the approach until the required reserve factor is The approach described in this paper described in this paper assumes that achieved. is intended to provide basic pressure calculations are undertaken in the vessel sizing and optimisation prior following sequence: Stress Categorisation and to undertaking a detailed stress • calculation of tentative pressure Allowable Stress Intensity substantiation of the vessel. The thickness for main shell and heads general approach is based on Principal stresses are required to be in line with ASME III NB-33241 calculating a tentative thickness for calculated for the assessment of the vessel shell under design pressure • assessment of stresses in shell design condition loadings. These and temperature conditions. This is and heads under design pressure consist of General Primary Membrane (P ), Local Primary Membrane (P) and then assessed to establish whether loading against ASME III criteria m l Primary Bending (P ) stress categories. an increase in thickness is required b • calculation of stresses in main from consideration of all design Figure NB-3221-1 in ASME III [1] shell and head remote from condition loadings. shows the allowable limits of stress Structural Dynamics discontinuities under dynamic intensity for Class 1 vessels and is This paper focuses on dynamic loading summarised in Table 2. loading resulting from shock, vessel • calculation of stresses in vessel support reactions and pipe loads on As stated in NB-3221.3 of ASME wall adjacent to nozzles and 1 the vessel shell as the key design III , the allowable value of primary mounting features under dynamic mechanical loadings. membrane (general or local) plus loading primary bending stress intensity is Sm The following regions on the vessel • calculation of principal stresses for multiplied by a shape factor, which and corresponding load cases are each load case for a solid rectangular section is 1.5 considered for assessment as part of (See Table 2). NB-3221.3 should this methodology. • calculation of stress intensities be referred to for other geometries. • calculation of reserve factors It should be noted that the shape
103 factor shall not exceed the value component, the calculated stresses Where reserve factors are found to calculated for bending only and in no in each direction translate directly be less than unity, it may be due to case shall it exceed 1.5. into three principal stresses. Under conservatism in the assumptions the assumption that the shell is thin and methods used to calculate the Assessment of stress walled, the radial stress component stress intensities. Where appropriate, is negligble, the remaining two are assumptions and methods should be intensity calculated as follows; refned to remove pessimism and the reserve factors recalculated. In order to assess the vessel shell Equation 1 If it is deemed that the treatment of thickness for suitability under 1 2 2 σ = (σ + σ ) + (σ - σ ) + 4.t design condition loading, it must p1 2 x y x y xy assumptions is independent from be established whether the stress the reserve factors being below unity, then the calculations should intensity in the shell exceeds the Equation 2 Table 2.3, Reference 2 specifed limits. These limits differ be repeated with an increased wall 1 2 2 depending on the category of stress σ σ σ σ .t thickness until acceptable reserve σp2 = ( x + y ) + ( x - y) + 4 xy present in the shell (see Table 2). 2 factors are achieved. The following sections describe the The principal stress σ is therefore In the case of assessing initial process by which the stress intensity p3 zero for the purposes of calculating pressure thickness calculated using is calculated and then compared with NB-3324; where the reserve factor the allowable limits. This procedure the stress differences S12, S23 and S31. is less than unity the wall thickness is described in ASME III NB-3215. should be increased in the frst Principal Stresses Stress Intensity instance. 1 At the location on the vessel being From ASME NB-3215(e) the stress Appendix 1 outlines an example investigated, an orthogonal set of differences are then calculated as calculation concerning a simple coordinate axes should be selected. follows: cylindrical shell subject to internal For many pressure vessels it is Equation 3 pressure plus dynamic loading. It demonstrates the initial vessel possible for these axes to be chosen S = σ - σ such that the shear stress component 12 p1 p2 thickness being increased in order is zero. This helps to simplify the Equation 4 to give an acceptable reserve factor calculation of principal stresses. For under dynamic loading. S23 = σ p2 - σ p3 cylindrical vessels, orthogonal axes in the radial, tangential and longitudinal Equation 5 Tentative pressure direction are recommended. S = σ - σ 31 p3 p1 thicknesses and At each location calculate the stress The stress intensity is the largest opening reinforcement components in each axial direction absolute value of the stress for each load case. These stresses differences calculated above which Initial Design Pressure are then assigned an appropriate can then be compared to the Thickness category in line with the guidance allowable stress intensities listed in set out in ASME III Table NB-3217- An initial value for vessel wall Table 2. 1. The algebraic sum of the stresses thickness can be calculated using the in each category should then be formulae given in ASME III NB-3324. found. As specifed in NB-32151, the Reserve factors Equation 6 sum of the stresses in the general P.R primary membrane stress, local Assessment of the stress intensity t = primary membrane stress, general is achieved by calculating reserve Sm - 0.5P primary membrane stress plus factors. The reserve factor is equal to bending stress and local primary the allowable stress intensity divided Where: by the calculated stress intensity. membrane stress plus bending stress t = Tentative pressure thickness are all assessed separately for each Generally, a reserve factor of unity or load case. These stresses are then greater indicates that the vessel wall P = Internal design pressure thickness and area reinforcements translated into principal stresses as R = Internal radius of vessel described in Roark’s Formulas for local to openings are adequate for Stress and Strain2. For thick walled the design condition loadings. Sm = Allowable stress intensity for vessels where the axes have been the material selected such that there is no shear 104 143 Determination of minimum vessel wall thickness under design condition loadings
This formula is based on the The radial stresses are assumed to be Vertical Dynamic Loading assumption that the vessel is thin negligible in comparison with hoop For vertical dynamic loading it will be walled. and axial stresses. assumed that the vessel is accelerated Initially, the thickness of the vessel Vessel Heads upwards. The resulting downwards heads is assumed to be equal to Primary membrane stresses will force will therefore be equal to the that of the main cylinder wall. also be present in the upper and mass of the vessel and contents The primary stresses in the vessel lower heads of the vessel. These multiplied by the acceleration. shell due to design pressure and are calculated using the appropriate Equation 7 temperature loading can then be load case based on the geometry of . calculated and assessed against the FZ = m (WZ) the head. This paper only considers relevant design criteria. spherical and torispherical head Where the upper and lower head of Nozzle and Opening Area geometries common on many the vessel have different geometries, Reinforcement pressure vessels. There is not the rather than considering an upwards scope to consider more complicated and downwards acceleration, the Nozzles and openings in the shell geometries. For a spherical head same dynamic loading will be applied require a minimum level of local under uniform internal pressure, to both heads. material reinforcement which should Roark’s gives formulae for the be considered when calculating meridional and tangential stressCase 3a, Axial Stress in Shell the minimum pressure thickness of Table 13.1, Reference 2. The crown region of The cylindrical shell will see an the shell. The calculation of this a torispherical head can be assessed increase in axial load due to the reinforcement is based on design using the same formulae. increase in effective weight of the pressure and temperature loading fuid in the vessel and similarly due to and supplements the minimum Discontinuity stresses resulting from the increase in effective weight of the pressure thickness. ASME III NB- the changes in section between the vessel material. 3332 gives rules for the calculation shell and the head are not assessed of nozzle reinforcement based on in this calculation neither is the Mass of Fluid design pressure loading. This can knuckle region of a torispherical When the vessel is accelerated then be assessed against dynamic head. upwards, the mass of the fuid is loading from pipe work. Assessment of Shell Thickness effectively acting downwards within under Mechanical Design the vessel. This will generate an axial Preliminary stress Condition Loadings stress in the vessel shell equal to the assessment of design downwards force of the fuid under Once the minimum shell pressure acceleration divided by the vessel condition load cases thickness has been established, shell cross sectional area. In order further hand calculations can be to ensure a conservative outcome, Assessment of Static Pressure undertaken to assess this thickness the total mass of the fuid will be Load for suitability under other design used and the stress analysed at the condition loading. The loads Once an initial pressure thickness thinnest section of the vessel shell. considered by this paper are vertical has been calculated for the vessel it dynamic loading, horizontal dynamic Mass of Material requires assessment to ensure that it loading, local loads applied to the can withstand the design condition The vessel shell loaded by its own vessel shell by mounting features and pressure loading. The following weight will experience an axial pipe work reactions. paragraphs describe the general membrane stress. When the vessel Structural Dynamics membrane stresses that are present The following section contains is accelerated upwards, the effective in the shell under such loading. guidance for approximating these weight of the vessel material will load cases and calculating the increase resulting in additional axial Main Cylindrical Body resulting stresses in the shell. These membrane stress. This load case is The main body of the vessel shell is stresses are then categorised and the same as that outlined in Case 1e 2 considered separately from the vessel assessed against the design criteria of Table 13.1 in Roark’s Formulas . heads and is a cylinder with capped outlined in Table 2. The aim of the The axial stress is calculated by ends. The axial and hoop primary assessment is to provide suffcient multiplying the force per unit volume membrane stresses in the shell under margin in the vessel thickness to of the material by the total height uniform internal or external pressure, withstand mechanical loadings of the cylindrical shell, where the can be calculated using Case 1c in before the design is progressed to force per unit volume is equal to Table 13.1 from Roark’s Formulas2. the detailed design phase. the density of the vessel material
105 multiplied by the acceleration. The stresses resulting from the mounts at opposite ends of the The increase in load caused by increase in the effective weight of vessel, a simply supported beam acceleration of the lower head is also the fuid will be calculated using Case approximation may be appropriate. included in the calculation. In order 3a, Table 13.1 from Roark’s Formulas To ensure a conservative calculation, to ensure a conservative calculation, for Stress and Strain2; however, the the entire mass of the vessel, the compressive stress in the shell hydrostatic pressure will be replaced including contents, is treated as a above the upper mounting position by the design pressure plus that uniformly distributed load applied caused by acceleration of the upper under acceleration as shown in along the length of the vessel. The head is neglected. Equation 8. maximum bending moment can Hoop Stress in the Shell If the lower and upper heads then be calculated and the simple have different geometries, then theory of bending used to fnd the The vertical acceleration of the vessel the stresses in both heads shall maximum axial bending stress. This will also result in an increase in be analysed, assuming the most stress is categorised as a membrane hoop stresses in the shell due to the conservative loading on each. stress, rather than bending stress, increase in the effective weight of due to the very small stress gradient the fuid. This is calculated based on Mass of Material created through the wall. See Table the total mass of fuid in the vessel. The vessel head loaded by its own NB-3217-1, ASME III1. In order to calculate the hoop stress weight will generate membrane in the shell, the increase in effective stresses. In this case both meridional Average Shear Stress in the fuid weight is treated as an increase and hoop stress will occur. The Shell in internal pressure in the vessel. This acceleration will cause the effective Treating the vessel as an elastic allows internal pressure load cases to weight of the material in the vessel beam, the average shear force can be used to calculate the hoop stress. head to increase and the resulting be found by dividing the total load The hoop stresses in the shell as a force per unit volume shall be on the vessel by the number of result of internal pressure loading are calculated by multiplying the density supports assumed under the beam found using Case 1c in Table 13.1 of the material by the acceleration. approximation. from Roark’s Formulas2. In this case The stresses are calculated in line The average shear stress in a hollow however, the pressure is calculated with the Case 3c given Roark’s 2 cylindrical beam or shell is calculated from the head of fuid above the Formulas Table 13.1 . by dividing the shear force by the lowest point in the vessel with Horizontal Dynamic Loading cross sectional area of the shell and acceleration due to gravity replaced Where the horizontal acceleration assessed against 0.6Sm in accordance by the acceleration. 1 has been split into two planes (e.g. with ASME NB-3227.2(a) . Equation 8 x and y) the greater of the two Hoop Membrane Stress in the ∆P = ρ.h.(Wz) accelerations should be used when Shell and the Vessel Heads due calculating the horizontal dynamic to Increase in Effective Weight Stresses in the Head loading. This approach relies on the of Fluid The lower head will see an increase assumption that the vessel can be in axial (meridional) and hoop considered symmetrical about the The method used in the vertical stresses due to the increase in vertical axis. loading case for evaluating increased effective weight of the fuid in pressure stresses in the shell due to Bending Stress in the Shell due the vessel and similarly due to the the increase in effective weight of increase in effective weight of the to Direct Loading the fuid contents is unsuitable for vessel material. Depending on the way the vessel is the horizontal loading. This is due to the pressure not being uniform Mass of Fluid mounted, axial and hoop bending stresses will be generated in the across the vessel diameter which The vertical acceleration of the vessel shell under horizontal dynamic will generate distortion and bending vessel will result in an increase in the loading. The method of calculation stresses. stresses in the lower head due to the of these bending stresses uses an However the vertical loading case increase in the effective weight of approximation of the vessel as considered here involves a much the fuid. Again as with the stresses an elastic beam under bending. greater height of fuid than the vessel in the vessel shell, this is calculated Different beam approximations can internal radius and so is assumed based on the entire mass of fuid and be used to most closely represent to provide suffcient margin on is treated as an increase in internal the way the vessel is mounted. the vessel thickness. Horizontal pressure load acting on the head. For example, in the case of two pressure stresses should therefore
106 143 Determination of minimum vessel wall thickness under design condition loadings
be accounted for by applying the laid out in ASME III Subsection NB1 The discontinuity stresses should be increase in pressure under vertical for consistency. calculated in accordance with the acceleration to the horizontal load methodology outlined in Welding Radial Loads Applied to the Vessel case. This will allow a conservative Research Council (WRC) Bulletin Shell assessment of the stresses in the 3685. shell under horizontal loading to be Loads on the vessel shell resulting Assessment of Discontinuity Stress included. from pipe work are assessed using a limit load analysis. Under horizontal These stresses are then added to Calculation of stresses dynamic loading, the reaction of those from external loadings to the pipe work is assumed to create get the total stresses in the shell in vessel wall adjacent a radial load on the vessel shell. and in the nozzle for comparison to nozzles and This shall be calculated assuming a with the ASME III limits. The maximum direct stress in the pipe inclusion of discontinuity stresses mounting features work of 1.5Sm based on the pipe as outlined here is intended to give work material. The load is then an indication of the local stresses Vessel Wall Adjacent to the maximum stress in the pipe prior to the undertaking of detailed Nozzles multiplied by the cross sectional area fnite element techniques during the The applied loads at pipe work of the pipe work attachment. The detailed design stage. corresponding stresses in the vessel attachments to nozzles are often Mounting Features not known at the concept design shell are then calculated as outlined stage. Therefore the maximum load in Subsection G.2.2 in Annex G of PD The stresses in the shell resulting (end thrust, bending, shear and 5500:2009. from the mounting features under torsion) that can be applied to the Shear due to Pipe Work dynamic loading are also required. nozzle by the pipe work shall be These stresses shall be calculated calculated based on the assumption The maximum shear load that can based on the local support loadings that the stress in the pipe reaches be applied to the nozzle by the pipe on the vessel shell. The reaction at the maximum value permitted by the work shall be calculated based on the the supports due to vessel mass and ASME design code for pipe work. ASME limit of 0.6Sm and the known external pipe reactions contribute Details of the approach are provided cross sectional dimensions of the to the local support loading. The below. pipe work. Note that in this case the exact method of assessment will allowable stress intensity value, Sm, depend on the nature and number External Moments Applied to the is that for the pipe work material. of mounts, but generally these Vessel Shell Similarly for shear stress as a result loads should be treated as moments The reaction of pipe work due to of torsion in the pipe work, the applied to the vessel shell and expansion and dynamic loading will maximum torsional moment that can calculated in a similar manner to apply a moment to the vessel shell. be applied to the nozzle by the pipe stresses as a result of pipe work This moment shall be calculated work shall be calculated based on the attachments. assuming a maximum bending stress ASME limit of 0.8Sm as defned in NB-3227.2(b) of ASME III1. The effects of the pipe work in the pipe of 1.5Sm. For most reactions at the vessel mounts can be cylindrical vessels that are intended to Gross Discontinuity Stress calculated using a moment balance be vertically mounted, the method by Adjacent to Nozzle Opening and represent the additional stress which these moments are calculated at each mounting point as a result Calculation of Discontinuity Stress is shown in Subsection 2.3, Annex of the pipe work attachments under G of PD 5500-20093 where vertical Both primary and secondary dynamic loading. Structural Dynamics dynamic loading translates to a categories of discontinuity stress The stresses in the shell as a result longitudinal moment and horizontal exist local to the nozzle opening. of the reactions at mounting points dynamic loading translates to a For the purposes of this paper shall be calculated using methods circumferential moment. These however, only those categorised as contained in Subsection G.2.3 of will be analysed using Subsection local primary membrane stresses in Annex G of PD 5500:2009 where G.2.3 and suggested working forms accordance with Table NB-3217-11 appropriate. Should the specifc G2 and G1 respectively. PD 5500- are considered. In order to assess the 3 mounting features of the vessel not 2009 has been selected in this case total stress in the region adjacent to be covered in Annex G, alternative because it contains relevant formula the nozzle, the gross discontinuity sources of load cases should be for calculating local component stresses are required in addition sought. stresses. The assessment of these to the average membrane stresses stresses will still be against the criteria resulting from pressure load. 107 The stresses in the shell adjacent to the mounting features as calculated Acknowledgments above shall be added to the appropriate hoop or axial stress in the This paper was previously published in the proceedings of the ASME shell due to internal pressure (plus Conference, Toronto, July 2012. the increase in pressure arising from The author would like to acknowledge the help and support of Jonathan increased effective mass of fuid due Edward Pope (Atkins) who has provided technical guidance and mentoring to dynamic loading) to determine throughout. Recognition should also go to Richard Russell-Johnson (Atkins), the total stress in the shell at the Peter Goodman (Atkins), Mark Selden (Atkins) and Sam Arnold (Atkins) for mounting. their help with the paper. And fnally to Atkins for funding this endeavour.
Conclusions References
This paper has described an approach 1. ASME, 2010, ASME Boiler & Pressure Vessel Design Code, Section III, for extending the structural analysis Division 1, Subsection NB, American Society of Mechanical Engineers. of ASME Class 1 pressure vessels to include all design condition 2. Young, W.C. and Budynas, R.G, Roark’s Formulas for Stress and Strain, loadings. These loads comprise McGraw-Hill, Seventh Edition, 2002. the combination of design pressure 3. BSI, 2009, PD 5500:2009, Specifcation for Unfred Fusion Welded and temperature, dynamic loading, Pressure Vessels, British Standards Institution, 2009. support reactions and external piping reactions on nozzles. Open literature 4. ASME, 2010, ASME Boiler & Pressure Vessel Design Code, Section II, and hand calculation techniques American Society of Mechanical Engineers. have been employed to determine 5. Mokhtarian, K. And Endicott, J.S, Stresses in Intersecting Cylinders minimum wall thicknesses and Subjected to Pressure, WRC Bulletin 368, Welding Research Council, nozzle reinforcement requirements. November 1991. Assessment of stress intensities has been in line with the ASME III Subsection NB design criteria. Appendix 1 demonstrates part of the methodology being applied to a simple cylindrical shell. An initial tentative pressure thickness is calculated and then dynamic loading applied. The calculation shows that in order to generate adequate reserve factors under high dynamic loading, the initial pressure thickness must be increased.
108 143 Determination of minimum vessel wall thickness under design condition loadings
Equation 9 and allows internal load cases to be Appendix A . . used to calculate the hoop stress. P R i ttent := The increase in pressure is calculated Example Calculation of Sm - 0.5P by multiplying the density of the Vessel Pressure Thickness and fuid, by the height of the fuid inside t := 18mm Assessment under Dynamic tent the vessel and then by the dynamic Loading acceleration. To check the acceptability of this Equation 13 The following calculation result, the stresses generated in a demonstrates the methodology shell of this thickness under both Increase in internal pressure outlined in the paper. The appendix vertical and horizontal dynamic under vertical dynamic loading is limited to assessing the pressure loading are calculated and assessed ∆P := ρ L W thickness and dynamic loading on against the stress acceptance criteria fuid i v a simple cylindrical shell excluding in ASME III. heads purely as a demonstration of Equation 14 the theory. The shell is assumed to Assessment under Vertical be orientated with its longitudinal Dynamic Loading Total increased internal pressure axis vertical and flled with an due to dynamic loading Using the tentative thickness incompressible working fuid. The calculated above, the shell has the Pv.shock := P + ∆P calculation will consider primary following physical values: membrane stress and primary The vessel is considered to be thick bending stress only. Equation 10 walled and therefore Case 1b, Shell outer radius Table 13.5 on page 683 of Roark’s Inputs Formulas for Stress and Strain is used Ro :=Ri + t shell Vessel internal to calculate the pressure stresses at L = 1500 mm Ro = 178mm length i any chosen radius, r. In this case, the internal pressure is equal to the Vessel internal Equation 11 R = 160 mm design pressure plus the increase radius i Total mass of the shell and fuid in internal pressure under vertical
Density of 3 2 2 2 dynamic load calculated above. ρ = 996 kg/m mtotal := (R o - R i ) π Li ρsteel + R i π L i ρ fluid working fuid fuid Equation 15 Design stress mtotal = 344kg intensity of Sm = 96 MPa Axial membrane stress due to internal pressure vessel material Under vertical dynamic loading the 2 Pv.shock R i Density of 3 effective weight of the entire mass of σam = 2 2 ρsteel = 7800 k/m vessel material the vessel and contents is increased. Ro - Ri Dynamic This is modelled as a downward force acting on the vessel and will generate Equation 16 acceleration Wv = 25g (vertical) axial membrane stress in the vessel Hoop membrane stress due to shell. Dynamic internal pressure acceleration W = 30g Equation 12 P R 2(R 2 + r2) h σ = v.shock i o (horizontal) hm 2 2 2 Axial membrane stress in the r (Ro - Ri ) Design pressure P = 100 bar shell due to vertical dynamic load Structural Dynamics Equation 17 m W σ := total v Calculation of Tentative a.v π (R 2 -R 2) Radial membrane stress due to Pressure Thickness O i internal pressure σ = 4.41 MPa -P R 2(R 2 + -r2) The calculation for the tentative a.v σ v.shock i o rm = 2 2 2 pressure thickness of a cylindrical r (Ro - Ri ) shell can be found in paragraph NB- The vertical acceleration of the vessel 3324 of Section NB and calculated as also results in an increase in the The membrane stresses at both the follows: membrane stresses in the shell due to inner and outer radius are calculated an increase in effective weight of the using equations 14 to 16 and the working fuid within. This is modelled mean average taken. as an increase in internal pressure
109 Mean axial membrane stress Stress intensity Equation 26
σam.v = 43.619 MPa Sv = 97.604 MPa Maximum bending moment 2 Mean hoop membrane stress The reserve factor is then calculated -F shell.h L i M := against Sm. bend 8 σhm.v = 92.421 MPa Equation 24 Mean radial membrane stress Equation 27 Reserve factor σrm.v = -5.183 MPa Second moment of area for a Sm cylindrical section The membrane stresses in each RFv := = 0.98 S v 4 4 plane resulting from vertical (R o - R i ) dynamic loading are summed before I := π The reserve factor calculated is less 4 calculation of the principal stresses. than 1 which indicates that the shell Equation 28 Equation 18 pressure thickness will not withstand vertical dynamic loading conditions Distance from neutral axis Axial membrane stresses and will need to be increased. R - R σ := (σ + σ ) y:= o i m.v1 am.v a.v Assessment under Horizontal 2 Equation 19 Dynamic Loading Equation 29 Hoop membrane stresses Under horizontal dynamic loading the vessel shell will see a force Resulting maximum bending σm.v2 := σ hm.v acting on it equivalent to the mass stress Equation 20 of the vessel shell and its contents M .y σ := bend Radial membrane stresses under horizontal dynamic loading b.shell I acceleration. This force will be σ := σ σ = -11.708 MPa m.v3 rm.v treated as a uniformly distributed b.shell The axes have been chosen such load acting over the length of the that the three principal stresses are vessel. The shell is modelled as a Under horizontal load the increase taken to equal the stresses calculated beam of hollow cylindrical cross in effective weight of the fuid will above. The stress differences and section, simply supported by a single again be modelled as an increase stress intensity can then be calculated support at both ends. This load will in internal pressure and therefore in accordance with paragraph NB- give rise to a bending moment in induce membrane stresses in the 3215 in ASME III. the shell and hence an axial bending shell. Since the length of the vessel stress. An average shear force across Equation 21 is signifcantly greater than the the shell will also be present. This diameter, the increase in vessel Stress differences will be assessed separately. internal pressure estimated under
Sv12 := σ m.v1 - σ m.v2 Equation 25 the vertical load case is considered to provide suffcient margin on the Sv12 = 44.392 MPa The total force per unit length of vessel vessel thickness and can be applied under horizontal dynamic loading. m .W Equation 22 total h Fshell.h := The shell stresses resulting from Li Sv23 := σ m.v2 - σ m.v3 horizontal loading are then used to calculate the principal stresses in Sv23 = 97.604 MPa The maximum bending moment will occur at the centre of the length the shell. The axial bending stress
of the vessel. The distance to the across the entire section of the Equation 23 neutral axis is taken as the mean vessel is considered to be a primary membrane stress in accordance with Sv31 := σ m.v3 - σ m.v1 radius. This calculates the average stress in the wall at the section of ASME III Table NB-3217-1 and so is S = -53.212 MPa v31 maximum bending moment. added to the axial membrane stress as a result of internal pressure. The stress intensity is equal to the stress difference of greatest magnitude.
110 143 Determination of minimum vessel wall thickness under design condition loadings
Equation 30 Equation 35 Membrane stress under horizontal dynamic loading Principal stresses Shell shear area
2 2 RFh = 1.09 σm.h1 := σ b.shell + σ am.h Ashell.shear := π (R 0 - R i )
Average shear stress under Equation 31 Equation 36 horizontal loading σ := σ Average shear stress in the shell m.h2 hm.h RF = 22.6 Q shear.h shell tshell := Equation 32 Ashell.shear
σm.h3 := σ rm.h tshell = 2.646 MPa
The stress differences and stress The average shear stress in the shell intensity can then be calculated as is assessed by comparing it to the shown previously. The reserve factor allowable stress intensity for pure is then found. shear as defned in ASME III Section Stress intensity under horizontal NB-3227-2. dynamic loading Equation 37 S = 97.604 MPa h Reserve factor for average shear Equation 33 0.6 Sm RFshear.h := = 21.77 Reserve factor tshell RF := Sm = 0.98 h Increased Shell Thickness Sh In order to provide confdence that The reserve factor calculated is the shell is able to withstand dynamic less than 1. This indicates that the loading conditions, the vessel wall shell pressure thickness will not thickness is increased until the withstand horizontal dynamic loading reserve factors under both vertical conditions and should be increased. and horizontal dynamic loading are Assessment of Average Shear greater than 1. The results in this case are shown below. The shear stress acting in the beam Updated shell thickness to due to bending is assessed separately. account for dynamic loading In general the average shear stress is signifcantly smaller than the tshell.new := 20mm membrane stresses but has been assessed to provide a more thorough Repeating the calculations using assessment. Using general beam the new shell thickness gives the bending theory the shear force acting following results for reserve factor. on the beam is calculated by dividing This demonstrates that the increased the total load on the vessel by the Structural Dynamics shell thickness now provides number of supports; in this case suffcient margin to withstand design assumed to be two. The average condition dynamic loading in both shear stress is calculated by dividing vertical and horizontal directions. the shear force by the cross sectional area on which the shear force acts. Membrane stress under vertical dynamic loading Equation 34 RF = 1.09 Shear force in the shell v m .W Q := total h shell 2
111 112 144
Jan Winkler Innovative optical measurement Structural Engineer Atkins Denmark technique for cable deformation Atkins analysis
Abstract
Jesper Schaarup In this paper, the localised bending fatigue behaviour of pretensioned high Regional Head of strength steel monostrands is investigated. Furthermore, a new methodology Bridge Engineering using an optical photogrammetry system, which can quantify surface Atkins Denmark deformations on the strand is presented. The system allows measurement of Atkins the strain distribution in the strand and helps in identifying potential failure mechanisms along the strand and at the wedge location. Initial analysis of the deformations shows that the bending fatigue behaviour of the monostrand may be controlled either by local bending deformations or by relative displacement (opening/closing and sliding) of the helically wound wires. Moreover, the results are a step towards understanding the bending fatigue damage mechanisms of monostrand cables.
Introduction Increasing bridge stock numbers and describing the failure criteria for a push for longer cable-supported multilayered strands have been span lengths have led to an increased proposed (Hobbs & Smith 1983, number of reported incidents of Hobbs & Raoof 1996), none of these damage and replacement of bridge can be applied to monostrands stay cables due to wind and traffc- composed of one layer of wires. As induced fatigue and corrosion the majority of modern stay cables (Winkler & Georgakis 2011). Limited comprise a number of individual work has been undertaken to assess high-strength steel monostrands, thoroughly the fatigue characteristics the understanding of the bending of bridge cables subjected to cyclic characteristics and failure mechanism transverse deformations as the of the individual monostrand has cables are in principle not expected become more relevant. It has been to experience bending. Furthermore, reported that the methods seeking the commonly applied qualifcation to evaluate the fatigue life of the tests for the fatigue resistance of cable should be further developed stay cables (fb 2005, PTI 2007) do to be consistent with observed not specifcally address fatigue issues fatigue failures of cables subjected to related to trans-verse cable vibrations transverse deformations (Jensen et al. and therefore do not require testing 2007, Laursen et al. 2006). for bending. However, recent In this paper, the localised bending Structural Dynamics bending fatigue tests on grouted and fatigue behaviour of pretensioned PE coated monostrands have shown high strength steel monostrands is that monostrands can experience investigated. Furthermore, a new fatigue failure due to high localised methodology employing an optical deformations (Winkler et al. 2011) photogrammetry system which and fretting (Wood & Frank 2010). can track coordinates and calculate Cable fatigue failure criteria deformations and strain is presented. The system enables measurement of The purpose of failure criteria is to the strain distribution in the strand predict or estimate the failure/yield and helps to identify potential failure of structural members. Although mechanisms along the strand and at a considerable number of theories the wedge location. 113 the experiments was limited to a contained within each facet of the Cable bending fatigue particular location along the wire computational mask. The system analysis where the gauges were positioned captures images during the loading (5.1mm from the wedge). process and then computes the To date, information about local deformation and the strain of the cable deformations and the documented surface using a post- resulting strain are often needed processing algorithm. to evaluate the failure criteria and Correlation analysis: strain have been measured with strain gauge measurement and gauges located in the vicinity of the cable anchorage (Miki et al. 1992). photogrammetric data However, the critical region of the Prior to the bending test, the strand in terms of fatigue is located correlation between the strains in the vicinity of the fxation point obtained with the photogrammetry (wedge) where placement of the system and using strain gauges was gauges is problematic and the strain established in an axial loading test. information obtained with gauges is The set up comprised an axial tensile limited to discrete locations along the Figure 2. Variation in wire strains during force applied to a high strength cable (i.e. where the strain gauges dynamic test steel monostrand instrumented with were placed). strain gauges at the upper anchorage As the relative movement between Cable hysteresis and strain and the surface prepared for optical the individual wires undergoing deformation analysis at the lower gauge measurement bending deformation and the anchorage (Figure 4). Winkler & Kotas (2011) have distribution of the wire strains at reported that in bending fatigue the wedge location was diffcult tests on PE coated monostrands to deduce from strain gauge a hysteresis was observed in the measurements, a new methodology load displacement diagram (Figure using image analysis was introduced. 1). This was an indication that the monostrand experienced some Methodology form of friction or internal energy dissipation mechanism which is Photogrammetry system and likely to be a result of interwire specimen preparation movements. In order to facilitate measurements with the photogrammetry system, adequate contrast in the grayscale and surface pattern on the specimen surface is required. This was achieved Figure 4. Test set up for the correlation using white and black spray paint test to apply a random pattern on the strand surface (Figure 3). The load was applied axially and the resulting strain was measured using image analysis and by physical strain gauges. Figure 5 shows good agreement between the wire strain measured using the two different methods. Figure 1. Variation of axial load and cable hysteresis The results of the correlation test provide confdence in the obtained Figure 3. Strand and computational Strain gauges placed on each of mask relationship between applied load in the outer wires of the monostrand the strand and the resulting strains monitored the response of the strand The spatter marks were of captured with the photogrammetry under fexural loading (Figure 2). suffciently small size such that system. This information obtained from uniquely identifable grayscales were
114 144 Innovative optical measurement technique for cable deformation analysis
Photogrammetry equipment and strains due to transverse displacement The monostrand cable was terminated at both ends with the generic anchorage. The photogrammetry equipment comprised of two high resolution cameras was focused on the vicinity of the wedge (Figure 8).
Figure 8. Test set up and photogrammetry equipment Figure 5. Correlation between strains measured using photo-grammetry and strain gauges The angular deviation φ at the anchorage was obtained by applying Experimental transverse deformations at mid-span of the cable. The following four investigation ranges of angular deviations φ were investigated: 0.5°; 1.0°; 1.5°; 2.0° Test set up and strains due to (Figure 9). pretension load Figure 6. Strain gauges on three bottom wires of the strand Full details of the cable specimens and testing arrangements have The average wire strain due to been described elsewhere (Winkler pretension load was measured to be et al. 2011) and only a summary is 0.43%. Figure 7 shows the strain presented herein. The high strength level of the three bottom wires steel monostrand was stressed to that will be used in the analysis 45% of the ultimate tensile strength. of the localised cable bending The transverse deformation was deformations. applied by a hydraulic actuator attached to a defection collar at the strand. With this test set up, Figure 9. Cable anchorage region
bending stresses were introduced Structural Dynamics at the anchorages. Strains due to Figure 10 illustrates the orientation pretension load were measured with of the strand with the different strain gauges (Figure 6) whereas viewing angles used for capturing of the localised bending behaviour of the photogrammetric data. the strand was analysed with the photogrammetric data.
Figure 7. Strain level of three bottom wires due to pretension load
115 Data analysis The red zones between the individual wires became more visible at an The post processing algorithm of the angular deviation above 1.0° photogrammetry system involved and indicate a relative movement a stagewise analysis, in which between wires. The interwire each stage consists of one camera movement is analysed further in image resulting in a description of section 4.5. displacements occurring on the surface of the strand. The system Moreover, the photogrammetric tracks the surface displacements data enabled the analysis of the wire throughout the duration of the test. strain distribution in the vicinity of the wedge (Figure 13). The optical deformation analysis of the monostrand bending behaviour Figure 10. Viewing angles of strand while applying an upward midspan specimen defection will be presented in It was possible to capture the this paper. Strains shown in the bending deformations of the strand deformation analysis represent within 55mm from the wedge the change in wire strain due to location. The photogrammetry increasing angular deviations (strains system enabled the simultaneous from pretension are not captured). Figure 13. Strain distribution in vicinity of documentation of the top and the Localised bending the anchor side of the cable (Figures 11a, b). deformations The diagram in Figure 14 shows Photogrammetric data from the the maximum top, side and bottom camera placed on the side of the wire strain measured at the wedge strand was used to analyse local location. bending deformations. Figure 12 illustrates the change in the compressive and tensile strains in the strand due to an upward midspan defection. Increasing localised bending stresses correspond to an increase in angular deviation φ.
a)
Figure 14. Wire strains measured with photogrammetry system
Figure 15 illustrates the tensile strain measured at different locations at the cable anchorage location. It can be seen that the monostrand under applied transverse load is not behaving like a solid section since each of the individual wires experienced different strains due to bending (Figure 14). As each single wire remained at a different Figure 12. Change in wire strain due to b) upward mid-span defection strain level, the monostrand behaved Figure 11. a) Side and top view of strand more like a helically wound fourlayer specimen b) Strand specimen with strain laminate. overlay 116 144 Innovative optical measurement technique for cable deformation analysis
Measurement of the tensile strains along the wire strand allowed for the analysis of the distribution of the localised bending stresses. The results show that the high localised tensile strains on the bottom of the strand were distributed over a distance of 40mm. Beyond this distance the strains due to bending are negligible (Figure 15).
Figure 19. Transverse movement between monostrand wires
Flexural load and yielding of steel monostrand cable Figure 16. Wire strain distribution due to upward mid-span defection The strain level of the bottom wire (180) due to the combination of the pretension load and angular deviation of φ = 1.5° was measured to be 0.83%. The infuence of the strain due to pretension and fexural Figure 15. Measurement of tensile load on the overall strain in the strains at cable anchor strand is shown on the stress-strain curve (Figure 20) of the monostrand Relative movement of wires provided by the manufacturer. Photogrammetric data from the Figure 17. Measurement of transverse camera placed above the strand (T) and longitudinal (L) movement of individual wires were used to analyse the relative movement of wires. Figure 16 The diagrams below show the illustrates the distribution of the longitudinal (Figure 18) and compressive strains in the strand transverse (Figure 19) movement due to applied upward mid-span of the monostrand wires. It can be defection. Similar to the previous seen that longitudinal sliding and analysis, increasing localised bending transverse opening of the wires stresses correspond to an increase in increase with increasing distance angular deviation φ. from the wedge location. The transverse (T) and longitudinal (L) movement of the individual wires was measured at different locations in the vicinity of the wedge (Figure Figure 20. Stresses due to pretension 17). and bending in the steel monostrand Structural Dynamics cable (φ = 1.5°)
It can be noticed that the bottom wire is close to the yielding point that represents an upper limit of the load that can be applied to the cable.
Figure 18. Longitudinal movement of monostrand wires
117 Strains due to bending: strain gauge measurement vs. photogrammetric data The comparison between the measurement with gauges and photogrammetric data of the bottom wire strain due to fexural load is shown in Figure 23. Strain information obtained with the gauge measurement was taken from the test where gauges were located 5.1mm from the wedge (Figures 21a, b). Consequently, strain measured at the same distance (5/180) with the photogrammetric data was used in the comparison (Figure 22). a) The diagram in Figure 23 shows that the results obtained with strain gauges and photogrammetric measurement are essentially the same. The results provide additional confdence in the presented outcome of the optical deformation analysis.
b) Figure 21. a) Wire strain measured with strain gauges. b) Location of strain gauges
Figure 22. Wire strain measured with photogrammetric data
Figure 23. Wire strains measured 5mm from wedge with pho-togrammetric data and strain gauges
118 144 Innovative optical measurement technique for cable deformation analysis
Conclusions
A novel methodology using a non- contact strain measurement and optical deformation analysis was used to study the localised bending behaviour of high-strength steel monostrands. The correlation between the strains obtained with the photogrammetry system and using strain gauges was established and the results provide confdence in the presented outcome of the optical deformation analysis. Photogrammetry equipment captured both the relative movement (opening/closing and sliding) of the individual wires as well as localised bending strains at the wedge location. Localised cable bending deformations captured with the photogrammetry system were distributed over a distance of 40mm from the wedge. It was shown that the high localised curvatures due to bending (φ = 1.5°, φ = 2.0°) may cause yielding of the strand. The results reported in this paper show that the bending fatigue life of the monostrand may be controlled either by the local bending strains or by the relative movement of the helically wound wires. The results obtained with the new methodology are a step towards a better understanding of the governing fatigue failure criterion for monostrand cables. Structural Dynamics
119 120 Structures 121 145 solution compared to conventional solution compared or methods of strengthening solutions. ‘demolish and rebuild’ Initial material outlay costs can be costs can be these high. However, to the minimal when compared potential cost and time savings the ease and speed of from resulting application. Historically the take up of FRP in the UK has been slower than anticipated. was an earlier Quality control concern clients, leading numerous designers and specifers to become somewhat uncomfortable when Introduction Introduction Polymers (FRP) have Reinforced Fibre been widely used in the engineering and construction sector over the past carbon 10 to 20 years. Additionally, been used for over 30 years has fbre in structural applications within and motor sport. Typical aerospace applications within the bridges sector have seen FRP used for structural Carbon Fibre where strengthening plate bonding and wrapping have traditional techniques more replaced such as steel plate bonding and FRP conventional strengthening. is a very cost effective strengthening Optimised design of an design of an Optimised using aerospace FRP bridge for ultra-lightweight technology solutions Abstract aerospace the design of a footbridge is discussed, utilising In this paper, to bridge ultra-lightweight solutions to offer materials and processes in the construction combines Atkins’ vast experience design. The approach industry. aerospace together with its ever expanding expertise in the industry, and motorsport. wind turbines widely used in aerospace, Composites are to take benefts into the each of these, Atkins looks By taking aspects from in weight and signifcant improvements potentially offering bridge industry, maintenance. lightweight by offering overall costs, The focus is to achieve reduced materials Aerospace spans to be covered. solutions, and enabling greater aims to keep but in a way which proposed are and manufacturing processes use of moulding, By considered component and tooling cost to a minimum. to the With part count can be achieved, easing installation. reduced regard many alternative clever use of adaptive tooling enables sizes manufacture, specifc needs yet keeping adaptability to meet to be made, hence providing adaptability and greater allowing cost down. A modular concept is proposed, use of aerospace The requirements. fexibility to meet specifc installation because lower volumes of products grade materials enables lighter weight enhanced through quality is also improved and product required, materials are Reinforced Fibre in defects within the The reduction material properties. in service longevity. Polymers (FRP) should also improve The paper discusses the analysis of a typical footbridge with the above design and overall weight are Resulting defections, natural frequencies approach. could easily be advantageous the approach show, explained. As the results overall cost and reduced for a wide range of bridge applications where important. maintenance are Pavel Vrana Design Engineer & Defence, Aerospace Communications Atkins James Henderson Engineer Group Highways & Transportation Atkins Iain Bomphray Principal Engineer & Defence, Aerospace Communications Atkins Mike Stephens Principal Engineer & Defence, Aerospace Communications Atkins The Authors 20 in Aerospace Mike Stephens – Background: and 12 years in F1 specialising in composite structures. 15 years in F1 Iain Bomphray – Background: specializing in and automotive and aerospace composite structures. 15 years James Henderson – Background: experience in bridge design and management, specialising in inspection, assessment and techniques. strengthening 3 years in – Background: Pavel Vrana calculations) and (design and stress Aerospace engineering-CNC milling, 1 year in production design. fxture considering work of this nature. a team which can provide cross Hence one of the key drivers Atkins sector innovation. The objectives Bridge concepts sought to challenge in this study are to develop a bridge solution was perceived quality control issues bringing design methods, materials Design Constraints – Input through the application of aerospace and manufacture processes from Variables methods in the development of an advanced high-tech composites • An initial bridge span of 24m and FRP footbridge. Atkins has expertise communities more commonly found 36m will be considered in both Highways and Transportation in aerospace, motor sport and wind and Aerospace industry sectors, and turbine industries. • Bridge section shall be 12m long for transportation purposes is therefore able to combine these The methods employed are highly skills, taking a different approach to mechanised with exceptionally high • Inside dimensions: width to be bridge design. levels of quality control, which is an 2.5m, height 2.5m Signifcant improvements in material aspect Atkins wished to pursue to • Live loading of 5kN/m2 technology in recent years, coupled reinforce the quality of the composite (un-factored) applied with potential future developments offerings to the construction sector. • Wind loading of 2.5kN/m2 in this industry will without doubt This paper discusses details of the (un-factored) applied push the composites industry into current ‘work in progress’, where new emerging markets. An example Atkins is designing a modular • Defection criteria dmax = of this development in materials footbridge capable of spanning 12m Span/200. technology is the current research to 36m. being carried out into sustainable The FE Model with its constraints is bio-composites. Hence composites shown in Figure 1. ATL Automated Tape Laying will inevitably become a much more CFRP Carbon Fibre Reinforced Plastic A listing of the main material used widely used material to the beneft of in the conceptual design analysis is GFRP Glass Fibre Reinforced Plastic the construction sector. shown in Table 2. UD Unidirectional FRP Bridges FEA Finite Elements Analysis There are many advantages in using FEM Finite Elements Model FRP in modern bridges. Typically the RF Reserve Factor strength to weight ratio is improved, and the bridges will require Table 1. Abbreviations signifcantly less maintenance. Of greater importance is the fact that FRP can provide major buildability enhancements which can lead to signifcant improvements in overall cost, time and programme. To date in the UK numerous FRP bridges have been built using a combination of pultruded glass fbre reinforced polymers (GFRP), FRP wet lay ups using bespoke moulds and lay ups utilising vacuum bagging techniques including resin infusion. Hence some key benefts have already been recognised. This keeps component costs low, but may not always lead to the most overall cost and structurally-effcient solution. Atkins Approach For this study Atkins has established a team comprising experienced bridge engineers and composites designers with a view to establishing Figure 1. Realistic boundary conditions
122 145 Optimised design of an FRP bridge using aerospace technology for ultra-lightweight solutions
Density Tensile Strength Ply Thickness Material Modulus (MPa) Structure optimisation (kg/m3) (MPa) (mm)
A number of feasible structural E11 = 40,000 GFRP (UD, ATL) 1900 1000 0.25 forms were reviewed, with several E22 = 8,000 FEMs created and analysed by FEA E11 = 110,000 CFRP (UD, ATL) 1600 1700 0.5 (using MSC Nastran). The model E22 = 10,000 was simplifed for a 24m span with Aluminium E11 = 280 60 N/A 20 simply supported restraints. Initial Honeycomb (3/8”) E22 = 140 calculations reviewed minimal live Steel EN24T 210,000 7850 850 N/A loading, targeting a maximum Aluminium Alloy 74,000 2780 550 N/A defection of no more than 120mm. 2024 Various design concepts were Table 2. Materials used evaluated, but a common theme was a CFRP “U” channel as the main section. The aim is to manufacture this section using Automated Tape Laying (ATL) to produce consistent aerospace quality laminates ideally suited to the modular design approaches chosen. Initial concepts had no roof, but a semi-structural roof was found to be effcient together with stiffening ribs. A typical ATL machine by M.Torres used in aerospace applications is shown in Figure 2. The ATL process comprises tapes of CFRP pre-impregnated with resin rolled onto a mould using a robotic head. This enables a large quantity Figure 2. An “M.Torres” ATL Machine (copyright M.Torres) of material to be laid up quickly and consistently and is ideal for large Bridge structure 2 relatively simple mould shapes. The ATL process was intended almost overview - current exclusively for aerospace use, concept 5 but recent developments make it Only 1 displayed 1 more suitable for a wider range of Each 12m section is constructed from applications. main structural parts listed below, Figure 3 and Figure 4. Initial designs of the structure have 6 3 4 achieved maximum deformation Floor Panels Only 2 Only 2 119mm which occurred on the end displayed displayed Joint to the main structure of unsupported roof. The structure has good mass properties about Floor panels (5) will be bolted by a 1. U section - ATL 3450kg. During the optimisation, it single row of countersunk fasteners 2. Roof - ATL (transparent) was found that deepening the box M14 to the U section (1) and C 3. I beam in CFRP – pultruded, or ATL section under the foor to 600mm, beams 600x75 (6) around its edge. 4. Frames - ATL was an effcient way to improve The initial solution is to join each 5. 3 Floor panels – Monolithic CFRP ATL or stiffness. This reduced the maximum foor panel (5) to C beams 600x75 (6) CFRP Sandwich panels (ATL Skins) Structures defection to less than 40mm, only by 4 countersunk screws around 6. Channel sections for stiffening CFRP – pultruded, or possibly ATL occurring in the middle of the foor its edge. If required for structural section. The next sections describe purposes, each foor panel can be Figure 3. Bridge 12m section overview the current design in more detail. bolted to “C” beams 600x75 (6), by up to 80 countersunk fasteners M14 via a typical sandwich insert. This is similar to that shown in Figure 6. 123 Figure 4. Bridge section dimensioning
Figure 7. Joint - foor panels
a
b Figure 5. Floor panel – Main structure joint
Figure 8. Plan view of foor panel layout, two options
a) Easy to assemble, possibility be protected against such cleaning to joint 2 12m sections in water. tapered angle b) Stiffer structure. Floor Panel Cover Figure 6. Honeycomb sandwich inserts A thin protective cover should be considered for the whole foor. Such Floor panels joint cover has to protect CFRP sandwich As position of box, created by panels against impact from heels bottom side of U section and foor of shoes and also seal any gaps panels, is low, it has been expected between foor panels. Cover must and confrmed by FEA that all be anti slip to create a safe and Figure 9. Drainage boxes will be loaded by tension. comfortable surface for pedestrians. Ideal structure should be one 12m Drainage Frames long foor panel. For maintenance purposes, foor will be split into 3 or As the overall bridge is covered by The main purpose of frames is to 4 foor panels (5) which have to be a roof there is no need to solve the support sides of the U section and jointed together by C beams 150x75 problem of storm water drainage. roof. Initially, such frames will be (6) such joint will described by However, it is expected to clean jointed just into the U section via Figure 7. the inside areas by pressure water, barrel nut. Joint frame to roof is not therefore a small drainage gutter needed as FEA has shown that the Floor Panel layout has been considered next to the roof defects downwards. Therefore Two possible options can be foor panel on each side. If the joint is expected that an interface frame considered for foor panel layout, foor panel (U section) is sealed, – roof will be just pressure. This Figure 8. then the inside area of the box can solution can allow relatively simple
124 145 Optimised design of an FRP bridge using aerospace technology for ultra-lightweight solutions
change of damaged roof. Frames Other joints in the 12m sections are: can also be used as fttings for any • Floor panel connection, Figure 7, useful items such as signage, light or used for foor panel layup handrail. • Roof connection by seal and L Connections profle, Figure 12 The current FEA model completed • Connection of C beams 600x75, highlights the forces in the has not been detailed at this connection. For the 24m span stage. bridge (split into two 12m sections), six connection points have been simulated as steel bushes with a diameter of 30mm. The joint forces were enveloped for calculation of the typical shear plate used to joint two Figure 13. Duct 12m section together. Such joint is shown in Figure 10. The 24m span structure comprising 2 x 12m spans Mass prediction using connections comprising 30mm diameter bushes has achieved a Mass prediction, for the 24m span maximum deformation of less than bridge based on described design, is 55mm. summarised in Table 3. Calculation is only for primary structure and excludes following: • Fasteners • Additional deck cover Figure 11. Shear plate • Sealant • Joints to supporting piers • Any other additional protection. By comparison a typical steel/ concrete footbridge may expect to be around 13,500kg. Hence, the FRP solution can offer a very signifcant weight saving.
Figure 10. Simulated connections Connection to piers In detailing these connections 6 shear plates (thickness 14mm) are One end of the bridge must be described in Figure 11. The joint has fxed to restrict all 3 translations Figure 12. Roof joint been calculated from load case - live in directions X, Y, Z and the other load (nominal) and has been sized Services end must be fxed to restrict two for RF ≥ 5 against yield material translations X, Y and allow thermal characteristics. The drive factor for A service duct to accommodate expansion in Z direction. Because joint sizing was the bearing stress power for lights can be ftted to each the allowable direct bearing stress in U section and shear plate drilled side of U section just under the joint of CFRP is not high, it is not possible holes. Therefore the U section has a U section – roof, Figure 13. Such to set any bearings directly on CFRP locally thicker shell thickness set for duct can be made from any suitable surface. Therefore the bridge must be Structures 20mm. omega profle on the market. grounded through a saddle, Figure 14 which can be bolted around a For the 36m span structure the above Any other services such as bottom edge of U section. joints will still be used albeit with communication cables pipes and all elements upsized accordingly (by power cable can be hidden in the about 125%) box underneath the foor.
125 Mass Mass perBridge Item Items inBridge perItem [kg] [kg] U section 2 1,142 2,284 Roof 2 446 892 Frame 5 15 75 C beam 600x75 4 109 436 CFRP Skin 12 32 384 Honeycomb Core 6 11 66 Floor panel 4m x 2.5m Bar 60x20 long 12 13 156
Bar 60x20 short 12 8 96 Figure 14. Saddle C beam 150x75 10 3 30 Shear plate 6 24 144 Conclusion L profle – Roof connection 1 9 9 Total 4,572 As already mentioned, the study is “work in progress” as Atkins looks Table 3. Mass prediction to design an FRP footbridge using more advanced design, materials and there is no need for any complicated In addition, the use of FRP together manufacture processes. mould. Bridges can cover span range with improved quality, will lead up to 36m and the width of the to signifcantly reduced long term The work to date shows very bridge section can vary if U section is maintenance. signifcant weight savings; around split in bottom fat surface. 4.5 tonnes against 13.5 tonnes for a In summary, the concepts and typical steel/concrete design appear This manufacture process allows processes assessed in this paper offer to be possible. This intern will lead the design to be further optimised very interesting alternative solutions to much easier installation. It is here by controlled placing of fbres more to the bridge building industry. that major benefts are anticipated. effciently at the best orientation, The type of plant required to install allowing for weight reduction in low such a bridge will be considerably stressed areas. reduced, leading to reduced installation costs. Furthermore, the Acknowledgement design concepts have focussed on 24 to 36m span, thereby negating the This paper was presented and published in the proceedings of the FRP Bridges need for central supports. This will conference, held in London from 13-14 September 2012. again lead to easier installation and reduced costs. It is clear that the unit cost of a single bridge designed and manufactured in this way could be more expensive than the current FRP bridge design approaches. However, the modular concept chosen lends well to manufacture of a range of bridges of varying span (based upon a maximum of 12m per section). Manufacturing in this way using automated processes such as ATL, enables realistic unit costs to be achieved. The concept has good potential for future development. Manufacturing processes can be relatively simple as
126 146
Chris Mundell Reconstruction of drystone Structural Engineer Highways & retaining walls using composite Transportation reinforced soil structures Atkins Abstract
Phil Raven Drystone retaining structures are found throughout the UK, with many Structures Manager supporting sections of the country’s transport infrastructure. The majority of Gloucestershire these structures were constructed in the 19th and early 20th centuries, and Highways are now subject to traffc loads far in excess of those they were originally designed for. Therefore, it is not uncommon for stretches of drystone retaining walls to collapse, often with little or no warning. Following the collapse of a section of a drystone retaining wall supporting a carriageway in Northleach, Gloucestershire, a unique repair solution was designed and implemented. This comprised a reinforced earth retaining wall acting compositely with a rebuilt drystone wall. The design provided a low carbon, aesthetically pleasing and cost effective solution that allowed the structure to withstand modern traffc loads with codifed factors of safety, reusing almost all the excavated stone and soil and requiring very little material to be imported. The scheme was commissioned by Gloucestershire County Council and designed and constructed by Atkins, building directly on research carried out by the author at the University of Bath. This paper discusses design and construction of the scheme, outlining the advantages of the solution, lessons learnt and future use. Keywords: Retaining Walls, Masonry, Reinforced Earth
Introduction
Drystone walling is an ancient traffc loads safely, although due to construction form that has been used their bespoke nature it is diffcult to historically for free-standing walls, ascertain the exact capacity of any buildings and retaining structures. given drystone structure. In the UK, much of the country’s With increasing traffc loading, transport infrastructure is still combined with the continual supported by drystone retaining walls weathering and ageing of the that were constructed in the 19th component stone, it is unsurprising and early 20th centuries (O’Reilly and that some drystone walls will begin Perry, 2009). The stability of such to deform or fail at some point. For structures is diffcult to ascertain, local authorities with large stocks and failures may occur in response of drystone walls, these structures to a number of changes, such as provide a signifcant challenge, and vegetation growth, increased water it can be diffcult to differentiate pressures, material weathering,
a bulged but perfectly stable wall Structures vehicle impacts, excavations by utility from a wall on the brink of collapse. companies or from a combination of Furthermore, when a wall has been factors. To exacerbate these issues, found to be moving, it is often modern traffc loads are now many assumed that preventing further times in excess of what was originally movement with pointing or injecting anticipated and built for. Despite grout into joints will improve stability. this, the majority of these structures This can have the opposite effect, are still stable and able to carry 127 and either due to a sudden decrease in ductility, or the presence of a barrier to water fow, collapse may be accelerated. With several local sources of walling material, Gloucestershire has a signifcant number of drystone retaining walls supporting the local infrastructure. Typically, these walls range in height from 1m to 3m, however there are some structures in excess of 7m (Claxton et al. 2005). There is also very little information available for the majority of these structures, sometimes the ownership of the walls is in question. To complicate matters further, the majority of the drystone walls in Gloucestershire are located within the Cotswolds and the Forest of Dean, which are designated Areas of Outstanding Natural Beauty (AONB). As such, the County Council has Figure 1. Full-scale testing at the University of Bath (Mundell et al. 2010) a duty to retain their heritage and visual appearance where possible, This provided the opportunity to trial approximately four metres apart, requiring sympathetic repair a scheme which could potentially each measuring roughly four metres techniques and methodologies. provide a structure which is more in length and three metres in height Each year, a number of the drystone sustainable and cost effective than (see Figure 2), although the ends walls in Gloucestershire collapse or standard concrete retaining walls, of the collapsed sections were also are identifed as being in danger of whilst being quantifably stable under found to be unstable. Examination collapse, often after several decades codifed loading. of the collapsed wall and the of gradual deterioration. The repairs surrounding location indicated and replacements to such walls Site details that the failure was induced by a are often costly. Gloucestershire combination of water pressure and County Council has supported recent The village of Northleach is situated vegetation growth; the adjacent research into the subject to attempt 10 miles to the north of Cirencester, sections of wall all had signifcant to gain a better understanding of and being within the Cotswolds is amounts of vegetation growth on these unique structures. This work, deemed an AONB. East End Road the supported verges, with root carried out at the University of Bath, runs east out of the village and joins systems visibly growing out of the included constructing full-scale walls the A40 heading towards Oxford. wall faces. In addition, a gully above in a bespoke laboratory, and testing East End Road is constructed on the collapsed section was found to them to destruction to examine the an embankment that is supported be blocked with debris. mechanisms that can induce failure on both sides by drystone retaining Figure 2 shows the collapsed wall (Figure 1, Mundell et al. 2010). walls. There is a single lane of traffc section. From inspection of the failed Through this work, analysis tools in either direction, with trees and area it was possible to determine were developed to assist calculations dense vegetation growing in the the wall construction, which was of any given drystone wall’s stability, verge adjacent to either side of the found to be a standard Cotswold in addition to allowing a much road. wall structure. There were two faces, greater understanding of behaviour In 2009, two sections of wall internal and external, with a rubble such as bulging and bursting infll through the centre. As with (Mundell et al. 2009). supporting the verge and carriageway on the south side many walls of this type there was Following the completion of this of the East End road collapsed, some evidence of ‘through stones’ research, a section of drystone about 200 metres from the village tying these two faces together, retaining wall supporting a road in border. The two failed sections were however the number or spacing of Gloucestershire partially collapsed. these could not be determined. 128 146 Reconstruction of drystone retaining walls using composite reinforced soil structures
Design proposals
Atkins’ Highways and Transportation team in Bristol was engaged by Gloucestershire Highways (a partnership between Atkins and Gloucestershire County Council) to investigate the failure of the two sections of retaining wall and provide design proposals for replacement. Initial investigations involved the use of the analysis tools developed at the University of Bath, which confrmed the normal usage of the road was not endangering the stability of the rest of the wall. However, under a rigorous design to Highways Agency loading criteria, a like-for-like rebuild would not have suffcient factors of safety to comply with current standards. A geotechnical inspection and desk study were carried out, indicating that the ground conditions Figure 2. Collapsed Wall at East End, Northleach below the wall were stable, and that a global slip plain was unlikely. There was also no evidence that the failure had been related to a bearing failure, which was later confrmed when the lower courses of the wall were unearthed. Following the initial investigations, a report was presented to Gloucestershire County Council detailing a number of design proposals. These included a like-for- like replacement, a mass concrete gravity wall, a reinforced concrete Figure 3. Composite Design Sketch retaining wall, a soil nailed wall and a reinforced earth/drystone composite volume of concrete required, giving a which was a concept developed by design. As discussed earlier, the large carbon footprint but also often the research team at the University site is within an AONB and visible necessitating large volumes of the of Bath. Reinforced earth walls are across the valley for some distance. retained earth to be exported off site. often faced with concrete to allow Therefore, both concrete walls would This solution is also diffcult to detail the reinforcement anchorage to be require a masonry facing to blend in at the ends of the wall where it ties frmly held at the face of the wall, with the adjacent sections. in to the existing sections, and due to however it was proposed to replace Of the proposed options, the the increased stiffness and reduced the concrete face with a rebuilt concrete solution proposed is the permeability of the replaced section, drystone wall (see Figure 3). The most common solution for many there may be other detrimental wall would provide the required Structures collapsed retaining walls of this effects on the adjacent lengths of anchorage for the reinforcement, but size. The design is very simple, and wall. would also allow some ductility to account for any settling in and initial relies on the concrete to act as a As a recommended option, the tensioning of the reinforcement. The gravity retaining wall to withstand report detailed a composite system also provides a free draining sliding and overturning loads. The reinforced earth wall integrated into façade, and gives additional stability disadvantages relate mainly to the a rebuilt drystone retaining wall, from the added weight of the stone 129 wall. Other advantages include the potential to reuse most, if not all of the collapsed wall and as-dug material, the ability to found the structure on the original footings and the elimination of any diffculties when tying into adjacent wall sections. Following discussion with Gloucestershire County Council, it was decided that the preferred solution of the reinforced earth/ drystone wall composite would be Figure 4. Geogrid Connection Design taken forward for detailed design and construction. the bar is bent to a standard shape Involvement in the design phase code, and formed of galvanised and close liaison throughout the steel. Transverse bars, or ‘bodkins’ construction works. The labourers Detailed design run parallel to the face of the wall involved had substantial experience between adjacent eyes of the of building masonry walls in As the scheme was begun in early hooked bars, to which the geogrid Gloucestershire, and made valuable 2010, the design was carried out is connected. Thus, a full-strength contributions to improve the to British Standards rather than connection is created between the buildability of the fnal scheme. Eurocodes. The soil reinforcement wall and the geogrid, providing was designed using the Tensar RE The works began with the demolition suffcient restraint for the soil uniaxial geogrid, spaced vertically at of the wall around the collapsed reinforcement. 600mm centres. The reinforcement area. An initial site investigation lengths were 4m long at the A simpler detail than that shown found that sections of wall adjacent uppermost layer, reducing near the by Figure 4 would be to run the to the collapse were unstable, base of the structure to minimise the geogrid straight into the wall and would require rebuilding. In extent of the excavations necessary, between two courses, and pin it addition, although a section of wall as well as allowing the backfll to between the stones. However, with approximately 4m between the be benched back to provide a safe this detail there is the potential for two collapsed sections was partially working area. damage to the geogrid where it is intact, it was not suffciently stable pinned between stones, in addition to leave in place during the repair The critical component for the design to a potential reduction in joint works. In total, a length of wall of was the connection detail that friction and the formation of slip approximately 20m was demolished anchors the geogrid reinforcement planes within the wall. Initial testing and replaced, retaining 2.7m to 3m into the facing. This is normally done at the University of Bath confrmed of material. The retained fll was with steel anchors which are secured that there is a reduction in joint excavated as required, being benched into the concrete facing via a resin friction, and signifcant material back up to the carriageway level fxing. A threaded connection to the damage can occur to the geogrid (Figure 5). geogrid allows movement to induce (Dixon, 2011). This research also tension in the geogrid once it has The walling material was separated investigated mitigating these factors been fxed into position. as it was excavated, to be used in by bedding the geogrid in sand at the rebuild of the wall. In addition, For the composite drystone structure, the joint to prevent material damage; the retained fll was also separated the standard connection design however the long-term durability of according to its potential for re- was replaced with a hooked bar such a connection has not yet been use. The upper two metres of the to be built into the rear face of the tested. retained fll was generally a stony, drystone wall, as shown in Figure 4. granular material, commonly found The vertical leg of the bar is seated so Construction sequence in made ground, and classifed in the that it rests on the inside face of the Highways Agency Design Manual for rear masonry skin, providing restraint To carry out the works at East End, Roads and Bridges (DMRB) as a 6N against pull out. The vertical weight a Gloucestershire Highways/Atkins material. The bulk of this material of the wall above the connection labour gang was utilised. This had was suitable for re-use within a ensures that the anchoring stone is signifcant advantages for this reinforced earth structure, after not pulled out of place. For simplicity, scheme, allowing Early Contractor removing some of the larger stones 130 146 Reconstruction of drystone retaining walls using composite reinforced soil structures
and organic matter. Below this level, the ground was formed of a soft, cohesive clay. This was found to be unsuitable for re-use within the retaining structure, but was used instead to create an embankment adjacent to the wall to use as a working platform to avoid the necessity for scaffolding. The material was later used in the ground re- profling once the construction works were complete. As previously discussed, a signifcant advantage of rebuilding the drystone wall is the ability to build off the existing foundation, providing that Figure 5. Extent of Excavations they are of suffcient standard and the ground bearing pressures are adequate. In this case, there was no indication of bearing issues, and the geotechnical studies concluded that the original wall failure was not the result of any such factors. Furthermore, the exposed courses of the wall to be used as footings consisted of large, well-laid stones in good condition, and ideal for re- use. This saved a signifcant amount of work, as the construction team did not have to excavate far below ground level, reducing the volume of excavated material and the amount of wall to be rebuilt. The wall was rebuilt in as similar manner as possible to the existing Figure 6. Through Stones structure. It was approximately 800mm wide at the base, tapering were brought in and positioned was used, which was supplied in a to 400mm at the top of the retained using slings, and then shaped with roll 1.3m wide. The edges of the roll height. The construction was a a mechanical breaker to suit the were slightly overlapped, creating standard Cotswold construction, position (Figure 6). Due to the a continual layer of the geogrid having two faces with a rubble large size of these stones, they were (Figures 7a and 7b). Once placed, core. Regular through-stones were spaced at greater intervals of 2m. all of the geogrid in the layer were manually stretched and covered with specifed at 1m centres along the The wall was constructed in tandem fll and compacted. This process was length of the wall, spaced at 0.5m with the retained fll. Generally, the then repeated until the full retained centres vertically. These through- wall was frst built up by 600mm, height was reached. The completed stone spacings were the standard and the retained fll placed in layers wall comprised four layers of geogrid specifcation as used by the masons and compacted until the same height during the research at the University reinforcement, which extended to a was achieved. The anchor bars were Structures maximum of 4m behind the rebuilt of Bath, who were members of built into the wall, with the eyelets drystone retaining wall. the Drystone Wallers’ Association. resting level with the top of the However, for the lower courses of the retained fll. The geogrid was then Despite being an inherently free- rebuilt wall at East End, there was positioned and secured to the anchor draining structure, several drainage some diffculty in sourcing adequate bars with the transverse bodkins pipes have been installed, bedded in through-stones due to the thickness and laid out to the required length the retained fll and passing through of the wall. Therefore, large stones on the fll. A Tensar uniaxial geogrid the face of the wall. It is likely 131 that over time the walls’ joints will inevitably be flled with vegetation and soil, and this may prevent or restrict the passage of water. With the addition of the weep pipes near the base of the wall, this should prevent any future build-up of water pressures, and further improve the longevity of the structure. The scheme was completed within eight weeks, under a full road closure on the supported road, a) b) although provision for pedestrians Figure 7. a) Geogrid Anchors; b) Completed Layer of Geogrids and emergency vehicles was maintained. The majority of the works were carried out by a team of four labourers, with the use of a wheeled dump truck and a large excavator for demolition, earthworks, and transportation of the material. To complete the scheme, some additional walling stone and graded fll were required; however with the exception of the excavated area of carriageway surfacing, no material was required to be exported from site at any stage of the project. Figure 8 shows the completed works. Figure 8. East End, Completed Wall
Scheme Thickness Grade % Volume % Earth Volume tCO2 Cost and carbon type of Stone Volume Stone of Earth Imported of comparisons Facing of Stone Reused Excavated Concrete Required Using the Environment Agency Reinforced 600mm 1.8m3 100% 10.5m3 0% All N/A 10.4 Earth (average) backfll carbon calculator (version 2.1), the Composite reused embodied energy in the materials Reinforced 600mm 1.8m3 50% 10.5m3 50% Half N/A 13.8 used was determined, and compared Earth (average) reused, against those of a concrete gravity Composite Half wall. The reduction in the carbon imported footprint for the composite scheme Reinforced 600mm 1.8m3 0% 10.5m3 100% N/A 20.0 largely depends on the amount of Earth (average) All fll re-use that is possible. Table 1 shows Composite imported the relative amounts of embodied Concrete 300mm 0.9m3 100% 7.5m3 0% All N/A 36.4 energy used in the scheme for the Gravity (facade) backfll Wall reused different construction methods and Concrete 300mm 0.9m3 0% 7.5m3 100% N/A 38.0 amounts of recycling. The concrete Gravity (facade) All fll is assumed to have no recycled Wall imported components for these calculations. Table 1. Comparison of Embodied CO2 Table 1 shows that this scheme can be substantially more carbon effcient conditions assumed for its concrete more effcient construction methods than a concrete gravity wall. In most counterpart, it is still 2.75 times more and by utilising a non-metallic cases, such as East End wall, there carbon effcient than option E. The connection as discussed in this paper, is a signifcant amount of material majority of the carbon footprint is the footprint could potentially be that can be re-used. Scheme Type B embodied in the steel bars and the further reduced by a signifcant in Table 1 represents East End wall, estimated plant use over the eight amount. and even with the most favourable week scheme duration. Through 132 146 Reconstruction of drystone retaining walls using composite reinforced soil structures
The scheme costs to Gloucestershire In general, this methodology will to the traditional connection with the County Council were approximately require larger excavations than adjacent sections, the new repaired £70k, including the feasibility study, alternative designs, so where space wall will also provide additional detailed design, materials and works. is at a premium it may not be the support for a much longer length. The majority of the costs were optimum solution. Other potentially As discussed, one of the most associated with the plant hire, as unsuitable locations would be where restrictive factors that prevents new a large excavator was required to there are services close behind the drystone retaining walls being built achieve the necessary reach. This cost proposed wall location, or where to support modern infrastructure is gave an approximate cost of £3.5k/m the structure deterioration is due the diffculty in ensuring their stability length of wall, which compares to insuffcient bearing pressures. under today’s loading standards. This favourably with other construction Furthermore, if this system is used, scheme effectively overcomes this forms used in Gloucestershire the potential need for future issue, whilst providing a retaining Highways for walls of this height. As excavations for services should be structure that blends seamlessly into a trial scheme, it is also expected that considered. This may be achieved the existing historic infrastructure with repetition and implementing by fagging the location as a Site of where modern alternatives may more effcient designs, this cost can Engineering Diffculty (SED), marking not. It will not be suitable for every be further reduced. the geogrid with warning tape or location, however where the space is installing spare ducts for future use available, and particularly where the within the backfll. Lessons learnt as-dug material is suitable for re-use, Preventing walls such as these from this scheme provides the required As previously discussed, the majority collapsing or becoming destabilised design capacity within a sustainable of the cost was related to the plant in the frst instance would be the and aesthetically pleasing structure. hire for the scheme. Therefore, optimum solution for maintaining increasing the construction time authorities. As discussed, a large would be the most effcient way number of recorded failures are due of providing an increased cost to vegetation growth or failures saving. The most time-consuming of the structure drainage, and element of the construction of ensuring regular maintenance in the retaining structure at East End these areas would substantially was in rebuilding the drystone wall reduce the number of failures. One and laying the through-stones. of the diffculties the maintaining Therefore, reducing the thickness of authorities face in achieving this is the wall as much as possible would frstly identifying the existing stock reduce the construction time and within their jurisdiction, and even if the scheme cost. The reduction in such records exist, most will not be thickness would also allow smaller regularly inspected. With the current through-stones, further saving fnancial climate, the additional time and cost. To account for the funding required to achieve reduced wall thickness, the length such proactive inspections and of the geogrids would undoubtedly maintenance is diffcult to obtain, but increase, however the additional could have substantial benefts. excavations and time required would be comparatively minor. Conclusion
Further time, cost and CO2 savings may be achieved, although some This system successfully combines of the potential improvements modern technology with a traditional would require additional research construction form. The trial proved and development. For example, the that these schemes can be effective connection detail may be simplifed at reducing cost at the same time Structures as discussed in previous chapters, or as signifcantly reducing embodied the wall construction may be reduced energy. The inherent fexibility of to a single skin of walling. However, the drystone wall allows for any these methods would require minor movements that might occur laboratory and full-scale testing during the service life of the structure before being validated. without any undue damage, and due
133 Acknowledgement
This paper was previously presented at, and published in the proceedings of, the Structural Faults & Repair Conference 2012.
References
1. Claxton, M., Hart, R., McCombie, P. and Walker, P. (2005), “Rigid Block Distinct-Element Modelling of Drystone Retaining Walls in Plane Strain,” ASCE, Vol. 131, No. 3, 381-389. 2. Dixon, M. (2011), “Investigation into Drystone Retaining Walls with Soil Reinforcement,” MEng Dissertation, Dept of Architecture and Civil Engineering, University of Bath. 3. Mundell, C., McCombie, P., Bailey, C., Heath, A. and Walker, P. (2009), “Limit Equilibrium Assessment of Drystone Retaining Structures,” Proceedings of the Institution of Civil Engineers - Geotechnical Engineering, Vol. 162, Issue 4, 203-212. 4. Mundell, C., McCombie, P., Heath, A., Walker, P. and Harkness, J. (2010), “Behaviour of Drystone Retaining Structures,” Proceedings of the Institution of Civil Engineers - Structures and Buildings, Vol. 163, Issue 1, 3-12. 5. O’Reilly, M. and Perry, J. (2009), “Drystone Retaining Walls and their Modifcations – Condition Appraisal and Remedial Treatment”.
134 Structures 135
16 14, 147 . Chatterjee 12 investigated the free investigated the free 11 analyzed the dynamic 13 studied the dynamic and impact behavior of half-through arch arch behavior of half-through a method bridges and proposed for estimating the dynamic loading bridges. In of this type of arch and vehicle both bridge his study, dimensional as three treated were models. Lacarbonara and Colone behavior of arch bridges under a behavior of arch moving load, using both lumped and uniform mass methods. Huang and Matta and force vibration of arch bridges vibration of arch and force and developed an approximate impact factor equation for predicting the dynamic loading of railway arch bridges due to moving trains. In his was modeled the moving train study, as a concentrated periodic loading. In 1973, Li studied pedestrian induced vibration of a highway steel observed during the bridge, arch bridge open ceremony 15 on the effects that moving vehicles on the effects have on the dynamic loading of bridges. By neglecting deck arch of spandrel effect the stiffness Li structures,
. Due to the 1 to 10 Introduction Introduction decades, many arch During recent bridges have been built throughout the world, especially in China. With the development of new materials and new types of structures, a bridges remains designing arch for bridge engineers. challenge great Shitanxi Bridge, located in Fujian, China, vibrated signifcantly after This bridge it opened to traffc. flled steel tube arch is a concrete bridge with a span length of 136m. Many light bulbs on the bridge were bridge vibration soon after by broken installed. Pedestrians on they were uncomfortable the bridge felt severe, vibration. The dynamic behavior due to moving vehicles is of major concern in bridge design. While considerable been made to better have efforts understand the dynamic behavior of highway bridges due to moving research vehicles, most previous work in this feld is focused on girder and beam bridges Vehicle-induced vibration of a vibration of Vehicle-induced tube arch flled steel concrete bridge Abstract vibrated signifcantly bridge, flled steel tube arch Shitanxi Bridge, a concrete study is to investigate the The purpose of this after it opened to traffc. cause of such signifcant vibration. First, a brief description of the bridge and forced The bridge free is given, followed by an analytical theory. accelerations of some key elements are vibration characteristics, including the deck at traveling over a rough investigated with both single and multi-trucks arch of the deck and the effects vehicle speeds. Then, the stiffness different a is deck stiffness show that insuffcient studied. Analytical results ribs are two on the analytical results, vibration. Based main factor causing the severe retroft. during a recent added to the bridge longitudinal beams were stronger loading of moving vehicles bridge vibration due to the dynamic As a result, are results The research to an acceptable level. was considerably reduced bridge design and rehabilitation. applicable to arch bridge model; flled steel tube; vehicle model; bridge; concrete arch Keywords: impact. vehicle induced vibration, acceleration; surface roughness; road inherent complexity of arch bridges, complexity of arch inherent few papers have been published Dongzhou Huang Consulting Engineer/ Senior Engineer IV TS Transportation Design Atkins North America studied the dynamic responses of arch bridges due to high speed trains using Ritz’s energy method. The purpose of the investigation presented here is to identify the cause of such a signifcant vibration and develop a possible rehabilitation method. First, a brief description of a) the bridge is given. Then, analytical theory is presented, including the vehicle model, bridge model, and road surface model. Then, the stiffness effect of the deck and the arch ribs is studied. Finally, a comparison of the maximum accelerations of deck and lights between existing and retroftted bridge was given.
Description of bridge b)
Shitanxi Bridge is a half-through concrete flled steel tube arch bridge. Its span length, rise, and rise-to-span ratio are 136.0m, 27.2m, and 1/5 respectively. The roadway width is 9.0m. The shape of the arch rib is a second-order parabola. The bridge consists of two ribs which are hinged at both ends. The bridge deck is c) supported by thirteen stringers of reinforced concrete T-beams which are simply supported on seventeen reinforced concrete foor beams. The entire bridge deck system is supported from the arch ribs by hangers. Each hanger consists of 110 f 5mm structural strands and is anchored to the end of the foor beams and attached to the ribs. There are six 6m high lighting poles on each of the outsides of the arch d) ribs along the edges of the sidewalks. Figure 1. Dimensions of Shitanxi Bridge, (a) Elevation,(b) Deck Plan, (c) Cross- The diameter of the lighting poles is section,(d) Arch Plan 220mm at the bottom and 80mm at the top respectively. The wall Floor Stringer Items Arch Rib Bracing thickness of the lighting poles is Beam Exterior Interior 3.5mm. The primary data of the Area (m2) 1.2446 0.7426 0.262 0.2377 0.0201 bridge can be found in Figures 1 Ix (Vertical) (m4) 1.7448 0.1566 0.056 0.0510 0.0270 and 2 and Table 1. Iy (Transverse) (m4) 0.3160 0.8899 0.1371 0.0153 0.0004 Unit Weight (kN/m) 29.069 5.,301 6.168 5.601 1.855
Table 1. Primary Bridge Data
136 147 Vehicle-induced vibration of a concrete filled steel tube arch bridge
velocities of the system components, w = transverse displacements in x-, D= dissipation energy of the system y-, and z-directions, respectively; and
obtained from the damping forces, θ x, θy , θz ,= rotational displacements
and {δt} = the generalization in the x-, y-, and z-directions. The velocities. The equations of motion element stiffness matrix can be of the vehicle can be written as written in the form:
[M t] {δ t tδ t tδ t t} l
where [K ] = the stiffness matrix in which, � and are the standard } +t [D ] { } + [K ] { } = {p � = k + k l g of the vehicle, [Dt] = the damping linear stiffness matrix and geometric k k matrix of the vehicle, [Mt] = the mass stiffness that represents the effect of
matrix of the vehicle,{pt}=general initial axial force P on the bending loading matrix. The basic derivation stiffness of the element15. The procedure and data can be found in element consistent mass matrix is Wang and Huang8,10. used in the study and can be found in Wang and Huang8. The equations Figure 2. Cross Section of Arch Rib of motion of the bridge are: (Unit = mm) [M B]{ δ B } + [DBB ]{ δ } + [K BBB]{ δ } ={p }
Simulation of vehicle in which [MB]=global mass matrix of
bridge; [KB]=global stiffness matrix of
Chinese Design Trucks T-20 and T-40 bridge; [DB]=global damping matrix of two-axle tractor type are chosen of bridge; {δB}, {δB} and {δB} global for the bridge dynamic analysis. The nodal displacement, velocity, and trucks are modeled as a non-linear acceleration vectors; and {pB} is the vehicle model consisting of three global nodal loading vector that is sprung masses of the tractor, steer a) caused by the interaction between wheel/axle set, and tractor wheel/axle the bridge and the vehicle. set (see Figure 3). The displacement vector of the truck model can be written as
T {δt } = [yt1 ya1 y a2θt1 ft1 f a1 fa 2 ] where yt1 and yai are vertical displacements of tractor and wheel/ axle sets respectively. θt1 is tractor rotation about the transverse axis. ft1 and fai are the rotations about Figure 4. Bridge Model longitudinal axis for tractor and the wheel/axle sets individually. The b) The following equations of truck suspension force consists of Figure 3. Vehicle Model, (a) Side View, interaction forces are used to connect the linear elastic spring force and (b) Front View the vehicle and bridge: 10 the constant interleaf friction force . Fi = K + D (i=1 to 4) The tire springs and all dampers Simulation of bridge TB tyi tbi tyi tbi in which K = stiffness of the ith are assumed to be linear. The Utyi U equations of motion of the vehicle Dynamic response of the arch bridges tire; Dtyi = damping coeffcient of can be derived by using Lagrange’s is analysed by the fnite element the ith tire; and tbi = relative vertical formulation as follows: method. The bridge is divided into displacement between the ith tire a series of three-dimensional beam and the bridge. Also,U = - ∂T ∂T ∂V ∂D tbi tyi byi ( )- elements with six degrees of freedom -w . A dot superscript denotes a Structures t ∂{δ } ∂{δ } ∂{δ } ∂{δ } ryi 풹 t t t t differential with respectU to time.U U + + = 0 at each end (Figure 4). The nodal- 풹 displacement parameters of the where V = the total potential element are: energy of the system computed {δ}e δ δ T from the spring stiffnesses, T = the = [ i j] total kinetic energy of the system T in which {δi}=[ui, vi, wi, θxi, θyi, θzi] , calculated by using the masses and T {δj}=[uj, vj, wj, θxj, θyj, θzj] ; u, v, and
137 Simulation of road surface
The bridge deck profle is assumed f1 = 0.538 Hz f2 = 1.196 Hz to be a realization of a stationary Gaussian random process that can be described by a power spectral density (PSD) function and can be written as follows: N f3 = 1.269 Hz f4= 1.489 Hz
W sr(x) = ∑ 4S(ωi)∆ωcos(ωix+θi) i
=1 where wst(x) = simulated road vertical profle; x = longitudinal f5 = 2.340 Hz location of generated point; θI f6 = 2.366 Hz = random number uniformly Figure 5. Vibration Modes distributed from 0 to 2π; and N = 200 in this study. S(ωi) = PSD 5 Frequency No. (Hz) function and can be written as: Cases 1 2 3 4 5 6 7 2πf -2 S(ω) = S(2πf) = A ( 0.526 1.162 1.182 1.225 2.289 2.291 2.308 r f 0,2* EI X (L) (L,T) (V) (L) (L) (L) (L) where ω = circular frequency;0 ) f = 0.538 1.196 1.269 1.489 2.340 2.366 2.564 I EI wave number = 0.005 to 3(cycle/m); X (L) (L,T) (V) (T) (V) (V) (L,T) f = discontinuity frequency = 1/2π 0.543 1.209 1.450 1.640 2.377 2.516 2.670 0 5*EI X (L) (L,T) (L) (V) (V) (V) (L,T) (cycle/m); Ar = roughness coeffcient = 5×10-6 , 20×10-6 , and 80×10-6 Add two 0.832 1.234 1.314 1.659 2.421 2.729 2.953 m3/cycle for very good, good, and Bracings (L) (L,T) (V) (L) (L) (L) (L,T) average roads respectively; theory Table 2. Frequencies detail can be found in Wang and Huang10 and Liu et al17. were added to the arch as shown in Assumptions Figure 1 (d) in dashed lines. In this The damping matrix is assumed to be table, “V”, “L” and “T” represent Free vibration proportional to mass and stiffness18. vertical bending, lateral bending, and Based on the test results, three torsion individually. From this table, Figure 5 shows the frst six vibration percent of the critical damping is we can see that deck vertical stiffness mode shapes of the arch bridge. taken for the frst and second modes. has little effect on the frst frequency From this fgure, we can see that the A time step of 0.001s gives good and that the additional two arch frst and ffth vibration modes are accuracy for all types of dynamic lateral bracings signifcantly increase dominated by arch rib lateral bending responses. and that the third and sixth vibration the arch lateral stiffness and the frst modes are controlled by vertical frequency, which is expected. The bridge decks are assumed to 5, 6 bending. The second and fourth have “good” roughness . The vibration modes are dominated by road profles are hypothesized to be Forced vibration 4 torsion and vertical bending. For a the same transversely . In order to better understanding of the effect Vehicle data obtain the initial displacements and of the stiffness of deck and arch velocities of a vehicle’s degrees of ribs, Table 2 shows the frequencies Table 3 shows the data of the freedom (DOFs) when the vehicle for four different bridge model Chinese Design Truck T-20. These entered the bridge, it started to move cases: Case 1 represents the actual values are determined based on at a distance of 20m, ie, a fve-car structure in which EIx represents the Chinese Specifcations and test data length, away from the left end of of trucks reported in Huang7 and the bridge. The roadway approaches vertical stiffness of deck stringers. In 10 Cases 2 and 3, the vertical stiffness Wang and Huang . Chinese Design were assumed to have the same road of the deck stringers is reduced and Truck T-40 has similar confgurations surface as the bridge. increased by 5 times respectively. and twice the weight of T-20. In Case 4, two lateral K-bracings
138 147 Vehicle-induced vibration of a concrete filled steel tube arch bridge
Wheel Set Suspension Tractor Mass Tire Stiffness Suspens. Suspension Friction Mass Stiffness Tire Space (kN/cm) space force (kN) 2 2 (m) (kg-s /m) (kg-s /m) l3(m) l4(m) (kN/cm) (m) Front Rear Front Rear Front Rear
1744.32 148.25 2.70 1.30 2.56 19.03 8.75 35.02 1.12 1.8 5.81 25.5
Table 3. Primary Data of T-20 Truck
Effect of damping ratios Damping Location Tables 4 and 5 show the effect 0 0.01 0.02 0.03 0.05 0.06 of damping ratios on bridge Deck 0.523 0.166 0.153 0.148 0.131 0.124 accelerations and impact factors, Arch 0.262 0.074 0.060 0.055 0.048 0.046 individually. The impact factor is Light 0.816 0.172 0.160 0.156 0.146 0.140 defned as Table 4. Effect of Damping Ratio on Acceleration Im dm sm in which dm and sm = absolute Internal Damping (%) = (R /R -1) x 100% Section maximum dynamic and static Force 0 0.01 0.02 0.03 0.05 0.06 responses,R respectively.R The results Axial Force 33.9 23.4 19.1 15.8 12.4 12.2 were obtained based on the Rib End conditions of 88.5 km/h and two Moment 34,0 11,1 7,3 5,6 3,9 3,6 trucks side by side, asymmetrical Axial Force 23.9 15.5 13.7 12.6 11.1 10.8 Span Quarter loading Case 2 (see Figure 6). Moment 15.2 12.1 10.2 9.3 8.4 8.1 From these tables, we can see that Mid-span Axial Force 21.6 13.6 12.8 12.1 11.4 10.7 completely neglecting the damping effect will signifcantly overestimate Table 5. Effect of Damping Ratio on Impact Factors bridge response. Vertical Acceleration (g) Member T-20 T-40 One Truck Two Trucks One Truck Two Trucks Arch Rib 0.0301 0.0553 0.0298 0.0543 Deck 0.0889 0.1184 0.101 0.1432 Light 0.1148 0.1334 0.1139 0.1439
Table 6. Effect of Number and Weight of Moving Vehicles
Figure 6. Loading Cases speed for different stiffness of deck a shape of a half-sine curve and the stringers. The following conclusions static defection of the deck along Effect of number and weight can be drawn from this Figure: (1) bridge longitudinal direction is in a of moving vehicles The vehicle speed slightly affects wave shape which forces the moving the acceleration of the arch rib vehicle up and down quickly, thus Table 6 shows bridge accelerations and amplitude of the deck; (2) increasing bridge vibration. With due to different types and number The acceleration of deck and light the decreasing of the vertical stiffness of loading trucks. The results shown tends to increase with vehicle speed of the stringers, the amplitude of the in this table were obtained based increasing, especially when the wave curve increases and the vehicles on a vehicle speed of 88. 5km/h. vertical stiffness of the stringers is are forced to change direction of From this table, we can see that reduced. This can be explained as travel from downhill to uphill. This increasing the number and weight of
follows. The stringers are simply change in direction causes a sudden Structures loading trucks tends to increase the supported on the foor beams which increase in the rate of vehicle spring acceleration of the deck and light of are suspended on the hangers and deformation, especially for a high this bridge. have comparatively smaller vertical speed, and thus an increase in Effect of vehicle speed defections at the support and larger the amplitude of the interaction defections at the mid-span. When force and the response level of the Figure 7 shows the variation of the vehicles move over the bridge, bridge15. bridge accelerations with vehicle each of the stringers will defect in
139 Figure 7. Variation of Bridge Acceleration with Vehicle Speed, (a) Arch Rib, (b) Deck, (c) Light, (d) Deck
Effect of stiffness and increasing the vertical stiffness of vertical, horizontal, and longitudinal the stringers can signifcantly reduce accelerations of the lights have Table 7 presents the variations of bridge accelerations; (4) Increasing reduced more than 34%, 57%, 51% bridge accelerations for different arch lateral stiffness has little effect respectively. vertical stiffness of the deck on the bridge accelerations and stringers and arch lateral stiffness. appears to be unnecessary for 299 x 8 The results shown in the table reducing bridge vibration. were obtained based on Loading Case 2 (see Figure 6) and are the Response comparison between maximum accelerations determined existing and retroftted by changing the vehicle speeds bridges 219 x 8 from 24.1 km/h to 120.6 km/h. The following can be observed Based on the aforementioned from this table: (a) The maximum analysis, the best way to reduce 219 x 8 vertical acceleration of the deck of bridge vibration is to increase the 110 the existing bridge exceeds 0.13g vertical stiffness of the deck stringers. and the corresponding amplitude Therefore, during the recent bridge closes to 1.3cm which can cause retroft work, two continuous unpleasant or intolerable vibrations longitudinal steel tube truss beams for pedestrians; (2) The maximum (see Figure 8) were added to each accelerations of the lights exceed side of the deck system along the 19 0.15, 0.13, and 0.12 in vertical, arch ribs . The accelerations of the 50 horizontal, and longitudinal retroftted bridge are given in Table 8. From this table, we can see: (1) Figure 8. Cross-section of Steel Tube directions respectively, which may Truss Beam (Unit = mm) contribute to the damage to the the maximum vertical acceleration lights; (3) The stiffness of stringers and amplitude have reduced more greatly affects the bridge response than 30% and (2) the maximum
140 147 Vehicle-induced vibration of a concrete filled steel tube arch bridge
Accelerations (g) Amplitudes (cm) Case Member Vertical Horizontal Longitudinal Vertical Horizontal Longitudinal Arch Rib 0.0625 0.0082 0.0221 1.236 0.193 0.406
EI x Deck 0.1323 0.0083 0.0183 1.273 0.056 0.132 Light 0.1501 0.1355 0.1208 0.871 0.250 0.259 Arch Rib 0.0565 0.0082 0.0229 0.922 0.211 0.465
0.2EI x Deck 0.2425 0.0114 0.0171 1.519 0.0838 0.137 Light 0.2681 0.3521 0.2891 1.567 0.133 0.551 Arch Rib 0.0554 0.007 0.0183 0.671 0.149 0.330
5EI x Deck 0.0958 0.005 0.0141 0.991 0.0381 0.094 Light 0.1068 0.0625 0.0665 0.739 0.206 0.143 Arch Rib 0.0621 0.0079 0.0203 1.218 0.186 0.396 Add Two Arch Deck 0.1301 0.0081 0.0181 1.268 0.053 0.129 Bracings Light 0.1498 0.1333 0.1199 0.729 0.246 0.238
Table 7. Effect of Deck Vertical and Arch Lateral Stiffness on Accelerations and Amplitudes
Conclusions and Existing Retroftted Location Direction Acceleration Amplitude Acceleration Amplitude recommendations (g) (cm) (g) (cm) Deck Vertical 0.1323 1.273 0.0913 0.891 This paper presented dynamic Vertical 0.1501 0.871 0.0986 0.705 analytical results for Shitanxi Concrete Filled Arch Bridge due Light Horizontal 0.1355 0.250 0.0583 0.189 to moving vehicles by using three Longitudinal 0.1208 0.259 0.0591 0.133 dimensional models of both bridge Table 8. Response Comparison and moving vehicles. The analytical results show that the observed severe bridge vibration is due mostly to Acknowledgment insuffcient vertical stiffness of the deck system. The maximum vertical The writer would like to express his sincere appreciation to Mr. John Previte, PE acceleration of the deck of the for his valuable comments and support received during the research. existing bridge exceeds 0.13g and the corresponding amplitude closes References to 1.3cm which can cause unpleasant or intolerable vibrations for 1. Huang, D. Z., Wang, T. L., and Shahawy, M., “Dynamic Behavior of pedestrians. The maximum resulting Horizontally Curved I-Girder Bridges”, Int. J. Comput. Struct., Vol. 57, No. acceleration of the lights exceeds 4, 1992, pp. 703-714. 0.23g which may contribute to the 2. Huang, D. Z., Wang, T. L., and Shahawy, M., “Impact Analysis of damage to the lights. The bridge Continuous Multigirder Bridges due to Moving Vehicles”, J . Struct.Eng., retroftting design with two stronger Vol. 118, No.12, 1992, pp. 3427-3443. longitudinal truss beams added to the existing bridge has been 3. Huang, D. Z., Wang, T. L., and Shahawy, M., “Impact studies of proved to be effective and reduced multigirder concrete Bridges”, J. Struct. Eng., Vol. 119, No. 8, 1993, pp. the accelerations of the deck and 2387-2402. light by more than 30% and 45% 4. Huang, D. Z., Wang, T. L., and Shahawy, M., “Vibration of thin walled respectively. It is recommended that box-girder bridges excited by vehicles”, J. Struct. Eng., Vol. 121, No. 9, Structures two continuous longitudinal girders 1995, pp. 1330-1337. connected with the foor beams be used for the arch deck system to 5. Huang, D. Z., “Dynamic Analysis of Steel Curved Box Girder Bridges”, J. reduce local vertical deformations Bridge Eng., Vol. 6, No. 6, 2001, PP. 506-513. in future design for this type of arch 6. Huang, D. Z., “Dynamic Loading of Curved Steel Box Girder Bridges due bridges and the similar. to Moving Vehicles”, J. of the Int. Association for Bridge and Structural Engineering (IABSE), Vol. 18, No. 4, 2008, pp.365-372. 141 7. Huang, T., “Dynamic Response of Three-span Continuous Highway Bridges”, PhD dissertation, University of Illinois, Urbana. 111, 1960, p. 369. 8. Wang, T. L. and Huang, D. Z., “Computer Modeling Analysis in Bridge Evaluation, Phase II, Dynamic Response of Continuous Beam Bridges and Slant-legged Rigid Frame Bridges”, Final Research Report, Florida Department of Transportation, Report No. FL/DOT/RMC/ 0542-4108, Tallahassee, Florida, 1992, p.368. 9. Shahabadi, A., “Bridge Vibration Studies”, Joint Highway Research Project JHRP 77-17, Interim Report, Purdue University, West Lafayette, Indiana, 1977, p.154. 10. Wang, T. L., and Huang, D. Z.. “Computer Modeling Analysis in Bridge Evaluation”, Research Report No. L/DOT/ RMC/0542-3394. Florida Dept. of Transp.. Tallahassee, Fla., 1992, p.303. 11. LI, G.H., “Vibration of Arch Bridges”, J. of Tongji University, Shanghai, China, Vol. 56, No. 3., 1956, pp. 1-11. 12. LI, G.H., “Vibration of Steel Arch Bridges”, J. of Highway Design Record of China, China, Vol. 33. No. 2., 1973, pp.3-16. 13. Chatterjee, P.K. and Datta, T.K., “Dynamic Analysis of Arch Bridges under Traveling Loads”, Int. J. of Solids and Structures, Vol. 32, No. 11, 1995, pp1585 -1954. 14. Huang, D. Z., “Vibration of Concrete Filled Steel Tube Arch Bridges due to Moving Vehicles”, Proceedings of 15th National Bridge Conference of China, Chinese Society of Civil Engineering, Tongji University Publishing House, Shanghai, China, 2002, pp.469-475. 15. Huang, D. Z. 2005. “Dynamic and Impact Behavior of Half-through Arch Bridges”, J. Bridge Eng., ASCE, Vol. 10, No. 2, pp. 133-141. 16. Lacarbonara, W. and Colone V., “Dynamic Response of Arch Bridges Traveled by High-speed Trains”, J. of Sound and Vibration. Vol. 304, No.1-2, 2007, pp72-90. 17. Liu, C. H., Huang, D. Z., and Wang, T. L., “Analytical Dynamic Impact Study Based on Correlated Road Roughness”, An Int. J. of Computers and Structures, Vol. 80, No. 3, 2002, pp. 1639-1650. 18. Bathe, K. J., “Finite Element Procedures in Engineering Analysis” Prentice Hall, Englewood Cliffs, N.J., 1982, p.618. 19. Peng, G.H. and Cheng, B.C., “Research on Strengthening Suspended Deck System for Half-through CFST Arch Bridge by Setting Longitudinal Steel-tubular Trusses”, Proceedings of 6th International Conference on Arch Bridges, ARCH’10, Fuzhou, China, 2010, p.898.
142 Systems Engineering 143 148 A SPAR model is described using A SPAR Reliability Block Diagrams (RBD), statistical distributions and operation in simple logic code. rules expressed uses the system operating SPAR rules and logic to model the effects as well as effects of events (direct cascaded ones) on the behaviour of logic modelling the system. SPAR’s capabilities include, among others, active-passive and standby relations, induction cannibalisation of spares, changing the age and the of failures, load of components, and many other operations that enable illustrating phenomena of the life any real system and its supportive resources. Mission profles Usage Equipment selection Sparing levels times logistics delay times and active repair Increased
• • • • • Highlighting potential areas of weakness in the support solution; of weakness in the Highlighting potential areas AR&M performance by varying: Understanding the impact on global Validation of consolidated spares recommendations and identifcation of and identifcation recommendations of consolidated spares Validation as the at multiple levels of support (as many spares, with insuffcient areas user requires) The ability to demonstrate the impact of management system downtime; impact the availability of the system, but may which would not directly time) of a co-incident failure. delay the identifcation (and hence repair
An overview of the SPAR Modelling Platform An overview of the SPAR The following description of the modelling platform has been SPAR the Clockwork- constructed from Solutions website (http://www. clockwork-solutions.com/tec_ whatmakessparunique.php). simulation uses Monte The SPAR Carlo simulation techniques to model the life-cycle behaviour of systems. modelling platform The SPAR includes a wide range of distributions (including bathtub and non- parametric distributions), to represent the time-dependent behaviour of shipment, replacement repair, failure, and other time-dependent phenomena. A SPAR modelling platform case platform case modelling A SPAR 5 study: Skynet Abstract Reliability and a case study into the Availability, This paper documents the Skynet 5 Beyond modelling activity undertaken for Maintainability (AR&M) January 2006 and July between Line Of Sight (BLOS) service programme completed using the Monte Carlo 2011. The AR&M modelling activity was by Clockwork Solutions. produced simulation tool SPAR, of models tool which allowed the development is a fexible software SPAR its complex logistic support Skynet 5 system, to include the end-to-end core Service availability metrics. The network, and the calculation of bespoke a number of model has provided development of this end-to-end type benefts, including: • • • • Ian Miles Engineer Supportability Astrium Iain Davison AR&M Consultant & Defence, Aerospace Communications Atkins An assessment was completed into on the availability of paths and the different modelling tools available the bandwidth). Only SPAR at the time. There were a number of was identifed as being able to reasons for utilising SPAR, including perform such calculations. the following: • All other modelling tools assessed A brief overview of used pictures/fow diagrams/ Skynet 5 RBDs to describe the system in question. Since some elements The Skynet 5 programme provides of the Skynet network are so the UK Armed Forces with secure Figure 1. Satellite Ground Station (SGS) complex in terms of all the BLOS services (henceforth referred different routing options based to as Services). Management of the on which equipment had failed, Services takes place at two Satellite it was not possible to construct Ground Stations (SGS) (see Figure all the different possibilities 1). The Services are then broadcast in pictorial form. SPAR uses a over military hardened Skynet 5 bespoke logic code to describe communication satellites (see Figure what happens when, for 2) in orbit, to two types of remote example, components fail, and terminals; SCOT5 Maritime terminals based on any number of other (see Figure 3) and Reacher ground conditions (e.g. which particular mobile terminals (see Figure 4). communications services were Each remote terminal undertakes Figure 2. Skynet 5 Satellite effected, if any other components a number of missions throughout are failed at the same time, or if its life, with each mission including a particular remote terminal was defned periods of transmitting and in the feld at the time) the end receiving Services, periods of transit effect on Service and Operational and periods of maintenance. availability can be investigated. Two exam questions were placed on • The SPAR models created were the Skynet 5 system, to be answered completely transparent: The using the SPAR modelling platform: fact that logic code was used to describe the systems meant 1. Calculate the predicted end- that checks in the code could be to-end Service availability to Figure 3. SCOT5 Maritime Terminal included throughout to ensure Reacher and Maritime terminals. that the models were correct, This involves calculating the and to pull out results at any average availability of Services point in the model run. This passing through an SGS, a gave confdence in the results satellite and a remote terminal produced and also enabled the (Reacher or Maritime); identifcation of the point at 2. Calculate the predicted which, for example, a particular operational availability for component ran out of spares or a Reacher and Maritime terminals. particular communication service failed. This feature is limited in the other modelling tools. Modelling the Skynet 5 system in SPAR Figure 4. Reacher Terminal • The modelling tool was required to calculate the availability of Construction of the models in SPAR The equipment within the remote communications services passing began through identifcation of terminals was divided into two through the Skynet network. The equipment and systems directly and groups: those responsible for carrying Service availability was not equal indirectly required to support Services Services and operational success, to the equipment availability (creating Service paths through the and those just required to achieve due to the ability to route Skynet 5 system) and to achieve the the operational availability. RBDs communication services between operational availability of the remote were constructed within SPAR for network paths with different terminals. each remote terminal to represent switching times (dependent 144 148 A SPAR modelling platform case study: Skynet 5
the successful achievement of the in-built redundancy and failure User-defned data arrays were operational and service availability. management systems. employed in the SPAR models to identify various equipment features The SGS and satellites utilise The SPAR models were developed to infuence and direct the logic sophisticated redundancy paths with no common spares between code. These features include: and routeing options to ensure the remote terminals and SGSs. minimal downtime in the event of Therefore they could be modelled • Statistical distribution parameters equipment failure. The complexity of separately (with the metrics representing the time to repair/ these systems meant that it was not combined after each model run) replace the equipment and the possible to construct conventional to simplify the problems and allow time taken to restore Services RBDs such as those used for the them to be developed, verifed and carried by each equipment remote terminals. Instead, logic code validated in stages. (the restoration time can also within SPAR was used to model represent the time taken to re- Systems Engineering
Figure 5. Skynet 5 Logistics Network Overview 145 route Services to an alternate path Spares holding are represented in the within the SGS or Satellite); SPAR model by ’Storages’, containing Conclusion a user-defned quantity of spares • The quantity of Services carried at the beginning of the model run. The development of the end-to-end (and therefore affected) if each If equipment fails, the logic code modelling approach to the Skynet 5 equipment type fails; interrogates the Storages in turn to system, including its complex logistic • For SGSs and Satellites, determine where the closest available network, through the fexibility parameters identifying the spare is located. The logic code provided by the SPAR modelling redundancy confguration of uses this spare to replace the failed platform, has allowed the following equipment types, for example equipment and the Storage is then validation and scenario modelling the minimum number of items replenished by spares (if available) activities to be performed: required to be operational to carry from the next holding in line (e.g. as • Highlighting areas of weakness Services. shown in Figure 5, Reacher terminal in the current support solution Using equipment failure distributions on-board spares are replenished by updating model inputs input by the user (from manufacturer by the Forward Spares Pack, which with in-service reliability and data, in-service data, etc.) the SPAR is then replenished by the Spares maintainability data Depot). modelling platform utilises Monte • Varying mission profles to Carlo simulation techniques to Upon failure, repairable items are model future deployments and generate failure events. At each returned through the support highlight potential problem failure event the logic code randomly network to the Repair facility (as areas early to allow for prompt selects (from the Services defned in shown in Figure 5). These items contingency planning. This the data arrays) the specifc Services are repaired before re-entering the included demonstrating affected by the equipment failure. support network to act as a spare. the impact on Service and The time to restore the Services Non-repairable items are removed Operational availability of (taken from the data array) is then from the model upon failure and changing the mission profles applied to each affected Service and replaced with a spare. If all spares of remote terminals – i.e. if a the average Service availability is then have been used, the system is terminal is going to be used for calculated at the end of the model defned as failed for the remainder of a longer period, the Service and run. For remote terminals, the time the model run. Operational availability drops to a to repair/replace the equipment is All timings associated with the certain level, if the sparing levels also recorded for each Terminal and forward supply of spares and return are not replenished the average operational availability is of failed equipment (shown in Figure calculated. • Validating long-term sparing 5 as purple and blue dotted lines recommendations, especially The total time to repair/replace respectively) are contained within pertinent with life-time buys the equipment is dependent on a another user-defned array and the for obsolete equipment where complex logistic support network, logistics delay times for each type of there will be no opportunity to which is also represented in the equipment on each terminal can be replenish supplies in the future. SPAR models and logic code. Figure modifed individually. Spares were recommended for 5 presents a representation of the Each remote terminal undertakes individual sub-systems in isolation; Skynet 5 logistic network. a pre-defned number of missions the SPAR model was used to As shown in Figure 5, each Maritime throughout its life. These missions validate that suffcient spares terminal is supported by its own are defned within the SPAR platform (in order to meet the Service on-board spares holdings and by the as periods of uptime (i.e. sending/ and Operational availability spares depot whereas each Reacher receiving Services) and downtime (i.e. requirements) had been terminal is supported by three spares undergoing planned maintenance recommended for the system as holdings: and transit). Failure events can a whole • On-board spares occur during periods of uptime or • Modelling scenarios to aid trade- downtime, however only those off studies • A Forward Spares Pack (FSP) occurring during the period of supplying spares to a number of uptime contribute to Service and • Investigating the impact of supply Reacher terminals Terminal availability. chain issues such as equipment losses and increased logistics • A spares depot, supplying the two delay times. The SPAR model was SGS’s, all Reacher terminals and used to demonstrate the impact all Maritime terminals. of extending the logic delay
146 148 A SPAR modelling platform case study: Skynet 5
times on Service and Operational availability. Acknowledgement
By developing this end-to-end type This paper was previously published in The Journal of the Safety and Reliability of modelling, it has been possible to Society, Winter 2012, Vol. 32 No 4, ISSN 0961-7353. take a holistic approach to the Skynet 5 system: identify and account Astrium Ltd, Paradigm Ltd and Atkins Ltd owns the copyright of this for all the interdependencies and document which is supplied in confdence and which shall not be used for any interactions and show the impact the purpose other than that for which it is supplied and shall not in whole or in above scenario modelling activities part be reproduced, copied, or communicated to any person without written have on each aspect of the system. permission from the owner. The Skynet 5 SPAR model has increased the confdence in the system designs and support solution, forms part of the system assurance case (by answering the exam questions), and provides potential long-term through-life cost savings. For these reasons, it is recommended that all large and complex programmes should consider developing this end-to-end style of modelling. Systems Engineering
147 148 Systems Engineering 149 149 , for both the model with the capacity than the current train capacity than the current and allows a system control tighter headway in the timetable signalling system gives better which allows the reliability space planners to use less free for recovery. channels or free 1
out by Atkins in cooperation with Rail Net Denmark. CBTC impacts the service on the ways: railway in two different 1. A CBTC system has a higher 2. Renewal of the current The analyses have been performed with the simulation tool RailSys in combination with estimating minimum headway in different scenarios. of the Copenhagen Suburban Railway show how planning of the Copenhagen Suburban Railway 1 the most suitable travel speed will increase capacity, but upgrading the but upgrading capacity, the most suitable travel speed will increase more system is a much advanced train control to a more infrastructure capacity and punctuality. way to improve effcient on operation by the effects This paper deals with investigations of carried out for were system, which implementing a CBTC train control This was done by using the the Copenhagen Suburban Railway network. infrastructure different tool RailSys. Two simulation software rail traffc in Danish HKT (Acronym one with the existing models have been created, train & Trainstop) – in English SpeedControl & Togstop HastighedsKontrol CBTC system. The system and the other with the proposed/planned control by running extra trains. models have been stressed analysis of the central tube was In addition to the simulations, a headway to the UIC 406 method carried out according frst European country Denmark frst European decided to change all signals and to interlocking systems in order Railway Traffc follow European Management System (ERTMS) by implementing European standards System (ETCS) level Control Train 2 on all national lines/stations except the Copenhagen suburban decided to invest heavily in renewal decided to invest heavily in renewal of the Danish and improvements an to ensure Railway Infrastructure national railway, future effcient vision which supports the European As the railway. of an interoperable lines, which will be equipped with Control Communication-Based Train (CBTC). This paper will consist of the analysed of a CBTC impact of the introduction system on the suburban network in Copenhagen, which has been carried Introduction Introduction In 2009 the Danish Government How can CBTC improve the CBTC improve How can railway a saturated service on system? Abstract studies Previous existing signalling system and for the model with the new CBTC signalling existing signalling system and for the system. Suburban CBTC, Simulation, Headway analysis, Railway capacity, Keywords: railway. Anders H. Kaas Head of Department Planning & Analyses Atkins Denmark Atkins Analysis
The suburban railway infrastructure (S-bane) in Copenhagen consists of three lines in the south and three lines in the north connected through a bottleneck called the “tube” through the central part of Figure 1. Track layout of the central tube K benhavn H (Kh) - Svanem llen (Sam) Copenhagen between the stations K benhavn H (Copenhagen Cetral Station) and Svanem llen. The current Suburban Railway timetable is based on a 10 minute service on all lines and 5 minute service on the lines with most passengers. This leads to 30 trains per hour in each direction in the “tube”. Beside the “tube” lines an outer “circle” line (yellow line F) is operated with a 10 minute service. Figure 2 illustrates the service on the network.
The existing HKT signal system
The current signalling system on the Copenhagen Suburban Railway is a fxed block system with HKT train control (speed control and train stop) on most of the sections. Much of the HKT system is from the seventies but upgraded several times to date. HKT keeps the trains’ speed under surveillance and makes sure that the trains stop at stop signals. Figure 3 shows how the HKT blocks are implemented between Valby and Dybb lsbro Stations. The fgure shows how the line section is divided Figure 2. Copenhagen S-train Network in several “HKT” block sections. Each at the end of the block and stop Figure 4 shows the HKT section can send different speed there implementation in RailSys. The grey information to the train, taking into train in the graphical timetable must account the available length of clear • “30”, “60” or “80” are speed stop at Enghave (Av), and the train track in front of the train. information [km/h] from the line follows a stepwise slow down from section to the train. If a train The current block number 2128: 90 km/t to stop according to the enters the block at a higher information given to the train from • A hatch square means that the speed than the speed information the line sections. block is occupied indicates, then the train must • “Sv” is stop information from the lower the speed to the current line section to the train. The train speed information and proceed is allowed to proceed to the mark at that speed until the speed information changes.
150 149 How can CBTC improve the service on a saturated railway system?
The future CBTC system
The future signalling system is a train control system based on radio communication instead of fxed signals at the side of the tracks as for existing signals. CBTC uses moving block instead of fxed block as the existing HKT. The size of the moving block separating two trains takes into account their relative location and individual performance. Therefore, headway is minimised as compared to fxed blocks. It leads to an optimal use of the infrastructure by shortening headways, which is suitable for an urban rail system with a high Figure 3. HKT step diagram from Valby (Val) passing Enghave (Av) to Dybb lsbro (Dbt) frequency. The integrated CBTC system knows the position of each train very accurately. It can control the behaviour of the train at all times and, in response to changing conditions, can modify behaviour to ensure the safety of the trains while offering maximum service with a minimum number of failures. It can adapt its algorithms to take advantage of individual train behaviour, and change parameters to ensure optimum use of resources, such as platform availability and traction power. (e.g. Thales3). The CBTC system will have moving blocks at all sections except point areas. The safety parameters for the new CBTC signal system used in this analysis are as follows: Safety distance: 50 metres Block lengths: 100 metres
Point setting time: 7 sec Systems Engineering CBTC signalling systems have been installed at numerous urban railway transit systems around the world both in brand new systems and lines, and as an upgrade of existing lines with old signalling systems to a new CBTC signalling system. For example in New York City on the Carnesie Line in the subway network there has been an upgrade of an existing interlocking to CBTC. It Figure 4. HKT implementation in RailSys (Upper graph: Speed profle – Lower graph: has been in revenue service since Graphic timetable) 151 January 2006 (e.g. Siemens4). As seen in Figure 5 it relies on a wireless radio communication system. This makes the installation of equipment dedicated to data transmission easier as there is no continuous medium on the track and equipment is mostly installed in stations.
Simulation tool
The simulations were carried out in the simulation software RailSys. RailSys is a timetable and infrastructure management software system for analysis, planning and optimisation of operational Figure 5. The principal elements of a CBTC moving block system (Illustration from 4 procedures and facilities in rail traffc Siemens ) networks of any size. Operational procedures are displayed on desktop computers and the investigation of whole systems is as easily accomplished as the processing of specifc, local problems. RailSys is a widely accepted software tool used by companies and universities over the world.
Headway
In the Copenhagen S-train network all lines except Line F, the ring line, run through the central tube between K benhavn H and Svanem llen. This section has one track allocated for traffc in each direction. The scheduled headway at this section is the shortest in the network with scheduled distance between the trains at 120 seconds in the current timetable. Headway examination is made in RailSys by moving the trains in the graphical timetable with block occupation shown, as close as possible without conficts between the trains. This is illustrated in Figure 6 with the black arrow demonstrating how the graph can be compressed. The method is a part of the UIC 406 capacity method. First the model of the existing Figure 6. Block occupation with existing signals at Østerport station (Kk) network with HKT signal system is investigated by the minimum
152 149 How can CBTC improve the service on a saturated railway system?
technical headway in the central tube of 110 sec and a scheduled headway of 115 seconds. By using the new CBTC system, the minimum technical headway at the central tube is reduced to 75 sec and a scheduled headway of 78 seconds. By comparing Figure 7 and Figure 8, it is clear that reductions in headway are mainly caused by a shorter length of clear track in front of the train, and this is most noticeable at stations.
Ninety seconds headway in the central tube
Based on previous headway analysis a timetable which has 90 seconds headway through the central tube has been evaluated. Figure 9 shows a graphical timetable with 90 second headway, through the central tube on the infrastructure with the new CBTC signalling system (with block occupation around the trains). The station dwell times are the same as in the current timetable. Figure 7. Minimum headway with the existing signals and scheduled running time in The Figure shows there are no central tube at the bottleneck Vesterport Station (Vpt) conficts, with a buffer time between the trains. The same timetable in the existing HKT signalling system in Figure 10 shows a timetable with many conficts and no buffer time indicating 90 second headway in the current HKT system is not possible. Only the headway in the central tube with the existing scheduled dwell
times is analysed in this scenario. Systems Engineering Where the trains are headed, where they will turn around and the trains’ stopping pattern outside the central tube are not analysed in this scenario. The new CBTC signal system will make it possible to operate a timetable with 90 second headway in the central tube, though the punctuality of a timetable with this headway will be lower than a Figure 8. Minimum headway with CBTC signals and scheduled running time in the scenario with the current timetable central tube at the bottleneck Østerport station (Kk) implemented. 153 Figure 9. Scenario with a 90 second headway timetable in the central tube with CBTC signals
154 149 How can CBTC improve the service on a saturated railway system?
2008
Signals 15Operator and external +6421 Tracks
Figure 11. Amount of delays related to different groups
to reach the same punctuality as the punctuality from the delay statistics. The delay function in RailSys is implemented as an exponential distribution. The delay function uses at each station two parameters: 1. Percentages of delayed trains at the current stations with and without signal failures. The percentages of trains affected by an initial delay at all station are taken from the Banedanmark RDS data 2. Average delay was set to 1.2 minutes after calibration and maximum delay was set to 6.0 minutes after calibration, The average lateness and maximum lateness were calibrated to reach Figure 10. Scenario with 90 second headway timetable in the central tube with around the 96.7 % punctuality existing signals from 2008. delays are due to the old signalling In the RailSys model punctuality for Systems Engineering Delays system. all stations on the Suburban Railway Network was 96.6%, which was A train on the Copenhagen The model for the delay data will close to the 96.7% real observed Suburban Railway is, according to the be based on data from Rail Net punctuality from the RDS data. operator DSB and Rail Net Denmark, Denmark. Delay data for 2008 were defned as delayed if the train is more analysed and used in this model. than 2½ minute late. Therefore, These are divided into three different Multiple simulations this minimum delay is used in the causes of the delayed train. Both the current network and the punctuality analyses. The new CBTC system will mainly network when a CBTC system is remove the delays caused by signal Today signalling failures are the cause implemented have been simulated. failures. The delays are implemented of many train delays at most rail The current train control system in the RailSys model for the existing sections in Denmark. Many of those allows 100 seconds minimum network and the model is calibrated 155 headway in the tube and planned 120 seconds headway. It is expected that the CBTC system will result in a 75 second minimum headway, but the results of the simulations show that the implementation of CBTC will result in much higher punctuality. The lower number of failures in the signalling system and the improved headway will together result in a much better performance. The better performance of a CBTC system can be exploited to give a higher punctuality (B), a higher frequency (C) or both (D) as illustrated in Figure 12. The question now is how close can we get to the capacity limit, when the current signalling system has Figure 12. Illustration of capacity and punctuality changed to a modern CBTC system?
Calibration of New CBTC signal To show the impact of some different model to reach real system punctuality ways to increase the traffc in the Delay Existing CBTC system network some different scenarios Data from infrastructure without signal have been simulated and compared, statistics with HKT signals failures where: • As a reference the current suburban railway network with the current traffc was simulated • The current situation plus a new line running through the tube and continues on a new single track Removing Removing line to the end station signal failures signal failures from input from input • The current situation plus a new delay data delay data line running through the tube and continues on a new double track line to the end station. All these cases result in a much lower punctuality compared with the current situation independent of the number of new tracks. Therefore, the Existing HKT CBTC system traffc in the tube was isolated in the signals without without signal next phases of the simulations. signal failures failures For this phase the scenario was based on the current traffc and then added a line, 3 extra trains per hour in each Figure 13. Simulation overview direction, which were only running in the tube and cut off at the end of the tube. The impact of the added line to the punctuality was nearly as big as the impact of the complete line as simulated before.
156 149 How can CBTC improve the service on a saturated railway system?
RDS Data
Existing system model
Future CBTC model Percent of trains at time Percent
All Failures Without signal failures
With all failures Without signal failures Delay statistics 96.7 % Model of existing network 96.5 % 97.7% Model of future network with CBTC 99.0 % 99.2%
Figure 14. Results of the simulation
Roll out plan for the implementation of the CBTC signal system
According to Rail Network Denmark the implementation of the new CBTC signal system should be fully implemented in 2020 (e.g. Banedanmark5). The signal programme will initially be provided by one supplier. The same supplier should thus provide and install the new signal system on the S-Bane - including the signal equipment to be installed inside the
rolling stock. Systems Engineering The Remote System must be clear, so it can control train traffc when the new signal system is used on the frst line. It kept open the tender for the supplier, whether to establish a new remote control system in a newly built centre, or whether the existing remote control system can be reused.
Figure 15. Roll out plan for the Signal Programme on the Copenhagen S-Bane network 157 The rollout of the new signalling takes place in four phases from the References time the policy decision is taken: 1. Kaas, A.H.; Landex, A.; Schittenhelm, B.; Schneider-Tilli, J. Practical • Tender use of the UIC 406 capacity leafet by including timetable tools in • Design of the new signaling the investigations Proc. Of the 2nd International Seminar on Railway Operations Modelling and Analysis, eds. I.A. Hansen, F.M.Dekking, R.M.P. • Deploying and testing on the frst Goverde, B. Hindergott, L.E. Meester, Hannover, 2007. section (Early Deployment) 2. Kaas, A.H. & Landex, A., the most suitable travel speed for high • Rollout of the other lines. frequency railway lines. Proc. Of the 1st International Seminar on Railway The roll out on the S-Bane, will Opera¬tions Modelling and Analysis, eds. I.A. Hansen, F.M.Dekking, be in sections. First roll out (Early R.M.P. Goverde, B. Hindergott, L.E. Meester, The Netherlands, 2005. Deployment Project) will take place 3. Thales, Selftrac CBTC, Communications-Based Train Control For Urban at the section between Hiller d and Rail. Jægersborg in 2014, where the new CBTC will be rigorously tested before 4. Siemens, Trainguard MT CBTC – The Moving Block Communications- being rolled out on other sections. Based Train Control Solution. 5. Banedanmark, Nye Signaler på Banen www.bane.dk. Conclusions
The conclusion of this simulation was that no extension of traffc through the tube is possible before the signalling system is changed to a high performance CBTC system, but some extensions are possible outside the tube. Another fnding from the investigations was a comparison between the effects of the new system running without failures against the effects of a new system with higher capacity. Here the conclusion was very clear – extra capacity within the CBTC system improves punctuality on the saturated system much more than having a future signalling system with no failures.
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