THE ARUP JOURNAL

2/1994 Front cover: The Marly courtyard at the Richelieu Wing Louvre Museum. Paris. (Photo: Peter Mackinven) Back cover: Kansai International Airport. with its mile-long terminal building, on the THEARUP artificial island offshore from Senshu, Japan. (Photo: C.K. Hiwatashi)

Vol.29 No.2 Editor: JO2/1994 URNALDavid J. Brown Published by Art Editor: Ove Arup Partnership Desmond Wyeth FCSD 13 Fitzroy Street, London Deputy Editor: W1P6BQ Hel�ne Murphy 3 Transport pollcy This article outlines the facts and examines the issues behind In the UK transport provision in the UK: the demand for travel; attitudes to the Malcolm Simpson supply of road and rail infrastructure; and the need for a balance to be maintained between demand and supply so that accessibility can be preserved, but with a minimum of environmental damage.

5 Edinburgh Weatem Arup Transportation looked at the suitability of a bus-based Light Corridor Bu•way Study Rapid Transit system to alleviate Edinburgh's traffic congestion. The Gavin Dunnett study went on to assess various combinations of private and public Gordon Henderson sector ownership and funding for the scheme.

8 Hong Kong Kai Tak Airport: Ove Arup & Partners gave major assistance to the contractor's design Taxiway Bridge 3 - for this seven-span, 225m bridge across a waterway in Hong Kong Wing-Huen Fok '------harbour for aircraft up to the 400 tonne Boeing 747-400F taxiing from - -- the runway to a new parking apron in Kowloon Bay. - �-'\-\tl�-· 10 Rlchelleu Wing Eight floors of former government offices in one wing of the Louvre Louvre MuMUm,Parl• have been converted into a further 22 000m2 of museum space, Alistair Lenczner including three sculpture courtyards and many painting galleries. Andrew McDowell Two teams from Arups designed the courtyard roofs and the natural Andrew Sedgwick lighting schemes for the top-floor galleries.

14 Oldham Broadway Ove Arup & Partners have made a major contribution to this scheme Bu•lne•• Park to transform 54ha of derelict, former industrial land north-eastof Colin Curtis Manchester into a well-serviced new business development. Arups' Nick Fennell team carried out a comprehensive study of the site; developed a Roger Milburn scheme masterplan; designed the new infrastructure and land reclamation schemes; and supervised construction. 17 Kan .. 1 Airport Terminal, The 300 000m2 terminal building, for which Arups carried out o ..ka,Japan structural, services, and fire engineering, opens in September 1994. Philip Dilley A full-scale article will appear in a future Arup Journal.

18 Cono•lon: This article outlines modern electrochemicalcorrosion monitoring I• there a problem? techniques, and discusses their use by Arup Research & Graham Gedge Development to predict flue corrosion in the 21 Orn chimney of the Pagbilao power station, at present under construction in the Philippines.

2 Transport policy in the UK Malcolm Simpson

1.

Background Councils in the Home Counties which Transportation provision affects all have traditionally been the staunchest aspects of life, not as an end in itself, -- Air supporters of the current but as a means of achieving most 500 --Rall Government. The environmental activities. It affects us socially, it in­ -- Pedal cycles effects of new transport infrastructure fluences our work locations, and has Motorcycles range from local impacts such as E 400 a direct or indirect bearing on all x -- Cars & vans pollution, visual intrusion and loss of other activities in which we indulge. .. Buses & coaches amenity space, to the global effects of cC> It also has a direct impact on the work .. increased C02 emissions . ~ 300 that many people in Arups undertake ll. We are currently in a period of funda­ c: to provide the necessary infrastruc­ ~ mental change in approach to trans­ ffi ture and its future operation. 200 portation issues which will affect all of The problems are evident. Roads are us socially, environmentally, and becoming more congested, not only financially. There are very many mis­ in urban areas where peak periods 100 conceptions, and the wealth of trans­ are lengthening and speeds steadily port data can be used to prove virtu­ decreasing, but also on inter-urban ally any point that a particular interest routes and in places with high leisure O c =====------...l group wishes to make. This article attraction, such as roads to holiday ~'l, ,$ ~ ~~ ,# ;? .i>ro .i' °'~ °'~ ,g,'l, attempts to present some basic facts, destinations, and in national parks like " " " the issues, and the possible ways for- the Lake District. This congestion is 2. Passenger transport by mode. ward in preserving accessibility and matching this with sustainability. bad for the nation's health and its 3. Cars and taxis stock 1991 . economy. However, public transport The process can be split into three 600 use is reducing. Bus patronage is simple aspects: the demand for steadily declining and rail services travel; the supply of transport infra­ are often less attractive in terms of 500 structure; and thirdly the balance cost and reliability than they were a between these two and the options to few years ago. achieve the balance. Solutions to these problems are not Demand simple and the challenge facing The demand for travel is increasing. transport planners and politicians We are making more trips and longer covers a broad field of political, social, trips. Fig. 2 shows the pattern of economic, and planning aspects. The growth which is dominated by the complex inter-relationships between dramatic and continuous increase in all these factors is not clearly under­ .. car use - not surprising in view of ll. stood and much research is being the car's unmatched flexibility for undertaken into them. The general 100 shopping, delivering children to desire for more movement set against school, and family holidays through­ the inevitably slow evolution of the out Europe. Rail use has been steady, built environment means that change but road-based public transport has is slow, even if current trends can be declined continuously over the years. influenced. Apart from very minor reductions in Whilst attitudes to transport are growth rate at times of economic changing rapidly, the speed of this - Actual traffic growth to 1992 recession, the trend in car ownership change cannot be matched by the 800 - NRTF 1989 rebased to 1992 has been and will continue to be necessary changes in social be­ 700 steadily upwards. Fig. 3 shows the haviour or the time needed to 600 comparison of British car ownership implement any major new transport E with the major European countries ; 500 infrastructure. Such development .II and USA. It is evident that there is takes up to a generation from concept ~ 400 scope for further major increases in to implementation, so any solutions g 300 car ownership and use, as we are a must look to the longer term and be in long way from saturation level and set against the background of 200 below our European neighbours. increasing environmental awareness 100 Fig. 4 shows the Government's and the desire for sustainability. current prediction for road traffic Opposition to new transport infra­ growth and this demand will continue structure comes from all quarters, unless restrained by legislative or not only left wing activists, but also 4. National road traffic forecast. financial means. THE ARUP JOURNAL 2/1994 3 Fig. 5 shows the increase in freight users, and travel to alternative loca­ movement, again dominated by road tions would be more expensive and use, with a steady decline in rail use. less convenient for the vast majority of One current myth is that by increasing _ 120 the population. In addition, recent E the latter our road traffic problems ,c research on office locations has a, c would be solved, but the reality is that c shown that, even if good public trans­ even if we increase rail freight use by g port exists, the desire will remain to 50% - a major change against the ~ 90 use a car for access. Possible trend - the difference in road traffic €. changes in overall travel demand would amount to only a few months I cannot be immediate as land-use growth, a totally insignificant amount ~ 60 changes are very slow and travel in overall volume although there could patterns well-established. Social use well be justification in terms of environ­ I of cars has increased significantly, mental benefits. 30 with leisure trips the fastest-growing Supply component. Would we accept restric­ Growth in supply of transport infra­ tions on use of our car for holiday and structure does not match demand social purposes? It would be difficult growth. Fig . 6 shows the recent enough to stop the current trend, let increase in road length in Britain: the alone reverse it, but many people believe that this is essential if we are density of vehicles in this country is 5. Freight transport by mode. over twice that in France and the USA, to achieve sustainability. and 40% higher than in Germany. 6. Increase in British road length. Options Provision of road space does not, We must make better use of our entire 1981 1991 % increase therefore, match our neighbours and 81 - 91 existing infrastructure. Road space the increase is but a small proportion All roads should be effectively managed: of the increase in demand. Growing (1000km) 342 360 5.3 London 's Red Routes. for which pressures are put on urban main Motorwajs Arups carried out the pilot study, are 14.8 roads: the laudable provision of traffic (1000km 2.7 3.1 an example of urban road optimiza· Road traffic lion where parking is limited, through calming schemes to prevent rat­ (billion vehicle km) 2n 412 48.7 running through sensitive areas tends traffic including buses has priority, to put more traffic on already con­ and effective management systems gested major roads. for largely by annual payments, but The effect of British Rail privatization operate. Another approach is prioriti· public transport is paid for fully at is at present unknown. If any guid· zation of certain types of road users: The length of rail lines in the UK has time of use. This leads to an incentive ance can be obtained from bus priva­ commercial and public transport halved since the War. No new main to use cars but a constant deterrent to tization, the trend is that more ser­ vehicles would have priority through line has been built this century, public transport use. vices operate and costs are reduced measures such as segregated lanes although there has been some new In order to obtain a real choice of - largely because bus fleets are or pricing mechanisms. An example rail construction in urban areas, ageing and have not been renewed is our work on bus priorities in mainly London. Tramways reached travel mode, the balance of spending should be reviewed as choice is - but the net result has been a Edinburgh (see facing page). their peak in the 1920s and then vir· decline of approximately 25% in tually disappeared. Recently, new currently getting less. The road lobby It is essential that a major effort is claims, rightly, that the income from patronage since privatization in 1986. made to change modal split, which light rail systems have been opened The current imbalance between road in Manchester and Sheffield which, road-based transport is up to four can only be done by making public times the expenditure on road con­ and rail is therefore likely to increase transport relatively more attractive in whilst providing a good local service, if current policies are pursued. have had little overall impact. struction and maintenance. The convenience and cost terms. It is counter argument is that if full costs The desire to reduce car travel is at inevitable that car use will be limited Detuncl versus supply including environmental effects are the forefront of the planning debate. by increasing fuel cost and taxes and Balance between supply and demand taken into account, the balance is in Guidance from the Department of the tolling in appropriate areas. Urban is at the centre of the current debate. fact reversed. Rail fares are increas­ Environment is focusing development parking controls will be increasingly Demand growth far outstrips the pos­ ing. Commuting fares into London are on town centres where it is claiming introduced, by limiting provision or by sible increase in supply of road· the highest in Europe and are three to that public transport will reduce car higher charges. It is mainly by based transport infrastructure, which four times the equivalent fares in other use. Out-of-town shopping and increasing the cost of car use that clearly cannot be increased signifi· major European cities. Britain's rail business park developments have growth will be contained. It will also cantly in terms of new provision. Even system receives less Government become very popular in recent years. be necessary to invest in public trans­ the Department of Transport accepts subsidy than any other in Europe. These are extremely attractive to car port to provide a real alternative. that there is no way that environmen­ tally acceptable schemes can match 7. British Rail investment 1948-1992. demand. 2000 .---- c As supply cannot meet demand , the G> demand must be limited to the supply E E in order to avoid costly congestion. f 0 How can an optimum balance be C) achieved between the demand for l! iij and provision of travel, with accept· 1500 'ii, able consequent environmental con­ Q) j ditions? Achieving this balance is .!,!a. made more difficult by the totally g; different appraisal and pricing tech· 0 niques used for road and rail. The -m former is done on an economic basis ~ 1000 with the benefits being primarily user iii ~ time savings and accident savings. ~ c Rail , on the other hand, is assessed Q) E on a financial basis in terms of cash .; Q) received from fares and the need to > provide a return on investment. Even E the thinking is biased. Road expen­ 500 diture is often described as an invest· ment, whilst rail funding is called a subsidy. It is essential that a coherent appraisal method be developed for UK trans­ port systems in order to achieve balanced solutions. Road use is paid 4 THE ARUP JOURNAL 2/1994 One idea is that increased road charges can be used to improve public trans­ port. Transport planning should cover Edinburgh Western Corridor all modes, not just roads . The work Arups are doing on multi-modal plan­ Busway Study ning in West Glamorgan and Southampton, and public transport alternatives to motorway construction. Gavin Dunnett Gordon Henderson are forerunners of this approach. Background the integrity of the unique commercial in 1985, although bus remains an Walking and cycling should be In common with many UK cities, travel and cultural life of Scotland's capital. important part of city centre travel. In encouraged by provision of segre­ patterns in Edinburgh are gradually Edinburgh's population has been contrast. car ownership in Lothian gated, environmentally acceptable changing in response to population slowly declining over the past decade grew from 220 to 317 cars per 1000 routes , but these will have a limited and land-use pressures. With around with a corresponding rise in surround­ head of population between 1981 and impact on car use, particularly in view 425 OOO population it is not large, but ing areas (although significant num­ 1990. the fourth highest rate in the of the growing safety and social prob­ it remains a vibrant commercial , legal, bers still live in the city centre). Similar UK. In the same period, traffic flows in lems associated with these modes. and financial centre, as well as an decentralizing pressures have been the study corridor increased by 40%. The way that an acceptable balance internationally renowned cultural experienced through businesses and In past years, Lothian Regional between transport modes can be focus. Having successfully resisted shopping moving to the fringes . Council (LAC) have tried to enhance achieved is at the forefront of political some of the more excessive road­ Although notable successes have public transport's attractiveness, both debate. It is interesting that there is building plans of the '60s and '70s, been achieved in revitalizing for those with and without cars. In little difference between the main when the city enhanced its reputation Edinburgh's local and suburban rail 1989 they decided on a metro system political parties and that they both for cultural conservatism, the chal­ services. these only account for some - street-running trams on two main wish to involve a maximum amount of lenge for today's transport planners is 4% of the morning peak of journeys to alignments. north-south and east-west private sector investment, but this can to find solutions to the ever-increasing the city centre. The use of buses has - but it was later recognized that only be made against a logical back­ problems of congestion which respect declined by 12% since deregulation funds were likely to preclude its ground of risk definition. It is not implementation for many years. reasonable for the private sector to bear the planning and political risk of City of Edinburgh District Council new transport infrastructure. but quite (CEOC) subsequently commissioned reasonable for them to bear the con­ a preliminary study into the potential struction and operating cost risks . for a low-cost busway using existing The current Government has not roads: an interim solution on a much clearly defined these rules and this is shorter timescale than a metro, but hampering private sector involvement offering significant improvements over in the transport field . Rail investment existing bus services. LAC in turn has been intermittent. Fig.7 shows the resolved to commission a more historical trend in real terms. It can be detailed operational, financial , and seen that there is no clear pattern engineering feasibility study into a related to the political party in power busway in the city's western corridor. and we are still below the investment In September 1992 Arups were levels of the 1960s. The apparent appointed to carry this out by a client optimism of the recent increases in consortium comprising both Councils funding has been dampened by the plus Lothian and Edinburgh Enterprise Government's latest proposals to re­ Ltd. and the British Airports Authority. duce investment in the next few years. The objectives were to provide: Governments have never displayed • a connection to Edinburgh Airport a long-term commitment to public • links to and from the South Gyle transport. None has prepared national development area forecasts for public transport use • an express connection between although all have published road the city centre and the western traffic forecasts. suburbs What are the conclusions? We will • 'Park & Ride '. inevitably see less building of major The study was to include an assess­ new infrastructure to provide for ment of the potential role of the demand. There should be positive 1. Edinburgh. private sector in financing and demand management. There will be operating a system. increasing emphasis on public trans­ port. Ways to manage the existing Bus-based Light Rapid Transit network efficiently will be developed The concept of Light Rapid Transit including on- and off-vehicle road (LAT) is generally associated in the information systems. There is a need UK with the reintroduction of street­ for better integration of public trans­ running trams, as in Manchester and port services to improve flexibility, Sheffield. Buses have a poor image although privatization could well and are seen as a last resort, subject hamper this aim. There will be to the same delays as other traffic, increasing emphasis on control even when priority measures are systems to manage movements of introduced. There are, however, many vehicles and limit and control parking . examples around the world of buses We are going to pay more for our as a form of LAT; indeed a successful travel, but the main conclusion is that segregated busway network has we should demand an overall trans­ been operating in Runcorn New Town port strategy for the country which for over 20 years. The use of segre­ achieves an appropriate balance gated rights of way for conventional between all modes and will help us to buses is the key component of achieve the sustainable goals that systems in France (parts of the Paris have been set. orbital tramway), Belgium (Liege), Netherlands (Arnhem). Germany Illustrations: (Essen and Mannheim), Turkey 1: M40 Motorway alongside Paddington­ Birminghamrailway (photo Keith Law). (Istanbul and Ankara). Brazil (Sao 2-7: Peter Speleers. Paulo), and Australia (Adelaide) Malcolm Simpson is a Director of Ove Those in Adelaide and Essen use a Arup & Partners Transportation and kerb-guidance system, giving some Environmental Groups. 2. Guided busway in Essen. of the advantages of rail-based LAT. THE ARUP JOURNAL 2/1 994 5 3. Guidance system. Road wheel Right-of-way of bus The basic route runs from a Park & I Ride site near the Airport, through SouthGyle, and along the existing Glasgow railway corridor into the city centre, where it uses existing roads before terminating close to St. Andrew Square at the centre's east end. The arm route can be largely segregated from existing roads and traffic - an important factor when competing with on-street services running on existing radial routes. For the same reason, it was decided to design the alignment to the highest practical speed (85kph) 2.9 0.4 2.9 that avoided unreasonable cost or Guide wheel environmental penalties. 4. Cross-section of guideway. The choice of system was not obvious at the outset. However, on several The bus is steered via a small guide sections of the route the alignment from surrounding areas. Differentiation Vehicle characteristics wheel attached directly to its steering passed close to existing property by price is also possible. To evaluate The buses themselves are an impor - axle, which bears on a concrete where land-take would be an issue, and comply with the study brief, three tant factor and in this, as in other upstand similar to a conventional so three differentcross-sections were sets of services were postulated, aspects of the system definition, the kerb. In the guideway the vehicle examined and costed: conventional although in practice many variants notional 'ownership' is fundamental. requires no directional intervention are possible: 7.3m single carriageway, reduced Clearly, with a public or semi-public from the driver, so the required right­ 6.75m carriageway, and 6.2m guide­ system the promoter and/or operator of-way is reduced and level boarding way. The latter was based on a pro­ • Park & Ride: express five-minute of the busway will have littlecontrol at stops is possible. Also, noise levels prietary German precast concrete service (10 minutes off-peak). over the type of vehicles using the can be reduced if grass is planted system and was more expensive, but Everysecond bus would also system. between the guides; reflection from the increased costs were offset by serve the Airport. the road surface is a significant con­ savings on structures, earthworks, For a private system, where it is pos­ tributor to conventional bus noise. and land. sible to specify vehicles, choice will Away from the guideway, the vehicle • Wester Hailes suburban service: be governed by two things: image can operate as a standard bus; this To maintain maximum segregation it limited-stop, five-minute service and function. A distinctive image is flexibility distinguishes guided bus was decided to restrict access to (10 minute off-peak); on-street important for a private service and the from conventional rail. A short section trunk sections of the route to one feeder service joining the trunk novelty value associated with guided of guideway will be introduced in intermediate point, where localser­ section of the Busway midway. operation or articulated 'bendy' buses Leeds as partof a package of bus vices serving the western suburbs of would be a consideration in vehicle priority measures in 1995. Edinburgh could join the trunk • SouthGyle circular service: choice. It would also be desirable to busway via grade-separated limited-stop, 10-minute service(in replace the fleet at reasonable inter­ System specification sliproads. Public transportsystems are defined each direction); on-street feeder vals; five years was assumed for the by elements specificto their own Operatingcharacteristics serviceserving existing and future purposes of evaluation. objectives and locations, so the One of the advantages of a bus­ development. The strictly functional requirements of Edinburgh Western Corridor Busway based system is the ability to differen­ the assumed service patterns would would always be unique to its own tiate servicesfor particular market Both existing regional bus services require a maximum unit capacity of environment. However, it is also segments by running a mixture on the and seasonal tours and excursions 50, so a standard luxury coach could potentially the only system of its kind same infrastructure without the inter­ would also be likely to use the suffice without crush loading. On local in the UK, and in order to evaluate its change penalty common with rail­ busway. In addition, Murrayfield services, where some peak period viability, a specification was evolved based systems. Thus, express trunk Stadium is on the proposed line - crush loading might be more accept­ which both met localobjectives and services can co-exist with localstop­ another potential source of additional able, smaller vehicles could reduce was consistent within itself: ping services feeding into the system revenue. capital and operating costs.

Transport Proposal

Development Proposal 2nd FORTH BRIDGE Dl INGUSTON D7 MURRAYFIELD BARNTON BYPASS D2 GOGARBURN D8 BREWERY RUNWAYEXTENSION D3 HERMISTON D9 HAYMARKET AIRPORT LINK/STATION D4 EDINBURGH PARK/ D10 MORRISON ST MB GYLE D 11 CONFERENCE & A71 D5 SCA FINANCIAL CENTRE SIGHTHILL STATION D6 TYNECASTLE PORT HAMILTON GREENWAYS

5. Transport and development proposals.

6 THE ARUP JOURNAL 2/1994 Alternative sources of motive power under the New Roads and Street­ and arrangement costs would be paid Because there would be no support­ were considered unlikely because of works Act 1991 . The timescale to for by a 25-year leasing arrangement. ing local authority guarantee to cover the additional costs of vehicles and of promote such a scheme would be no Similarly the vehicle fleet would be any shortfall in the payments, BOOC overhead wires and supports for use different from that for any major road purchased using a five-year leasing would have to be given grant monies by electric trolleybuses or duo-buses. proposal. Any scheme promoted arrangement with renewal at each - c.£6M - to cover the security Forecasting under existing legislation would in change of fleet date. These leases needed to reduce or support the The basic demand forecasts for the theory be open to any bus operator. would be taken out by BOTLACO, lease payments, or both. The higher busway came from LRC's strategic An alternative would be to seek backed by a guarantee from the local the grant element the lower, up to a transport planning models. However parliamentary powers by the promo­ authority owners to cover any shortfall point, would be the annual lease cost. an important objective of the system tion of a Provisional Order under the in monies available to meet the lease payments. BOTLACO would appoint Comparison is to attract existing car drivers to Private Legislation Procedure (Scot­ One way of comparing the four transfer to Park & Ride - not covered land) Act 1936. This is effectively a an operator under a contract for a monthly usage charge, plus an options is to present a net present adequately by these models - so the shortened private bill procedure and value of the financial surplus indicated data was processed on Arups' can in some instances become a con­ annual percentage of net profit over a given amount. This option involves in the funding case for each option. EMME/2 transport planning program. ventional private bill. A local authority These are remarkably similar, with Some 4000 questionnaires were also could not promote a Provisional Order total transparency of public sector ownership - perhaps a problem Option 4 (pure private sector) margin­ distributed to drivers on the AB and for a conventional busway since other ally best at £7.44M and Option 1 A71 radial routes, to gain information p~wers are available. However, they under Treasury rules - although the publicly-owned but privately-operated (pure public sector) a close second on journey origins, purpose, and might be able to promote a guided with £7.22M. Options 2 and 3 pro­ degree of 'captivity' to car. In addi­ busway in this manner. A private enterprise companies in Scotland may provide the necessary precedent. duced values of £6.96M and £6.89M tion, detailed market research was company could use the procedure in respectively. undertaken to measure drivers' re­ either case. Option 3: sponses to the new travel opportunity. The fundamental problem in obtaining Private sector corporate ownership Conclusion 25 000-30 OOO passengers per day Parliamentary powers containing any for a 25-year concession The study findings indicate that, as a are predicted to use the system. form of exclusivity to a particular bus In this, a Build Own Transfer transport infrastructure investment, operator is the provisions of the Concessionaire Company (BOTCO) the Edinburgh Western Corridor The busway's basic attraction is its would be formed with a nominal Busway shows great potential both as relatively high benefit-to-cost ratio Transport Act 1985, which makes it illegal to inhibit competition in any private sector shareholding. The local a joint public/private sector project compared with a rail-based solution, authorities would grant BOTCO a 25- and as a conventional public sector attracting a high proportion of avail­ way between operators seeking to promote services. year concession, who would enter a project. Its eventual form as a trans­ able benefits at an order of magnitude joint venture arrangement with an port system will depend on which of lower cost. Social cost-benefit analy­ Funding operator. This would stipulate a these two broad paths is followed in sis, where time and accident savings Four financing options were con­ minimum operator fee of, say, 1o/o net its promotion. The success of the are given a notional monetary value, sidered, ranging from fu ll public sector revenue, but thereafter lease pay­ Busway will, however, depend on its shows that the project has a substan­ ownership to the maximum level of ments would have first call on net promotion as an LRT system, distinct tial return in conventional public private sector ownership: revenue. BOTCO would pay 50% of from on-street services in terms of sector project terms. A £30M surplus Option 1: the net revenues it received to the journey time and image. of benefits over costs (net present Public sector local authorities as a fee for lease value) is predicted for the project. The project has engendered con­ ownership and operation short term guarantee. If this were siderable interest in the two local Project Implementation Based on predicted operating costs called in, BOTCO would pay up to authorities despite impending re­ Legislative context and revenues, it is likely that a typical 100% of the net revenue it received to organization. Further work is currently The roads authority could obtain public sector loan for the full out-turn the local authorities until the shortfall being carried out to identity a pre­ powers to construct the busway using cost could be repaid with interest at payment made by them had been ferred alignment for formal adoption existing legislation. Following in­ 6% p.a. (real). In testing an option repaid. by LRC and CEDC. Also, because of clusion of the project in the Regional based on local authority borrowing, it Option 4: the project's relationship to the Structure Plan review, the route would was assumed that the required Private sector corporate ownership 'Setting Forth' proposals and its be promoted as a Special Road by powers would be available. The in perpetuity potential to attract private finance, the application to the Secretary of State financing regime tested was based Here a Build Own Operating Scottish Office have jointly with LRC for definition of an appropriate Use on a 25-year 50% European Company (BOOC) would be formed commissioned Arups to investigate Class. The option would then remain Investment Bank loan and a 20-year with private sector shareholders and the potential to eX1end the Busway open for the promotion of a Toil Order 50% local authority bank loan. equity funds sufficient to meet land across the Forth estuary as part of the Option 2: costs and working capital needs - overall Setting Forth package. Public sector corporate ownership say £3M. Construction and arrange­ There is little doubt that if we are to 6. Service patterns. under a 25-year concession ment costs {less the £3M equity pay­ In this option a Build Own Transfer avoid the creeping paralysis of con­ ment) would be paid for using a 25- gestion and pollution in our cities, our Possible Local Authority Concessionaire year leasing arrangement. Similarly Airport future attitude to and investment in public Company (BOTLACO) would be the vehicle fleet would be purchased extension 10 transport must move more in line with Forth Bridge formed with a nominal shareholding using a five-year lease with renewal at our European competitors. The Edin­ owned by, and with management each change of fleet date. The land . supplied by, the local authorities, who burgh Western Corridor Busway • would be purchased by BOOC. would be unique in the UK. At a time would grant BOTLACO a 25-year con­ cession. Construction , land purchase, when central funds are limited, we must also seek imaginative funding and solutions to achieve these overall West St Andrew End Square aims and ensure that the quality of life provided by cities such as Edinburgh can be retained in the future. Edinburgh Park Lothian Road Credits Client: Lothian Regional Council S,ghthlll Stenhouse Murrayfield Conference Centre City of Edinburgh District Council Broomhouse 9 Lothian and Edinburgh Enterprise Ltd. (Interchange) British Airports Authority Lead consultant: Arup Transportation Gordon Henderson Gavin Dumett. Paul Roberts, David AndefSO,:,, Trunk section (segregated) Mdre,, Marsay. Joe Mclaughlin. Alasdair Macleod. Stephen Harrison. lain Bell ~ alder Road Dlllcan Birrell, Ian Stenhouse. Euan Atkinson ' Express Park & Ride Airport Specialist consultants: Murrayburn Accent Marketing & Research 9 L1m11ed stop South Gyle (directional) Finance for Enterprise Alan Howes Associates Limited stop Wester Hailes Illustrations: C) Wester Hades 1, 2: Gavin Dunnett. 3-6: Jon Carver. TI1E ARUP ~ 2/199-1 7 1.

Introduction The T-beam was chosen over a variety of TRACK program. The envelope of the swept A bridge on which aircraft can taxi sounds shapes as it provided the most economical paths, plus a margin of 4.5m, forms the interesting. As part of improvement works to structural section, the flange acting as form­ central region where both serviceability and Hong Kong's Kai Tak Airport, one has been work for the in situ topping. The T-beams ultimate limit states were considered. Other built across the Kai Tak nullah to link the were designed to span simply supported special loadings include emergency and existing taxiway with the new parking apron in under self-weight and topping slab loading, maintenance vehicles at 10kN/m2, and im­ Kowloon Bay. and as a continuous structure under aircraft pact on the bridge structure from a vessel of In January 1992 the Airport Division of the live loadings. The continuous deck structure 350 tonnes displacement travelling at 4 knots. Hong Kong Civil Engineering Department eased the problem of lack of structural depth Deck drainage invited tenders from contractors to design at the navigation span, and made it possible The deck drainage system was designed to and construct the bridge, including its light­ for lateral loads (seismic, ship impact, aircraft cater for 1 in 200-year storms. A W-shaped ing, utilities, and associated pavement works braking) to be shared by all the piers. deck crossfall was chosen above the naviga­ (which included repaving a section of taxiway Alignment and deck profile tion channel to save about 110mm structural along the Kai Tak runway), in a 15-month con­ The vertical alignment had to tie in with exist­ depth compared with a conventional inverted tract period. Dragages et Travaux Publics ing levels (about Sm Principal Datum) and V-shape crossfall. The W-crossfall gradually were awarded the job for HK$109M (£9M) in gradients at both ends of the bridge, while transforms, with the maximum slope of 1.5%, May 1992. They co-ordinated the design; the navigation channel , up to 4.86mPD under into the inverted V-shape at both ends of the their sister company, VSL Hong Kong Ltd .. the bridge, had to be maintained. The align­ bridge to tie in with the drainage profile. All designed and supplied the precast deck ment design follows International Civil Avia­ gully gratings in the taxiway can withstand structure; and Ove Arup & Partners were tion Organisation (ICAO) rules, which require aircraft wheel load, and are suitable for use in appointed for all the remaining works in­ a taxiway slope not exceeding 1.5% , a mini­ airports. cluding the alignment, drainage, aircraft load mum vertical transition radius of 3000m, and Bearings and movement Joints geometries, substructure and foundations for an unobstructed 300m view of the taxiway Purpose-made 600mm square elastomeric the bridge, utilities and lighting, and the air­ from any point 3m above it. The final align­ bearings between 250mm and 300mm thick field pavements. Taxiway Bridge 3 was the ment adopted suits all requirements, and a were used under the intermediate supports, first major bridge in Hong Kong tendered on transition strip 112m long in the existing taxi­ and sliding elastomeric laminated bearings a design and build basis. Part of it is located way ties in the levels and gradients at the end with PTFE and stainless steel surfaces within the Airport Restricted Area and certain of the bridge. catered for the high movements at end sup­ work, including some foundations, could only Deck loadings ports. At the free ends of the deck structure, be carried out at night, after the airport closed. The major special loading was the full taxiing movements of up to 190mm due to shrinkage, Span anangement and weight and braking load of a 400 tonne creep, and thermal effects were predicted. To deck structure Boeing 747-400F. Boeing provided informa­ cope with these, and the 747-400F's ex­ With a total length of 225m over seven spans, tion on wheel positions and loadings, but the tremely high wheel loads (up to 31 350kg), it is one of the longest such bridges in the orientat!ons of the aircraft to give critical load 40mm thick finger plates weighing in excess world, its 44m taxiway about as wide as 12 combina•ions were predicted by the swept of 500kg/m bridge the gaps between the highway trattic lanes. The deck, supported by path of che landing gear generated by the ends of the superstructure and abutments. 22 precast prestressed concrete T-beams per typical span, is only 1.6m deep overall, in­ 2. Section through deck. cluding a 2.20mm thick in situ concrete top­ ping, but has to carry the current heaviest Centreline Centreline passenger aircraft, the 400 tonne Boeing of pier of pier 747-400F. The need for a 20m navigation channel for emergency and maintenance vessels, and to match existing levels at both 36m (for typical span) 36m (for typical span) ends of the bridge, meant reducing the struc­ tural depth to 1. 125m depth for the navigation span, but apart from this, there were no 46.2m total width Continuity Diaphragm reinforcement i" particular contractual constraints on span for hve load 'f lengths and pier positions. Ground conditions implied relatively long piles, favouring longer spans, but lack of land access made it prefer­ able to maximize precasting within the limits of maximum weight and length of precast members. The optimum span length was found to be about 36m, and an arrangement of 29.6+36+36+21 .5+36+36+29.6m was finally adopted. 8 THE ARUP JOURNAL 2/1994 Marine piers and abutments Both the crossheads and abutments were The piers are reinforced concrete crossheads shaped to fall in the same profile as the deck Constn,ction on driven tubular steel piles with concrete surface, thus allowing a more uniform thick­ infill. A relatively large diameter of 1.2m was ness for the deck structure. As 'design and build' has the advantage of a shorter chosen to avoid raking the piles, lateral forces implementation programme it is interesting to look at Pavement being taken by their bending resistance. the actual progress achieved: The airfield pavements are classified into The reinforced concrete abutments are sup­ stressed and non-stressed types and are Start of construction: 18 May 1992 ported on minipiles and H-piles. Piling on the either rigid or flexible. The non-stressed pave­ runway side was only possible after closure ment is located beyond the edge of taxiway Design of main structure: 3 months of the airport at midnight, and by 6am the where the chance of supporting aircraft load First pile driven: July 1992 runway had to be ready for use again. All is low. Pavements were all designed to US Total duration of piling: 4.5 months construction, including mobilization and de­ Federal Aviation Administration standards. mobilization of all plant and equipment, and The structural concrete topping of the deck Installation of 44 minipiles: 3.5 months cleaning and inspection of the runway prior to forms the running surface for the bridge Precasting of 154 beams with seven moulds: 5 months operation, had to be packed into six night taxiway. On both ends of the bridge, the First beam placed: December 1992 hours. Percussive and bored piling were both pavement is mainly rigid: 350mm thick rec­ unsuitable for various reasons, but minipiles tangular concrete pavement panels on top of First pour of 1n situ deck concrete: February 1992 were ideal, needing only small, easily mov­ a 150mm thick concrete subbase above soil, Duration of in sttu concreting : 3.5 months able drilling rigs. For the abutment on the the latter either compacted so that a 100 E&M works and other installations: 3 months. parking apron side there were no particular tonne proof roller could pass over without any constraints except the proximity of the sea­ noticeable depression, or prepared as a thick Handover to client: 15 August 1993. wall and its rubble mound foundation. Vertical layer of graded rock and granular materials. and raked steel H-piles were adopted. Along the existing taxiway, a strip of flexible pavement was repaved and extended to suit Conclusion the new geometry and levels. It is remarkable for a new bridge of this kind 3. Utilities, lightings, signs serving an airport to be replaced by another Bridge and markings in a few years' time. Kai Tak Airport will be plan. These followed ICAO rules and are consistent superseded by Chek Lap Kok by 1997, when with the present systems at Kai Tak Airport. China resumes sovereignty of the Territory. Covers of drawpits and lightings in the taxi­ Meanwhile, this bridge is a very successful way are all capable of withstanding aircraft application of 'design and build': despite the wheel loads. Installations above ground, such short construction time and severe restric­ 55m as signs and fire hydrants, are away from the tions of working at an operating airport, it taxiway, and are sufficiently low to prevent opened on time and within budget - a .... c c damage to the outboard engines of aircrafts . fine example of co-operation between client, authorities, consultant, contractor, and designers. 4. Aircraft taxiing onto bridge. Reference (1) FUNG. H.K.C., FOK, W.H., and YOUNG. B. Design of the Kai Tak Taxiway Bridge No. 3. Hong Kong Engineer, pp.39-44, October 1993. Credits Client: Hong Kong Civil Engineering Department Contractor: Dragages et Travaux Publics Contractor's designer: Ove Arup & Partners Mike Kaye, Roger Alley. Alan Kam, Fergal Whyte, Brian L1nlechild, Wing-Huen Fok. Ke, Fung , Michael Ho, Kelvin Tang, WeslWOOd Hong Deck design & build sub-contractor: VSL Hong Kong Ltd. Illustrations: 2. 3: Ove Arup & Partners Photos: 1: Colin Wade. 4: W-H . Fok

Wing-Huen Fok is a civil engineer and Associate of Ove Arup & Partners Hong Kong Ltd. TIIE ARUP JOURNAL 2/199' 9 Richelieu Wing, Louvre Museum, Paris

l I Alistair Lenczner Andrew McDowell Andrew Sedgwick

Introduction The Decorative Arts Department is on the first Courtyard glass roofs In November 1983 President Mitterrand set in floor of the new wing, with the Paintings Structural scheme motion a major redevelopment of the Louvre Department at the top of the building on the The design of the glazed roofs to cover the Museum and the adjacent Tuileries Gardens. second floor. Here, over 40 new painting three interior courtyards (now called Marly, 10 years later, almost to the day, he returned galleries are dedicated to the works of the Puget and Khorsabad) of the Richelieu Wing to open the newly-restored Richelieu Wing, Northern Schools, such as Van Eyck, Rem­ was a critical part of the architect's overall adding 22 000m2 and 178 rooms to one of the brandt and Vermeer. A further 19 rooms show plan for the Louvre remodelling. largest museums in the world. the early. 14th-17th century, part of the French The three courtyards all have irregular taper­ Until this time the Museum was contained paintings collection. A further set of basement ing plan geometries, with the internal north­ within the south and east wings of the Palais galleries display for the first time the south width reducing from over 41 m at the du Louvre, now named the Denon and Sully Museum's extensive collection of Islamic art, western end of Marly to under 28m at the Wings. Since 1989 public access has been and connect the new wing to the public eastern side of Khorsabad. In designing the through I. M. Pei's glass pyramid in the centre entrance hall beneath the pyramid. structures to cover them, careful studies of of the Cour Napoleon. The Richelieu Wing different structural plan setting-out options (L'aile Richelieu), to the north between the were made to find one which best resolved Cour Napoleon and the Rue de Rivoli, was the irregularities without drawing undue atten­ built in the mid-19th century as government tion to them, and which allowed the number offices. In the late 1980s the Ministry of of different glazing sizes to be rationalized. Finance vacated it for new offices in Berey, The general shape of each new roof is that of and redevelopment began. a shallow vault with hipped ends of similar The eight cramped office floors have been curvature, the roof heights being limited to removed and replaced with three floors of preserve the Louvre's existing roofline sil­ new museum space. Sculpture and Oriental houette. The roof structures are propped off Antiquities are at ground floor, which includes the cornices topping the existing courtyard three internal courtyards transformed from car faQades by a series of short vertical posts. parks for civil servants into covered sculpture This allows openable smoke outlets to be courts. The design of the new glazed roof incorporated into the space provided be­ structure over these was inspired by Peter neath the eaves of the new roof, and also Rice, who worked closely with I. M. Pei to gives the impression that the new structures create dramatic spaces. Two teams from Ove hover over the courtyards. Arup & Partners, both under Peter Rice's 2. leadership, were commissioned by the Etab­ Site location. lissement Public du Grand Louvre (EPGL) to design these roofs and to develop a scheme for the natural lighting of the Paintings Department.

3. Elevation of fan-braced arch of Marly roof. 10 TIIE AIIUP JOURNAL 2/1994 . 1. Long section through the Richelieu Wing, showing from left to right the Khorsabad, Puget and Marly courtyards.

l l JI 4.~ Interior view of roof over Cour Puget. In the foreground is a marble statue (c.1830) of Spartacus by Denis Foyatier (1793-1863).

The two larger courtyards, Marly and Puget, in-plane shear stiffness by series of diagonal structure was loaded. The same software was have similar types of roof structure to each criss-crossing ties which intersect with the also used to demonstrate the overall buckling other, incorporating fan-braced tubular steel tubular junctions. These tie members allow behaviour of the arch, which would otherwise arches spanning across their width. The gravity forces to be redistributed between have proved difficult to justify. smaller Khorsabad has a simpler tied-arch arches and help support the corners of the Separate computer models were analyzed structure, though with a similar external roof by shell-type action. The diagonal tie firstly to study the two-dimensional behaviour shape. The dimensions of the structural ele­ bracing is also important in providing overall of the fan-braced arch and later the overall ments were an important consideration in the sway stability for the roof under horizontal three-dimensional performance of the com­ roof design, not only to reduce visual 'weight' wind loads or asymmetric snow loads. The plete roof. Wind pressures on the roof were but also to avoid casting deep shadows at roof structures are stabilized horizontally based on wind tunnel tests carried out by the floor level within the sculpture courts. Each of parallel to each side of the respective court­ CSTB at Nantes, and snow loadings allowed Marly and Puget's main arch members has a yards by vertical bracing between the props for the possibility of deep drifting at the edges tubular section 0 139.?mm, whilst the purlins midway along each side. This arrangement against adjacent roofs. spanning between them have a 0 114.3mm allows the whole structure to expand or con­ tubular section. The hip members forming the tract symmetrically under thermal loads. In The justification method used fell outside corners of each roof are a thicker 0 168.3mm. the unlikely event of a net vertical uplift load­ those outlined in the normal French codes The butterfly-fan bracing in the arches of case under very extreme wind conditions, used for justifying steel structures. Special Marly and Puget was devised to reduce the vertical loads are transmitted through the technical meetings with the checking buckling length of the main arch members. structure by the combined action of the grid authority, Veritas, therefore took place to thus allowing their section size to be mini­ shell with the hip members and spine-truss, explain in detail the approach used for struc­ mized. The cables forming this fan bracing forming a shallow quadrapod working in tural justification and answer any queries they pass through a special node clamp detail tension. had. Once convinced of the correctness of beneath the arch crown. The roof structure Structural Justification the Arup method they were able to give their supports gravity loads by a combined action The non-linear structural behaviour of the approval. of systems. A three-dimensional spine truss arches restrained by the fan cables required Glazing running under the top ridge of the roof is a special analytical method to demonstrate its The glass skin consists of double-glazed supported by the fan-braced arches which performance under load. Computer software units over the grid of tubular steelwork which traverse it across the width of the courtyards. specially developed by Arups to analyze non­ defines the enclosure geometry. The framing Additional support is provided by the action linear behaviour took into account the pos­ system for the glazing was designed specifi­ of the fan-braced arches linking to the ends sibility of certain ties going slack as the cally for the project. with special aluminium of the spine truss. Alternating with the fan­ braced arches on each side of the ridge are chord-tied arches spanning between the spine truss and the outside edge of the roof. • 5. Central clamp node detail to fan-braced arch in Cour Puget. The curved grid surfaces formed by the inter­ T 6. Roof of Cour Puget with Khorsabad roof in the background. secting tubular arches and purlins are given . 7. Daylight effect on wall of Cour Marly. 8. Close-up of skylight louvre sunscreen just visible against the roof glazing . ....

9 . .... Typical square gallery: structural crossbeam supports light-directing plaster blades. 10. Cour Puget. .... Design for natural lighting Criteria One of the primary reasons for putting paint­ ings on the top floor was to take advantage of natural overhead lighting through remodelling the roof of the building. I. M. Pei and Arups developed a number of criteria for the design of the skylight system. These, summarized below, attempt to balance conservation con­ straints against viewing conditions, and also address items like cost and maintenance: • Annual illumination exposure of no more than 850 kilolux-hours • Filter out harmful ultraviolet light • Uniformity of light levels over the picture-hanging area of the wall: 2 to 1, maximum to minimum • Predominant angles of illumination between 25-40" to the vertical • Floor illuminance less than twice average wall illuminance • Maintain contact with the external environment • Simple maintenance, i. e. no mechanical parts • Save artificial lighting energy and electricity costs. Some conservation experts recommend an annual illumination exposure level for oil paintings of 650 klux-hours - corresponding extrusions being made and cast aluminium On the inside of the glazing, framed sets of to an average illumination level of 200 lux. pieces used for the framing intersections. An 'paralumes' are set within the open panels in However, several scientists have shown that important part of the framing system design the plane of the steelwork. These hollow 200 lux is too low a light level for many, parti­ was to ensure that any possible moisture due aluminium tubes, 32mm in diameter at 53mm cularly older, people to perceive detail and to condensation or accidental leakage in the centres, serve to filter the daylight entering discriminate between colours accurately. seals should drain away within the system the courtyards, and provide some diffusion of Optimum viewing levels, i.e. 1000-1200 lux, without dripping onto the floor below. Full­ the light reaching the pieces of sculpture. The were obviously not feasible for conservation scale mock-ups of the glazing system were paralumes incorporate a form core which reasons. so a compromise of 850 klux-hours assembled to test for construction tolerances helps improve the acoustics within the court­ (representing an average of average 250 lux) and watertightness. yards by reducing sound reflections. was proposed.

12 ntE ARUP JOURNAL 2/1994 Daylight availability and variation (2) Sun screen: a matt white eggcrate louvre blades also ensure that light arriving on the Before any roof light designs could be con­ made of aluminium blades installed directly paintings is incident from the optimum sidered, the Paris daylight had to be studied, beneath the glass. Direct sunlight must not direction (25-40. to the vertical). and in particular its variability during the day land on the paintings at any time, so the throughout the year and in different weather dimensions and depth of the screen were Only inter-reflected light arrives from angles greater than conditions. Due to lack of reliable information, calculated for the exact location, orientation, 40·. external illuminance data for Kew, London, and gradient of each rooflight. The blades are supported by structural ele­ was adjusted for Paris by analyzing the This form of screen is an ideal passive device ments designed to cross the roof at regular radiation data and sunshine data available in for removing some of the variability of natural intervals. Architecturally, the system of plas­ Paris and London. It was found that the differ­ light by transmitting more from the sky's terwork and beams provides a very dramatic ence between maximum and minimum exter­ zenith, and less of the highly variable com­ ceiling to the high gallery spaces, as well as nal light levels is around 9:1 during summer, ponent from the sun . concealing banks of fluorescent tubes to and more in spring and autumn. If both sun­ supplement the daylight when necessary by light and sky light are allowed to enter the Arups had initially advocated the use of two illuminating the white sun screen from below. galleries then variations in internal light levels or three different interchangeable screens in of a similar order would occur, so the natural each gallery- 'seasonally adjusting' the per­ Contact with the outside lighting system must transmit significantly formance of the screen. This would have The three layers were designed and co-ordi­ less sunlight than diftuse sky light. Any direct allowed the galleries to be naturally lit alone nated to meet the requirements of the eight sunlight landing on the gallery surfaces would for more of the opening hours each year. design criteria described above. The most be visually very disturbing, so the system is However, it was decided that a single passive difficult to achieve was 'maintain contact with arranged to allow diffused sunlight only to device without mechanical parts or motors the external environment'. The architect was enter. was more suitable for a museum of the type concerned that in many museums with strictly controlled light levels one feels cooped up in Layered approach and size of the Grand Louvre, and the use of In order to meet these quite demanding further artificial lighting in winter months was an insulated box with no feeling of external criteria, three distinct layers in the roof of the accepted. light or weather conditions, or even that the space is illuminated by daylight. galleries were conceived: (3) Light-directing layer: white painted plaster (1) Glass roof lights: an area equal to about blades which 'direct' light from the rooflights Vertical windows are not suitable as a means 40% of the gallery floor, and incorporating a to the gallery walls. In any top-lit space. the of providing visual escape because they UV filtering laminate. A study was made of the horizontal plane (in this case the floor) will introduce significant glare and shading prob­ colour shift of light passing through normal tend to receive more illumination than the lems for galleries. Pei wanted a clear view double glazing with a UV filter. It was found vertical surfaces. The form of the plaster through the rooflights. with clouds, blue sky, that the iron content of normal float glass blades was developed to allow the wall to and changes in lighting conditions visible. No causes a slight colour shift towards green, receive light directly from the underside of the diffusing glass was thus allowed, and the sun but the additional cost of installing 'white', low sun screen. while ensuring that in most cases screens were designed so that persons look­ iron, clear glass could not be justified. the floor was obscured from the screen. The ing up could see the sky. continued IJ>,

11. The largest gallery, the Salle Rubens, on the second floor between Marty and Puget.

THE ARUP JOURNAL 2/1994 13 Louvre Mu-um continued The Rochdale Canal runs through the eastern part of the site, where the Chadderton Computer analysis Oldham Broadway Sewage Works are located. Two large opera­ using finite element techniques tional electricity switchyards are also present, A suite of programs was developed to ensure Business Park the 275kV National Grid Whitegate Substation that the performance of the lighting control and the 132kV Norweb Station where the system meets the agreed design criteria. A power is connected to the distribution net­ three-dimensional computer model of some Colin Curtis work. of the galleries was constructed. All the A number of aspects enhanced the re­ model's surfaces, including the 'cells' of the Nick Fennell development prospects. An undeveloped sun screen, were divided into a number of Roger Milburn area this size close to Oldham, adjacent to finite elements. Light rays were then cast from the planned M66 Manchester Outer Ring each to every other element and to the sky. motorway, in single ownership, and available Checks, of course, were made to ensure an Introduction not only for DLG and UP grants but also the The Broadway Business Park is a major urban element had an unobstructed view of the European Regional Development Fund, ob­ regeneration project some 9km north-east of other elements or of the sky. viously had great potential. In addition the Manchester near the periphery of Oldham In order to analyze the performance of the Rochdale Canal was there as a potential borough, located on 54ha of derelict land first layer - the sun screen - the luminance water feature. with over a century of varied industrial use of the sky had to be represented numerically. behind it. Oldham Metropolitan Borough Site history Using internationally agreed procedures, the Council bought the site with a view to eco­ The first part of Arups' work was a compre­ luminance of the sky vault at each angle of nomic redevelopment, to be funded in part by hensive desk study into the site history. The view was calculated, and elements on the cell Derelict Land Grant (DLG) and Urban Pro­ area had originally comprised farmland, with walls of the sun screen assigned illuminance gramme (UP) monies. In 1989, they appointed a deep valley (Slacks Valley) heading east to values depending on their view of the sky. Ove Arup & Partners and EGS Design as west across the northern part; the Rochdale The illuminance of each element on the masterplanners for the development. Canal, which opened in 1804, was built on an gallery walls and floor was eventually embankment over Slacks Valley. The Man­ The principal aim of the development is to obtained by calculating the light received chester and Rochdale Railway, opened in stimulate employment in Oldham by attract­ directly from the screen and from the plaster 1839, was also constructed on an embank­ ing new business to the borough and offering blades, and indirectly from the other room ment over Slacks Valley and the watercourse facilities to existing businesses to expand surfaces. running in this valley, Wince Brook, was cul­ and relocate locally. The first phase of new verted under both canal and railway. Full-scale mock-up infrastructure works began in October 1990 The most extravagant prediction method was and the final phase was completed in In the latter half of the 19th century a chemi­ to build a full-size mock-up of a typical December 1993. cal factory (vitriol works) and the Gibraltar square gallery in a temporary building in the Works (a soap and candle factory) were The site and Its opportunities Jardin des Tuileries, next to the Louvre. All operating in Slacks Valley - indeed, a signal The site is divided into distinct areas reflect­ aspects of the architecture were tested in box on the railway is named 'Vitriol Works'. ing its former uses. It is mainly flat except in this, from the plaster blades and the sun Tipping of domestic and industrial waste into the north-east, and is bounded to the west by screen to the colour of the walls and the floor Slacks Valley to bring it up to canal level com­ a railway, the north by Grimshaw Lane, and finish. This allowed the architect himself and menced in the 1930s and finished about south by the A662 Broadway. This road pro­ many of the Museum curators to have a pre­ 1975. This was subsequently called the Grim­ vides an important link between east Man­ view of the new galleries and to experiment shaw Lane Tip. chester and the M62 motorway. with the lighting. Oil paintings were brought In the 1920s, a small coal-fired power station from the Louvre to add to the realism! 1. Site history. was constructed in the southern part of the Conclusion site for Oldham Corporation, plus auxiliary The new Richelieu Wing is now open to the facilities such as railway lines, coal stock public, and there has generally been a very ~ areas, and wooden cooling towers. By the positive response from the art and archi­ N late 1950s this power station was demolished tecture world. The courtyards have a very to make way for the much larger CEGB coal­ pleasant spatial ambience beneath the new fired Chadderton Power Station. Again there roofs for the public to amble and pause were many ancillary facilities including exten­ amidst the sculptures. Within the top galleries t sive railway sidings, coal and ash handling the true benefits of the natural lighting scheme plant and the two switchyards already des­ become evident during brighter days, and a cribed. Three concrete cooling towers were Wince located on the east bank of the Rochdale little sunlight brings variation and life to the Brook galleries of the Paintings Department. : : Canal. In 1984 this power station was in its Credits turn demolished to ground level, except for Client: administration buildings and workshop/stores. Etablissement Public du Grand Louvre Architects: Pei Cobb Freed and Partners, with Michel Macary Consulting engineers: Ove Arup & Partners International Peter Rice, John Thornton, Alastair Hughes, Alistair Lenczner, Etienne Trlcaud, Amanda Gibney, Alexandre Cot (design engineers for courtyard glass roofs) Grimshaw Lane tip Peter Rice, Andrew Sedgwick, Andrew McDowell D (lighting design consultants) D 1948 tip area Glazing sub-consultant: Ian Ritchie Architects, with RFR D Cooling towers Electric lighting consultants: Claude and Danielle Engle D Former vitriol works Steelwork contractor: D Chadderton power station Viry SA Glazing contractor: D Sub-stations Dutemple D Former canal basin Illustrations: 1: Damien Cabiron. 2: Dennis Kirtley. D Area of power station ash and PFA 3: Viry Dutemple. 4, 7, 8: Alistair Lenczner. D Gibraltar worlls 5, 9, 10, 11 : Peter Mackinven. D Slacks Valley sewage worlls & 6: CEPGL Springs Road tip

O 100 200m

14 THE ARUP JOURNAL 2/1994 ~ 2. Dredging the Rochdale Canal, June 1993.

3.~ New road bridge over Rochdale Canal, with canalside features.

To the east of the canal embankment towards Substations, underground and the buried foundations wherever possible the north of the site, the Chadderton UDC overhead cables and tried to avoid conflict with the under­ Sewage Works were constructed by about The two substations are the remaining opera­ ground and overhead cables, whilst the hard 1909. In the 1970s they ceased operation tional areas of the Power Station and are a and soft landscaping was devised to mini­ and were partly tipped over with domestic strategic part of the power supply to Oldham mize the impact of site features that could not refuse. leaving an area with very variable and eastern Manchester. To relocate such be incorporated into the development or topography. This is now called the Springs important facilities was considered impracti­ infrastructure proposals. The final masterplan Road Tip. cal. A further constraint associated with such provided a coherent physical framework Oldham Council submitted the desk study installations is that large electrical currents which underpinned and helped promote report to the Department of the Environment can be induced in copper telephone cables future development, but was also flexible (DoE) to help gain funding for redevelopment. should a fault occur in the substations and enough to adapt to changing requirements. It was well received: and the DoE apparently the energy is passed to the earth. Such cur­ Water had a strong influence on the master­ regard it as a 'model' for this type of report. rents are hazardous to users and can melt plan concept; in particular the Rochdale telephone handsets. The area within 40m of a Canal alongside was seen to be a major Site Investigation and major power substation is known as a 'hot asset. Its reclamation as an environmental ground conditions zone' and special protection is required for amenity was vital to encourage potential Following the desk study, a number of investi­ individual telephone circuits. developers to invest in the site. Other sepa­ gations were carried out including: Here. there are many underground cables, rate water features were also proposed. • checks on chemical contamination of the including 132kV, 33kV, 11kV and 6.6kV cir­ The masterplan allowed the infrastructure to ground and groundwater of the site as a cuits, together with numerous telemetry and be phased over three years. The develop­ whole control cables. In the southern part of the site ment was divided into five zones in terms of • assessment of contamination to the Roch­ as many as 20 HV cables are laid in the constraints, complexity of engineering and dale Canal ground in a single cable route. There are also reclamation works, and, significantly, the time • Investigation of landfill gas in the Grim- major cables connecting the substations. needed to prepare a particular zone for re­ shaw Lane and Springs Road Tips. The overhead cables and the associated development. Into these considerations was • investigations of individual building plots. pylons bisect the site. These are principally added the arrangements necessary to secure The ground conditions succession comprises the 400kV circuits of the National Grid funding. variable thicknesses of made ground over Company connecting to Rochdale and Road system alluvium locally. Below this is interbedded Yorkshire. There are also a number of 33kV The roads for the old power station were in a glacial clay and sands/gravels over un­ Norweb circuits crossing the site. variable state of repair but it was decided to worked coal measures rock. In the Grimshaw Burled foundations and incorporate as much of them as possible. The Lane Tip, nine types of made ground were substantial existing power distribution equip­ identified (the most recent evidenced by Ken underground structures The foundations and basements for the ment made it necessary to compensate by Dodd LP covers). power station buildings, the cooling towers, introducing high quality finishes and features. Site constraints and coal handling plant had been left largely The alignment of the 7.3m wide roads was A comprehensive geotechnical desk study intact. The only available drawings indicated selected to minimize the effect of existing site clarified the major problems: extensive piling and ground floor slabs 700- features on the development areas, and they were designed with 3.5m wide verges to give • poor access and service provision 900mm in thickness. Additionally, the twin 2.5m diameter cooling water culverts con­ a generous feel to the landscaped strip. This • the existing substations, with extensive verge also provides a corridor for the new underground and overhead cables con­ necting the main building to the cooling towers via a bridge over the canal remained. services. as well as a facility to widen the car­ necting these to the distribution networks riageway should future need arise. High qual­ • buried foundations and underground struc­ Areas of landfill ity lighting was designed to complement the tures remaining from the former power Data collected in the desk study had indi­ finishes. stations cated that. though there were no records of • significant depths of landfill material in the tipping activities in the former Grimshaw Drainage system The power station area is generally flat and both the former tips Lane Tip, depths up to 14m could be ex­ discharged surface water to the Canal. The pected. In addition, at Springs Road tipping • landfill gas generation and contaminated design of the surface water drainage was had taken place over the abandoned sewage land. constrained by the outfall levels and the need works with no attempt to prepare the location In addition, the generally flat site had few to achieve minimum pipe gradients with mini­ beforehand. This area was left in two distinct attractive features. mum cover depth. In preparing the drainage portions with approximately 7m difference in design, allowances were included to enable Access and servicing levels, separated by Wince Brook. The only way in was by two 6.5m wide roads future developments to be drained without from Broadway. These had serviced the Development masterplan imposing unnecessary constraints on them. eastern and western parts of the Chadderton From its initial conception Oldham Broadway The masterplanning work also identified the Power Station and were interconnected at its has been seen as a high quality business minimum amount of drainage works required northern limit. Vehicle access across the cen­ park, with Stockley Park as a possible model. for the initial development area. Petrol inter­ The client's objective was to provide 1Mft 2 ceptors of up to 30 OOO litres capacity were tral part of the Station was prevented by a 2 retaining wall built to support the sidings for (90 OOOm ) of development in a landscaped provided on each of the outfalls to the Canal. the coal wagons. Drainage was available, but environment. The proposal to construct the Site services water supplies were only available at the M66 Manchester Outer Ring Motorway New site services were incorporated into the remaining main Station building. A telephone across the southern part of the site and to masterplan to supply the various develop­ network was installed but this was for the provide a major junction with the A662 ment plots, which involved considerable Station's internal use. A gas main crossed the Broadway would assist these objectives and liaison and negotiation with the statutory southern part of the site but there was no dis­ enhance the Business Park's status. undertakers. The services were planned using tribution. There was limited distribution for The masterplan aimed to reduce the impact the common service trench technique that electrical power as the major demands were of the site constraints and maximize develop­ had proved highly successful on the Salford within the principal buildings. ment potential. The proposals incorporated Quays project.

TH!; AA\IP JOUl!!!M. 2/111114 15 ~ 4. Landscaping New road alongside The original intention for the hard landscap­ canal, looking north, ing was to use brick or concrete block pavings showing block for the carriageways. However, for economic footway construction. and technical reasons an alternative was developed incorporating brick block paving for footways, kerb , and channel detail. Red medium-temperature asphalt was selected for the carriageway, the colour complement­ ing the footways. Soft landscaping features including sculptured mounds and water fea­ tures were planned to provide the site with some visual interest. Contracts Phase 1 new Infrastructure This began in October 1990, and comprised 860m of new roads plus 400m of resurfaced original road , together with new site services and street li ghting. This contract, completed in June 1991 , also included extensive soft landscaping of the approaches to the main core of the development, together with a new water feature. Phase 2 new Infrastructure This contract comprised a further 800m of new road construction with a new 20m span bridge, designed by Oldham MBC, across the Canal. This bridge utilized the old founda­ tions from the cooling water culverts bridge over the Canal. Work began 14 months after completion of Phase 1. The main feature of this contract was the 450m of new road along 6. the edge of the Grimshaw Lane Tip and near Aerial view showing the Rochdale Canal. The solution was to par­ progress by May tially remove some of the tipped material and 1994 . effectively float the road construction. ....

Grimshaw Lane N Ju~ t Phase 2

Line of methane barrier O 100 200m I I D Sub stations

5. Oldham Broadway: new infrastructure.

16 TliE ARUP JOURNAL 2/1994 The services provided in Phase 1 were also extended in the verges and footways. Drain­ age for this area of the site was connected to Kansai Airport Terminal, Osaka, Japan the principal outfalls by an 11 m-deep drop shaft, constructed partly in the original Canal Philip Dilley embankment and partly in the landfill. Phase 3 new Infrastructure The construction of the new international airport The design of the 300 ooom2, 1800m Phase 2 was completed in April 1993 and is complete, and the terminal building is being long terminal building was awarded Phase 3, completing the primary infrastruc­ opened officially in September of this year. to Renzo Piano Building Workshop ture work, began the same month. In this , and Ove Arup & Partners Inter­ another 250m of new road was built, of which national following an architectural 130m was along the edge of the Grimshaw competition in 1988. Together with Lane Tip. In addition, a new junction with the Japanese architect, Nikken Grimshaw Lane and the northern boundary of Sekkei, the airport planners Aeroports the site was constructed, together with a new de Paris, and the specialist advisers public car park. All this was finished in Japan Airport Consultants, Arups October 1993. were appointed to carry out the Rochdale Canal reclamation structural engineering, the mechani­ This vital element of the scheme got under cal and electrical services, and the way in March 1993 and was completed in fire engineering of the terminal eight months. 1.6km of the abandoned Canal building. was made navigable again, which involved 3 To minimize the effects of noise dredging approximately 8000m of silt and pollution, the airport is constructed depositing it in a specially constructed lagoon. About 1.4km of canal wall were repaired and about 5km offshore of the Senshu the towpath refurbished. region on a man-made island. When fully operational, the terminal building To enhance the environmental amenity of the will handle 25M passengers per year Canal , the reclamation contract included con­ through 41 aircraft parking spots structing a large basin, a wharf feature, and linked through boarding bridges. new access provisions to connect the tow­ path to the new road overbridge, together The speed and quality of construc­ with extensive soft landscaping. tion have indeed been impressive. Landf/11 gas barrier works Commencing in 1991 , the building Following extensive site investigation and gas was constructed by two separate monitoring, a contract was let to install a land­ contracting consortia, led by fill gas barrier across the southern boundary Takenaka Corp. and Obayashi Corp. of the Grimshaw Lane Tip and a venting The 40 OOO tonnes of steel in the facility at the northern end; the work was com­ main building frame was provided by pleted between October and December Kawasaki Corp. and Nippon Steel 1993. It included a 7m deep cut-off incor­ Corp ., who procured a large part of porating a High Density Polyethylene mem­ the 10 OOO tonnes of roof steel from brane in a cemenUbentonite slurry, together Watson Steel Ltd. in the UK. with a stone venting facility. The barrier inter­ A full article on this project is planned cepts the underlying clay stratum to prevent to appear in a forthcoming issue of the escape of landfill gas to the adjacent Phase 1 area of the development immediately The Arup Journal. to the south . Site investigations had shown 1. .& that the Canal and railway embankments The 'canyon', were acting as gas barriers on the east and a 30m high space for west sides of the Tip respectively. arriving passengers to orient themselves, Future proposals and summary links the kerbside The next major area to be tackled is the aban­ and station to the doned Chadderton Sewage Works and the main terminal. former Springs Road Tip. The proposal is to (Photo: Phil Dilley) infill most of this area with surplus excavated material from the M66 motorway construction. 2. 11> Development of this part of the site can then Roof of main begin. Currently 18 OOOm2 of new develop­ terminal building. ment has been completed or is currently (Photo: Rory under construction. McGowan) The regeneration of the former power station site demonstrates the importance of a well­ engineered masterplan capable of being implemented on time and budget. It is under­ stood this is the first power station site in the UK to undergo comprehensive regeneration. Credits Clients: Oldham Economic Development Unit, Oldham Metropolitan Borough Council (Technical Services) Architect: EGS Design, Manchester Landscape architect: Oldham Metropolitan Borough Council (Borough Planning Department) Agent: Dunlop Heywood Engineers: Ove Arup & Partners Roger Mil burn, Nick Fennell, Colin Curtis, Richard Summers, Bob Tyson, Jane Collins, Kevin Goodger, Simon Stocks, Mike Andrew, Tony Sumner, Eddie Carmichael, Paul Murphy, Paul Holder, Mark Elsegood, John Bennison, Sheila Nethercott, Mike Wilton Illustrations: 1, 5: Martin Hall. 2: Norman Edwards Associates (Manchester) Ltd. 3: Peter Mackinven. 4: Bob Tyson. 6: Jefferson Air Photography.

THE ARUP JOURNAL 2/1994 17 Corrosion: is there a problem? Graham Gedge

Introduction For continual immersion in seawater, There are a number of misconcep­ the last two factors are particularly tions about metal corrosion in con­ relevant, as build-up of corrosion struction. It is often assumed that in a deposits and marine growths does given environment it will happen at a alter the corrosion rate . Initially, rates uniform rate , thus making corrosion a are linear and of the order quoted life-limiting factor. The natural con­ above, but within only weeks they can clusion is that expensive preventive slow dramatically, and plots of rate measures need to be adopted or a versus lime become exponential. more exotic alloy material used . Long-term rates can thus be more Often, however, neither is necessary realistically assessed in the range and a different approach will give a 0.1-0.15mm/year, as confirmed by more economic solution. recent published data 1·2. It was there­ The corrosion process fore possible to show that, for the The crucial issues are how fast the components concerned , section loss metal is corroding and whether the would have been of the order of corrosion is local or uniform. For 2-3mm over 20 years - not 6-1 Omm. example, structural steel in an internal Thus it was highly improbable that controlled environment will corrode, integrity would be affected. but so slowly as to be negligible. This example shows that, where long­ There is no need to apply any pro­ term rate data are available and the tective coating, which saves costs macro-environment defined, uniform over the traditional remedy of blast corrosion is something that can cleaning and coating. effectively be allowed for in design. However, this is only possible in Another example is that of steel piles retrospect after considerable expo­ driven in undisturbed ground. It is sure periods, measured in years, in often assumed that soil type and clearly defined environments. chemistry control the durability. However, in most soils these are Recently, Arups have taken this secondary to the fact that the ground approach - looking at rates rather is undisturbed. The oxygen content is than the simple fact of corrosion - a 1. Model of Pagbilao power station. low and constant; corrosion rates stage further, and begun to consider under such conditions are controlled less clearly-defined and apparently Conventional solutions Corrosion Project3. This used recent by oxygen availability and are thus changeable environments. In these The traditional solution to acid dew­ developments in electronic and corro­ low. Long-term rates are less cases, conventional corrosion testing, point corrosion was always to keep sion research to monitor corrosion in because corrosion products formed such as short-term weight loss, is of the flue gas at 20-30'C above the power generation plants, in real time, under these conditions act as a limited use and one has to use dewpoint. This approach was based using a range of modern electro­ barrier to oxygen diffusion and charge modern electrochemical monitoring on short-term exposure tests in bulk chemical measuring devices. These transfer. In undisturbed soils rates are techniques. Arups were asked to acid solutions, which indicated that had few of the disadvantages of low- around 0.005-0.01mm/year - assess corrosion in the exhaust steels would corrode at high rates at previous techniques, and the great and are tolerable within design limits. chimney flues of Pagbilao, a coal­ all temperatures up to dewpoint. advantage of providing instantaneous fired power station currently under Following the 1970s oil crises, this corrosion rate data that could be Similar - but more surprising - construction in the Philippines (Fig .1). results can be found in harsher approach was increasingly ques­ correlated directly with plant environments, where corrosion is P•gbilao tioned as the temperatures involved operating parameters. perceived to be far more problematic. Defining the problem (c.150'C) led to inefficient power Arups were recently asked to assess The exhaust gases are to be expelled generation. This in turn stimulated via a 210m high slipformed reinforced research into dewpoint corrosion, the likely corrosion of sea water - N1alloy ballast system components that had concrete chimney with two steel flues. materials performance, and novel , - C-Mn-Cu steel The client asked if it was possible to techniques for monitoring and ., been operating for 15-20 years in the ~ northern North Sea. It is well-known fabricate the latter from plain carbon­ measuring corrosion. :;; that steel in seawater corrodes and manganese steels without either an It soon became apparent that the f that the rates can be high - typically internal protective coating or a refrac­ conventional approach was flawed for 0.3-0.5mm/year. The problem was tory brick lining. Flue gas tempera­ the following reasons: that this data did not correlate with tures were predicted as 110-130'C • Flue liners were often below the service experience: at such rates and the liner surface could be cooler, dewpoint temperature. Time although by how much was not components should have failed within • Flue liners performed satisfactorily 10-15 years. but they had not. The defined. The coal source was likely to 2. Weight loss with time - constant have significant chlorine and sulphur even at these temperatures. disparity was because data of this • Short-term tests can be misleading. environmental conditions. type are based on short-term (6-12 content, so the flue gases would con­ month) exposures and calculated tain hydrogen chloride and sulphur The first two of these were directly from weight loss. oxides. Under condensing conditions, related to the last, and this is the nub Electrochemical monitoring (EM) below the acid dewpoint, both hydro­ of the problem. Short-term tests in The aim of EM is to provide real-time The disadvantages chloric and sulphuric acid conden­ bulk solutions do not normally repre­ data on corrosion rates and to link of this type of testing are: sates could form on the steel surface. sent the conditions found in real these simultaneously to a series of • It is based on cumulative It is well-recognized that these acids engineering structures for reasons operating parameters like tempera­ historical data. can corrode unprotected steel rapidly given above. The inadequacy of ture, pH, flow rate, etc. To achieve short-term tests for corrosion rates is this, the corrosion process itself must • The data are averaged - indeed the effect has been likened to pouring watering-cans of battery demonstrated in Fig.2, which shows a in some way be monitored, as assuming uniform corrosion and clear retardation of rate with time for opposed to its consequences like ignoring pitting. acid over a car bonnet! Arups' Industrial Engineering group were steel, and also that expensive alloys weight or section loss. • The rate is assumed to be therefore understandably concerned do not always perform better in the As corrosion is an electrochemical continuous, constant, and about the durability of the flues and long term. process, it involves the transfer of linear with time. asked Arup Research & Development These anomalies were investigated current as electrons during the • It ignores the beneficial to investigate whether a 15-year during the late '70s and early '80s as chemical reaction. In general, EM effects of scale and deposits design life could be achieved without part of a combined research pro­ aims to measure polarization resis­ retarding corrosion. protection. gramme called The Acid Dewpoint tance and thereby calculate a value

18 fflE ARUP JOURNAL 2/1994 ('current equals electromotive force During start-up, steel is attacked by divided by resistance'). The monitor­ acid condensate for a while until a ing and subsequent analysis of these protective scale can form. During Equivalent circuits changes is referred to as ECN. shut-down the scale breaks down and (a) -- Charge transfer control also spalls as the flue cools. At the (b) -- Diffusion control In-service monitoring (a~~! A ~~ When used in power station flues, EIS same time the environment changes - vvv~ and ECN provided much information to that of the prevailing external con­ about the corrosion that was going on ditions. This usually means relatively and why carbon-manganese steel high humidity that can itself corrode can perform satisfactorily. More steel, but the rate is also increased by activating trapped acid on the Decreasing importantly, they also showed the corrosion rate importance of environmental changes surface. on corrosion and how good planVpro­ It is therefore possible to predict with cess management could minimize the confidence that even in an apparently effects in a much more controllable unfavourable environment conven­ • Diffusional Impedance manner than was previously the case. tional steels can perform satisfac­ • Polarization resistance • Double layer capacitance It was always assumed that corrosion torily. It was concluded for Pagbilao • Solution resistance rates in flues would be similar to those that the flue design (to avoid cold in bulk acids of a similar concentra­ spots) and plant operation (to avoid Zreal tion to that found in condensable films stop/starts) were far more influential in As inside flue liners. Indeed, monitoring controlling corrosion than the environ­ 3. Equivalent circuits and EIS responses. showed this to be the case for an ment itself. It was also recommended initial short period, after which the rate that the installation of EM could be

.--~~~~~~~~~ used to both confirm this and optimize e E"' fell significantly. EIS attributed this to .c 90°c Surface temperature N .c N plant operation. 'e so•c Surface temperature 'e an increase in charge transfer resis­ j u ~g u tance indicative of a build-up of pro­ "'Q, "'Q, Conclusions E 1Jl E tective scale on the steel surface. This EM represents the leading edge of ~g,N ~ -~ ~ 1 I~ I ~ .. observation was confirmed at flue sur­ assessing corrosion rates and clearly E e ~ c: ~ c: face temperatures as low as 90'C - shows that, by understanding envi­ c: .Q c: .Q well below the flue gas and dewpoint ~ "'g g "'g ronments and reactions, corrosion - 0 CD (Fig.4a). ..e> u e> 8 particularly the uniform type - can .c z .c z "'u (.) u"' (.) Despite this apparently satisfactory be more understood. And Arups' work w w Cl) Cl) in other areas has shown that under­ w w conclusion, anomalies still existed. It 0 1 2 0 1 2 was known that certain areas of flues standing corrosion rates can lead to (a) lime (hours) (b) lime (hours) could suffer severe local damage. It more economical design solutions. 4. (a+b) Monitoring - continuous operation. NOTE: As resistance increases rate decreases was also known that some plants The use of EM is an emerging tech­ suffered greater general corrosion nology that need not be restricted to for the corrosion current density (icor,l the EIS plot shape also gives other rates than others. It was shown - which can then be translated into a information about the corrosion the power industry. Its use to predict again using EIS - that local damage corrosion is obviously an advantage weight or section loss in a predictive mechanisms: a simple semicircle with would occur in areas that were exces­ to be exploited but represents a rather than reactive way. It is possible two intercepts on the real axis indi­ sively cooled due to air ingress or to measure icoo directly, but the cates a reaction controlled by metal limited use of the technology. poor insulation. In such locations, Because EM, particularly ECN, technique is sensitive because of the dissolution. Alternatively, a plot with a metal surface temperature could fall monitors the material behaviour in real small currents involved. Also. such low frequency tail at 45' to the real locally to as low as 40-50'C (Fig.4b). methods only give the current flow axis, and no intercept, indicates a time and is extremely sensitive to This is in the reg ion of the hydrogen small environmental changes, the and no information on the type of reaction controlled by diffusion; typi­ chloride dewpoint. As hydrogen attack. cally this would be found for corrosion possibilities for these techniques are chloride condenses, the charge trans­ significant. In power generation the two most of steel in water which is controlled by fer resistance falls because of a widely used techniques are Electro­ oxygen diffusion (Fig.3). change in the nature of the surface For the first time, there is no longer an chemical Impedance Spectroscopy A metal corroding in an environment scales. This results in the corrosion excuse to accept corrosion as an (EIS) and Electrochemical Noise has associated values of both corro­ rate increasing as hydrogen genera­ inevitable destructive force. It is now (ECN). EIS is based on the concept sion potential and current, often tion is facilitated, and the rates tend to possible even to use it as a surrogate, that a corroding interface can be assumed be defined and precise: for reach those of bulk solutions. employing its real-time measurement represented by a relatively simple example, steel can be described as to control plant plus process opera­ The difference between plants was tion, to improve operating efficiency, equivalent electrical circuit (Fig.3). corroding in seawater with a potential traced directly to the way in which programme maintenance, optimize The response of such a circuit to a of -450mV. In reality such a value is they tended to operate. Those operat­ materials performance, and when small amplitude input (either voltage better regarded as a mean about ing more or less continually on base things do go wrong to explain why. or current) at various frequencies which both current and potential vary load suffered little serious attack, This is all possible because of the allows individual components to be by small amounts, typically microvolts whilst those operating on a more technique's extreme sensitivity in evaluated from a complex plane plot and nanoamps - this is referred to cyclic loading condition were more detecting corrosion well in advance of of impedance, the low frequency as 'noise'. By monitoring simultane­ severely damaged because of higher conventionally-defined physical intercept being a direct measurement ously these small changes, icorr can corrosion rates associated with plant symptoms. of polarization resistance. However, again be calculated from Ohm's law start-up and shut-down (Figs.5 & 6). ...,_!CH (1) LARSEN-BASSE, J. and PARK, Y-H. Corrosion of slowly-flowing ocean thermal "'E - EIS energy conversion seawater. Materials .c - Gas temperature N j- E1s l - ECN ·e CD Performance, 28(2). pp.46-51, February u g j :g_ 1989. ~!!lo· E -~ (2) SAWANT, S.S. et al. Corrosion behav­ ~ ~ 150 ~ ~"' iour of mild steel in offshore waters of the :: .a e :;; a>E c: ui Arabian Sea. Corrosion Prevention and "@ !. -~ c: Control. pp.44-47, April 1989. EE 100 g ~ ;~ CD (3) HOLMES. D.R. Dewpoint corrosion. e> 8 e> .. z .c.. Ellis Horwood, 1985 . {i 50 (.) (.) w Cl)w 0 2 3 4 5 6 7 8 9 10 11 Graham Gedge is a metallurgist in Arup lime (weeks) Unit shut down Research & Development. 1 2 lime (hours) Illustrations: NOTE: As resistance increases 1. Photo: Ove Arup & Partners corrosion rate decreases • 5. Monitoring - plant start up. .& 6. Monitoring - plant shut down. 2-6: Martin Hall

THE AIIUP JOUIINAL 2/1994 11 Printed in England by Reedprlnt Limited, Windsor, Berkshire