Technical Journal Technical 04 04 Technical Journal Papers 051 - 066 © ATKINS Ltd except where stated otherwise. The ATKINS logo, the “open A” device and the strapline “Plan Design Enable” are trademarks of ATKINS Ltd. PAPERS 051 - 066 PAPERS Printed on 9Lives Offset, part of the family of ’born again’ papers, manufactured with National Association of Paper Merchants Certification (NAPM) using approved 100% recycled fibre pulp, 9lives Offset offers the ultimate in environmental management. The manufacturing mill and printer have also been accredited with the internationally recognised standard ISO 14001. Welcome to the fourth edition of the Atkins Technical Journal. This edition of the Journal is dedicated to Cressida Spachis who sadly passed away earlier this year. Her paper, “Delivery of bus priority projects - a partnership approach”, was submitted to the Technical Journal to showcase the success of working in partnership on the Route 38 Project. Cressida was Project Manager for the Route 38 Corridor Management Pilot Study which has developed principles for intensified bus priority now being used across London. The project received many accolades and Cressida was due to be part of the client/consultant team receiving the Improvements to Bus Services award at the London Transport Awards earlier this month. A further tribute to Cressida is made by Andy Southern, Managing Director for Transport Planning and Management, on page 69 immediately prior to the text of her paper. Once again there has been a great response to the call for papers across all businesses and it is particularly encouraging to have been able to publish papers from a wide range of staff grades covering Graduate Engineers to Technical Directors. The Journal continues to highlight the extensive range of technical disciplines Atkins can offer its clients and our Defence and Offshore Energy capabilities are prominent in this edition. With the recent appointment of three new Network Chairs we can look forward to even more effective showcasing of the diverse and complex problems that Atkins’ staff solve so well in their everyday activities. It is also particularly pleasing to see the excellent working relationships we have developed with our clients and partners being manifested in co-authored papers such as those written with the University of Bath, University of Southampton and English Heritage. This demonstrates that Atkins creates solutions that both we and our clients are proud of. I hope you enjoy the selection of Technical papers included in this edition. Chris Hendy Chair of H&T Technology Board Highways & Transportation F O R E W O R D 5 Technical Journal 4 Papers 051 - 066 051 - Structures The launching of the River Esk Bridge 5 052 - Structures Recommendations for assessment Eurocodes for bridges 17 053 - Structures Limit equilibrium assessment of drystone retaining structures 29 054 - Intelligent Transport Solutions ITSO smart cards in Welsh public transport 39 055 - Intelligent Transport Solutions On balance - the see-saws of congestion charge business cases 45 056 - Intelligent Transport Solutions Improvements to ramp metering system in England: VISSIM modelling of improvements 51 057 - Highways ‘Scrambled’ pedestrian crossings at signal controlled junctions - A case study 57 058 - Highways Delivery of bus priority projects - A partnership approach 71 059 - Water & Environment Water quality modelling as a tool for assessing new water resource management options: The case of the River Stour, Kent 81 060 - Water & Environment High accuracy recording for heritage applications - Dover Castle graffiti 87 061 - Aerospace Conjugate heat transfer study of a spin pit rig: Application to the lifing of HP turbine disc firtrees 93 062 - Aerospace Non-deterministic thermo-fluid analysis of a compressor rotor-stator cavity 105 063 - Energy The optimum position for a tidal power barrage in the Severn estuary 115 064 - Energy Greater Plutonio project - Subsea flowline design and performance 123 065 - Defence Development of an armour mass estimation tool for land vehicles 147 CONTENT 066 - Defence Explosives safety - An oxymoron? 155 S The launching of River Esk Bridge 51 Rob Liddle Abstract Senior Group Engineer The River Esk Bridge carries the southbound carriageway of the M6 Highways & Transportation motorway over the River Esk estuary and forms part of the recently constructed M6 Carlisle to Guards Mill Motorway Extension which provides the missing link in the motorway network between England and Scotland. The bridge is a 180m long four span steel composite viaduct. Due to site constraints the most economical and practical method of construction was to launch the steelwork into position rather than to lift the steelwork in by crane. The bridge steelwork, weighing over 800 tonnes, was assembled on the northern approach to the bridge and launched southwards over the River Esk estuary This paper demonstrates that the design and construction of a launched bridge can be significantly more complicated than the design of a comparable bridge which is constructed using conventional methods, and that there are many more load cases and construction details to consider. This paper covers the approach for carrying out the analysis, design, detailing and construction of the structure and focuses specifically on the key issues relating to launching steelwork. It serves as a useful guide and quick point of reference for the design of launched steel bridges. Introduction This paper covers the approach for carrying out the analysis, design and detailing of the River Esk Bridge on the M6 Carlisle to Guards Mill Motorway Extension. The Esk bridge is a four span 180m long steel composite viaduct over the River Esk and carries the southbound carriageway of the new section of M6 Motorway. The span arrangement is 31.4m/51.9m/51.9m/44.9m. The south abutment is fully integral, forming the point of fixity, and the superstructure is free to move longitudinally over Figure 1 - River Esk Launch the piers and north abutment. The bridge steelwork was assembled on the northern approach to the bridge and launched southwards over the River Esk estuary. The total weight of the steelwork was over 800 tonnes. STRUCTURE The reason for the launch was that access to the river for steelwork assembly and lifting was not possible due to the tidal nature of the river and the high risk of flooding. Also, lifting the beams in from the adjacent A74 ‘Metal Bridge’ was not possible due to traffic management issues. The A74 Metal Bridge was refurbished to carry the M6 northbound carriageway. Figure 2 - River Esk Launch S 5 51 The launching of River Esk Bridge Analysis, design and buildability Line beam analysis of launch phases Launch Phases The bridge steelwork was launched southwards in two phases: Phase 1 - The southern half of the steelwork was assembled on temporary land bases together with a launch nose and tail, and then launched southwards. The launch platform comprised the landbases, spaced at 28m/28m/28m, constructed in the partially completed approach embankment with the landbase levels set so that the steelwork could be set out and assembled to the Figure 3 - Views of the completed bridge adjacent to the existing A74 metal bridge vertical alignment required for the launch. The piers in the river were constructed in temporary cofferdams which were then converted into temporary islands to allow safe access and working at the piers without the risk of flooding. The cofferdams and islands were constructed higher than the maximum predicted flood level. Phase 2 - The tail was removed from the Phase 1 steelwork. The northern most steelwork spans were assembled and attached to the steelwork already launched. The tail was reattached to the rear of the Phase 2 steelwork. The whole bridge steelwork was then launched. On completion of the launch the temporary launch nose and tail steelwork were removed. The launch equipment comprised strand jacking tendons which were attached to the north abutment using Figure 4 - Views of the completed bridge adjacent to the existing A74 metal bridge a steel hauling frame which was embedded into the concrete stem of The M6 Carlisle to Guards Mill A temporary nose and tail assembly is the abutment to resist the hauling scheme provides the missing also required to be spliced to the main load. The tendons were attached link in the motorway network steelwork to accommodate the large to the launch tail via a large steel between England and Scotland. deflections that occur. Many bridge cross-beam which was attached to substructure and steelwork details The main difference between a static the end of all five beams to transfer were modified from a ‘standard bridge design and a launched bridge the hauling load into the beams. design is that each section of the design’ to accommodate the effects Choice of nose and tail length S steelwork elements is designed to of the bridge launch and use of work in different ways, depending on temporary launching equipment. The longer the nose, the less permanent steelwork would be RE its position during the launch and also This paper focuses specifically on in the completed in-service condition. the launch-related aspects of the cantilevering at the leading span U The main girders and splices act in design and construction of the prior to ‘touch down’ at a support. T both hogging and sagging and the bridge, not on standard bridge A longer nose tends to reduce the leading front span behaves as a very design and construction topics. cantilever moment as the nose long cantilever during the launch. weight per unit length is normally UC lighter than the permanent works. TR S 6 The launching of River Esk Bridge 51 Figure 5 - Cross section of the deck The use of a curved soffit is a different approach from that commonly used for post-tensioned incrementally launched concrete bridges in which the nosing usually has a hydraulic height adjustable tip to take up the deflection prior to touch down at a support.