River Bridges go steel

Two recently awarded highway contracts show the sustained improvements in economy of steel bridges against concrete. Tenders showed that steel is cheaper even after accounting for costs of commuted mainte­nance. For these bridges con­crete had been envisaged and the winning steel design is the Contractor’s alternative prop­osal. Both bridges are in scenic locations requiring the approval of the Royal Fine Art Commis­sion. Brief descriptions follow.

River Avon Bridge.

Evesham Bypass

The Bypass will be 6km long to carry the A435 road to the east of Evesham (Worcestershire). It comprises a single 12m carriage­way with 1m verges and crosses the River Avon with a skew angle of 17°. Clear width between river walls is 33m. The bridge has three continuous spans of 28m, 42m and 28m with curved soffit profile. Total deck width is 15.22m. The original design comprised an insitu pre-stressed multi-cell box girder.

Tenders were returned In August 1985 and Balfour Beatty Construction asked Cass Hayward & Partners to prepare alternative steel proposals. These were sub­mitted and accepted by the Engineer as a cheaper solution.

Twin main girders at 11.0m centres form the superstructure 2.33m deep as the piers, reducing to 1.23m at abutments and centre of the main span. They support a composite reinforced concrete deck 230mm thick via universal beam cross girders at 3.5m spac­ing. Bracings integral with cross girders are provided at piers with intermediate knee braces at 7.0m either side. Main girder site splices are welded. Bottom flanges are 850mm wide with top flanges 400mm, 500mm or 600mm wide. Web stiffeners occur on inside faces only except at supports. Bearings are proprietory ‘Disc’ type. Piers are twin circular r.c. col­umns 1.35m diameter. They are supported by a spread footing combined with river wall founded In clay at approximately 5.5m below ground. Abutments are of skeletal r.c. type within the embankments with spread foot­ings. The reduced weight of a steel bridge allowed footings to be reduced in size. The complete design conforms with B.S. 5400.

Work started on site In October 1985. Steel erection Is due In Sum­mer 1986 with bypass completion before the end of the year. Sub­contractor for steelwork is NEI Thompson Limited, Horseley Bridge. Main Contractor is Balfour Beatty Construction Limited for whom Cass Hayward & Partners of Chepstow are Consulting Engineers for the alternative design including foundations. Engineers for the Works are C.H. Dobbie & Partners who are also responsible for the independent check, and the client is the Depart­ment of Transport.

New Roding Bridge.

South Woodford to Barking Relief Road

The New Roding Bridge is part of the scheme for the A406 South Woodford to Barking Relief Road in north east London. A section of the A13 Is also to be improved under Contract 4 and includes con­struction of the New Roding Bridge to carry eastbound traffic over Barking Creek, alongside the existing reinforced concrete Barking Bridge. Tenders were returned In September 1985 and the Con­tract was awarded to Balfour Beatty Construction Ltd. Pre-ten­der the bridge was envisaged as an insitu prestressed concrete beam and slab structure and had seven spans. The steel alternative design was prepared by Cass Hay­ward & Partners on behalf of Bal­four Beatty and accepted as a cheaper solution.

New Roding Bridge Is 187m long with spans of 25m, 27m, 27m, 28m, 52m (over river) and 28m. It will be separated from Barking Bridge by a gap of about 2m. It is 14.1 m wide at the east end increasIng to 16.3m at the west end to carry a converging slip road. The two main piers are skewed at 15° to be parallel to river flow. One Is within the river whilst the other is located on the west bank. The superstructure consists of five steel plate girders continu­ous for the full length and support­ing a composite concrete slab 230mm thick. Girder spacing var­ies from 2.7m to 3.5m with edge cantilever of 1.25m. Transverse bracings are provided at piers and at intermediate locations. Main gir­der splices are bolted. Bottom flanges are 500mm or 600mm wide flats with top flanges of 400mm width. Girders are gener­ally 1.15m deep increased with curved soffit over the two river piers to 2.5m. Piers are of rein­forced concrete leaf type with piled foundations formed In Lon­don Clay.

Work started In January 1986. Steel erection Is due early In 1987 with completion by September. Subcontractor for the steel is Nusteel Structures Ltd. Main Contrac­tor Is Balfour Beatty Construction Limited, for whom Cass Hayward & Partners are Consulting Engineers for the alternative design including foundations. Engineers for the Works are Freeman Fox Limited and client is the Department of Transport. Freeman Fox Limited are responsi­ble for the independent design check.

A.C.G Hayward, Cass Hayward & Partners

Originally published in BCSA NEWS
September 1986