50 & 20 Years Ago
First British Rail bridge in weathering steel
The first stage of the British Rail Freightliner network was virtually completed in mid-summer 1967 and plans were then prepared for the next stage of the development. Market research had shown that a second terminal would be required in Manchester and that it would need to be a major terminal using Goliath cranes spanning six railway tracks.
The only railway site available with suitable connections in the area was at Trafford Park adjacent to a motive power depot which was to be closed. Existing road access to the site, however, was very poor and it could not be improved because of the position of the Manchester United F.C. ground and adjoining industrial premises. The solution was to construct a completely new access to the site from Westinghouse Road on the other side of the Bridgewater Canal. The scheme entailed the building of a bridge over the canal and the demolition of some premises of the Springfield Warehouse Company through which the northern approach to the bridge would pass.
The design of the bridge presented no great difficulties; the span, 61ft between bearings, is moderate and the skew, 17° 30´, not large. A simply supported welded steel plate girder bridge on piled concrete abutments was therefore decided upon. The question of maintenance naturally had to be considered and, in view of the limited headroom of little more than 12ft above water level, it was felt by the Chief Civil Engineer, London Midland Region, British Railways Board, that here was an excellent opportunity to gain experience of using a corrosion resistant, or weathering, steel. Such steels had successfully been welded for a number of bridgeworks in North America but there was no knowledge of their behaviour in this country and, although it was intended to use Cor-ten B steel produced under licence in Great Britain to the specification of the United States Steel Corporation it was considered desirable to call for welding tests before making a firm decision to order it. Consequently, the BCSA arranged for comprehensive tests to be carried out by the Welding Institute (formerly the BWRA). The results of these tests having proved satisfactory, British Rail decided to have the bridge at Trafford fabricated in Cor-ten B steel and the necessary materials were ordered.
The bridge consists of seven welded plate girders, 63ft long at 5ft centres, with 24in × 9in welded I-section diaphragms of ½in plate flush with the top flanges. Each girder. 2ft 8in deep, is fabricated from a web plate 29¾in deep and ½in thick, a top flange plate 12in × ¾in and a bottom flange comprising a plate 11in × ¾in welded under another 12in × ¾in plate. The total weight of Cor-ten B steel is 33 tons.
Stud shear connectors welded to the top flanges of both girders and diaphragms ensure composite action with the 8in thick concrete deck slab which is surmounted by a bituminous waterproofing membrane protected by a layer of quarry tiles and an asphalt wearing surface laid with a camber of 3in to both sides of the 24ft wide carriageway. An initial camber built into the plate girders provides for longitudinal falls from the centre of the bridge. The girders were welded up complete with diaphragm brackets, stiffeners and shear connectors in the shop, where a complete trial assembly of the steelwork was made before delivering all the components to the site. All welds are ¼in fillets and all site connections are made with 7/8 in diameter high tensile bolts in 15/16 in diameter holes. The bolts and washers are zinc plated and the nuts are cadmium plated. Site erection was carried out with the aid of a mobile crane.
The bridge and the associated roadworks are due for completion in May 1969 and the Freightliner terminal is expected to commence operating in August 1969.
The design of the bridge was carried out by the chief Civil Engineer, London Midland Region, British Railways Board, whose permission to publish this article is gratefully acknowledged.