Case Study

Sheffield Supertram System

• bowstring arch tram bridge
• linear and buckling analysis
• post-tensioned segmental structures

Design and Building Services (DBS) of Sheffield City Council have been involved with the design of the Supertram System in Sheffield, which incorporates a series of major bridgeworks designed with the assistance of the LUSAS Bridge analysis system.

The Commercial Street bridge carries the Supertram system onto the central island of the Park Square roundabout. Due to the bridge’s prominent position at the heart of the Sheffield City Centre, the City Planning Authority insisted that it should form a dominant feature in the area in sympathy with the contrasting styles of the adjacent buildings. The presence of a large sub-surface culvert, traffic site line requirements and provision for traffic access, dictated that the main bridge span should be 74 metres in length. Two further side spans of approximately 18 metres and 12.5 metres complete the three span arrangement. The headroom requirements below, and the vertical alignment of the track-way above, meant that the bridge had to be "through-form". After consideration of the various options, the City Planning Authority agreed to a bow-string arch arrangement in fabricated steelwork forming the main central span of the bridge. The bridge utilises some 350 tonnes of steelwork and the cost of the construction is approximately £2.4 million.

The DBS Project Engineer for this bridge used LUSAS Bridge to perform two different types of analysis: first, a static analysis of the space frame which forms the bow string arch of the main span; and second, a buckling analysis, to check for critical buckling of the arched members. A combination of LUSAS thick shell and beam elements were used. The beam elements modelled the space frame with the shell elements modelling the steel/concrete composite deck which had a surprisingly large influence on the buckling loads. The three spans were designed to be simply supported. In order to avoid the use of joints over the piers, the reinforced concrete deck is continuous over all three spans utilising a "concrete hinge", at the piers to cater for live load rotations.

LUSAS Bridge was also used for other parts of the Supertram system including the Parkway Viaduct. The viaduct is a post tensioned segmental concrete bridge consisting of six segments with an overall span of 300 metres. Due to the curvature of the bridge and the offset load of the trains on either one of the two tracks, torsional load and warping are involved. The engineer used LUSAS’s thick shell elements to conduct this analysis and to ensure that stresses from all load cases were within allowable limits.