Design and construction of two launched bridges

The 194 m long A500 railway bridge and the 63 m long New Relley bridge are both steel concrete composite bridges constructed using longitudinal launching with the concrete deck slab cast prior to the launch. This paper describes the design and construction of the two bridges and contrasts the different launching techniques used. The reasons for launching as opposed to conventional crane erection are explained, as are the design and fabrication details required. Information is given on the contract and planning framework for both schemes. The A500 railway bridge, passing over a total of 14 overhead electrified tracks, is believed to be the first example in the UK of a major steel–concrete composite bridge launched with the concrete deck in place. Both launches were successfully completed within tight railway possession periods. The safety advantages of having the permanent vehicle parapets in place directly after the deck installation are emphasised. This form of construction has proved itself to be effective for road-over-rail bridges where only short track possession periods are available and also where headroom constraints hinder normal crane operations.