This design for a lifting bridge was the winner in a design competition. The 50m span bridge is designed as a propped cantilever, with a hidden back span and
lifting mechanism. The main span is a stiffened, tapered steel box girder that forms both the deck and the balustrades. The force required to balance the loads from the main span is provided by a combination of the concrete-filled box back span, and four telescopic cylinder hydraulic rams, which are also used to lift the bridge. The rams and back span are housed below ground level in a chamber behind the river wall. This allows the bridge deck to appear as a simple cantilever as it rises up. For this project we were in contact with specialists Shepcote Engineering for the specification of the hydraulic rams. As part of the competition
we had to carry out preliminary structural analyses. These considered the bridge in its horizontal condition, in its condition as one end is just being lifted off its
supports, and in its fully lifted condition. The bridge was analysed under live, wind and ship impact loads, and dynamic analyses were carried out to check vertical and horizontal natural frequencies and accelerations in both closed and open positions. Proposed foundations are reinforced concrete piles, with sheet piling used as temporary retaining walls for construction of the lifting chamber.