Pier collision protection at Tay Road Bridge, Scotland

Tay Road Bridge is a 42-span, 2ṡ25 km-long twin box viaduct carrying the A92 over the Tay Estuary between Dundee and Fife. Two navigation spans are located on either side of pier 32. Cargo vessels of up to 3500 DWT regularly transit the bridge inbound or outbound from Perth 33 km to the west passing under the bridge 2 h before or after high tide to complete the trips in one uninterrupted movement. The 4 kn tidal flow and the vessels' need to maintain a ‘through the water’ speed of 8 kn for steering combine to necessitate an unusually high ‘over ground’ speed of over 12 kn. Consequently, while relatively small, transitting vessels possess high kinetic energy, and in the event of collision it is this energy that has to be absorbed by the pier protection system. Assessment revealed that the consequence of ship collision would be severe, affecting structural equilibrium. The structures provided are reinforced concrete fender beams. For the most severe collision events, the tubular steel supporting piles are designed to deflect beyond the point at which the end moments cause section yielding, and it is the work done in the rotation of these plastic hinges that absorbs the majority of the collision energy. This paper describes the development and design of the protection structures, early contractor involvement, contract form and construction.