2 3 4Tay Road Bridge is a 42-span, 2?25 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.
The replacement of Midmill Bridge, a reinforced concrete arch bridge crossing Cruden Water in north-east Scotland, was accomplished by the construction of an arch comprising discrete interlocking precast concrete voussoirs. By eliminating reinforcement entirely from the arch structure, durability was improved. The re-aligned road crosses the river obliquely and to maintain the spandrels parallel to the road the arch has an end skew of 35˚. Skewed arches pose a design challenge as the geometry of the coursing of the voussoirs is surprisingly complex. Three-dimensional computer-aided design modelling was deployed to obtain a single precast voussoir block that could be set out and placed on the barrel falsework requiring no more than conventional site skills and resources. In total 479 copies of this single voussoir were cast to construct the majority of the arch barrel. The voussoirs are placed in the English or helicoidal arrangement with special precast blocks to form the arch springings.
The A9 is the primary north–south trunk route in the Scottish Highlands and bypasses the city of Inverness by means of Kessock Bridge, a major cable-stayed structure spanning the Beauly Firth and opened to traffic in 1982. The bridge is a 1052 m long viaduct with a main cable-stayed span of 240 m, 80 m back spans and a number of 64 m and 72 m approach spans. At the ends of the 80 m back spans, four pendel-type bearings were installed to accommodate uplift reaction due to loading on the main span. These pendel bearings became excessively worn over time and required replacement. This paper describes the design and construction issues associated with replacement of these critical structural elements, an operation made more challenging by the very constrained geometry and the need to maintain overall stability of the bridge under operational traffic conditions.
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