Wednesday, 10 December 2008

Design and construction

The bridge's longevity may owe something to the fact that it was designed by a Royal Navy officer, Captain Samuel Brown. Brown's first design for the bridge was prepared in 1817, and reviewed by the eminent civil engineer John Rennie. Brown had built an experimental suspension bridge with a span of 110 ft, which impressed Rennie. Nonetheless, Rennie asked for changes to the design of the stone abutments and towers.

Brown would have been familiar with the fact that a wooden sailing ship is not totally rigid and designed the bridge on the same basis. Originally the deck was supported by three chains of iron bar links on each side. In 1902 a pair of wire rope cables was added. The decking is of timber and the whole structure is designed to flex slightly under load. Standing on it when a vehicle crosses is reminiscent of being on a ship. For this reason, traffic is now limited to one vehicle on the bridge at any one time.

The bridge proposal, received consent in July 1819 using an Act of Parliament that had been passed in 1802, and construction began 2 August 1819. It opened on 26 July the following year, with an opening ceremony attended by Robert Stephenson among others. Captain Brown tested the bridge in a curricle towing twelve carts, before a crowd of about 700 spectators crossed. The final cost was GB£6,449.

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