Thursday, 26 July 2012

After suspension bridges – what about Cable-Stayed bridges

Cable-stayed bridges seem to be taking over from suspension bridges so after discussing at Hungerford and Clifton, I thought I’d investigate this type. Although many have been built in the last 50 years or so, the design has been around for much longer. Some notable early bridges are either cable-stayed or a combination of suspension and cable-stayed:  the Victoria Bridge, Bath (1836) the Albert Bridge across the Thames (1872) and the Brooklyn Bridge in New York (1883)

Victoria Bridge and Albert Bridge
 The first modern cable-stayed bridge is usually quoted as the Strömsund Bridge in Sweden, built in 1955.

Strömsund Bridge

Since that date may have been built: the Queen Elizabeth II bridge which takes the M25 over the Thames and the Second Severn Crossing are two in the UK.

Second Severn Crossing

Probably the most famous is the Millau Bridge in France, designed by the French structural engineer Michel Virlogeux and British architect Norman Foster, it is the tallest bridge in the world. It also has the highest structure in France – one of the piers at 343M is taller than the Eiffel Tower (323M). The Millau has 7 piers and 8 spans. This, I believe, makes it the longest cable-stayed span in the world. Interestingly Wikipedia, in it’s list of longest cable-stayed bridges, doesn’t include the Millau because the others have longer approach bridges which are not cable-stayed.

Millau Bridge
The main difference between suspension and cable-stayed bridges is that in the latter, much of the weight of the bridge is taken by the cables to the anchorages which need to be substantial. In cable-stayed, the weight is taken to the piers. Also multiple-span suspension bridges are not possible.

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