Iconic Civil and Structural Engineering - Tower Bridge

Looking today at the broad Thames snaking its way through the heart of the capital, it's hard to believe that there was once only one bridge crossing the river - London Bridge. As the city grew, so did the number of crossing points and in 1876 a public competition invited ideas for building a new bridge downstream from London Bridge without disrupting river traffic. Although more than 50 designs were submitted, it was to be eight years before an acceptable solution was found in the form of a 'bascule' design by the City Architect, Horace Jones ('bascule' being French for see-saw). Sadly, although appointed architect and given a knighthood, Horace Jones died in the same year that his design was accepted, leaving John Wolfe Barry as the appointed engineer.

It then took a ndafurther eight years, involving the intense labour of more than 400 construction workers from several major contractors, to build the bridge. Firstly, two enormous piers were sunk into the bed of the Thames - 293 out high when measured from the level of the foundations - with 11,000 tons of steel columns and girders providing the framework for the whole construction. Many mistake it for a stone bridge, as the steelwork was faced with Cornish granite and Portland stone. The authorities insisted that the bridge's architecture must harmonise with the general style of the nearby Tower of London.

Including the approaches, Tower Bridge is half a mile long, with a 35 ft roadway and footways on either side. At the time of its construction it was the largest bascule bridge ever built. Although there were already bridges of this kind in Rotterdam and Copenhagen, they were on a much smaller scale. The Tower Bridge piers house the duplicated counterpoise and machinery that operate the bascules. Originally, these bascules were operated by hydraulics, using steam to power the massive pumping engines. Whenever power was needed to lift the bridge, energy was ready for immediate use, as power was stored in six enormous accumulators. These accumulators fed the driving engines, which in turn raised and lowered the bascules. Amazingly, they took only about a minute to raise to their maximum angle of 86 degrees. The bascules are still operated by hydraulic power to this day, although they are now driven by oil and electricity, which took over from steam in 1976. When the bascules come together, bolts carried on one bascule are locked by hydraulic power into sockets on the other.

For some years after the bridge's opening, the high level walkways were used by pedestrians. However, as people preferred to stay at street level until the bridge was ready to cross again, the walkways were closed in 1910 owing to lack of use. Although these have re-opened in recent years and large hydraulic lifts in the towers can carry passengers up to the overhead footway, most pedestrians still prefer to wait at street level when Tower Bridge is raised. With the whole process taking only about five minutes, many simply enjoy watching the ship pass through, marvelling at such a feat of engineering.

by Phil Byrne

About the Author

From their offices in Retford, HBPW have become one of the foremost civil and structural engineering companies within the UK. As pioneers of sustainable engineering, HBPW offer a wealth of experience within construction and the environment


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