Tower Bridge

Classic Projects: Tower Bridge

Opened in 1894, Tower Bridge is one of London's most iconic landmarks.

"A more absurd structure than the Tower Bridge was never thrown across a strategic river," wrote artist Sir Frank Brangwyn, referring to the most famous bascule bridge in the world. In fact, Tower Bridge is a fusion of three bridges, two of the suspension category emerging from the north and south banks of London's River Thames, with a central span comprising two leaves, or 'bascules', that can be raised to allow high-masted ships to pass.

It was the largest bridge of its type and is seen as not only an icon of Victorian engineering, but of London itself. The need for the bridge arose from cross-river traffic outstripping the capacity of existing bridges in the mid-1800s, with nearby London Bridge averaging more than 100,000 pedestrians and 20,000 vehicles per day.

By the 1870s, congestion had sparked 30 petitions to widen London Bridge. In 1878 architect Sir Horace Jones put forward a proposal for a low-level bridge on the bascule principle and an Act of Parliament allowing its construction was passed in 1885. This was not without controversy, as Jones had entered a public competition to solve the problem. He, along with other senior engineers of the day – including Sir Joseph Bazalgette, submitted their entries to a board of judges, of which Jones was one.

Jones was appointed architect but died the same year, allowing John Wolfe Barry to step in. Delivered late, after two deadline extensions, Tower Bridge was finally opened a decade later on 30 June 1894, at a cost of just over £1m.

Solving the problem of how to get big ships upstream while still allowing vehicles to cross the river by road using the bascule method was not new, but it had never been achieved in such a scale. While the Gothic exterior, allegedly designed to harmonise with the nearby Tower of London, may be one of the reasons it featured on the BBC series 'Britain's Best Buildings', it's the engineering that makes Tower Bridge so special.

The bascule raising system is the star of the show, with the original mechanism powered by water stored in hydraulic accumulators. Water at a pressure of 750psi was pumped into the accumulators by two 360hp stationary steam engines, each driving a force pump from its piston tail rod.

The system remained unchanged for almost a century, with the exception of the addition of a third engine in 1942. The third engine was supplied by Vickers Armstrong and remained in place until 1974, when the entire system was overhauled and replaced by an electro-hydraulic drive system designed by BHA Cromwell House, using oil rather than water as the hydraulic fluid.

As one of Britain's most popular buildings, Tower Bridge has often been in the limelight. Pilots have (illegally) flown light aircraft under the walkway, Bill Clinton's motorcade was famously split in two, and a protester dressed as Spiderman caused the Bridge to close for five days. There is even a popular urban myth that in 1968 an American called Robert McCulloch bought the old London Bridge under the mistaken impression he was buying the architecturally more florid Tower Bridge. There is no substance to this bizarre claim whatsoever.

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