London’s historic Tower Bridge is one of the city's main tourist attractions. Officially opened on 30th June 1894, it offers fantastic views from its high-level walkways, while visitors can also watch the spectacle of the bridge being lifted more than 1,000 times a year to let cruise liners, tall ships and other boats pass underneath.

The bridge is an amazing feat of engineering. Measuring 800 feet long and having two towers, each 213-foot-tall and built on piers, the central span between the towers measures 200 feet and is split into two equal parts. These are raised to an angle of 86 degrees, permitting boats to pass beneath.

Each half weighs more than 1,000 tons. They are counterbalanced, as this minimises the force needed to raise them and enables the process to be completed in around five minutes.


History of the bridge

In the second half of the 19th century, it was decided a new bridge was needed to cross the River Thames near the Tower of London. However, its design was challenging, since it couldn't be at street level because it would cut off access for ships.

A committee was formed in 1877 to finalise plans and more than 50 different designs were submitted, before members finally approved one in 1884, based on an idea by civil engineer Sir Joseph Bazalgette. Although his original plan was rejected because it lacked headroom, his design was modified to form the basis of the bascule bridge that was eventually built.

The total cost of the construction was £1.18 million - this equates to around £124 million today. Construction began in 1886, with five major contractors appointed to complete different aspects of the structure, including hydraulics expert Baron William George Armstrong.

The visionary inventor, scientist and engineer had founded the famous Elswick works on the bank of the Tyne. The company employed more than 25,000 people and manufactured hydraulic cranes, ships and armaments.


Hydraulic system

As well as creating Tower Bridge's hydraulic mechanism, Armstrong had also built Newcastle's Swing Bridge. He built Cragside, his magnificent stately home in Northumberland, planting seven million trees in its expansive grounds. It was the first house to be lit by hydroelectricity.

The hydraulic system he designed and manufactured for Tower Bridge was its main operating system for almost a century, until 1974. It raised the bridge using power created by pressurised water, stored in six hydraulic accumulators.

Two stationary steam engines pumped the water, at a pressure of 750 pounds per square inch, into the accumulators, which drove a force pump from the piston tail rod. Each accumulator comprised a 20-inch ram, with a very heavy weight resting on top to maintain the required pressure.

During World War II, a third engine was installed in 1942, as a precautionary measure against possible bomb damage. Built by Vickers Armstrong Ltd, it was a horizontal 150hp cross-compound engine.


Today's mechanism

Much of the original operating mechanism was finally replaced in 1974, after continuing virtually unaltered since it was constructed in the 1880s. The new electro-hydraulic drive system was designed by BHA Cromwell House.

However, the final pinions of the original system are still in use today, engaging with the racks fitted to the bascules. Modern hydraulic motors drive the system and the hydraulic fluid used is oil instead of water.

Although most of the 19th-century hydraulic machinery is no longer in use, it has been retained and is open to the public as part of the bridge's museum, which is a popular tourist attraction in the old engine rooms, located on the south side. On display in the museum are the original steam engines, two accumulators and one of Armstrong's hydraulic engines.


Refurbishments

In April 2008, the bridge was refurbished at a cost of £4 million to make it more aesthetically pleasing. The facelift took four years to complete and included stripping off the old paint to reveal the metal underneath and repainting it white and blue.

The structure was transformed for the 2012 London Olympics, when a set of giant Olympic rings were suspended from the bridge at a cost of £259,817. They measured a massive 82 feet by 38 feet.

In 2016, further refurbishments were carried out, including structural maintenance work on the bridge's lifting system, resurfacing the road and walkways, replacing the bridge's expansion joints and waterproofing the arches.


Tourist attraction

Today, Tower Bridge is one of London's top tourist attractions, thanks to its spectacular views - a result of installing glass flooring throughout the high-level walkways.

All sorts of events take place there, including the Tower Bridge Exhibition, the Family Learning Programme and various family-friendly activities, such as yoga in the walkways. This isn't for the faint-hearted, as adventurous participants perfect their moves 42 metres above the Thames!

You can also find out more about the bridge and its history, thanks to the 360 Tour devised by London and Partners using the City Visitor Trail app.

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