Tower Bridge is one London's great landmarks and 'The Tower Bridge Experience' is one of the capital's most unusual and exciting exhibitions.
By the middle of the 19th century traffic necessitated a new bridge close to the Tower of London. The new bridge would serve the people of east London who had to make lengthy detours across the capital to cross the Thames at London Bridge.
A major problem was that the new bridge had to be constructed to allow the passage of tall ships into the Port of London. In 1878 the City Engineer, Sir Horace Jones, suggested a double-leaf bascule bridge. In 1885 an Act of Parliament was passed authorising the construction of Tower Bridge. The Act stipulated that the bridge be clad to match the style of the Tower of London.
Tower Bridge, one of the great symbols of London, was built between 1886-94. Sir Horace died shortly after the foundation work began and his modified plan was carried out by Barry, assisted by Brunel (the younger) and the resident engineer, Crutwell.
Two major piers were sunk into the riverbed to support the construction. The piers are 185 ft long and 70 ft wide, with central areas of 70 ft square forming the base of the towers. The main towers have columns 120 ft high, while the smaller towers on the shore have columns 44 ft high.
The 270 ft side spans are suspension platforms supported by chains anchored in the rear of the abutments and carried over the two smaller towers to the main towers. Here they are joined by rods concealed in the decorative wrought-iron of the two walkways. The towers and linking catwalk provide support for the roadway's steam-operated lifting mechanism.
In all 11,000 tonnes of steel were required for the framework of the towers and walkways which was then clad in Cornish granite, with Portland stone for the dressings and window mullions. This provided protection the underlying steelwork and gave the bridge it's Gothic appearance.
On its completion, Tower Bridge was the world's largest and most sophisticated hydraulically operated bridge. Until 1976 the winding machinery was powered by steam but is now electronically operated. The bascules, which were also replaced in 1976, each weigh 1,200 tons and have to be counterbalanced with 422 tons of lead and iron. Taking around 3-5 minutes to open, the bridge is 135 feet (40 m) high and 200 feet (60 m) wide when raised.
Because the Act of 1885 stipulated that the public should have access over Tower Bridge at all times, walkways were built between the towers, 143 feet above the Thames. These enabled pedestrians to cross the bridge even if the bridge was open for shipping. However, in 1910 the walkways were closed to the public because of the large number of suicides.
During its first few years Tower Bridge's bascules opened, on average, 22 times a day. Today they still open at least once a day for large ships or for special and historic occasions. Advance notice must be given to the Bridge Master before the basules can be raised.
After a major renovation of Tower Bridge in 1982 the walkways were glassed in and re-opened as a tourist attraction. In 1984 a fascinating exhibition about Tower Bridge opened on the south side of the bridge. The tour ends in the pump rooms where the old steam engines can still be seen.