Tower Bridge is a combined bascule and suspension bridge . It is close to the Tower of London, which gives it its name.^{Name[›]} It has become an iconic symbol of London.

The bridge consists of two towers which are tied together at the upper level by means of two horizontal walkways which are designed to withstand the horizontal forces exerted by the suspended sections of the bridge on the landward sides of the towers.

The vertical component of the forces in the suspended sections and the vertical reactions of the two walkways are carried by the two robust towers. The bascule pivots and operating machinery are housed in the base of each tower.

Tower Bridge is sometimes mistakenly referred to as London Bridge, which is actually the next bridge upstream.^[2] A popular urban legend is that in 1968, Robert McCulloch, the purchaser of the old London Bridge that was later shipped to Lake Havasu City, Arizona, believed that he was in fact buying Tower Bridge. This was denied by McCulloch himself and has been debunked by Ivan Luckin, the seller of the bridge.^[3]

In the second half of the 19th century, increased commercial development in the East End of London led to a requirement for a new river crossing downstream of London Bridge. A traditional fixed bridge could not be built because it would cut off access to the port facilities in the Pool of London, between London Bridge and the Tower of London.

A Special Bridge or Subway Committee was formed in 1876, chaired by Sir Albert Joseph Altman, to find a solution to the river crossing problem. It opened the design of the crossing to public competition.

Over 50 designs were submitted, including one from civil engineer Sir Joseph Bazalgette. The evaluation of the designs was surrounded by controversy, and it was not until 1884 that a design submitted by Sir Horace Jones, the City Architect (who was also one of the judges),^[5] was approved.

Jones' engineer, Sir John Wolfe Barry, devised the idea of a bascule bridge with two towers built on piers. The central span was split into two equal bascules or leaves, which could be raised to allow river traffic to pass. The two side-spans were suspension bridges, with the suspension rods anchored both at the abutments and through rods contained within the bridge's upper walkways.

Construction

Tower Bridge under construction, 1892

Construction started in 1886 and took eight years with five major contractors – Sir John Jackson (foundations), Baron Armstrong (hydraulics), William Webster, Sir H.H. Bartlett, and Sir William Arrol & Co.^[6] – and employed 432 construction workers. E W Crutwell was the resident engineer for the construction.^[7]

Two massive piers, containing over 70,000 tons of concrete,^[5] were sunk into the riverbed to support the construction.

Over 11,000 tons of steel provided the framework for the towers and walkways.^[5] This was then clad in Cornish granite and Portland stone, both to protect the underlying steelwork and to give the bridge a pleasing appearance.

Jones died in 1887 and George D. Stevenson took over the project.^[5] Stevenson replaced Jones' original brick facade with the more ornate Victorian Gothicstyle, which makes the bridge a distinctive landmark, and was intended to harmonise the bridge with the nearby Tower of London.^[7] The total cost of construction was £1,184,000^[7] (£100 million as of 2011).^[8]

[edit]Opening

The bridge was officially opened on 30 June 1894 by The Prince of Wales (the future King Edward VII), and his wife, The Princess of Wales (Alexandra of Denmark).^[9]

The bridge connected Iron Gate, on the north bank of the river, with Horselydown Lane, on the south – now known as Tower Bridge Approach and Tower Bridge Road, respectively.^[7]

 Until the bridge was opened, the Tower Subway – 400 m to the west – was the shortest way to cross the river from Tower Hill to Tooley Street in Southwark.

Opened in 1870, Tower Subway was the world's first underground ('tube') railway, but closed after just three months and was re-opened as a pedestrian foot tunnel. Once Tower Bridge was open, the majority of foot traffic transferred to using the bridge, there being no toll to pay to use it. Having lost most of its income, the tunnel was closed in 1898.^[10]

Tower Bridge is one of five London bridges now owned and maintained by the Bridge House Estates, a charitable trust overseen by the City.  

(Tomorrow, the fascinating history with pictures of London Bridge.) companion blogging site here on MyBloggers.)


https://en.wikipedia.org/wiki/Tower_Bridge