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Tower Bridge is a combined bascule and suspension bridge in Londonmarker, England, over the River Thames. It is close to the Tower of Londonmarker, which gives it its 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. Its present colour dates from 1977 when it was painted red, white and blue for the Queen's Silver Jubilee. Originally it was painted a chocolate brown colour.

Tower Bridge is sometimes mistakenly referred to as London Bridgemarker, which is actually the next bridge upstream. A popular urban legend is that in 1968, Robert McCulloch, the purchaser of the old London Bridgemarker that was later shipped to Lake Havasu City, Arizonamarker, 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.

The nearest London Underground station is Tower Hillmarker on the Circle and District Lines.

The nearest Docklands Light Railway station is Tower Gatewaymarker.


History

Background

Elevation, with dimensions
In the second half of the 19th century, increased commercial development in the East End of Londonmarker 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 Londonmarker, 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 Horace Jones, the City Architect (who was also one of the judges), 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. – and employed 432 construction workers. E W Crutwell was the resident engineer for the construction.

Two massive piers, containing over 70,000 tons of concrete, were sunk into the riverbed to support the construction. Over 11,000 tons of steel provided the framework for the towers and walkways. This was then clad in Cornishmarker 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. Stevenson replaced Jones' original brick facade with the more ornate Victorian Gothic style, which makes the bridge a distinctive landmark, and was intended to harmonise the bridge with the nearby Tower of Londonmarker. The total cost of construction was £1,184,000.

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).

The bridge connected Iron Gate, on the north bank of the river, with Horsleydown Lane, on the south – now known as Tower Bridge Approach and Tower Bridge Road, respectively. Until the bridge was opened, the Tower Subwaymarker – 400 m to the west – was the shortest way to cross the river from Tower Hillmarker to Tooley Streetmarker in Southwarkmarker. 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.

Tower Bridge is one of five London bridges now owned and maintained by the Bridge House Estates, a charitable trust overseen by the City of London Corporation. It is the only one of the Trust's bridges not to connect the City of London to the Southwark bank, the northern landfall being in Tower Hamletsmarker.

Design

The bridge is 800 feet (244 m) in length with two towers each 213 feet (65 m) high, built on piers. The central span of 200 feet (61 m) between the towers is split into two equal bascules or leaves, which can be raised to an angle of 83 degrees to allow river traffic to pass. The bascules, weighing over 1,000 tons each, are counterbalanced to minimize the force required and allow raising in five minutes.

The two side-spans are suspension bridges, each long, with the suspension rods anchored both at the abutments and through rods contained within the bridge's upper walkways. The pedestrian walkways are above the river at high tide.

Hydraulic system



The original raising mechanism was powered by pressurised water stored in several hydraulic accumulators.

The system was designed and installed by Sir W. G. Armstrong Mitchell & Company of Newcastle upon Tynemarker. Water, at a pressure of 750 psi, was pumped into the accumulators by two 360 hp stationary steam engines, each driving a force pump from its piston tail rod. The accumulators each comprise a 20-inch ram on which sits a very heavy weight to maintain the desired pressure.

In 1974, the original operating mechanism was largely replaced by a new electro-hydraulic drive system, designed by BHA Cromwell House. The only components of the original system still in use are the final pinions, which engage with the racks fitted to the bascules. These are driven by modern hydraulic motors and gearing, using oil rather than water as the hydraulic fluid.

Some of the original hydraulic machinery has been retained, although it is no longer in use. It is open to the public and forms the basis for the bridge's museum, which resides in the old engine rooms on the south side of the bridge. The museum includes the steam engines, two of the accumulators and one of the hydraulic engines that moved the bascules, along with other related artefacts.

The third steam engine

During World War II, as a precaution against the existing engines being damaged by enemy action, a third engine was installed in 1942: a 150 hp horizontal cross-compound engine, built by Vickers Armstrong Ltd. at their Elswick works in Newcastle upon Tyne. It was fitted with a flywheel having a 9-foot diameter and weighing 9 tons, and was governed to a speed of 30 rpm.

The engine became redundant when the rest of the system was modernised in 1974, and was donated to the Forncett Industrial Steam Museum by the Corporation of the City of London.

Navigation control

To control the passage of river traffic through the bridge, a number of different rules and signals were employed. Daytime control was provided by red semaphore signals, mounted on small control cabins on either end of both bridge piers. At night, coloured lights were used, in either direction, on both piers: two red lights to show that the bridge was closed, and two green to show that it was open. In foggy weather, a gong was sounded as well.

Vessels passing through the bridge had to display signals too: by day, a black ball at least in diameter was to be mounted high up where it could be seen; by night, two red lights in the same position. Foggy weather required repeated blasts from the ship's steam whistle.

If a black ball was suspended from the middle of each walkway (or a red light at night) this indicated that the bridge could not be opened. These signals were repeated about downstream, at Cherry Garden Pier, where boats needing to pass through the bridge had to hoist their signals/lights and sound their horn, as appropriate, to alert the Bridge Master.

Some of the control mechanism for the signalling equipment has been preserved and may be seen working in the bridge's museum.

Reaction

Although the bridge is an undoubted landmark, professional commentators in the early 20th century were critical of its aesthetics. "It represents the vice of tawdriness and pretentiousness, and of falsification of the actual facts of the structure", wrote H. H. Statham, while Frank Brangwyn stated that "A more absurd structure than the Tower Bridge was never thrown across a strategic river".

Architectural historian Dan Cruickshank selected the bridge as one of his four choices for the 2002 BBC television documentary series Britain's Best Buildings.

Tower Bridge today

centre




Road traffic

Tower Bridge is still a busy and vital crossing of the Thames: it is crossed by over 40,000 people (motorists and pedestrians) every day. The bridge is on the London Inner Ring Road, and is on the eastern boundary of the London congestion charge zone. (Drivers do not incur a charge by crossing the bridge.)

In order to maintain the integrity of the historic structure, the City of London Corporation have imposed a speed restriction, and an 18-tonne weight limit on vehicles using the bridge. A sophisticated camera system measures the speed of traffic crossing the bridge, utilising a number plate recognition system to send fixed penalty charges to speeding drivers.

A second system monitors other vehicle parameters. Induction loops and piezoelectric detectors are used to measure the weight, the height of the chassis above ground level, and the number of axles for each vehicle.



River traffic

The bascules are raised around 1000 times a year.River traffic is now much reduced, but it still takes priority over road traffic. Today, 24 hours' notice is required before opening the bridge. In 2008, a local web developer created a Twitter feed to post live updates of the bridge's opening and closing activities.

A computer system was installed in 2000 to control the raising and lowering of the bascules remotely. Unfortunately it proved less reliable than desired, resulting in the bridge being stuck in the open or closed positions on several occasions during 2005, until its sensors were replaced.

Tower Bridge Exhibition

The high-level walkways between the towers gained an unpleasant reputation as a haunt for prostitutes and pickpockets and were closed in 1910. In 1982 they were reopened as part of the Tower Bridge Exhibition, an exhibition now housed in the bridge's twin towers, the high-level walkways and the Victorian engine rooms. The walkways boast stunning views of the River Thames and many famous London sites, serving as viewing galleries for over 380,000 tourists who visit each year. The exhibition also uses films, photos and interactives to explain why and how Tower Bridge was built. Visitors can access the original steam engines that once powered the bridge bascules, housed in a building close to the south end of the bridge.

2008–2012 facelift

In April 2008 it was announced that the bridge will undergo a 'facelift' costing £4m, and taking four years to complete. The work entails stripping off the existing paint and repainting in blue and white. Each section will be enshrouded in scaffolding to prevent the old paint from falling into the Thames and causing pollution. Starting in mid-2008, contractors will work on a quarter of the bridge at a time to minimise disruption, but some road closures are inevitable. The bridge will remain open until the end of 2010, but is then expected to be closed for several months. It is hoped that the completed work will stand for 25 years.

The walkway section of the renovation was completed in mid 2009. Within the walkways a versatile new lighting system has been installed, designed by Eleni Shiarlis, for when the walkways are in use for exhibitions or functions. The new system provides for both feature and atmospheric lighting, the latter using bespoke RGB LED luminares, designed to be concealed within the bridge superstructure and fixed without the need for drilling (these requirements as a result of the bridge's Grade I status).

Incidents

In December 1952, the bridge opened while a number 78 double-decker bus (stock number RT 793) was on it. At that time, the gateman would ring a warning bell and close the gates when the bridge was clear before the watchman ordered the lift. The process failed while a relief watchman was on duty. The bus was near the edge of the south bascule when it started to rise; driver Albert Gunter made a split-second decision to accelerate the bus, clearing a three-foot drop on to the north bascule, which had not started to rise. There were no serious injuries.

On 5 April 1968 a Hawker Hunter FGA.9 jet fighter from No.1 Squadron RAF, flown by Flt Lt Alan Pollock, flew under Tower Bridge. Unimpressed that senior staff were not going to celebrate the RAF's 50th birthday with a fly-past, Pollock decided to do something himself. Without authorisation, Pollock flew the Hunter at low level down the Thames, past the Houses of Parliamentmarker, and continued on to Tower Bridge. He flew the Hunter beneath the bridge's walkway, remarking afterwards it was an afterthought when he saw the bridge looming ahead of him. Pollock was placed under arrest upon landing, and discharged from the RAF on medical grounds without the chance to defend himself at a court martial.

In May 1997, the motorcade of United States President Bill Clinton was divided by the opening of the bridge. Thames sailing barge Gladys, on her way to a gathering at St Katharine Docksmarker, arrived on schedule and the bridge was duly opened for her. Returning from a Thames-side lunch at Le Pont de la Tour restaurant, with UK Prime Minister Tony Blair, President Clinton was less punctual, and arrived just as the bridge was rising. The bridge opening split the motorcade in two, much to the consternation of security staff. A spokesman for Tower Bridge is quoted as saying, "We tried to contact the American Embassy, but they wouldn't answer the 'phone."

On 19 August 1999, Jef Smith, a Freeman of the City of London, drove a "herd" of two sheep across the bridge. He was exercising a claimed ancient permission, granted as a right to Freemen, to make a point about the powers of older citizens and the way in which their rights were being eroded.

Before dawn on 31 October 2003, David Crick, a Fathers 4 Justice campaigner, climbed a tower crane near Tower Bridge at the start of a six-day protest dressed as Spider-Man. Fearing for his safety, and that of motorists should he fall, police cordoned off the area, closing the bridge and surrounding roads and causing widespread traffic congestion across the City and east London. The Metropolitan Police were later criticised for maintaining the closure for five days when this was not strictly necessary in the eyes of some citizens.

On May 11, 2009, six persons were trapped and injured after a lift fell 10 ft inside the north tower.

Gallery

Image:Tower Bridge Day.JPG|Tower Bridge during dayImage:Tower Bridge London Feb 2006.jpg|Tower Bridge at nightImage:Tower-bridge-air.jpg|Tower Bridge area from the airImage:Tower Bridge 2007 3.jpg|The south tower, showing pier at river level.Image:tower.bridge.7.basculecloseup.london.arp.jpg|Close-up of opened basculesImage:Tower-bridge-south-view.jpg|South view at duskImage:Tower Bridge from St. Paul.jpg|Tower Bridge viewed from St Paul's CathedralmarkerImage:Tower Bridge, London (41).JPG| Tower Bridge south tower from the River Thames.

See also



Historic places adjacent to Tower Bridge:


Notes

References

External links




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