Tower Bridge

Infobox_Bridge
bridge_name= Tower Bridge


caption= Tower Bridge from the North Bank at dusk
official_name=
also_known_as=
carries= A100 Tower Bridge Road - motor vehicles, pedestrians
crosses= Thames
locale= London
maint= Bridge House Estates
id=
design= Bascule bridge, suspension bridge
mainspan= 61 m (200 ft)
length= 244 m (800 ft)
width=
clearance=
below= 8.6 m (closed), 42.5 m (open)
traffic=
open= 30 June 1894
closed=
toll=
map_cue=
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longitude=

Tower Bridge is a combined bascule and suspension bridge in London, England over the River Thames. It is close to the Tower of London, which gives it its name. It has become an iconic symbol of London. Tower Bridge is one of several London bridges owned and maintained by the City Bridge Trust, a charitable trust overseen by the City of London Corporation.

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 to the left and the right. 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. Before this, it was painted a chocolate brown colour. [ [http://www.towerbridge.org.uk/TowerBridge/English/BridgeHistory/ Tower Bridge Exhibition - Bridge history ] ]

Tower Bridge is sometimes mistakenly referred to as London Bridge, which is actually the next bridge upstream.cite web | url = http://images.google.ca/images?hl=en&q=london+bridge&btnG=Search+Images&gbv=2 | title = Image Search for 'London Bridge' | publisher = Google | accessdate = March 30 | accessyear = 2007] A popular urban legend is that, in 1968 Robert McCulloch, the purchaser of the old London Bridge which was later shipped to Lake Havasu City, Arizona, believed mistakenly that he was buying Tower Bridge, but this was denied by McCulloch himself and has been debunked by Ivan Luckin, the seller of the bridge. [ [http://www.thisislocallondon.co.uk/archive/display.var.169982.0.how_london_bridge_was_sold_to_the_states.php How London Bridge Was Sold To The States (from This Is Local London) ] ]

Design

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 A. J. 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), [Roberts, Chris, "Cross River Traffic", Granta, 2005] was approved.

Jones' engineer, Sir John Wolfe Barry, devised the idea of a bascule bridge 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 was split into two equal bascules or leaves, which could be raised to an angle of 83 degrees to allow river traffic to pass. The bascules, weighing over 1,000 tons each, were counterbalanced to minimize the force required and allow raising in five minutes.

The two side-spans are suspension bridges, each convert|270|ft|m|0 long, with the suspension rods anchored both at the abutments and through rods contained within the bridge's upper walkways. The pedestrian walkways are convert|143|ft|m|0 above the river at high tide.cite journal
title =Tower Bridge
journal =Archive – The Quarterly Journal for British Industrial and Transport History
volume =
issue =Issue 3
pages =p47
date =1994
publisher = Lightmoor Press
issn =1352-7991]

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. [The Times, 2 July 1894] – 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,Roberts, op. cit.] were sunk into the river bed to support the construction. Over 11,000 tons of steel provided the framework for the towers and walkways. 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. 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 London.

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). [ [http://thames.me.uk/s00040.htm Where Thames Smooth Waters Glide] ]

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. It largely replaced Tower Subway, 400 m to the west, the world's first underground railway (1870). Until the bridge was opened, the subway was the shortest way to cross the river from Tower Hill to Tooley Street in Southwark.

The total cost of construction was £1,184,000.

Hydraulic system

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

The system was designed and installed by Sir W. G. Armstrong Mitchell & Company of Newcastle upon Tyne. Water, at a pressure of 750psi, 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. [cite web
last =Hartwell
first =Geoffrey
title =Tower Bridge, London
url =http://www.hartwell.demon.co.uk/tbpic.htm
accessdate =2007-02-27 ]

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. [cite web
title =The Tower Bridge Engine
publisher =Forncett Industrial Steam Museum
url =http://oldenginehouse.users.btopenworld.com/towerb.htm
accessdate =2007-02-27 ] This was 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 9 feet diameter flywheel 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 convert|2|ft|m|2 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 convert|1000|yd|m downstream, at Cherry Garden Pier, where boats requiring 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, [Statham, H.H., "Bridge Engineering", Wiley, 1916.] while Frank Brangwyn stated that "A more absurd structure than the Tower Bridge was never thrown across a strategic river". [Brangwyn, F., and Sparrows, W.S., "A Book of Bridges", John Lane, 1920.]

Architectural historian Dan Cruickshank selected the bridge as one of his four choices for the 2002 BBC television documentary series "Britain's Best Buildings".cite web | url=http://www.bbc.co.uk/history/programmes/programme_archive/best_buildings_06.shtml | title=Choosing Britain's Best Buildings | accessdate=June 3 | accessyear=2008 | author= | last=Cruickshank | first=Dan | authorlink= | coauthors= | date= | year= | month= | format= | work= | publisher=BBC History | pages= | language=English | doi= | archiveurl= | archivedate= | quote= ]

Incidents

At 21:35 on 30 December 1952, a crowded double-decker London bus (an RT), on route 78 to Dulwich, jumped over the gap when the bridge started to open while it was halfway across. [cite web
title =Frequently Asked Questions
publisher ="London's Transport Museum"
url =http://www.ltmuseum.co.uk/research/faqs/5.shtml#FAQ5
accessdate =2007-02-28 ]

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 Parliament, 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. [p.157, Shaw, Michael 'No.1 Squadron', Ian Allan 1986] [cite web | title = Hawker Hunter History | work = (scroll down half-way) | publisher = Thunder & Lightnings | date = 29 February2004 | url = http://www.thunder-and-lightnings.co.uk/hunter/history.html | accessdate = 2008-04-08] "(See also: Hawker Hunter Tower Bridge incident.)"

In May 1997, [cite web | title =Presidential visits abroad | work =(William J. Clinton III) | publisher =US Department of State | date = | url = http://www.state.gov/r/pa/ho/trvl/pres/5188.htm | accessdate = 2007-09-25 ] the motorcade of United States President Bill Clinton was divided by the "unexpected" opening of the bridge. Thames sailing barge "Gladys", on her way to a gathering at St Katharine Docks, 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." [cite web | last =Shore | first =John | authorlink = | coauthors = | title =Gladys takes the rise out of Bill | work = | publisher =Regatta Online "(Issue 100, July 1997)" | date = | url =http://www.rowingservice.com/regatta/100-gladys.html | format = | doi = | accessdate = 2007-09-25 ]

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 an 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. [cite web | title =Protest Freeman herds sheep over Tower Bridge | work = | publisher =BBC News | date = 19 August 1999 | url = http://news.bbc.co.uk/1/hi/uk/425364.stm | accessdate = 2007-09-25 ]

Tower Bridge today

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.cite web
title =Fix to stop bridge getting stuck
publisher = BBC News
date =17 January 2006
url =http://news.bbc.co.uk/1/hi/england/london/4620622.stm
accessdate =2007-09-25 ] The bridge is on the London Inner Ring Road, and (as of 2007) 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 convert|20|mph|km/h|0 speed restriction, and an 18 ton 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 piezo-electric 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. [cite web
title =Bridge Lifts
publisher = Tower Bridge Official Website
date = | url =http://www.towerbridge.org.uk/TowerBridge/English/BridgeLifts/
accessdate =2007-09-25 ] 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, the bridge's managers began using Twitter to post live updates of the bridge's opening and closing activities. [cite web
title =Twitter stream
publisher = Tower Bridge Official Twitter stream
date = | url =http://twitter.com/towerbridge
accessdate =2008-09-08 ]

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.

A Behind the Scenes tour can be booked in advance, during which it is possible to see the bridge's command centre, from where the raising of the bascules is controlled for a vessel to pass through, and go down into the bascule chambers too.

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 falling into the Thames causing pollution. Starting in summer 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 winter 2010, but is then expected to be closed for several months. It is hoped that the completed work will last 25 years. [cite web | title = Tower Bridge to get £4m facelift | publisher = BBC News Online | date = 07 April 2008 | url = http://news.bbc.co.uk/1/hi/england/london/7335380.stm | accessdate = 2008-04-08]

Gallery

ee also

*
*Crossings of the River Thames
*Historic places adjacent to Tower Bridge:
**Tower of London
**St Katharine Docks
**Shad Thames

References

External links

* [http://www.towerbridge.org.uk/ Official website]
* [http://twitter.com/towerbridge Official Twitter stream of opening/ closing moves]
* [http://www.towerbridge.org.uk/TowerBridge/English/BridgeLifts/schedule.htm Bridge Lifting / Opening Dates and Times]
* [http://www.hartwell.demon.co.uk/tbpic.htm Technical article on the building of Tower Bridge]
* [http://oldenginehouse.users.btopenworld.com/towerb.htm The third steam engine (includes photo)] "– now at Forncett Industrial Steam Museum, Forncett St Mary, Norfolk"
*structurae|id=s0000477
* [http://www.theengineer.co.uk/Articles/297483/March+1878+Tower+Bridge.htm 1878 article on Tower Bridge]
* [http://www.earthinpictures.com/world/great_britain/london/tower_bridge.html Tower Bridge information and photography]
* [http://www.fmschmitt.com/travels/England/london/towerbridge/towerbridge.html Tower Bridge PhotoEssay]
* [http://www.oldstratforduponavon.com/londontower Some Old Postcards of The Tower and Tower Bridge]
* [http://londonfish.blogspot.com/2008/06/london-bridge.html Tower Bridge Photos]
* [http://lltv.libsyn.com/index.php?post_id=305748 London Landscape TV episode (5 mins) about Tower Bridge]

Crossings navbox
structure = Crossings
place = River Thames
bridge = Tower Bridge
Grid reference: gbm4ibx|TQ336802
upstream = London Bridge (road)
Tower Subway (tunnel)
downstream = Thames Tunnel (railway)|location=TQ336802