Tower Bridge

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Coordinates: 51°30′20″N, 0°04′32″W

Tower Bridge
Tower Bridge from the South Bank at dusk.
Carries	A100 Tower Bridge Road - motor vehicles, pedestrians
Crosses	Thames
Locale	London
Maintained by	Bridge House Estates
Design	Bascule bridge, suspension bridge
Longest span	61 m (200 feet)
Total length	244 m (800 feet)
Clearance below	8.6 m (closed), 42.5 m (open)
Opening date	1894
Maps and aerial photos Street map from Google Maps or Yahoo! Maps Topographic map from TopoZone Aerial image or topographic map from TerraServer-USA Satellite image from Google Maps or Microsoft Virtual Earth

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 and is sometimes mistakenly called London Bridge, which is the next bridge upstream. The bridge is owned and maintained by Bridge House Estates, a charitable trust overseen by the Corporation of London.

[edit] Design

 

In the second half of the nineteenth 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 tunnel beneath the Thames, the Tower Subway, had been opened in 1870, for pedestrians only.

A Special Bridge or Subway Committee was formed in 1876 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)^[1], 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, with the suspension rods anchored both at the abutments and through rods contained within the bridge's upper walkway.

Construction started in 1886 and took eight years, employing five major contractors and 432 construction workers. Two massive piers, containing over 70,000 tons of concrete ^[2], were sunk into the river bed to support the construction. Over 11,000 tons of steel provided the framework for the towers and walkways^[3]. 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 ^[4]. Stevenson replaced Jones' original brick facade with the more ornate Victorian gothic style that makes the bridge a distinctive landmark.

The bridge was opened on 30 June 1894 by the Prince of Wales, the future King Edward VII, and his wife, Alexandra of Denmark.

[edit] Hydraulic system

One of the original steam engines: a horizontal twin-tandem compound engine, fitted with Meyer expansion slide valves

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 Gateshead. Water, at a pressure of 750psi was pumped into the accumulators by two 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.^[5]

Some of the original hydraulic machinery has been retained, although 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.

[edit] 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.^[6] This was a 150hp 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.

[edit] Tower Bridge today

Tower Bridge
Sequence showing the bridge opening

Tower Bridge in its river setting, looking east from the viewing platform of The Monument. City Hall is the building shaped like a motorcycle helmet, and below it is HMS Belfast.

Although the bridge is an undoubted landmark, professional commentators have generally been very 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^[7], while Frank Brangwyn stated that "A more absurd structure than the Tower Bridge was never thrown across a strategic river"^[8].

The high-level walkways between the towers gained an unpleasant reputation as a haunt for prostitutes and pickpockets and were closed in 1910. They have been reopened as part of the Tower Bridge Experience, an exhibition mostly housed in the bridge's twin towers. The exhibition also includes photos, holograms and a film detailing the build, along with access to 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, on 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. The bascules are raised around 900 times a year.

River traffic is now a fraction of what it used to be, but it still takes priority over road traffic. This nearly caused a diplomatic incident in 1996, when the motorcade of United States President Bill Clinton got stuck on Tower Bridge while the bascules were opened unexpectedly. Nowadays 24 hours' notice is required before opening the bridge.

The bridge largely replaced Tower Subway, 400 m to the west, the world's first underground tube 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.

A computer system was installed in 2000 to control the raising and lowering of the bascules remotely. Unfortunately this has proved less reliable than desired, resulting in the bridge being stuck in the open or closed positions on a number of occasions (most recently 2 June 2005).

[edit] Nearby places

The bridge is near the Tower of London, St Katharine Docks, and Shad Thames.

The north end is near Tower Hill tube station, Tower Gateway DLR station and Fenchurch Street railway station. The south end is about 10 minutes' walk from London Bridge station.

To the south is Tower Bridge Road, which is part of the London Inner Ring Road.

[edit] Gallery

An extremely high resolution image of Tower Bridge at night	South view at dusk	Bridge open	Close-up of fully opened bascules
Interior of high-level walkway (used as an exhibition space)	Tower Bridge area from the air	A slave ship moored by Tower Bridge to mark 200 years since the Slave Trade Act 1807 (April 2007)

[edit] See also

• Crossings of the River Thames

[edit] References

[edit] Trivia

• Many, particularly in the United States, confuse the bridge with London Bridge, another well-known London landmark bridge. In the video for her single "London Bridge", Fergie, of The Black Eyed Peas, wrongly refers to Tower Bridge as London Bridge.

• 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 half way across.^[9]

• Tower Bridge featured in movies such as: Pool of London, Bridget Jones's Diary, The Mummy Returns, The Boy in the Bridge,^[10] Spice World, The World Is Not Enough, Steamboy, and on July 13, 2007 in Harry Potter and the Order of the Phoenix.

[edit] External links

Wikimedia Commons has media related to:

Tower Bridge

• Official website

• Map and aerial photo of Tower Bridge from Multimap.com
• Other map and aerial photo sources
• Bridge Lifting / Opening Dates and Times
• Technical article on the building of Tower Bridge
• BBC News - 17 January 2006 - Fix to stop bridge getting stuck
• The third steam engine (includes photo) – now at Forncett Industrial Steam Museum, Forncett St Mary, Norfolk