Lattice truss bridge
|Function / usage:||
Skyway (skywalk, skybridge)
Awards and Distinctions
Tower Hamlets, London, England, United Kingdom
Southwark, London, England, United Kingdom
|Coordinates:||51° 30' 19.80" N 0° 4' 31.46" W|
|main span||79 m|
|length of side spans||82.3 m|
|total length||286.50 m|
|height of foot bridges||43 m|
Excerpt from Wikipedia
Tower Bridge is a combined bascule and suspension bridge in London, built between 1886 and 1894. The bridge crosses the River Thames close to the Tower of London and has become a world-famous symbol of London. As a result, it is sometimes confused with London Bridge, about 0.5 miles (0.80 km) upstream. Tower Bridge is one of five London bridges 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 directly to the Southwark bank, as its northern landfall is in Tower Hamlets.
The bridge consists of two bridge towers tied together at the upper level by two horizontal walkways, designed to withstand the horizontal tension forces imposed by the suspended sections of the bridge on the landward sides of the towers. The vertical components 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.
The bridge deck is freely accessible to both vehicles and pedestrians, whereas the bridge's twin towers, high-level walkways and Victorian engine rooms form part of the Tower Bridge Exhibition, for which an admission charge is made. The nearest London Underground tube stations are Tower Hill on the Circle and District lines, London Bridge on the Jubilee and Northern lines and Bermondsey on the Jubilee line, and the nearest Docklands Light Railway station is Tower Gateway. The nearest National Rail stations are at Fenchurch Street and London Bridge.
In the second half of the 19th century, increased commercial development in the East End of London led to demands for a new river crossing downstream of London Bridge. A traditional fixed bridge at street level could not be built because it would cut off access by sailing ships 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 1877, chaired by Sir Albert Joseph Altman, to find a solution. More than fifty designs were submitted, including one from civil engineer Sir Joseph Bazalgette, which was rejected because of a lack of sufficient headroom. A design was not approved until 1884, when it was decided to build a bascule bridge. Sir John Wolfe Barry was appointed engineer and Sir Horace Jones the architect (who was also one of the judges). An Act of Parliament was passed in 1885 authorising the bridge's construction. It specified the opening span must give a clear width of 200 feet (61 m) and a headroom of 135 feet (41 m). Construction had to be in a Gothic style.
Barry designed a bridge with two bridge 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 rods anchored both at the abutments and through rods contained in the bridge's upper walkways.
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. The first stone was laid by Albert, Prince of Wales.
Two massive piers, containing over 70,000 long tons (78,400 short tons; 71,123 t) of concrete, were sunk into the riverbed to support the construction. More than 11,000 long tons (12,320 short tons; 11,177 t) of steel were used in the framework for the towers and walkways, which were then clad in Cornish granite and Portland stone, to protect the underlying steelwork.
Jones died in 1887 and George D. Stevenson took over the project. Stevenson replaced Jones's original brick façade 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 total cost of construction was £1,184,000 (equivalent to £136 million in 2019).
Tower Bridge was officially opened on 30 June 1894 by the Prince and Princess of Wales. An Act of parliament stipulated that a tug boat should be on station to assist vessels in danger when crossing the bridge, a requirement that remained in place until the 1960s.
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. 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 among the world's earliest underground ("tube") railways, but it 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 is no toll to pay to use it. Having lost most of its income, the tunnel was closed in 1898.
The high-level open air walkways between the towers gained a reputation as a haunt for prostitutes and pickpockets; as they were only accessible by stairs they were seldom used by regular pedestrians, and were closed in 1910. The walkway reopened in 1982 as part of the Tower Bridge Exhibition.
During the Second World War and 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 (2.7 m) 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.
The southern section of the bridge, in the London Borough of Southwark, was Grade I listed on 6 December 1949. The remainder of the bridge, in the London Borough of Tower Hamlets, was listed on 27 September 1973. In 1974, the original operating mechanism was largely replaced by a new electro-hydraulic drive system, designed by BHA Cromwell House, with the original final pinions driven by modern hydraulic motors.
In 1982, the Tower Bridge Exhibition opened, housed in the bridge's twin towers, the long-closed high-level walkways and the Victorian engine rooms. The latter still house the original steam engines and some of the original hydraulic machinery.
In 2000, it was announced the bridge would need to close for a month in order to repair the bascules and perform other maintenance. A computer system was installed to control the raising and lowering of the bascules remotely. It proved unreliable, resulting in the bridge being stuck in the open or closed positions on several occasions during 2005 until its sensors were replaced.
In April 2008 it was announced that the bridge would undergo a "facelift" costing £4 million, and taking four years to complete. The work entailed stripping off the existing paint down to bare metal and repainting in blue and white. Before this, the bridge's colour scheme dated from 1977, when it was painted red, white and blue for Queen Elizabeth II's Silver Jubilee. Its colours were subsequently restored to blue and white. Each section was enshrouded in scaffolding and plastic sheeting to prevent the old paint falling into the Thames and causing pollution. Starting in mid-2008, contractors worked on a quarter of the bridge at a time to minimise disruption, but some road closures were inevitable. It is intended that the completed work will stand for 25 years.
The renovation of the walkway interior 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 luminaires, 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). The renovation of the four suspension chains was completed in March 2010 using a state-of-the-art coating system requiring up to six different layers of "paint".
On 8 July 2012, the west walkway was transformed into a 200-foot-long (61 m) Live Music Sculpture by the British composer Samuel Bordoli. 30 classical musicians were arranged along the length of the bridge 138 feet (42 m) above the Thames behind the Olympic rings. The sound travelled backwards and forwards along the walkway, echoing the structure of the bridge.
Following the Olympics, the rings were removed from Tower Bridge and replaced by the emblem of the Paralympic Games for the 2012 Summer Paralympics.
In 2016, Tower Bridge was closed to all road traffic from 1 October to 30 December. This was to allow structural maintenance work to take place on the timber decking, lifting mechanism and waterproofing the brick arches on the bridge's approaches. During this, the bridge was still open to water-borne traffic. It was open to pedestrians for all but three weekends, when a free ferry service was in operation.
The bridge is 800 feet (240 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 86 degrees to allow river traffic to pass. The bascules, weighing over 1,000 tons each, are counterbalanced to minimise the force required and allow raising in five minutes.
The two side-spans are suspension bridges, each 270 feet (82 m) long, with the suspension rods anchored both at the abutments and through rods contained within the bridge's upper walkways. The pedestrian walkways are 143 feet (44 m) above the river at high tide, and accessed by lifts.
One of the chimneys on the bridge, which can be mistaken for a lamp post, connects up to an old fireplace in a guardroom of the Tower of London. It is long-disused.
The original raising mechanism was powered by pressurised water stored in several hydraulic accumulators. The system was designed and installed by Hamilton Owen Rendel while working for Armstrong, Mitchell and Company of Newcastle upon Tyne.[page needed] Water at a pressure of 750 psi (5.2 MPa), was pumped into the accumulators by a pair of stationary steam engines. Each drove a force pump from its piston tail rod. The accumulators each comprise a 20-inch (51 cm) ram on which sits a very heavy weight to maintain the desired pressure.
The entire hydraulic system along with the gas lighting system was installed by William Sugg & Co Ltd. The gas lighting was initially by open-flame burners within the lanterns, but was soon updated to the later incandescent system.
In 1974, the original operating mechanism was largely replaced by a new electro-hydraulic drive system, designed by BHA Cromwell House. The only remaining parts of the old system are the final pinions, which fit into the racks on the bascules and were driven by hydraulic motors and gearing. Oil is now used in place of water as the hydraulic fluid.
Signalling and 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 were required to display signals. By day, a black ball at least 2 feet (0.61 m) 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 1,000 yards (910 m) 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 is housed in the bridge's museum.
The tall ship Wylde Swan passing under Tower Bridge decorated for the London Olympics in August 2012. Note the Olympic rings folded up to allow passage of the mast.
Tower Bridge is still a busy crossing of the Thames, used by more than 40,000 people (motorists, cyclists 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 the charge by crossing the bridge).
To maintain the integrity of the structure, the City of London Corporation has imposed a 20-mile-per-hour (32 km/h) speed restriction, and an 18-tonne (20-short-ton) weight limit on vehicles using the bridge. A camera system measures the speed of traffic crossing the bridge, using a number plate recognition system to send fixed penalty charges to speeding drivers.
A second system monitors other vehicle parameters. Induction loops and piezoelectric sensors are used to measure the weight, the height of the chassis above ground level, and the number of axles of each vehicle.
The bascules are raised about a thousand 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, and opening times are published in advance on the bridge's website; there is no charge for vessels to open the bridge.
The Tower Bridge Exhibition is a display housed in the bridge's twin towers, the high-level walkways and the Victorian engine rooms. It uses films, photos and interactive displays 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.
The exhibition charges an admission fee. Entrance is from the west side of the bridge deck to the northern tower, from where visitors ascend to level 4 by lift before crossing the high-level walkways to the southern tower. In the towers and walkways is an exhibition on the history of the bridge. The walkways also provide views over the city, the Tower of London and the Pool of London, and include a glass-floored section. From the south tower, visitors can visit the engine rooms, with the original steam engines, which are situated in a separate building beside the southern approach to the bridge.
Although Tower 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 Henry Heathcote Statham, while Frank Brangwyn stated that "A more absurd structure than the Tower Bridge was never thrown across a strategic river".
Benjamin Crisler, the New York Times film critic, wrote in 1938: "Three unique and valuable institutions the British have that we in America have not: Magna Carta, the Tower Bridge and Alfred Hitchcock."
Architectural historian Dan Cruickshank selected Tower Bridge as one of his four choices for the 2002 BBC television documentary series Britain's Best Buildings.
Tower Bridge is often mistaken for the next bridge upstream, London Bridge. A popular urban legend is that in 1968, Robert P. McCulloch, the purchaser of the old London Bridge that was later shipped to Lake Havasu City in Arizona, believed that he was in fact buying Tower Bridge. This was denied by McCulloch himself and has been debunked by Ivan Luckin, the vendor of the bridge.
A partial replica of Tower Bridge has been built in the city of Suzhou in China. The replica differs from the original in having no lifting mechanism and four separate towers. The Suzhou replica was renovated in 2019, giving it a new look that differs from the original London design.
On 10 August 1912 Francis McClean flew between the bascules and the high-level walkways in his Short Brothers S.33 floatplane.
On 3 August 1922, a 13-year-old boy fell off a slipway next to the south side of Tower Bridge. A man jumped into the Thames to save him, but both were pulled under a barge by Butler's Wharf and drowned.
In December 1952, the bridge opened while a number 78 double-decker bus was crossing from the south bank. At that time, the gateman would ring a warning bell and close the gates when the bridge was clear before the watchman ordered the raising of the bridge. 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, clearing a 3-foot (0.91 m) gap to drop 6 feet (1.8 m) onto the north bascule, which had not yet started to rise. There were no serious injuries. Gunter was given £10 (equivalent to £290 in 2019) by the City Corporation to honour his act of bravery.
On 5 April 1968, a Royal Air Force Hawker Hunter FGA.9 jet fighter from No. 1 Squadron made an unauthorised flight through Tower Bridge. Unimpressed that senior staff were not going to celebrate the RAF's 50th birthday with a fly-past, the pilot flew at low altitude down the Thames without authorisation, past the Houses of Parliament, and continued on towards the bridge. He flew beneath the walkway, at an estimated 300 miles per hour (480 km/h). He 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 the summer of 1973, a single-engined Beagle Pup was twice flown under the pedestrian walkway of Tower Bridge by 29-year-old stockbroker's clerk Peter Martin. Martin, who was on bail following accusations of stockmarket fraud, then "buzzed" buildings in the city before flying north towards the Lake District, where he died when his aircraft crashed some two hours later.
In May 1997, the motorcade of United States President Bill Clinton was divided by the opening of the bridge. The Thames sailing barge Gladys, on her way to a gathering at St Katharine Docks, arrived on schedule and the bridge was 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 flock 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 Chick, a Fathers 4 Justice campaigner, climbed a 100-foot (30 m) 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 11 May 2009, six people were trapped and injured after a lift fell 10 feet (3 m) inside the north tower.
Relevant Web Sites
- Back to basics. London's most famous bridge is getting a new coat of paint in time for the 2012 Olympics. In: Bridge Design & Engineering, v. 15, n. 57 (4th Quarter 2009), pp. 64, 66. (2009):
- Bridges. Macmillan Publishing Company, New York (USA), pp. 74-75. (1993):
- Bridges. A History of the World's Most Spectacular Spans. 2nd edition, Black Dog & Leventhal, New York (USA), ISBN 978-0316507943, pp. 64-65. (2017):
- Bridges. A history of the world's most famous and important spans. Black Dog & Leventhal, New York (USA), pp. 62-63. (1997):
- Bridges that Changed the World. Prestel, Munich (Germany), pp. 78-79. (2002):
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