Tower Bridge

• 1. Introduction

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  Tower Bridge crosses the River Thames close to the Tower of London, and it is one of the most recognised structures in the city of London. On the 30th of June 1894, the Prince and Princess of Wales officially opened it before a crowd that reporters described as a "semi-State" occasion, one that "few pageants" in the history of the City could rival. What stands today required more than eight years of construction, two extensions of parliamentary time, and a final bill of £1,184,000. The bridge connects two banks that had long been divided by the busiest stretch of river in Britain, a half-mile corridor of docks, quays, and wharves that no ordinary fixed bridge could be allowed to obstruct. How did engineers and architects solve a problem that had stumped more than fifty competing designs? And how did a structure once dismissed as tawdry and pretentious become the emblem of a city?

• 2. A Problem No Bridge Could Solve

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  By the late 19th century, the East End of London was growing fast, and about 39 percent of the city's population lived east of London Bridge. The source compared that mass of humanity to the combined populations of Manchester and Liverpool. Yet a conventional street-level bridge at that location was impossible. A fixed span would block sailing ships from reaching the Pool of London, the stretch of river between the Tower of London and London Bridge that teemed with commercial traffic, 11 active docks and quays on the north bank alone and 20 wharves on the south.

  Sir Albert Joseph Altman chaired a Special Bridge or Subway Committee formed in December 1875 to find a way through this impasse. The committee reported on the 7th of December 1876 that a crossing east of London Bridge should be built when funds allowed. More than fifty designs arrived in the years that followed, including one from civil engineer Sir Joseph Bazalgette, rejected because it lacked sufficient headroom for river traffic.

  It was not until the 24th of July 1884 that the Bridge House Estates Committee proposed "a low level bridge, with mechanical opening or openings." A delegation visited Belgium, Holland, and Newcastle Bridge, and on the 28th of October 1884 the Court of Common Council was presented with three models: a swing bridge, a variation of that swing bridge, and a bascule bridge. Design C, the bascule, was recommended. A bill was drafted for Parliament.

• 3. Parliament Sets the Rules

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  The Corporation of London (Tower Bridge) Act 1885 received royal assent on the 14th of August 1885, and it was unusually precise. The central opening span had to be 200 feet wide with a clearance of 135 feet above Trinity high water when open, and 29 feet when closed. Each pier had to measure 185 feet long by 70 feet wide. The two side spans each had to run 270 feet. During construction, a clear waterway of 160 feet had to remain open for river traffic at all times.

  The act also insisted that the bridge's design accord with the architecture of the nearby Tower of London, a requirement that would shape every aesthetic decision to follow. Completion was required within four years of the act passing, and the bridge had to open for vessels at any time regardless of delays to road traffic on land.

  John Wolfe Barry later noted that at one point the plans included provisions for mounting guns and for military occupation of the bridge, though that idea was "afterwards to a great extent discarded." The act still preserved a right for the senior officer commanding in the Tower of London to occupy the bridge at all times. Two further acts of Parliament were eventually needed: one in August 1889 extending the deadline to 1893, and another on the 29th of June 1893 adding one final year.

• 4. Building the Giant

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  Construction began on the 22nd of April 1886, when the Prince of Wales laid the foundation stone on the 21st of June. Edward Cruttwell served as resident engineer throughout, and he oversaw a workforce that averaged 432 people on site each day, though at least 1,200 individuals worked on the project overall. Cruttwell recorded that there were "only" ten fatal accidents during the build: four while sinking the foundations, one on the approaches, and five on the superstructure.

  The work was divided into eight contracts. John Jackson won three of them, covering the northern approach, the pier foundations and abutments, and the cast iron parapet for the northern approach, for a combined tender of £189,732. Sir W. G. Armstrong, Mitchell, and Co. Ltd won the hydraulics contract at £85,232. Sir William Arrol and Co. took the metalwork contract at £337,113, supplying about 12,100 tons of steel. The total accepted tender across all eight contracts was £830,005.

  Two piers containing over 70,000 long tons of concrete were sunk into the riverbed. The first caisson began in September 1886 and it was January 1890 before both piers were complete. The law required that 160 feet of clear waterway remain open throughout, so the second pier could not be excavated until the staging for the first had been removed. More than 11,000 long tons of steel went into the towers and walkways, which were then clad in Cornish granite and Portland stone.

  Horace Jones died in 1887, and Barry assumed the role of architect as well as engineer. Jones's original brick facade was replaced by a more ornate Victorian Gothic design by Stevenson, who had been Jones's architectural assistant, a change intended to bring the bridge into harmony with the Tower of London next door.

• 5. How the Bridge Works

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  Tower Bridge is unusual because it combines three different structural forms in a single crossing. The two spans from the banks to the main piers are suspension bridges. The central opening span is a bascule bridge, and the high-level pedestrian walkways were cantilever bridges until 1960, when suspension cables were added to reinforce them.

  The central span of 200 feet is split into two equal bascules, each projecting 100 feet outward and extending 62 feet 6 inches backward within the pier. Each bascule weighs about 1,070 tons including ballast and paving, and counterweights allow both leaves to be raised in five minutes. The arc of rotation is 82 degrees, with the pivot point 13 feet 3 inches inside each pier face.

  The original raising mechanism drew on pressurised water stored in six hydraulic accumulators. Two pairs of engines sat on each pier, each pair consisting of a larger engine 8.5 inches in diameter and a smaller one at 7.5 inches, all with three cylinders. Water at 750 psi was pumped into the accumulators by stationary steam engines. Hamilton Owen Rendel designed and installed the system while working for Armstrong, Mitchell and Company of Newcastle upon Tyne.

  In 1974, the original mechanism was largely replaced by an electro-hydraulic drive system designed by Geoffrey Beresford Hartwell of BHA Cromwell House, which uses oil rather than water as the hydraulic fluid. The original final pinions that mesh with the racks on the bascules were retained and are now driven by hydraulic motors. In the first twelve months after opening, the bascules were raised 6,160 times, an average of seventeen times daily. Today the bridge opens about a thousand times a year, and vessels must give 24 hours' notice in advance.

• 6. Incidents and Close Calls

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  On the 10th of August 1912, the stunt pilot Francis McClean flew his Short Brothers S.33 floatplane between the bascules and the high-level walkways, becoming a celebrity overnight. He then flew beneath London Bridge, Blackfriars Bridge, and Waterloo Bridge in the same outing.

  On the 30th of December 1952, a number 78 double-decker bus was crossing the bridge when the process of stopping traffic failed while a relief watchman was on duty. The south bascule began to rise while the bus was still on it. Driver Albert Edward Gunter, born in 1906, made a split-second decision to accelerate, clearing a drop of 1.8 metres onto the north bascule, which had not yet started to rise. The conductor broke his leg and twelve of the twenty passengers suffered minor injuries. Gunter received a £10 bonus from the City Corporation for his quick thinking.

  On the 5th of April 1968, a Royal Air Force Hawker Hunter FGA.9 jet fighter from No. 1 Squadron made an unauthorised flight through the bridge at an estimated 300 mph. The pilot, displeased that the RAF's 50th birthday would not be marked with an official flypast, flew down the Thames past the Houses of Parliament before passing beneath the walkway. He was placed under arrest on landing and discharged from the RAF on medical grounds.

  In May 1997, the motorcade of United States President Bill Clinton was split in two when the bridge opened for the Thames sailing barge Gladys, which was on schedule for a gathering at St Katharine Docks. Clinton, returning from lunch with Prime Minister Tony Blair at Le Pont de la Tour, arrived late, just as the bridge was rising. A Tower Bridge spokesman was quoted as saying: "We tried to contact the American Embassy, but they wouldn't answer the phone."

• 7. Critics, Legend, and Legacy

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  Not everyone welcomed Tower Bridge with admiration. Henry Heathcote Statham wrote that it "represents the vice of tawdriness and pretentiousness, and of falsification of the actual facts of the structure." Frank Brangwyn put it more bluntly, calling it "a more absurd structure than the Tower Bridge was never thrown across a strategic river."

  New York Times film critic Benjamin Crisler took a different view in 1938, listing Tower Bridge alongside Magna Carta and Alfred Hitchcock as one of three things Britain had that America did not. Architectural historian Dan Cruickshank selected it as one of his four choices for the 2002 BBC television documentary series Britain's Best Buildings.

  A persistent urban legend claims that in 1968, Robert P. McCulloch, who purchased the old London Bridge and had it shipped to Lake Havasu City in Arizona, believed he was buying Tower Bridge instead. McCulloch denied the story, and Ivan Luckin, the vendor of the bridge, has debunked it.

  A partial replica of Tower Bridge was built in Suzhou, China. It differs from the original in having no lifting mechanism and four separate towers rather than two. The Suzhou structure was renovated in 2019. Back in London, in 2019, Tower Bridge drew 889,338 visitors and ranked as the 34th most visited attraction in England among the 1,114 tracked by Visit England, and the 17th among those charging admission. The high-level walkways received glass floors in 2014, giving visitors a direct view down to the road and river 143 feet below.