Sunny Tower Bridge
In the second half of the 19th century, increased commercial development in the East End led to a requirement for a new river crossing downstream of London Bridge. But a traditional bridge 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 Sir Albert Joseph Altman, to find a solution to the problem and it opened the design of the crossing to public competition. Over 50 designs were submitted, including one from the famed civil engineer, Sir Joseph Bazalgette. Controversy around the evaluation of the designs meant it was not until 1884 that a design submitted by Sir 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. 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 started in 1886 and took eight years, employing 432 construction workers. 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 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, replacing 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 total cost of construction was £1,184,000 (£100 million in 2010 money).
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 Hamlets. The bridge is 244m in length with two towers each 65m high, built on piers. The central span of 61m between the towers is split into two equal bascules or leaves, which can be raised to an angle of 83° to allow river traffic to pass. The bascules weigh over 1,000 tons each and are counterbalanced to minimise the force required, allowing raising in five minutes. The original raising mechanism was powered by pressurised water stored in several hydraulic accumulators.
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, and is open to the public, forming the basis for the bridge's museum, which resides in the old engine rooms on the south side of the bridge.