About Tower Bridge, London

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, but a traditional fixed bridge was unsuitable as it would remove access to the Pool of London. Over 50 designs were considered by a Committee and in 1884 a design submitted by one of the judges, the City Architect Horace Jones, was approved.

Jones' engineer, Sir John Wolfe Barry, devised the idea of a bascule bridge 244 m (800 ft) in length with two towers each 65 m (213 ft) high, built on piers. The central span of 61 m (200 ft) 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 tonnes each, were counterbalanced to minimize the force required and allow raising in five minutes. The two side-spans are suspension bridges, each 82 m (270 ft) long, with the suspension rods anchored both at the abutments and through rods contained within the bridge's upper walkways. The pedestrian walkways are 144m (43 ft) above the river at high tide.

Construction started in 1886 and was completed in 1891 by the five contractors - Sir John Jackson (foundations), Baron Armstrong (hydraulics), William Webster, Sir H.H. Bartlett, and Sir William Arrol & Co. 432 construction workers were led by the resident engineer E W Crutwell.

Two massive piers, containing over 70,000 tonnes of concrete, were sunk into the river bed to support the construction. Over 11,000 tonnes of steel provided the framework for the towers and walkways, clad in Cornish granite and Portland stone. 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 total cost of construction was £1,184,000.

The original raising mechanism was designed by Sir W. G. Armstrong Mitchell & Company, with water, at a pressure of 750psi, pumped into six accumulators by two 360 hp stationary steam engines. This was largely replaced in 1974 by a new electro-hydraulic drive system and only the original final pinions remain in use, although the original hydraulic machinery now forms the basis of the Tower bridge Museum. Tower Bridge remains a busy and vital crossing of the Thames, used by over 40,000 motorists and pedestrians each day albeit with a 32 km/h (20 mph)speed/18 tonnes weight restriction.