Social Icons


Wednesday, November 25, 2009

Tower Bridge

Tower Bridge is an iconic symbol of London which is close to the Tower of London, which gives the name of the bridge. Tower Bridge is a combined bascule and suspension bridge in London, England, over the River Thames.

The bridge consists of two towers which are tied together at the upper level by means of two horizontal walkways which are designed to withstand the horizontal forces exerted by the suspended sections of the bridge on the landward sides of the towers. The vertical component 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 is 800 feet/244 m in length with two towers each 213 feet/65 m high, built on docks. 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 83 degrees to allow river traffic to pass. The bascules, weighing over 1,000 tons each, are counterbalanced to minimize the force required and allow rising 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.

Tower Bridge is still a busy and vital crossing of the Thames and it is crossed by over 40,000 motorists 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. In order to maintain the integrity of the historic structure, the City of London Corporation has imposed a 20 mph or 32 km/h speed restriction, and an 18-tonne weight limit on vehicles using the bridge.

The bascules are raised around 1000 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. A computer system was installed in 2000 to control the raising and lowering of the bascules remotely. Unfortunately it proved less reliable than desired, resulting in the bridge being stuck in the open or closed positions on several occasions during 2005, until its sensors were replaced.

Tower Bridge is sometimes mistakenly referred to as London Bridge, which is actually the next bridge upstream. The nearest London Underground station is Tower Hill on the Circle and District Lines. The nearest Docklands Light Railway station is Tower Gateway.

No comments: