how was towerbridge built?

Answer 1

http://www.hartwell.demon.co.uk/tbpic.htm

Answer 2

Bridge History Image of Tower Bridge
Tower Bridge was completed in 1894, after 8 years of construction. However, many people don't realise why it was even built in the first place, or why it is so different from London's other bridges. The information below will fill you in on some of Tower Bridge's fascinating history.

The need for a new bridge
Originally, London Bridge was the only crossing over the Thames. As London grew, so more bridges were added, but these were all to the west of London Bridge, since the area east of London Bridge had become a busy port. In the 19th century, the east end of London became so densely populated that public pressure mounted for a bridge to the east of London Bridge, as journeys for pedestrians and vehicles were being delayed literally by hours.

Finally in 1876, the City of London Corporation, who were responsible for that part of the Thames, decided that the problem could be put off no longer.

How a design was chosen
The big problem for the City of London Corporation was how to build a bridge downstream from London Bridge without disrupting river traffic activities. To get as many ideas as possible, the "Special Bridge or Subway Committee" was formed in 1876, and opened the design of the new crossing to public competition.

Over 50 designs were put forward for consideration, some of which you can see when you visit the Tower Bridge Exhibition. However, it wasn't until October 1884 that Horace Jones, the City Architect, in collaboration with John Wolfe Barry, offered the chosen design for Tower Bridge as a solution.

The building of the bridge
It took 8 years, 5 major contractors and the relentless labour of 432 construction workers to build Tower Bridge.

Two massive piers had to be sunk into the river bed 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 more pleasing appearance.

You can find out more about the building of Tower Bridge and the people involved in its construction when you visit The Tower Bridge Exhibition.

How it works - then and now
When it was built, Tower Bridge was the largest and most sophisticated bascule bridge ever built ("bascule" comes from the French for "see-saw"). It was a hydraulically operated bridge, using steam to power the enormous pumping engines. The energy created was then stored in six massive accumulators so that, as soon as power was required to lift the Bridge, it was readily available. The accumulators fed the driving engines, which drove the bascules up and down. Despite the complexity of the system, the bascules only took about a minute to raise to their maximum 86 degrees.

Nowadays, the bascules are still operated by hydraulic power, but since 1976 they have been driven by oil and electricity rather than steam. The original pumping engines, accumulators and boilers are on show as part of the Tower Bridge Exhibition, and you can also see the current machinery and control cabins when you come on a "Behind The Scenes Tour". (Behind The Scenes Tours must be pre-booked)
Interesting facts

Tower Bridge has a fascinating history, which is explored in full in the Tower Bridge Exhibition. Here are a few interesting facts you may not have known:
Interesting facts about the Tower Bridge 1910 The high-level walkways, which were designed so that the public could still cross the Bridge when it was raised, were closed down due to lack of use. Most people preferred to wait at the bottom and watch the bascules rise up!
1912 During an emergency, Frank McClean had to fly between the bascules and the high-level Walkways in his Short biplane, to avoid an accident.
1952 A London bus had to leap from one bascule to the other when the Bridge began to rise with the bus still on it.
1977 Tower Bridge was painted red, white and blue to celebrate the Queen's Silver Jubilee. (Before that, it was painted a chocolate brown colour).
1982 Tower Bridge opened to the public for the first time since 1910, with a permanent exhibition inside called the Tower Bridge Exhibition. The Walkways were glazed for the first time to house the new Exhibition.
1993 The centenary exhibition - The Tower Bridge Experience opened, featuring animatronic models telling the story of Tower Bridge.
1994 Tower Bridge became available to hire for parties and receptions.
2002 The current Tower Bridge Exhibtion opened, refocusing on the magnificent views from the Walkways and the history of the Bridge.
2003 Tower Bridge Exhibition came of age celebrating its 21st Birthday!