Friday Fact: Tower Bridge has a Metal Skeleton
Although 31 million bricks and nearly 23 000 litres of paint give the Tower Bridge the iconic look we have grown to love; the actual framework is made of 11 000 tons of steel held together by 2 million rivets standing on the two massive piers containing 70 000 tons of concrete. Due to the proximity to the Tower, the City has decided that this architectural marvel should not look too different; arrangement had to me made to create a familiar look. Hence the 31 million bricks.
Before the bridge, the river was crossed by using the Tower Subway, a 1300 feet long tunnel. As a cable car subway tunnel, it proved uneconomic, then redesigned as a foot tunnel, it gained a notorious reputation after the alleged sighting of Jack the Ripper in 1888.
The alternative was already under way; after choosing the most satisfying design from over fifty applications, the construction of Tower Bridge began in 1887.
This bascule bridge is the only one on the Thames that can be raised for the tall ships to pass; and that is why the bridge has an upper walkway to allow pedestrians to cross the river while the lower section is raised. In theory it at least. The staircase leading to the upper walkway was heated during winter, and served as a perfect little romantic getaway for lovebirds and ladies earning their daily wages in a rather unclothed fashion. Not to mention those poor souls who fell into the river accidentally or, every so often, after being pushed not so accidentally. It was seldom used by pedestrians, so sixteen years after opening the bridge, they closed down the upper walkway.
The bridge is raised 850 times every year and it is considered a lucky charm to see it happening. When a vessel has registered her wish to pass, the bridge is raised no matter what. In 1997 the presidential convoy of Bill Clinton was split in half when they thought they would have right of way.
When Tower Bridge has been built, they raised the bascules with the help of pressurised water pumped into hydraulic accumulators by twin-tandem compound steam engines. The original system designed by Hamilton Owen Rendel was replaced in 1974, following the removal of the 700 tons of the old equipment.
And that is where Vanguard came into the picture; the company was contracted in 1973 to undertake the dismantling and removal of the old engines and associated components and accumulators. Huge accumulators which had to be lifted out through a rather small aperture. In the chamber beneath the water level, it involved thermal lances, usually operated on 3000 – 4500 °C; a spectacular indoor firework.
And that notorious upper walkway was reopened in 1984, with the necessary safety precautions as well. Though nowadays it is mostly used for the Tower Bridge Exhibition.