Issue 9 - June 2002
One of the wonders of the world, The Leaning Tower of Pisa in Italy, has been saved from collapse by a British Professor who directed the operation by fax from London. "It really was like riding a bicycle by fax," said Professor John Burland, from Imperial College London.
The tilting tower, which was originally constructed in stages between 1173 and 1350, has been tilting further to the south at the rate of roughly 1 millimetre per year. Computer models calculated that once it reached a tilt of 5.44 degrees the tower would topple, but it was still standing in 1990 with the tilt at 5.5 degrees. By this time the bell tower at the top was hanging a mere 4.5 metres above the ground.
This peculiarity occurs because although 60m high, the bell tower is 1.5 degrees closer to the vertical than the base, so the tower has a banana shape. It is thought this effect was brought about over the years by builders over-compensating for the lean and trying to balance the tower which was sinking into the soft ground on which it was built. The engineer Professor John Burland says it is, '.like building a tower of bricks on a soft carpet' - after a certain height it gets wobbly and can collapse.
Things were made worse in 1838 when a walkway dug out around the bottom of the tower weakened the base further and it began to lean even more. The ground beneath the south of the 19.6m wide tower - which has a mass of 14,500 tonnes - has subsided by 3.75m. The salvation operation, begun in 1999, consisted of putting lead weights on the north side, and digging underneath the tower to stop the leaning process. The team tied steel cables around the middle of the tower to hold it in place in case anything went wrong.
So by moving the tower back by 45 centimetres the tower hangs steady, at least for the next 200 years. For more towering facts visit the unofficial Leaning Tower of Pisa website at:
Source: BBC News Online
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