Archive for the ‘Construction’ Category

Why Does the Leaning Tower of Pisa Lean?

Saturday, September 5th, 2009

The Tower of Pisa wasn’t leaning when it was built in 1173; it was as straight as a pole. It only began to shift direction shortly after construction due to a poorly built foundation and a loose layer of subsoil. It was leaning to the southeast, at first, before the unstable foundation shifted and started leaning towards the southwest. After a phase of structural strengthening in the early twenty-first century, the Leaning Tower of Pisa now leans at an angle of 3.97 degrees.

The shift in direction was first observed in 1178 when construction had progressed to the third floor. The weight of the tower was too heavy for the three-meter foundation that was built on a weak spot of land. Aside from the obvious architectural design flaw, the tower’s controversial history added to its problems.

The construction was stopped for almost a century because Pisa had been involved in wars with Genoa, Lucca and Florence. It’s a good thing though that this happened because it gave time for the subsoil to settle underneath, or else the tower would have surely toppled.

Leaning Tower Why Does the Leaning Tower of Pisa Lean?

To compensate for the leaning position, the builders began constructing the upper floors with one side higher than the other. This made the tower begin to lean in the other direction. Because of this quirky structure, the tower is actually curved. Despite these efforts, the tower continued to lean.

In 1964, the Italian government began planning for the prevention of the total collapse of the tower. However, the authorities specifically requested that the tower’s leaning position be preserved because of the region’s tourism industry.

In 1990, after two decades of strategic planning involving mathematicians, engineers and historians, the stabilization efforts for the Leaning Tower of Pisa began. The tower was closed to the public and the neighboring residents were evacuated. To lessen the total weight of the tower, its seven bells, representing the seven musical notes in a major scale, were removed and supporting cables were attached.

The final solution to prevent the collapse of the tower was to slightly straighten the tower to a safer angle. This was done by removing 38 cubic meters of soil from underneath the raised end. As a result, the tower straightened by 18 inches, which places it at the exact position that it occupied in 1838. After a decade of corrective reconstruction and stabilization efforts, the tower was reopened to the public on December 15, 2001. The authorities had declared it stable for at least another 300 years.

Then in May 2008, after the removal of another 70 metric tons of earth, engineers announced that the Leaning Tower had been finally stabilized. It had stopped moving for the first time in its history. The authorities at Pisa have declared that this time the tower would be stable for at least 200 years.

Currently, repairs are continuously done to restore the tower’s appearance from damage due to corrosion and blackening. This is especially important since the tower’s age and its massive size and height make it vulnerable to wind and rain.

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