By Cailey Rizzo
May 13, 2018
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The Tower of Pisa has been leaning for more than 800 years, but it has never fallen.

For more than 20 years, researchers have been trying to figure out what makes the Leaning of Tower of Pisa such a unique landmark. And, in a twist that seems like a moral from Aesop’s fables, engineers and soil scientists have concluded that the very reason the tower leans is the same reason it has never collapsed.

In 1173, construction began on the Pisa cathedral’s new bell tower. By the second year of construction, it was already starting to tilt. It took almost 200 years to complete, with engineers and architects constantly trying — and failing — to stop the lean.

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Upon completion in 1370, the tower was leaning at about two degrees. In the 20th century, it was estimated that the tower was shifting about 0.05 inches per year. By 1990, the tower was tilted at a 5.5-degree angle (about 15 feet). Between 1999 and 2001, work was done on the tower to reduce its tilt by 0.5 degrees.

But despite all of this precarious leaning and correction, the tower has never fallen — despite being impacted by at least four very strong earthquakes.

The new study, led by a professor from Roma Tre University, has attributed this to something called dynamic soil-structure interaction.

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Basically, because the tower is so rigid and high (191 feet) and the ground beneath it so soft, every time an earthquake hits, the “vibrational characteristics of the structure” are changed to make it so “the tower does not resonate with earthquake ground motion.”

The Leaning Tower of Pisa is just another lesson why we should all embrace flaws. It may wobble, but it never falls down.

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