The Leaning Tower of Pisa isn’t the first tower to lean. It’s not even the leanest building out there. What set it apart is its sheer size and the fact that, despite its severe angle, it’s been standing up since the 14th century. Now, scientists have determined how it has managed to stay stabilized. Turns out it’s the same reason that it started leaning in the first place.
The Leaning Tower of Pisa is one of the most remarkable architectural structures from medieval Europe built in the 14th century. It is also referred to as the bell tower or campanile. Despite leaning precariously at a five-degree angle, leading to an offset at the top of over five meters, the 58-meter tall Tower has managed to survive, undamaged, at least four strong earthquakes that have hit the region since 1280.
Scientists until now had a puzzle that how this Leaning Tower of Pisa survived the strong earthquakes. A research group of 16 engineers has investigated, including a leading expert in earthquake engineering and soil-structure interaction from the University of Bristol. They have found that it is all to do with the structure of the soil.
According to the report from the University of Bristol, the thing that keeps the tower standing is the very same thing that caused it to lean in the first place. The tower is positioned between the Arno and Serchio rivers, making the ground loose and soft, being composed of silt, clay, fine sand, and shells.
It’s easy to see how a 14,500-ton building could get stuck in that substance. But the softness of the soil is also instrumental to the building’s longevity. It’s all due to an effect called dynamic soil-structure interaction (DSSI), which describes the way that stiff buildings built in soft soil handle major vibrations. These vibration changes would prevent an earthquake from affecting the tower along with everything else around it.
This has been the key to its survival, the team said, and the unique combination of these characteristics gives the Leaning Tower of Pisa the world record in DSSI effects.
Prof. George Mylonakis from the university’s department of civil engineering said,
“Ironically, the very same soil that caused the leaning instability, and brought the tower to the verge of collapse, can be credited for helping it survive these seismic events.”
Now, the Leaning Tower of Pisa which used to lean at a 5-degree angle, but restorative efforts has decreased its tilt to around 4 degrees.