Leaning Tower of Pisa, which is 55.86 m and 56.67 m from both ends, is known worldwide for its unplanned tilt. It gained our hearts and it has become one of the most seen tourist spots. It is also a third oldest structure in the city. The tilting started during construction itself which is in the 12th century. The reason behind tilting is due to the foundation. The foundation consists of too soft soil on one end, leading to this tilt. It was not until restoration work between 1990 to 2001, the tower leans 3.99 degrees. Before it was 5.5 degrees.
However, the main question that is bothering engineers and normal people is how even after a significant number of earthquakes since 1920 the towers still managed to be in the same form. Normally, with the tilt and the earthquakes happening, the tower would have collapsed by now. To study this, a professor at the University of Bristol namely Professor George Mylonakis and Professor Camillo Nuti studied the effect.
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The structure which barely stands, and the seismic activity and soil structure interaction puzzled the engineers for very long time. These professors, after studying seismology, structural and geotechnical information, they comprehend and come to a conclusion that says the key role is performed by a phenomenon called “Dynamic soil-structure interaction”.
“The considerable height and stiffness of the Tower combined with the softness of the foundation soil, causes the vibrational characteristics of the structure to be modified substantially, in such a way that the Tower does not resonate with earthquake ground motion. This has been the key to its survival. The unique combination of these characteristics gives the Tower of Pisa the world record in DSSI effects.“
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The mystery behind its survival has been solved and thanks to the engineers and professors for their hard work to understand the soil-structure interaction which happens to be not so easy. And I wish, this tower will not get collapsed or damaged, and it should forever remain as a masterpiece and should give a vast knowledge to the young engineers.