A research group of engineers has investigated why the Leaning Tower of Pisa has survived many strong earthquakes.
The group, led by Roma Tre University, has explored why the 58m tower, which leans at a 5° angle with an offset at the top of over 5m, has managed to survive at least four strong earthquakes that have hit the region since 1280.
According to the University of Bristol, which is involved in the research, given the vulnerability of the structure, it was expected to sustain serious damage or even collapse because of moderate seismic activity.
After studying available seismological, geotechnical and structural information, the research team concluded that the survival of the tower can be attributed to a phenomenon known as dynamic soil-structure interaction (DSSI).
The group reported that because of the considerable height and stiffness of the tower combined with the softness of the foundation soil, this causes the vibrational characteristics of the structure to be modified substantially, in a way that the tower does not resonate with earthquake ground motion.
According the research, this has been the key to the tower’s survival and the unique combination of these characteristics gives the it the world record in DSSI effects.
The University of Bristol’s chair in geotechnics and soil-structure interaction George Mylonakis, 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.”
Results from the study have been presented to international workshops and will be formally announced at the 16th European Conference in Earthquake Engineering taking place in Greece next month.