Leaning Tower of Pisa Sustainability

Leaning Tower of Pisa :

Sustaining The Structural Integrity of a Global Icon

Introduction :

Some of the strongest earthquakes ever recorded in Europe have hit the small town of Pisa, so how has the leaning tower been able to stay in the position that it is? This question has been around for many years and engineers have always been puzzled by its integrity. The tower leans at a five degree angle, and comes off the ground on the west side on a fifteen foot cliff. Despite these defects the tower has pushed the limits, surviving for eight hundred years.

The tower has been an extremely vulnerable piece of architecture for as long as it has been standing, and architects have always suspected it to sustain severe damage or collapse with any earthquake 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.

How has it stayed secure?

The tower is considerably tall and is extremely solid, and the foundation soil at the base of the tower is extremely unstable and soft. These aspects cause the vibrational characteristics of the structure to be modified substantially, in such a way that the tower does not resonate with earthquake ground motion. Through the years the center of gravity within the tower has been kept in its base, and the tower is actually falling all the time, at an extremely slow rate. 

 tower had originally started to lean in 1178, and the construction for the top half of the tower hadn't even started. The basic solution was to reinforce the soil around the base of the tower, which helps the southern lean of the tower. The original project was started by putting counterweights on the base of the north-side of the tower, which then moved it's barycenter deeper and more northern. The tower was then harnessed with suspension bridge cables to stop the tower from collapsing by pulling the north side while the soil was being placed in. Under the tower, clay and water was removed which proved extremely unstable. Then forty five foot concrete pillars were placed underground to support the side that the tower leans on. 

Future of the Leaning Tower of Pisa

The engineers recovered two hundred years of lean on the tower, and the stabilization methods used have proved to be working, as the tower has only moved two and a half centimeters over the past twenty years. The tower continues to be visited by millions each year, and the preservation of it's structural integrity by engineers is crucial to it's sustained stature.