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Leaning Tower of Pisa-A successful Foundation Failure!

 
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Dr. N. Subramanian
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PostPosted: Thu Aug 26, 2010 8:27 pm    Post subject: Leaning Tower of Pisa-A successful Foundation Failure! Reply with quote

Leaning Tower of Pisa, A Magnificent Engineering Failure
                                          

The Leaning Tower of Pisa is a Magificent Engineering Failure



in 1173, in Medieval Italy, a cathedral complex was begun in Pisa, Italy. Ultimately,the complex would include four structures and be known as the Campo dei Miracolior Piazza dei Miracoli, which means Fields of Miracles. If you are going to build a cathedral complex, it’s probably best to start with the cathedral and so the first building constructed was Duomo di Pisa. It’s a fabulous example of Roman architecture and is set upon a white marble pavement. Just to the west of the cathedral dome, the baptistry was constructed. The third part of the Campo dei Miracoli was the bell tower, more properly referred to as the campanile. While the entire complex is considered by many experts to be the most spectacular assembly of Roman (Romanesque) architecture (though the cathedral is topped with an Islamic-style dome), the bell tower has become one of the world’s iconic structures and iconic engineering failure.
Photographer Dan Heller Provides a Look Inside the Cathedral in Pisa



The tower’s design called for a 185 foot tall, circular, eight-story column made of white marble. The bottom floor consists of 15 arches with the next 6 stories containing 30 arches each and the top floor utilizing 16 arches for structural integrity probably more than asthetics. A spiral staircase of 297 steps leads to the top floor which houses the actual bell chamber. Truly, it is an astonishing engineering feat when one considers that construction was begun 9th Aug 1173. The tower was perhaps the tallest of its type in all of Europe and was not built for any religious purpose. Instead, it’s construction came about as a symbol of the wealth of the city. This was the time of the rise in the city-state in Italythat eventually led to the Renaissance. Pisa went to war with many of its city-state neighbors, including its chief rival, Florence. The first order of business was the foot of the tower but the effort was halted due to the outbreak of war with Florence.  

The tower began to sink after construction had progressed to the third floor in 1178. This was due to a mere three-metre deep foundation, set in weak, unstable subsoil, a design that was flawed from the beginning.  


Work ceased for 100 years, because the Republic of Pisa was almost continually engaged in battles with Genoa, Lucca and Florence. During that period the self weight of the tower consolidated the underlying sediments. Otherwise, the tower would have toppled. In 1198, clocks were temporarily installed on the third floor of the unfinished construction.  

Construction resumed in 1272, under Giovanni di Simone, architect of the Camposanto. In an effort to compensate for the tilt, the engineers built upper floors with one side taller than the other. This made the tower begin to lean in the other direction. Because of this, the tower is actually curved. Construction was halted again in 1284, when the Pisans were defeated by the Genoans in the Battle of Meloria. The seventh floor was completed in 1319. The bell-chamber was finally added in 1372, with seven bells, one for each note of the musical major scale.  

Aerial view of the Tower




Inside the Bell Tower

However, it is not known as the Campanile of the Campo dei Miracoli or the Bell Tower of Campo dei Miracoli. Instead, it is most often referred to as the Leaning Tower of Pisa. No one knows for certain who designed the tower but he must have been someone of great skill, capability and guts. But, it seems when they began the footing, they only went to a depth of about 3m on a dry stone bed. When they finished the third floor and construction was halted, the building had sunk by about 40 cm and there was a lean of 5 cm.


When they got to the 6th floor, one side of the upper floors were raised to try and correct the lean which was then obvious to the eye as it had grown to 90 cm. Curiously, it is thought that the numerous delays in construction due to war or political unrest allowed the structure to settle to a relative state of stability. Over the years, many people have come up with ways to correct the lean. One suggestion was to dismantle the tower and rebuild it at a different location. If that had been allowed to come about, I doubt that the tower would be nearly as famous as it is today. In the 1920′s, a cement solution was injected into the foundation that may have provided extra stability.


Cable Scheme Proposed to Save Tower



Today, the tower leans about 14 feet from center and it is estimated that the lean grows at about 1 mm per year. Maybe it’s still settling. It’s six feet shorter than it was originally and some estimates say that it will fall in about 175 years. Efforts to find a permanent stablization method continues today, includingthe use of steel cables to hold up the Leaning Tower of Pisa. That might keep it from falling down but it sure wouldn’t look too good.



It is well known that the foundations of the Leaning Tower of Pisa were stabilised using the method of underexcavation to reduce the southward inclination of the Tower by about 10 percent in combination with controlling the seasonally fluctuating water table beneath the north side. Having been closed to the public since early in 1990, the Tower was re-opened in December 2001. The recent paper by Burland, Jamiolkowski, and Viggiani in the International Journal of Geo-engineering Case Histories summarises the response of the Tower during the period of implementation of the stabilisation works. Monitoring of the movements of the Tower has been continuing and the observations obtained since 2001 are presented. It is shown that over the six years between 2003 and 2008 the induced rate of northward rotation of the Tower has been steadily reducing to less than 0.2 arc seconds per year. Similarly the rate of induced settlement of the centre of the foundation has been steadily reducing and is approaching the background rate of settlement of the Piazza. Piezometer measurements close to the north side of the foundation shows that the drainage system has been successful in stabilising the groundwater levels beneath the north side of the Tower’s foundation. The paper concludes with a brief discussion on the possible future behaviour of the Tower.



Italian engineers claim the work means the Leaning Tower of Pisa won’t fall for 300 years. Some say the 800 year mystery of the Leaning Tower of Pisa has been solved. But, it does continue to lean further each year. But it remains an iconic tourist destination that gives people an extra reason to visit the small town of Pisa.

References:

  1. http://symonsez.wordpress.com/2010/08/09/leaning-tower-of-pisa-a-magnificent-engineering-failure/
  2. Burland, J.B., Jamiolkowski, M.B., and Viggiani, C., Leaning Tower of Pisa: Behaviour after Stabilization Operations, International Journal of Geo-engineering Case Histories, 2009, Vol. 1, No.3, pp.156-159
  3. Subramanian, N. and Muthukumar, D., Leaning Tower of Pisa -Will it be reopened for Tourists?, ICI Bulletin, No.63, April-June 98, pp. 13-16.


Dr.N.Subramanian,Ph.D.,F.ASCE, M.ACI,

Maryland, USA


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PostPosted: Mon Sep 20, 2010 7:22 am    Post subject: Reply with quote

Thank you for such nice info on the leaning tower of pisa,

I had seen video on leaning tower of pisa on discovery or national geography channel
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