The Leaning Tower of Pisa An Engineering Failure

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The Leaning Tower of PisaAn Engineering Failure

• Located in Pisa, Italy
• Construction began in 1173 AD
• 8 stories tall
• Slants 5.5, 4.5 m off the vertical
• Failure from consolidation

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Consolidation

• Consolidation occurs when water seeps out of the
  voids between soil particles causing settlement.

Force
Force
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Qualifications

• Joshua Reese Civil Engineering
• Concrete and geotechnical studies
• Kim Uyemura Mechanical Engineering
• Relevant specialties?
• Bob Hall Mechanical Engineering
• Relevant specialties?
• Nehal Dalal Mechanical Engineering
• Relevant specialties?

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Methodology

• Topics
• Failure causes
• Repairs
• Protection
• Resources
• University library
• Online databases
• EBSCO
• Others

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The Building of the Leaning Tower of Pisa

• 1173-1370

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3 Stages of Build

• The Leaning Tower of Pisa was initially built in
  three stages.
• During its entire construction it was leaning
  either north or south.
• The bell tower at Pisa tilted gradually during
  its construction.
• The construction spanned over nearly 200 years.

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The first stage 1173-1178

• The first stones were laid in 1173, beginning the
  build.
• During the initial stage of work, the monument
  tilted slightly north.
• Evidence for this incline can be seen in the
  design of the tower itself
• To keep the first few stories level, workers made
  the columns and arches of the third story on the
  sinking northern side just slightly taller than
  the features on the southern side.
• Political turmoil in Pisa halted construction in
  1178, in the middle of work on the fourth level.

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The second stage 1272-1278

• The second stage began when work on the tower
  resumed almost 100 years later, in 1272.
• By that time, the tower had tilted toward the
  south--the direction in which it still points
  today.
• Designers hoped to correct for the lean, this
  time by adjusting the height of the fifth story.
• This would make the southern side somewhat taller
  than the northern side.
• In 1278, with seven stories completed, work on
  the tower ceased once again because of political
  unrest.
• By 1292 the tower's tilt was so pronounced that a
  group of masons was asked to investigate the
  problem
• The first of many commissions to study the tower.

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The third stage 1360-1370

• The eighth story and final addition, the bell
  chamber, was built between 1360 and 1370.
• Once more, architects attempted to correct for
  the southward lean, this time by angling the bell
  chamber northward.
• The various corrections by early designers can be
  seen best in a cross-sectional view of the tower.
• These efforts, combined with the slow time scale
  of construction (which gave the building's
  foundation time to compress and thereby gain
  strength to compensate for the slant), have so
  far prevented the tower from toppling over.

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The Tower LeansThe Middle Aged Years

• 1370 - 1970

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I like this picture!!!
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Inclination Summary(off the vertical)

• 1278 Seventh level complete0.6 degrees
• 1360 Belfry complete with 1.6 degrees
• 1817 British Architects plumb line measurement 5
  degrees
• 1911 Precise measurements begin

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Alessandro della Gherardesca

• Architect
• 1838
• Dug out the sunken/submerged first level
• Laid a concrete walkway 0.7 meters thick
• Increased the lean by 0.25 degrees

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Benito Mussolini

• Dictator of Italy
• 1934
• Injected 80 tons of concrete on the south side
• Tower tilted 10 mm south that year
• Lean increased to 5.5 degrees

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Since 1900

• 1911
• Precise measurements of the towers
  inclination commenced using a theodolite.
• 1928
• Officials added four level stations around
  the towers plinth level to help monitor changes
  in the inclination.
• 1934
• Engineers installed a plumb line and a
  spirit level to measure both the north-south and
  east-west tilt of the tower. Even 361 holes were
  drilled into the masonry foundation and injected
  80 tons of grout. The purpose of the grout was to
  strengthen the masonry, which results for sudden
  increase in the towers tilt by 31 arc seconds (5
  arc seconds 1.5mm)

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Since 1900

• 1966
• Soil and masonry drilling within and
  beneath the foundations engenders a modest but
  not insignificant increase in the tilt of six arc
  seconds.
• 1985
• Ten arc seconds were added to the tilt
  after boring both into the masonry foundations
  and accidentally into the soil beneath them.
• 1990
• With the tower continuing to tilt naturally
  at the rate of a little over five arc seconds per
  year, Italian government closes the Leaning Tower
  of Pisa on January 7, 1990.

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Since 1900

• 1992
• The Pisa Commission stabilizes the masonry
  by wrapping plastic-coated steel tendons around
  the tower up to the second story which closed
  many cracks and hence reduced chances of buckling
  collapses
• 1993-94
• Workers poured a temporary concrete ring
  around the base of the tower which served as a
  foundation upon which counterweights were laid on
  the north-side. From May 1993 to January 1994,
  crews laid down a series of specially cast lead
  ingots. By July 1994, the tower has leaned back
  toward the north the desired direction i.e.
  52 arc seconds

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Since 1900

• 1995
• After deciding to replace the unsightly
  lead counterweights with an anchored cable
  system, the crew began freezing the ground with
  liquid nitrogen in preparation for installing
  cables. But as soon as the freezing stops, tower
  begins to lean south at the rate of four arc
  seconds per day, this begins in the middle of a
  September night, which crew members remembered as
  Black September. Thus the further operation was
  halted and the search for the permanent solution
  continued with new urgency
• 1996
• In March, engineers successfully completed
  a test of soil-extraction to reduce the towers
  lean.

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Since 1900

• 1998
• In December engineers installed temporary
  cables, which could be tensioned to steady the
  tower if detrimental movements occurred during
  stabilization efforts.
• 1999
• In February, engineers began a very careful
  process of soil extraction. Almost dozens of
  boreholes over a width of about 18 feet which
  removed almost five gallons every two days the
  underlying soil.
• By mid-June the tower leaned back towards north
  by 90 arc seconds.

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Since 1900

• By the end of August the lean had decreased by
  130 arc seconds (1.5 inches)
• Soil-extraction proved almost positive to lessen
  the lean of the tower, thus on September workers
  removed some lead weights and progressive removal
  of all the ingots during full under excavation.
• 2001
• After a decade of corrective
  reconstruction and stabilization efforts, the
  tower was reopened to the public on December 15,
  2001.

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The Solutions

• Heres the video presenting the task performed by
  the crew of engineers and workers to prevent
  further leaning of Tower of Pisa

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Conclusion

• Failure from consolidation
• Corrections during construction
• Failed corrective attempts
• Final solution

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