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The Leaning Tower of Pisa An Engineering Failure


... 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 ... – PowerPoint PPT presentation

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Title: The Leaning Tower of Pisa An Engineering Failure

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

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

  • 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?

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

The Building of the Leaning Tower of Pisa
  • 1173-1370

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.

The first stage 1173-1178
  • The first stones were laid in 1173, beginning the
  • 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.

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
  • 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
  • By 1292 the tower's tilt was so pronounced that a
    group of masons was asked to investigate the
  • The first of many commissions to study the tower.

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.

The Tower LeansThe Middle Aged Years
  • 1370 - 1970

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
  • 1911 Precise measurements begin

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

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

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)

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
  • 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.

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
  • 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

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

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.

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,

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

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

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