structural collapse
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1 1 8.0 STRUCTURAL COLLAPSE 8.1 Common causes of structural collapse Structure collapse can result in serious physical injury and death to people. Many factors can contribute to the collapse of structure. The factors are :- i) Bad Design ii) Faulty Construction iii) Foundation Failure iv) Extraordinary Loads v) Unexpected Failure Modes vi) Combination of Causes 2 8.0 STRUCTURAL COLLAPSE i) Bad Design Bad design does not mean only errors of computation, but a failure to take into account the loads the structure will be called upon to carry, erroneous theories, reliance on inaccurate data, ignorance of the effects of repeated or impulsive stresses, and improper choice of materials or misunderstanding of their properties.
Transcript of structural collapse
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8.0 STRUCTURAL COLLAPSE8.1 Common causes of structural collapse
Structure collapse can result in serious physical injury and death to people. Many factors can contribute to the collapse of structure. The factors are :-
i) Bad Design ii) Faulty Construction iii) Foundation Failure iv) Extraordinary Loads v) Unexpected Failure Modes vi) Combination of Causes
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i) Bad Design
Bad design does not mean only errors ofcomputation, but a failure to take into account theloads the structure will be called upon to carry,erroneous theories, reliance on inaccurate data,ignorance of the effects of repeated or impulsivestresses, and improper choice of materials ormisunderstanding of their properties.
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ii) Faulty Construction
Faulty construction has been the most importantcause of structural failure. The engineer is also atfault here, if inspection has been lax. This includesthe use of salty sand to make concrete, thesubstitution of inferior steel for that specified, badriveting or even improper tightening torque ofnuts, excessive use of the drift pin to make holesline up, bad welds, and other practices well knownto the construction worker.
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iii) Foundation FailureEven an excellently designed and constructed structure willnot stand on a bad foundation. Although the structure willcarry its loads, the earth beneath it may not. The LeaningTower of Pisa is a famous example of bad foundations, butthere are many others. The old armory in St. Paul,Minnesota, sank 20 feet or more into soft clay, but did notcollapse. The displacements due to bad foundations mayalter the stress distribution significantly.
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iv) Extraordinary Loads
Extraordinary loads are often natural, such asrepeated heavy snowfalls, or the shaking of anearthquake, or the winds of a hurricane. A buildingthat is intended to stand for some years should beable to meet these challenges. A flimsy flexiblestructure may avoid destruction in an earthquake,while a solid masonry building would be destroyed.Earthquakes may cause foundation problems whenmoist filled land liquefies.
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v) Unexpected Failure ModesUnexpected failure modes are the most complex of the
reasons for collapse.
Suppose you have a beam supported at the ends, with aload in the center. You know the beam will bend, and if theload is too great, it may break apart at the bottom, or crushat the top, under the load. This you expect. However, thebeam may fail by splitting into two beams longitudinally, orshearing, or by the top of the beam deflecting to one side orthe other, also called buckling. In fact, a beam will usuallyfail by shearing or buckling before breaking.
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vi) Combination of causesThe impact of aircraft on the upper stories had only a localeffect, and did not impair the integrity of the buildings,which remained solid. The fires caused weakening of thesteel, and some of the floors suddenly received a load forwhich they were not designed. Example The World TradeCenter, New York
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8.2 Case studies
Building Collapsed In Shanghai (06/27/2009) At around 5:30am on June 27, an unoccupied building still under construction at Lianhuanan Road in the Minhang district of Shanghai city toppled over. One worker was killed. According to information, a 70 meter section of the flood prevention wall in nearby Dianpu River and that may have something to do with this building collapse. But the high-resolution photos are really amazing. Improper construction methods are believed to be the reason of last Saturday's building collapse in Shanghai, according to a report from the investigation team. The investigation team's report said that workers dug an underground garage on one side of the building while on the other side earth was heaped up to 10 meters high, which was apparently an error in construction, according to a report on eastday.com, Shanghai's official news website. "Any construction company with common sense would not make such a mistake," said an expert from the investigation team.
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8.2 Case studiesCracks on the flood-prevention wall near the building, as well as the special geological condition in the water bank area, may be part of the reason for the collapse. Nine people linked to the building collapse, including the real estate developer, contractor and the supervisor for the project, have been put "under appropriate control“.
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8.2 Case studiesThe collapse of an unfinished building in Shanghai has said that the accident was due to the construction company's "ignorance", rather than flaws in the design or building materials. However, the report stopped short of apportioning blame, and has been criticised for failing to address key issues. The collapse was caused by earth, excavated to make a 4.6-metre deep pit for an underground car park alongside the building, being piled to depths of up to 10 metres on the other side of the structure. The weight of the pile created a "pressure differential" which led to a shift in the soil structure, eventually weakening the foundations and causing them to fail. This situation "may" have been aggravated by several days of heavy rain leading up to the collapse, but investigators would not say whether this was a crucial factor. The report said the construction company - Shanghai Zhongxin Construction - "did not consider clearly" that the earth pile could have such a devastating effect.
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(1) An underground garage was being dug on the south side, to a depth of 4.6 meters(2) The excavated dirt was being piled up on the north side, to a height of 10 meters(3) The building experienced uneven lateral pressure from south and north(4) This resulted in a lateral pressure of 3,000 tonnes, which was greater than why the pilings could tolerate. Thus the building toppled over in the southerly direction.
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1) The apartment building was constructed
2) Then the plan called for an underground garage to be dug out.The excavated soil was piled up on the other side of the building.
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3) Heavy rains resulted in water seeping into the ground.
4) The building began to shift and the concrete pilings were snapped due to the uneven lateral pressures.
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5) The building began to tilt. 6) The building collapsed.
