Seminar - PowerPoint Presentation

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SeminaronFORENSIC STRUCTURAL ENGINEERING

SUPERVISED BY:

Dr. M. K. Shrimali (H.O.D.)DR. S. D. BHARTI (Associate Professor)Dept. Of Structural Engg.

PRESENTED BY:

AKSHITA CHOUDHARY

2010 PST101

M.Tech

III Semester

Dept. Of Structural

Engg

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OutlineIntroductionGoals of Forensic Engineering InvestigationQualification of the Forensic EngineerFailure of StructuresCauses of Structural FailuresTypes of Failures2/35Slide3

Cont.Initiation of Failure InvestigationGeneral Investigation ProcessCASE STUDY: Hyatt Regency Walkway CollapseBibliography3/35Slide4

IntroductionForensic Structural Engineering:Application of the engineering sciences to the investigation of failures or performance problems.Highly specialized field of engineering practice. Requires engineering expertise and knowledge of legal procedures.From an engineering perspective, forensic engineering deals with the investigation and reconstruction of failures.4/35Slide5

Cont.From a legal perspective, forensic engineering is a fact-finding mission to learn the most probable cause or causes of a failure.5/35Slide6

Goals of Structural Failure InvestigationsTo determine the causes of failure.To compare statements by witnesses or injured parties with physical evidence.To ascertain whether an illegal or improper activity was causative.To assess damage to materials, products or structures and evaluate repair estimate.6/35Slide7

Qualification of Forensic EngineerTechnical CompetencyKnowledge of Legal ProceduresDetective SkillsEffective Oral and Written CommunicationHigh Ethical Standards7/35Slide8

FAILURE OF STRUCTURES According to Jack Janney (1986), the structural failure can be divided into:Structural Distress: an impairment of the strength or load response of a structure which may limit its use as intended. Structural Failure: the reduction of the capability of a structural system or component to such a degree that it cannot safely serve its intended purpose.8/35Slide9

Cont.Structural Collapse: Gross movement of major members or a significant portion of a structural system manifested by the creation of rubble from breakage of the members themselves and elements supported by themselves.9/35Slide10

Cont.Gerald Leonards (1992) defines “failure” as an unacceptable difference between expected and observed performance. This definition can be used to describe a catastrophic failures as well as minor failures such as roof leaks.The ASCE Technical Council on Forensic Engineering has adopted the above definition provided by Gerald Leonards. 10/35Slide11

Causes of Structural Failure Causes of failures fall into five general areas:Design deficienciesConstruction deficienciesMaterial deficienciesAdministrative deficienciesMaintenance deficiencies11/35Slide12

Initiation of Failure InvestigationEstablishing a preliminary objective and scope of work, Checking on conflicts in interest, Executing a contract agreement, and Establishing an investigative plan.12/35Slide13

General Investigation ProcessThe steps involved are:Definition of investigation objectiveCollection of background information and documentsInitial site visitFormation of investigation plan and project teamFormulation of initial failure hypotheses13/35Slide14

Cont.Comprehensive document reviewSite investigation, field testing, and sample collectionStructural analysis and laboratory testingRevision of failure hypothesesFinal conclusionReport14/35Slide15

CASE STUDY: Hyatt Regency Walkway CollapseBackground:The Hyatt Regency Walkway Collapse was the worst structural failure in the history of the United States.111 people were killed and more than 200 were injured.15/35Slide16

Sequence of EventsThe Hyatt Regency hotel opened in Kansas City, Missouri, USA in 1980.It comprised a 40-story tower, an atrium, and a function block, housing all of the hotel’s services.Three walkways suspended from the atrium’s ceiling by six 32-mm-diameter tension rods each spanned the 37-m distance between the tower and the function block.16/35Slide17

Cont.The 3rd and 4th floor walkways hung from the ceiling.The 2nd floor walkway was suspended from the beams of the 4th floor walkway, directly below the 4th floor walkway.On the July 17, 1981, around 1500-2000 people occupied the atrium floor and the suspended walkways to see a dance competition.17/35Slide18

Cont.A loud crack echoed throughout the building and connections supporting the ceiling rods that held up the 2nd and 4th floor walkways across the atrium failed.The 4th floor walkway collapsed onto the 2nd floor walkway and then both walkways collapsed onto the crowded 1st floor atrium.18/35Slide19

Failure Hypothesis Initially, the investigators had assumed two possibilities of the collapse as follows:Walkways buckled from “harmonic vibration” set up by people swaying or dancing at the same times. This wave like motion generated violent stress and caused vibration failure of the structure.Collapse due to inadequate design of structure.19/35Slide20

Investigation ApproachThe investigation approach that had been carried out is as follows:Eyewitness and Expert InterviewsSite InvestigationConnection Design Check and Document StudyLaboratory Test20/35Slide21

Eyewitness and Expert InterviewsRoger McCarthy, an expert of failure analysis, had stated that there were telltale signs in the skeleton of a structure well before it suffered vibration failure, and in Hyatt Regency walkway collapse, there were no such signs.21/35Slide22

Cont.Eyewitness accounts gave another point that indicated there was a loud crack echoed while the 2nd and 4th floor walkway crashed to the ground. Hence, according to the eyewitness and expert point, the collapse was related to the sudden failure mechanism.22/35Slide23

Site InvestigationThe following photographic evidence was taken by Dr. Lee Lowery, shortly after the collapse:General view of the lobby floor, during the first day of the investigation23/35Slide24

Cont.Walkway sections still remained as a piece-form.24/35Slide25

Cont.Photo of intact hanger rods from 4th floor walkway opening25/35Slide26

Cont.Photo of still hanging 3rd floor walkway26/35Slide27

Cont.Photo of Deformed 4th floor beam27/35Slide28

Cont.From the photographic evidence it was observed that there were no failure signs on the walkway section, indicating that the collapse was not caused by inadequate design of the section of the walkway. The photograph had provided significant proof to show that the walkway collapse was most likely caused by connection failure.28/35Slide29

Connection Design Check and Document Study The National Bureau of Standards (NBS) found that the details of the connection of the walkway beam to the suspender was not constructed as drawn but was changed by the contractor for constructability reason.29/35Slide30

Cont.Original connectionAs built connection30/35Slide31

Laboratory TestType of connectionCapacity(kN)Original design90

As-built

45Loading test result of connections

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Cont. Analysis of these two connection details revealed the following:The original design of the rod hanger connection would have supported 90 kN, only 60% of the 151 kN required by the Kansas City building code. This showed that the design of the connection was inadequate. As-built, however, the connection only supported 30% of the minimum load which explains why the walkways collapsed well below maximum load.32/35Slide33

Investigation Results The National Bureau of Standards (NBS) discovered that the cause of this collapse was quite simple: the rod hanger pulled through the box beam causing the connection supporting the 4th floor walkway to fail.33/35Slide34

Conclusion of Case StudyCase StudyStructureProblemMain FindingHyatt RegencyWalkway collapseReinforcement concrete suspended walkway, with steel to steel connection.

Walkway suddenly

collapsedCollapse due to fracture of the brittle connection. This fracture of connection was caused because the contractors did not follow the design drawing.

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BIBLIOGRAPHYNational Bureau of Standards (NBS). Investigation of the Kansas City Hyatt Regency Walkways Collapse, NBS-BSS 143. Washington: U.S. Department of Commerce. May 1982.Robert T, Ratay. “Forensic Structural Engineering Handbook”, McGraw. Hill. 2000.Robert T. Ratay. “Structural Condition Assessment”, John Wiley & Son, Inc., 2007.J. R. Janney. Guide to Investigation of Structural Failures, New York: ASCE, 1986.Bell, Glen. “Failure Information need in Civil Engineering, Reducing Failures of Engineered Facilities”, ASCE, New York. 1985

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