seminar on forensic structural engineering supervised by: dr. m. k. shrimali (h.o.d.) dr. s. d....
TRANSCRIPT
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Seminaron
FORENSIC STRUCTURAL ENGINEERING
SUPERVISED BY:Dr. M. K. Shrimali (H.O.D.)DR. S. D. BHARTI (Associate Professor)Dept. Of Structural Engg.
PRESENTED BY:AKSHITA CHOUDHARY2010 PST101M.Tech III SemesterDept. Of Structural Engg.
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Outline• Introduction
• Goals of Forensic Engineering Investigation
• Qualification of the Forensic Engineer
• Failure of Structures
• Causes of Structural Failures
• Types of Failures
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Cont.
• Initiation of Failure Investigation
• General Investigation Process
• CASE STUDY: Hyatt Regency Walkway Collapse
• Bibliography
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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.
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Cont.
• From a legal perspective, forensic engineering is a fact-finding mission to learn the most probable cause or causes of a failure.
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Goals of Structural Failure Investigations
• To 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.
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Qualification of Forensic Engineer
• Technical Competency
• Knowledge of Legal Procedures
• Detective Skills
• Effective Oral and Written Communication
• High Ethical Standards
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FAILURE OF STRUCTURES According to Jack Janney (1986), the structural failure
can be divided into:
1. Structural Distress: an impairment of the strength
or load response of a structure which may limit its
use as intended.
2. 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.
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Cont.
3. 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.
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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.
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Causes of Structural Failure Causes of failures fall into five general areas:
1. Design deficiencies
2. Construction deficiencies
3. Material deficiencies
4. Administrative deficiencies
5. Maintenance deficiencies
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Initiation of Failure Investigation
• Establishing a preliminary objective and scope
of work,
• Checking on conflicts in interest,
• Executing a contract agreement, and
• Establishing an investigative plan.
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General Investigation Process
The steps involved are:
1. Definition of investigation objective
2. Collection of background information and
documents
3. Initial site visit
4. Formation of investigation plan and project team
5. Formulation of initial failure hypotheses
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Cont.6. Comprehensive document review
7. Site investigation, field testing, and sample
collection
8. Structural analysis and laboratory testing
9. Revision of failure hypotheses
10. Final conclusion
11. Report
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CASE STUDY: Hyatt Regency Walkway Collapse
Background:
• 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.
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Sequence of Events
• The 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.
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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.
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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.
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Failure Hypothesis
Initially, the investigators had assumed two possibilities
of the collapse as follows:
1. 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.
2. Collapse due to inadequate design of structure.
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Investigation Approach
The investigation approach that had been carried
out is as follows:
1. Eyewitness and Expert Interviews
2. Site Investigation
3. Connection Design Check and Document Study
4. Laboratory Test
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Eyewitness and Expert Interviews
• Roger 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.
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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.
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Site Investigation
The 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 investigation
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Cont.
Walkway sections still remained as a piece-form.
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Cont.
Photo of intact hanger rods from 4th floor walkway opening
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Cont.
Photo of still hanging 3rd floor walkway
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Cont.
Photo of Deformed 4th floor beam
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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.
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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.
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Cont.
Original connection As built connection
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Laboratory Test
Type of connection Capacity(kN)
Original design 90
As-built 45
Loading test result of connections
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Cont. Analysis of these two connection details revealed the
following:
1. 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.
2. As-built, however, the connection only supported 30% of
the minimum load which explains why the walkways
collapsed well below maximum load.
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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.
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Conclusion of Case StudyCase Study Structure Problem Main Finding
Hyatt RegencyWalkway collapse
Reinforcement concrete suspended walkway, with steel to steel connection.
Walkway suddenlycollapsed
Collapse 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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BIBLIOGRAPHY1. National Bureau of Standards (NBS). Investigation of the Kansas City
Hyatt Regency Walkways Collapse, NBS-BSS 143. Washington: U.S.
Department of Commerce. May 1982.
2. Robert T, Ratay. “Forensic Structural Engineering Handbook”, McGraw.
Hill. 2000.
3. Robert T. Ratay. “Structural Condition Assessment”, John Wiley & Son,
Inc., 2007.
4. J. R. Janney. Guide to Investigation of Structural Failures, New York:
ASCE, 1986.
5. Bell, Glen. “Failure Information need in Civil Engineering, Reducing
Failures of Engineered Facilities”, ASCE, New York. 1985.
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THANK
YOU