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.

2/35

Outline• Introduction

• Goals of Forensic Engineering Investigation

• Qualification of the Forensic Engineer

• Failure of Structures

• Causes of Structural Failures

• Types of Failures

3/35

Cont.

• Initiation of Failure Investigation

• General Investigation Process

• CASE STUDY: Hyatt Regency Walkway Collapse

• Bibliography

4/35

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.

5/35

Cont.

• From a legal perspective, forensic engineering is a fact-finding mission to learn the most probable cause or causes of a failure.

6/35

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.

7/35

Qualification of Forensic Engineer

• Technical Competency

• Knowledge of Legal Procedures

• Detective Skills

• Effective Oral and Written Communication

• High Ethical Standards

8/35

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.

9/35

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.

10/35

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.

11/35

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

12/35

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.

13/35

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

14/35

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

15/35

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.

16/35

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.

17/35

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.

18/35

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.

19/35

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.

20/35

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

21/35

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.

22/35

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.

23/35

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 investigation

24/35

Cont.

Walkway sections still remained as a piece-form.

25/35

Cont.

Photo of intact hanger rods from 4th floor walkway opening

26/35

Cont.

Photo of still hanging 3rd floor walkway

27/35

Cont.

Photo of Deformed 4th floor beam

28/35

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.

29/35

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.

30/35

Cont.

Original connection As built connection

31/35

Laboratory Test

Type of connection Capacity(kN)

Original design 90

As-built 45

Loading test result of connections

32/35

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.

33/35

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.

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.

34/35

35/35

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.

THANK

YOU