1. Seminar on 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 CHOUDHARY
2010 PST101
M.Tech III Semester
Dept. Of Structural Engg.

2. Outline Introduction Goals of Forensic Engineering Investigation
Qualification of the Forensic Engineer
Failure of Structures
Causes of Structural Failures
Types of Failures
2/35

3. Cont. Initiation of Failure Investigation
General Investigation Process
CASE STUDY: Hyatt Regency Walkway Collapse
Bibliography
3/35

4. Introduction
Forensic 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.
4/35

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

6. 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.
6/35

7. Qualification of Forensic Engineer
Technical Competency
Knowledge of Legal Procedures
Detective Skills
Effective Oral and Written Communication
High Ethical Standards
7/35

8. 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.
8/35

9. 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.
9/35

10. 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.
10/35

11. Causes of Structural Failure
Causes of failures fall into five general areas:
Design deficiencies
Construction deficiencies
Material deficiencies
Administrative deficiencies
Maintenance deficiencies
11/35

12. 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.
12/35

13. General Investigation Process
The steps involved are:
Definition of investigation objective
Collection of background information and documents
Initial site visit
Formation of investigation plan and project team
Formulation of initial failure hypotheses
13/35

14. Cont. Comprehensive document review
Site investigation, field testing, and sample collection
Structural analysis and laboratory testing
Revision of failure hypotheses
Final conclusion
Report
14/35

15. 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.
15/35

16. 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.
16/35

17. 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 people occupied the atrium floor and the suspended walkways to see a dance competition.
17/35

18. 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.
18/35

19. 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.
19/35

20. Investigation Approach
The investigation approach that had been carried out is as follows:
Eyewitness and Expert Interviews
Site Investigation
Connection Design Check and Document Study
Laboratory Test
20/35

21. 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.
21/35

22. 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.
22/35

23. 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
23/35

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

25. Cont.
Photo of intact hanger rods from 4th floor walkway opening
25/35

26. Cont.
Photo of still hanging 3rd floor walkway
26/35

27. Cont.
Photo of Deformed 4th floor beam
27/35

28. 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.
28/35

29. 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.
29/35

30. Cont.
Original connection
As built connection
30/35

31. Loading test result of connections
Laboratory Test
Loading test result of connections
Type of connection
Capacity(kN)
Original design 90
As-built 45
31/35

32. 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.
32/35

33. 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.
33/35

34. Conclusion of Case Study
Structure
Problem
Main Finding
Hyatt Regency
Walkway collapse
Reinforcement concrete suspended walkway, with steel to steel connection.
Walkway suddenly
collapsed
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. BIBLIOGRAPHY
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.
Robert T, Ratay. “Forensic Structural Engineering Handbook”, McGraw. Hill
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
35/35

36. THANK
YOU