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.

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

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

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

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

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

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

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

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

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

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

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. 12/35

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

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

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

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

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. 17/35

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. 18/35

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

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

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

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

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

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

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

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

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

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. 28/35

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. 29/35

Cont. Original connection As built connection 30/35

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

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

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

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

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. 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. 35/35

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