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Introduction and Basics 

B S C RAO

The Genesis

17^th July 1981 dawned like any other day in Kansas City, USA. The 40-storey tall Hyatt Regency Hotel had, as usual, organised the weekly tea dance. Several hundred people had gathered together in the hotel’s vast many-story high lobby to watch and take part in the dance being held on the lobby floor. The hotel’s great attraction and biggest draw, in those days, was its spacious atrium which enclosed three steel, glass and concrete walkways at the second third and fourth levels (Fig.1).

Fig. 1, 2: The Hyatt Regency Hotel Atrium (Before and after the Collapse) ^{1, 2}

These walkways spanned 37 metres (120 feet) across the atrium bridging the two wings of the hotel on either side of it,  and were suspended by steel hangers from the ceiling above. The fourth level walkway was directly above the second level walkway, while the one at the third level was actually several metres away. The dance competition was on in full swing and people crowded everywhere to find the best vantage points to watch the dance. The three walkways too had dozens of people standing on them, some dancing in tune with the music blaring from the floor below. And then, out of the blue and with no warning at all, a disaster of unimaginable horror occurred!!

At 7.05 pm a loud popping sound was heard and, before anyone realised what was happening, the fourth level walkway came     crashing down on to the second level walkway and the two together crashed down on the crowded dance floor below (Fig.2 and 3), instantly killing 114 people and seriously injuring more than 200 people.

Fig. 3 :  The Hyatt Regency Hotel Atrium (After the Collapse) ¹

It was the worst disaster in terms of loss of life and injuries until then in US history (surpassed only 30 years later by the collapse of the twin World Trade Centre towers on September 112001). The hotel was designed to be a masterpiece of architecture and engineering, and would, if things had been done right, have been a spectacle of awe and wonder. Tragically it became a salutary lesson in how the best intentions, and even good design, can turn into deadly calamity through errors in communication, detailing and construction.

The immediate cause of the collapse of the two walkways was  the rupturing of the connection between the fourth level hanger rod and the box beam supporting the platform, because of a design change by the fabricator (to avoid having to thread the entire hanger rod) from a single through rod hanger to an offset double hanger (Fig. 4) that effectively doubled the load on the restraining nut supporting the fourth level platform. As a result, the restraining nut punched through the welded channel box beam which just opened up (Fig.5).

Fig. 4 - Design Change in Hanger Support ²

Fig. 5      Close-up of the Failed Connection ³

The detailed inquiry subsequently held to investigate the accident went on for three years till November 1984. During the investigation it came to light that even the basic design of the hangers was flawed, and that it was just barely enough to support the self-weight of the steel and concrete walkway platform, leave alone the incident live load, nor did it conform to the Kansas City Building Code!². There was also a series of miscommunications between the structural designer (G.C.E. Engineers) and the structural fabricator (Havens Steel Company). The designer initially proposed a single threaded hanger rod to support both the second- and fourth - level walkways, but the fabricator suggested modifying the design to have two hanger rods - one between rod and the fourth level walkway and another from the fourth- to the second level walkway, to avoid having to thread the entire single length proposed in the original design. The designer accepted the fabricator’s proposal but neither the designer nor the fabricator felt he was responsible to re-check the effect of this design change.⁴ There was a series of (mis) communications between the two, and neither checked the design. The fact remained however that the changed design drawings were signed by the design engineer.

The aftermath of the Hyatt Regency walkway collapse resulted in a series of decisions that had far reaching implications for the civil engineering profession. The changed hanger design was the root cause of the disaster; that was quickly established. How it happened was also established - failure in proper communication and follow-up between the designer and fabricator.

More than a hundred people had died and more than two hundred had been seriously injured. Somebody was responsible and somebody had to pay! So it became important to determine who was responsible - the designer or the fabricator? The Court found the designer "guilty of gross negligence, misconduct and unprofessional conduct in the practice of engineering" as he was responsible for design, approval of fabrication drawings and inspection to ensure conformance with design.  Consequently a number of the partners of the design firm went bankrupt, two principal designers lost their licenses to practice in two states (Missouri and Texas), the firm lost its engineering licence, and the American Society of Civil Engineers (ASCE) "adopted a report that states structural engineers have full responsibility for design projects^5". It was also decided that suspended walkways would henceforth not be allowed. As all the principal actors (the designers) went bankrupt, Hyatt was forced to pay compensation to the victims in the sum of USD 140million. And fabricators became unwilling to have (licensed) professional engineers on their staff or provide professional design services as part of their portfolio.⁵

Epilogue:  The hall was restored, and instead of the two walkways only the second level walkway was rebuilt - but this time supported by many columns below. Several rescuers suffered post-traumatic stress and one of them committed suicide, being unable to bear the stress. In 1987 the hotel was renamed the Hyatt Regency Crown Centre, and again in 2011 as the Sheraton Kansas City at Crown Centre, and has been renovated several times, but without any change in the layout and design. But in order to bury the tragedy with the dead, there is no memorial or plaque to indicate what happened on that fateful day in 1981.²

What Is Forensic Engineering?

Every major failure or disaster leaves in its wake not only serious damage, but quite often death and destruction. Nevertheless, from each of them we can learn several useful lessons that will ensure that such failures will not recur.  The Hyatt Regency walkway collapse has been described in some detail mainly to illustrate some salient features of how failures can occur from the simplest of causes, how miscommunication between designer and builder (or any of the involved parties) can cause serious errors in design and construction which can go unnoticed, and what happens when there is a failure.

In the above example, investigators had to sift through the wreckage, collect every piece of evidence, conduct and record interviews and pore over volumes of paperwork to determine and understand exactly how and why the accident had happened and who was responsible. The Court of Law decided who was ultimately guilty and what their punishments should be, and awarded the compensation payable to the victims and who would pay it. The forensic investigations conducted were exactly similar to what would be done in the case of a crime like a murder or arson - except that here the "crime" was an engineering failure resulting in structural collapse.

And that is what we broadly understand by the term "forensic engineering". That broad term encompasses within itself a huge field of investigative engineering techniques, analyses, testing equipment etc. It also raises important questions of ethics and the social responsibility of the engineer - what he owes, and how answerable and responsible he is, to society. The forensic engineer comes into his own when he is called on to provide the engineering background and support to the due process of law which generally is set into motion after any accident, failure or disaster. In forensic engineering there is an intimate connection between the practice of two professions - engineering and law. Unfortunately, this is either not fully appreciated or is played down as not being important.  And that brings us to the need to define formally what forensic engineering is. There are several "definitions" available in the literature and between them cover almost all the facets of "forensic engineering".

Forensic Engineering - Some Definitions

There are, however, several formal, and comprehensive, definitions available in the literature some of which given here for information.

• Forensic engineering can be considered to be "the investigation of materials, products, structures or components that fail or do not operate or function as intended, causing personal injury or damage to property. The consequences of failure are dealt with by the law of product liability. The field also deals with retracing processes and procedures leading to accidents in operation of vehicles or machinery. The subject is applied most commonly in civil law cases, although may be of use in criminal law cases. Generally the purpose of a Forensic engineering investigation is to locate cause or causes of failure with a view to improve performance or life of a component, or to assist a court in determining the facts of an accident. It can also involve investigation of intellectual property claims, especially patents.^6"

• A "legalistic" definition of forensic engineering has been provided by Milton F Lunch, former General Counsel to the National Society of Professional Engineers (NSPE) as follows : "Forensic Engineering is the application of the art and science of engineering in the jurisprudence system, requiring the services of legally qualified professional engineers. Forensic engineering may include the investigation of the physical causes of accidents and other sources of claims and litigation, preparation of engineering reports, testimony at hearings and trials in administrative or judicial proceedings and the rendition of advisory opinions to assist the resolution of disputes affecting life and property.^7"

• Yet another definition is given by Randall K Noon : Forensic Engineering is the application of engineering principles, knowledge, skills and methodologies to answer questions of fact that may have legal ramifications⁸

History⁵

As the field of engineering has evolved over time so has the field of forensic engineering. Early examples include investigation of bridge failures such as the Tay rail bridge disaster of 1879 and the Dee bridge disaster of 1847. Many early rail accidents pioneered the use of tensile testing of samples and fractography of failed components. With the prevalence of liability lawsuits in the late 1900s the use of forensic engineering as a means to determine culpability spread in the courts. Edmond Locard (1877-1966) was a pioneer in forensic science who formulated the basic principle of forensic science: "Every contact leaves a trace". This became known as Locard's "exchange principle".

The Process

Materials and structures behave in predictable ways, and when subjected to loads and stresses greater than what they have been designed for will fail - partially or completely. Human beings and organisations, on the other hand, behave in unpredictable ways, and therein lies a major problem for the investigator when he has to find out who was responsible, why and how.

Every failure ultimately has one immediate cause which precipitated the failure, which may be the resultant culmination of multiple contributory causes. The effects can be minor, major or disastrous and the consequences can have deep and lasting impact on the people and on the profession. The term "failure" -  whether accidental or intentional -  is  understood in its broadest sense which could include a failure of structure, component or even performance which results in damage to, or loss, of life,  property or money.

Thus the process of forensic engineering investigations requires one to follow a series of steps, working backwards from the failure. These steps would involve, in simplified terms, the following:

1. Describe or "define" the failure
2. Collect evidence - physical, material, photo/video, oral (through interviews), documentary
3. Analyse the evidence - which itself would involve several activities including material testing
4. Hypothesize the possible sequence of events that led to, and the root causes for, the failure
5. Validate the hypothesis through structural analysis, model testing, research, literature review etc.
6. Arrive at a conclusion regarding the cause(s) that resulted in the failure
7. If required the forensic engineer may also have to make an estimate of loss. How thorough this is done will play a crucial and vital role in a court of law or in any settlement between the involved parties.

This process is graphically illustrated in the flowchart shown in Fig. 6.

It is not the role of the forensic engineer to fix culpability or responsibility. He only presents facts, and it is for the court to rule on responsibility, culpability and damages.

Qualifications of a Forensic Engineer

The particular skill-sets required to qualify as a forensic engineer will depend upon the specific engineering discipline or field of forensic investigation. There are however some common skills that will be required in all forensic engineers.

• He must be technically competent - A forensic engineer must be technically competent and proficient in his field of specialisation. Active membership of professional organisations, and authorship of articles in professional journals point him out as a professional in good standing amongst his peers greatly add to his credibility and acceptability in court as an expert witness. But he must also be a generalist with a broad knowledge of science and engineering as a whole with the ability to understand the relationship between cause and effect. His services are called on after a failure and are presented with its aftermath.
• He must be a detective - He must patiently and diligently collect all the evidence that can be found and be able intelligently to interpret the data before him. With his experience and engineering knowledge he has to become a detective and glean from the mass of seemingly disjointed and sometimes unconnected pieces of evidence before him the plausible cause and build a strong case that can stand up under close scrutiny in a court of law. This takes a lot of time and effort for the pieces to be fitted together, much like solving a jig-saw puzzle, for theories to be tested and proved and for the final picture to emerge. He must be able to reconstruct what happened and provide solid scientific and engineering bases for his conclusions.
• He must be articulate with good communication skills - A successful forensic engineer will possess the valuable ability to articulate and communicate well, both orally and in written reports and presentations, comprehensively and in simple language (without losing focus) the essence of the methodology and findings to what would be essentially a lay audience (the court, in particular, and to a lesser extent the public, in general). He should be able to interact effectively with the media and use the opportunity to educate the public.  These communications may be required, not only to facility owners, contractors and other professional engineers, but also in reports to lawyers and statutory bodies, in expert witness statements in legal proceedings, and in statements to the press and the public. In many cases, the expert’s report may be confidential or protected by legal professional privilege. It is probable that only a low percentage of cases for which forensic engineering investigations are undertaken and expert witness reports are prepared, actually reach the courts (e.g. Brookes, 2006). However, the information contained in the reports may be protected by legal privilege and remain confidential so  that the results cannot be published and the potentially valuable information that the reports   contain never reach the engineering profession.¹⁰
• He must be skilful in court -In all those cases which reach the court and the forensic engineer is called as an expert witness, it is essential that he is not only able to clearly enunciate his thoughts but also more importantly, be able to maintain his composure and self-confidence, especially under cross-examination. A diffident, nervous and flustered witness who does not have a full command over his subject will be considered unreliable and could jeopardise the outcome of the case and even destroy the reputations of the people involved. But he must also not be dogmatic, assert his position or be arrogant. As Carper says, Forensic practice is not a profession for stubborn "know-it-alls^7"
• He must be ethical -Above all, and this cannot be overemphasized, the forensic investigator must maintain the highest standards of honesty and integrity. He must be absolutely objective and impartial in all that he does and use his "education, training, experience, skill and knowledge" in the most professional manner. Most importantly he must not be swayed by extraneous pressures and inducements, which inevitably will come into play. Thus the forensic "expert" engineer must be a person who has great integrity with exemplary ethical standards. This is amplified later in this article.