Forensic Engineering (2000)

At the time of this writing, three months after the 18 Aug. 1999 Kocaeli-Golcuk earthquake in northwest Turkey, the available data on the impact of the earthquake are still in a state of flux. The reported casualty count from the Kocaeli event has been slowly approaching 20,000 with almost twice as many reported injured. Over 100,000 residential units are reported to have been lost. The following major event of 12 November 1999 (the Duzce-Bolu earthquake, M_w=7.2) claimed over 700 lives. Approximately 5000 were reported injured. Statistics of structural and environmental damage have not yet been compiled for the Duzce-Bolu event.

The expert witness provides a crucial part of a litigant's story. In order to communicate effectively, the witness must prepare in consultation with the attorney who retains him or her. Attorneys often hire consultants to assist in this process. Witness preparation entails learning new rules of communication that arise out of legal rules and procedures, and it requires learning better strategies of communicating with varied audiences.

On July 17, 1981, a tragic structural collapse occurred at the Hyatt Regency Hotel in Kansas City, Missouri. The failure of a critical connection in a suspended walkway caused 114 deaths and nearly 200 serious injuries. Much has been written about this event, with various conclusions and implied lessons. Yet, few sources provide the information contained in the four papers included in this session. As the story unfolds in these four papers, some important questions come to mind: Have the proper lessons truly been learned? Have the design and construction communities really adopted changes that will prevent the recurrence of a similar tragedy? The introductory paper by Piotr Moncarz and Robert Taylor is presented from the viewpoint of forensic engineers who were involved in the investigation and analytical work. They describe the design concept for the walkways and review the technical cause of the failure.

The tragedy of this hotel atrium walkway collapse claimed 114 lives leading to a great public and professional outcry, and a dramatic impact on careers and lives of many fine professionals. The Architecture and Engineering (A&E) community in the United States began a soul-searching debate on issues as diverse as how project workflow is managed to professional responsibility and ethics. Fundamental errors were identified in the project interaction within the A&E group as well as the construction industry. As a result changes to the code of ethics and professional practice were introduced. Engineering issues of load, stress, and deformation are quite simple in the case of the walkway collapse. The issue of how much each of the inadequacies in the design and construction contributed to the tragic failure is significantly more complex. This review provides a presentation of the demand-capacity ratio associated with elements primary to the failure. Why did it take a year for the walkway's suspension system to fail? Results of detailed structural analysis, including inelastic finite element analysis of the box girder-to-hanger rod connection are discussed. Large inelastic deformations under the dead load alone are calculated. Why wasn't this desperately precarious condition noticed earlier? What were the safety margins of its individual components prior to the collapse? By how much could good construction practice and plain good old common sense have influenced these margins? In summary, the collapse occurred because of the doubling of the load on the connection resulting from ill-considered change of an ill-defined structural detail. However, this lesson on how any minor additional effort might have substantially improved the connection capacity, or even prevented the failure of the structure, should be studied and remembered.

This paper presents a brief chronology of the events that preceded the collapse of the walkways at the Kansas City including the prior failure that occurred during construction and the evolution of the detail that caused the catastrophe. Many of the facts surrounding the case were not publicized due to the litigation. Some were not brought out during the litigation. No attempt will be made to affix responsibility, as these issues were resolved years ago. The chronology is followed by a discussion of the events that contributed to the collapse and what changes have been made in the industry that would prevent a similar occurrence.

Nearly twenty years ago an elegant Kansas City hotel was the site of one of the most famous engineering failures in recent history. The collapse of two elevated walkways in the lobby left 114 people dead and nearly 200 injured, and plunged the engineering profession into a dilemma over how to deal with the engineers who were involved. In the mid-1970s, as the Kansas City Hyatt Regency was under construction, the engineering profession's codes of ethics were under construction as well. ASCE leaders argued that their society's new code should reflect a new hierarchy of engineers' responsibilities. "Public welfare," they agreed, should be the "primary concern" of engineers, according to the new code. Second should come the engineer's duty to his "clients, employer or employees," and third should be an engineer's loyalty to his profession, thus turning the earlier code on its head. The implications of the new ethics code became disturbingly clear with the Hyatt. This paper tells the story of how the engineering profession struggled to transform an unspeakable disaster into a powerful, if painful, lesson about the meaning of ethics in engineering.

For nineteen years since the tragic collapse of the Kansas City Hyatt Hotel's walkway on July 17, 1981, the engineering profession and construction industry has studied and endeavored to understand what happened; why it happened; who was at fault; what should have been done to prevent it and how can the engineering and construction industry guard against future structural collapses. This paper, by the Structural Engineer of Record, addresses the events during and subsequent to the design, bidding, construction and investigation that followed the collapse. It discusses the tragedy and its continuing impact on the public and the standard of the professional practice of engineering, and the continuing two fundamental issues.

A 48-story temporary, aluminum-pipe, hoist-support structure supporting the personnel lift of the Conde Nast Tower under construction at Times Square, suddenly started to collapse in the early morning of July 21,1998. A two-story segment of the pipe structure between the 20^th to 22^nd floor buckled and crashed onto itself. The 30 stories above the crashed portion was hanging precariously from the building, leaning outwards onto the Times Square below. With hundreds of people and vehicles in the immediate area below during the morning rush hour, the situation was dangerous and life threatening. The Office of Emergency Management of the City of New York was summoned to the scene to assist in the handling of this major emergency. The NYC Commissioner of Buildings assembled a team of technical experts form the Public and Private sectors to evaluate and stabilize of the partially collapsed structure. LZA Technology was retained to lead the technical efforts of the evaluation, stabilization and eventual demolition. This paper chronicles the author's experiences during this emergency. It also outlines the approaches and methods used to evaluate, stabilize and eventually demolish the partially collapsed structure.

On July 21, 1998, an exterior scaffold/personnel hoist system being used to construct a 49 story building in the Times Square area of New York City partially collapsed. This paper summarizes the investigation procedures used to determine the cause of the partial collapse and the findings of the investigation.

Collapses usually occur when the parties to the construction process do not have sufficient knowledge or do not understand or ignore their responsibilities. This paper describes the collapse of a trunk storm sewer during construction of a building, due to the improper actions of the design-build contractor and the improper design of the building foundation by the structural engineer.

Shopping malls have large roof areas and large paved areas for parking. In many cases, during heavy rainfall, the drainage from these roofs and parking lots will overload the municipal storm sewer system. Therefore, many municipalities require a temporary storm water detention system on the property of the mall, when the mall is being built or enlarged. Many of these detention systems are located under the parking lot pavement and have various constructions.

The slide of a large part of the core and upstream shoulder of Carsington Dam in July, 1984, took place against an unusual background. One of the largest earth-fill dams in Britain, it was designed by a team that appeared to show limited geotechnical expertise. Far too few shear strength tests were undertaken, unrealistic slip surfaces were analysed, instrumentation data was not utilised; and the design factor of safety was not adequately specified. The dam incorporated an oddly-shaped core which maximised the length of potential slip surface through this comparatively weak element of the dam cross-section. Towards the end of the second earth-moving construction season, as the dam embankment rose towards 5m of its final height, movements in the fill and the Engineers' concern about a high pore pressure and no consequential change of design, caused the contractor to seek an assessment of the dam's stability from its specialist consultant, an experienced earthfill dam designer. In a report reviewing stability, undertaken by both Authors with assistance from a number of colleagues, the eventual failure mode was identified, and likelihood of failure, due to low factors of safety, was correctly predicted. Appropriate corrective measures were identified. This could have been a "near miss" case — if the original designers had discussed technical issues. In the event, strained relationships arising out of other issues prevented action being taken to rectify matters. Further earthfill was instructed to be placed in the third construction season, and the avoidable failure took place just as the embankment dam was being completed to full height. Post-failure investigations were carried out and published by others, including a Governmental Report and several technical papers. The dam has been rebuilt satisfactorily on the same site. There are several lessons to be learnt from Carsington, including that clear channels for the debate of technical issues must be provided, so that they can be debated free from commercial or personality related issues, without fear of litigation.

In June 1993, a massive "sinkhole" developed in a surface parking lot of a hotel facility located in the Piedmont Geologic Province of Georgia. The hole was the result of the soil erosion associated with a failed, 4-meter diameter combined sewer tunnel. Two fatalities occurred with the collapse. The subsequent forensic study uncovered a series of contributing factors, including a disregard for site history during the planning stage of the development, mis-application of the use of geogrids in the design of a "safety net", mis-interpretation of the signs of impending failure in both the preventative maintenance inspections conducted by the city and forensic studies conducted by consultants immediately prior to the collapse. The paper discusses the planning and design process, the technical inadequacies of the design, and the involvement of consultants and engineers leading up to the time of the collapse.

The January 17, 1994 Northridge earthquake (Magnitude 6.7) was the most costly natural disaster in the United States. The Northridge main shock was followed by thousands of aftershocks ranging up to a magnitude 5.9. For a variety of reasons, earthquake-related insurance claims often report damage from not only the main shock, but from aftershocks that can occur many months later. The focus of this paper is the structural damage claimed to be caused by aftershocks of the Northridge earthquake, and the analytical basis for differentiating between aftershock and main shock damage. Methodology is suggested for estimating the ground shaking intensity at a site due to aftershocks, particularly for those cases where nearby ground motion records are not available. Mechanisms of aftershock damage estimation, including site-specific effects and cumulative damage from main and aftershocks, are also reviewed.

Instead of investigating accidents, Incident Reporting Systems (IRS) analyze incidents. Because incidents happen more often than accidents, larger samples can be obtained by collecting incident reports. Incident reports can be used to gain insight into the factors leading to failures. IRS have been successfully used in the aviation industry and in anesthesiology. This paper discusses the use of IRS in the prevention of construction failures. Anonymous, Internet-based IRS in construction offer a unique opportunity to increase the safety of the construction process and constructed facilities, to improve the quality of construction materials and to optimize the allocation of construction research funds.

Hazardous waste sites in the United States have moved from a period of intense study (remedial investigation/feasibility study) to intense construction (remedial action.) Once remediated, sites enter a years-long period of operation and performance monitoring. Site specific performance of remedial actions is reviewed every five years. The uses of forensic engineering, failure analysis, and reliability engineering tools at typical waste sites are discussed from the perspective of failure avoidance. Although many of these techniques have been employed in the management of waste sites, their application is neither uniform nor universal.

A methodology for the systematic study of the condition of concrete in structures is presented in this paper. Historical review of the site and the environment, condition surveys and tests of engineering properties of the concrete are complemented by examination of the concrete using the stereomicroscope, optical microscope, electron microscope, analysis by wet chemistry, thermal analysis, and X-ray diffraction. The step-by-step progression from large scale to submicroscopic scale allows for the selection of specimens that appropriately represent the concrete, gives context to the detailed test methods and ensures reliable interpretation of the results. The authors believe that the methodology employed will be of value to investigators.

Recent applications of nondestructive evaluation (NDE) techniques developed for timber have made possible condition assessment of structures that have previously been difficult to evaluate. Condition assessment using stress wave velocity and resistance drilling has been subjected to limited field trials. Stress wave velocity is used as a means of rapidly screening the timber to identify areas which require more detailed inspection. Resistance drilling is then used to quantify the extent of degradation. The combined use of these techniques allows for efficient condition assessment of critical timbers. This paper presents a case study of how these techniques were integrated to assess the condition of foundation piles.

This paper discusses the maturity concept as a valid non-destructive evaluation method to predict strength gain of concrete. It discusses how the concept can be used to help prevent early-age strength failures in concrete, as well as how maturity may provide forensic investigators a tool in determining the cause of failure. Two case studies are presented that illustrate how the maturity concept can be utilized in a forensic investigation. Finally, a research case study describes a procedure for developing a maturity-strength relationship based on current research at the University of Colorado at Denver.

The national Forensic Engineering Award, given by the ASCE Technical Council on Forensic Engineering, recognizes individuals for outstanding contributions to the field of forensic engineering. The award has been given six times since its establishment in 1989. Past recipients of the award are: John P. Bachner Jack R. Janney, Joseph S. Ward, Lev Zetlin, George F. Sowers, and Kenneth L. Carper.

This paper compares the earthquake hazard environments of the Kocalei (Izmit), Turkey and Puerto Rico regions. This comparison helps to understand what happened in the August 17, 1999 Kocalei earthquake and to develop scenarios on what is likely to happen in the future. It also provides a framework for hazard assessments that give realistic answers to the questions: where? how big?, and how severe?. The aim is to transfer the new data, lessons, and experiences from the Kocalei earthquake to other earthquake-prone regions in Turkey as well as to other locations like Puerto Rico. This assessment is a contribution toward the integration of all aspects of the hazard, built, and policy environments. Such integration can lead to long-term sustainable development in global perspective for earthquakes.

In this paper the acceptability criteria, in terms of human comfort, for vertical flexibility of residential building floor systems are reviewed. Examples of post-earthquake forensic investigations of home-owners' claims relating to earthquake damage resulting in excessive flexibility are described and conclusions are drawn with respect to the probable validity of the allegations.

The Northridge earthquake revealed a serious lack of knowledge and understanding of earthquake damage assessment and repair for ordinary structures. No generally accepted definition of damage, guidelines for engineering investigation of damaged structures, procedures for quantifying damage, or standards for repair exist. As a result, there were gross variations in the evaluation and repair of similarly damaged structures resulting in great inequity amongst the affected population. Consensus protocols (or guidelines and standards) can bring order and consistency to the process by providing much needed guidance to engineers retained to evaluate and repair earthquake damage. This paper summarized the authors' experience with a limited scope protocol following the Northridge earthquake, and presents recommendations for the structure of more general, consensus-based, earthquake damage assessment and repair protocols.

This paper has been prepared in a manner that will address various aspects of forensic evidence photography for use in civil litigation as well as non-litigation matters. The reader is assumed to have basic engineering knowledge applicable to the examples given. While the suggestions and analyses described herein may be applied to criminal investigation matters, it is not intended to address all which applies to that area of forensic engineering investigation.

Historically, attorneys would call upon an engineer whom they believed had technical knowledge on specific issues, while frequently overlooking the consequences of the engineer's limited "legal" experience. Today however, attorneys who use engineers in litigation (which in reality still make up a very small percentage of the attorney population) have become increasingly aware of the importance of the engineer's prior testifying experience. It is nearly imperative that a prospective attorney-client will ask, "How many times have you testified?" before proceeding into the details of a specific case.

By education and experience, engineers approach a problem systematically and with use of requisite investigation and testing. Occasionally, an emergency leaves the engineer with a multiplicity of options, but with inadequate knowledge. Critical cases of this type challenge an engineer to use experience, judgement and general background to make decisions mostly based on gut reaction. This decision exposes the engineer to the risk of litigation, because of a claim of excessive caution resulting in needless expenses, but also to the possibility of exposing life to danger. This paper describes two experiences during my practice that exposed me to multiple risks, and the need for a "quick" decision. Making such an on-the-spot decision is quite different from the 20/20 hindsight vision displayed by attorneys if the engineer's judgement is later brought into question because of claimed economic losses allegedly caused by such a decision.

The tragedy of Hurricane Mitch presented a rare opportunity to conduct forensic studies to evaluate bridge design procedures for extreme flooding events. Following the rescue operations technical information was collected to this end. A preliminary examination of this information substantiates the prevailing practices for the design against extreme flooding events.

This paper describes the emergency inspection and evaluation of large amplitude vibration of cable stays on the Cochrane Bridge in Mobile, Alabama. Under specific weather conditions, some of the cable stays were observed to vibrate with amplitudes of over 1.5 m. The course of the emergency action in observing, documenting, and mitigating the aerodynamic stability problems on the Cochrane Bridge is described in this paper.

It is often seen while driving underneath the overpass bridges that the exterior girders are slightly bent laterally due to damage from trucks and other vehicles that may have hit them or that may have scraped against them as they were passing underneath. It becomes somewhat of a complicated process to determine exactly how much stiffness (and strength) the damaged girder has and whether or not it needs to be replaced (or repaired) immediately. With an aim to develop some charts or curves that may be used to quickly assess the loss in strength of these girders as they deflect more and more, some parametric studies were carried out. The result of the first of such studies is presented here.

The present Dome of the U.S. Capitol Building, designed and built from the 1850s to the 1860s, is a masterpiece of 19^th -century engineering and construction. The majority of the Dome is comprised of cast iron; remaining elements are wrought iron. LZA Technology (LZA), A Division of The Thornton-Tomasetti Group, utilized investigative techniques in the practice of forensic engineering to perform a comprehensive structural analysis of the Dome and concluded that, 1) the U.S. Capitol Dome was brilliantly designed and well built and, 2) the Dome is structurally sound and capable of resisting all reasonably anticipated loadings.

Metal-plate-connected wood-roof-trusses (trusses) are used extensively, both within the housing industry and in commercial buildings. With engineering that is fine-tuned and precise, trusses are part of most contemporary wood-frame buildings, and often support the roof over masonry buildings as well. With truss use so widespread, a practice in forensic engineering that includes wood structures wilt inevitably lead to calls about buildings with wood-roof-trusses. In reviewing the nature of building problems where trusses are present, and in working on the design of new buildings that incorporate trusses, I have begun to consider what it is about the trusses themselves; in their specification, design and engineering, and in their deployment that makes them different, possibly more prone to problems, but in any case special. This paper identifies some of the consequential changes that result from the use of manufactured trusses. In addition to the obvious structural substitutions, there are systemic changes that may go unnoticed. Further, the paper explores the nature of some of the most prevalent problems that its author has encountered in working with trusses and studying the buildings that employ them. Considering their widespread use overall, trusses and the buildings that exploit them seem to find their way into trouble only rarely, but when they do, the reasons may reflect shortcomings in their design and fabrication, in the flow of communication between and collaboration among participants in the design and construction industry, or misunderstanding about their use. This paper explores some of the reasons why and how using trusses differs from other practices, it reviews the truss design process, and identifies conflicts inherent in the current design-fabrication-erection process, and it proposes some steps to reduce the risks associated with using trusses. Throughout, the paper notes that there are ongoing efforts within the truss industry trade organizations that address many of these problems.

This paper discusses two different, but related cases. The first case involves a roof failure at a manufacturing facility. The second case involves the remodeling of a very old residential roof system. The study of the roof failure was part of an insurance claim investigation. The engineers, who were engaged to provide professional insight, chose different analytical models, and arrived at very different conclusions. The second case is a remodeling case which is included because it serves to remind the designer that a safe and reasonable load path to the ground must be identified. The roof structure of this very old building needed to be modified to accommodate the remodeling being proposed. This old structure had not been engineered, and the remodeling proposal required the altering of the existing load path which had been demonstrated by history to be safe. When the assumed existing safe load path was analyzed, it was not found to be safe.

Before starting a forensic study, it is very desirable to make an initial assessment of the anticipated behavior of the subject structure or process. Two approaches can sometimes be particularly useful. The first is serendipity, i.e., being inspired to apply to the investigation an analogy involving unrelated phenomena, materials, and/or processes. Three examples are given of serendipity in solving problems in the steel-producing industry. The second approach involves noting significant differences between predicted behavior and the structure's actual behavior. The need to explain the differences can help orient the investigation, giving it a head start. Two examples are given of prior work extended for orienting early stages of forensic investigations.

Although accident prevention signs were standardized as early as 1941, and the guidelines have remained relatively unchanged, signs written today often do not conform to these standards. Accident prevention signs, if they are to be effective, must alert the observer to the level of the hazard and should always be presented in the prescribed format. This paper presents a historical survey of accident prevention signs as presented in standards published by the United States of American Standards Institute (later to become the American National Standards Institute, ANSI), Occupational Safety and Health Administration (OSHA), the Society of Automotive Engineers (SAE) and other standards publishing agencies. Emphasis is on the prescribed format and color for the designated signs. Examples of conforming and non-conforming signs are presented. The paper does not deal with the psychology of warnings, other than the aspects associated with color and format.

The paper presents basic data on the Czech forensic experts system and activities of Czech forensic engineers. It discusses categories of failures, problems in general approaches to their definitions and criteria and shows a few selected illustrative cases from the expert witness practice.

Recent court decisions have created case law concerning the admissibility of expert testimony. Daubert v. Merrell Dow Pharmaceuticals, Inc., 509 U.S. 579 (1993) interpreted the Federal Rules of Evidence concerning scientific testimony. A March 23, 1999 U. S. Supreme Court decision, Kuhmo Tire Company, Ltd., et al., v. Patrick Carmichael, 526 U.S. (1999) deals with the admissibility of technical expert testimony. In an amicus curiae brief to the Supreme Court filed in the Kuhmo case, the National Academy of Engineering wrote, "Expert testimony in engineering, just like expert testimony in the sciences, should be admitted only if the testimony is found to have a reliable basis in the knowledge and experience of the engineering discipline. Testimony that is not rooted in such knowledge and experience is at best useless, and at worst misleading to the trier of fact." As part of the background for expert testimony regarding the duty of care of structural engineers, an expert may need an awareness of the knowledge and experience currently practicing structural engineers possess, including their understanding of the standard of care. This paper examines the understanding among practicing structural engineers of their duty of care as professionals. A pilot study designed to assess this understanding is described, and the evaluation tool, a survey questionnaire, is presented. The results of the pilot study are summarized. The derivation and design of a survey sample for a larger study of the issue are presented, including justification of the sample size and treatment of special sampling concerns.

Engineers and attorneys often form a team of expert witness and advocate, respectively, in the preparation for either the prosecution or defense of a given case. For decades prior to the 1993 decision of the United States Supreme Court in Daubert v. Merrill Dow Pharmaceuticals, Inc., 509 U.S. 579 (1993), attorneys and their experts very rarely concerned themselves with the admissibility of the expert's proposed testimony if his resumé showed sufficient education, training or experience to qualify him as an "expert" in the field. Once qualified, the substance of the opinion was not routinely challenged or reviewed by the court. As a result, expert testimony has become common place in virtually every type of case, a trend often negatively commented on as often obscuring the actual facts and turning cases into a battle of the experts. While this trend will most likely not reverse itself by reason of the ever increasing complexity of society, there is a growing trend in law to be more skeptical of the quality of the opinion after the exert has been qualified. This trend is in large part the result of the Daubert case, where the Supreme Court rewrote the standards of admissibility of expert testimony in federal court and, in so doing, threw out years of accepted practice and procedure with respect to the use of expert testimony and the preparation of experts for use at trial. While the scope of the Daubert case focused on a case involving "junk science," its holding was later expanded to reach all experts, including engineers, in the 1999 decision of the Supreme Court in Kumho Tire Company, Ltd. v. Carmichael,—U.S.—, 119 S.Ct. 1167.

A Chicago Developer contracted for architectural services and construction work for approximately seventy housing units. The project is located at the south end of Lincoln Park in Chicago, with units having views of Lake Michigan. From the beginning of occupancy, some of the homeowners experienced leakage during wind driven rain. The Eugenie Terrace Town Homeowners Association retained the Author to investigate the leakage complaints, catalogue the defects, and recommend mitigative efforts. The arbitration included a pre-hearing mediation. Subsequent to the completion of the mediation and the execution of settlements, the arbitration proceeded, with the arbitrator rendering a judgement of liabilities.

Restoration of the exterior stone at the Washington Monument required a unique structural system which allowed for access to the 8,300 square meters (90,000 square feet) of vertical surface area on this historical monument. An aluminum pipe scaffold system was designed and constructed which provided surveyors and restoration workers with unobstructed access to the entire stone facade while not disturbing the existing stone's integrity. Parameters constraining the design of this scaffold system included an aggressive construction schedule as well as aesthetic requirements established by the monument's administrators. The following paper discusses the unique solutions used to achieve a safe and economical structural design of the scaffolding system.

Approximately 3,500 State or Federal-aid highway bridges are built in the United States every year. The majority of these bridges are built without incident, which is a credit to the construction industry. However, in the past 30 years, several major bridge failures occurred during construction and were attributed to construction practices and procedures. Statistically, bridge falsework represents over one-third of the total recorded falsework collapses, and most of these occur during construction of conventionally reinforced concrete beam or box-girder bridges. This paper examines failures that occurred during construction of the Arroyo Seco Bridge in Pasadena, California; the Cline Avenue Ramp in East Chicago, Indiana; the I-75 Bridge near Zilwaukee, Michigan; the Sunshine Skyway in Tampa Bay, Florida; and the Lake Street/Marshall Avenue Bridge in Minneapolis, Minnesota. Primary and contributing causes of these failures are identified. From a forensic perspective, errors that contribute to falsework failures are almost always obvious after the fact, generally result from human error, and could have been avoided. A clear need exists to adopt unified design criteria and standards for the temporary structures used to construct highway bridge structures, addressing both the technical and procedural requirements of temporary construction.

Accessing elevated work platforms is not a typical experience for most engineering professionals. However, those of us involved in the practice of Forensic Engineering routinely ride a swing stage or climb pipe scaffolding to perform our investigative work. While the equipment we use for access may appear peripheral, we should not treat it with idle regard. Rather, we must become familiar with the safe use of this equipment, take an active role in guarding our own safety, and be cognizant of the safety of others around us. This paper first outlines the basic technical and legal guidelines that establish responsibilities regarding the safe use of suspended and supported scaffold equipment. Then, through a discussion of actual job site situations, it presents the challenging political and ethical factors that can develop when engineering professionals take an active role in ensuring safe use of the equipment. These factors frequently include: conflicting responsibilities for ensuring the safety of others, respecting hierarchies in job-site control, and consideration for the client's priorities concerning timely and incident-free project completion.

Folding bleachers were installed in a school gymnasium during 1952. After 46 years, the bleachers were repaired in the spring of 1998. The repairs consisted of tightening of hardware, replacement of worn parts, upgrading of railings and making a welded repair to a support leg. The bleachers collapsed two weeks later while supporting students during a school assembly. Although the recent repairs prior to the collapse were suspected to have caused or contributed to the collapse, it was discovered that these repairs did not contribute to the long-term unstable condition of the bleachers. The collapse was caused by the removal of a latching mechanism in approximately 1983.

In this paper we discuss the research efforts and present the finding of a study performed on the use of precast, prestressed stay-in-place formwork panels for bridge deck construction. The performance and strength of the system is discussed in light of the measured response of a recently completed bridge deck to a series of concentrated loads.

This paper is about physical causes for loss of shape stability of marble panels for facades due to weather influences. The analysis performed allows fundamental insight into the process of damage in grain boundaries and so makes it possible to scientifically explain the loss of shape stability of marble façades conclusively. Along the lines of the knowledge gained, effective measures and methods are proposed to maintain shape stability of marble panels in outdoor applications and to minimize the potential of damage and risk of hazards.

The dissemination of construction failure information is of use to the designers and constructors of facilities. This information will minimize the likelihood of future failures of a similar nature. The forensic engineer is a prime source of this information derived from investigations of actual construction failures. The Committee for the Dissemination of Failure Information of the ASCE Technical Council on Forensic Engineering has been developing seminar formats for such dissemination to architects, engineers and contractors. This paper discusses these procedures for use by teachers and presents two typical case histories for use by them.

The study of engineering failures can offer students valuable insights into the associated technical, ethical, and professional issues. In many cases, lessons learned from failures have substantially affected civil engineering practice. For the student, study of these cases can help place design and analysis procedures into historical context and reinforce the necessity of lifelong learning. Of course, it would be impossible to add an undergraduate course on failures and lessons learned to an already overcrowded curriculum. A more practical solution is to integrate failure case studies into existing undergraduate courses. In this paper a master plan for the use of failure case studies in an undergraduate civil engineering curriculum is discussed. First, for a selected number of courses, several relevant principles are identified. Examples include drawing correct and complete free body diagrams (statics), compression member buckling (mechanics of materials, structures), shear strength of concrete beams (reinforced concrete design), and connection detailing and behavior (structural steel design). For each of these principles, failure case studies have been identified. They are discussed in some detail within this paper, and resources and references for further development of the case studies are indicated. Some of the cases have been developed and used in courses at the United States Military Academy and the University of Alabama at Birmingham.

Since 1989, the American Society of Civil Engineers (ASCE) Technical Council of Civil Engineering (TCFE) has conducted 2 surveys to gauge the need for teaching failure analysis topics in the civil engineering curriculum. Although the surveys addressed different topics, the limited availability of instructional materials is a recurring theme. The purpose of this paper is to respond to each of the questionnaires by reporting on the ongoing development of a preliminary Internet site whereby consultants can contribute failure case studies. These case studies will then be readily available for professors and instructors to use in stand alone failure analysis courses. The case studies can also be used as supplemental material and can be integrated into existing general civil engineering curriculum courses as well.

Early traditional building walls were usually constructed of stone or brick, sometimes several feet thick. Such massive walls served not only to support the floors and roof but also to keep out the weather. In the early 1900's economic pressures and the need for taller buildings led to the development of thinner, lighter, and less costly wall systems. While these thinner walls did not usually carry structural loads, they often involved a combination of materials and multiple wythes requiring more complex leak control and connection/support mechanisms. A wide variety of unanticipated problems, such as accumulated differential thermal expansion, increased water leakage due to a lack of drainage redundancy, and cracking or displacement related to material incompatibility, sometimes accompanied these new wall systems.

Diagnosing structural distress is usually difficult. If that diagnosis is not correct, the planned intervention can be worse than the original problems and possibly irreversible. Investigating the effectiveness of interventions planned by others offers a unique opportunity to learn both good and bad repair techniques. This paper will illustrate four case studies, unrelated to litigation, where previous efforts to solve facade problems of buildings were not successful. Thus, it was necessary to deal with the initial problem made worse by the previous intervention. Each case study involves a facade which was previously repaired but which developed new, and sometimes worse, problems in subsequent years. In each case, it was evident that previous repairs addressed symptoms rather than the underlying problems.

During routine maintenance involving replacement of joint sealant on a medium story high rise office building, a 300 pound granite panel fell 8 stories to the ground. Within two days, a second and third panel was found dislodged, but was safely removed before falling. The building was eight years old at the time of the failures. Through swift action and commitment by the building owner, the immediate failure and the risk of future failures was addressed, the building was made safe for the tenants, and a comprehensive solution was implemented to correct the design and construction deficiencies causing the stone failure. Unfortunately, this is not always the case. Too often the anchors for exterior stone cladding systems are designed without adequate capacity, structural redundancy, or regard for long term performance of the materials used. Some systems rely solely on the adhesion of the system components to support significant, permanent loads. Commercial pressures have forced designers and fabricators to minimize anchor expense and limit quality control procedures. This paper will focus on the concerns surrounding stone anchor systems that suffer from a lack of adequate design, fabrication quality control, and inspection during construction. It will do so through discussion of a granite cladding failure case study that illustrates all of these deficiencies.

The final report to FEMA of the $M11 SAC Joint Venture project is scheduled to be made early in 2000. Some of the individual components of the report have been finalized already. Much activity, including component testing, will be completed by the end of 1999. In this paper progress towards the ultimate objective of the SAC project, namely to study and report on the seismic performance of Welded Steel Moment Frame connections and to develop design recommendation, is presented.

Since the January 17, 1994 Northridge earthquake, practicing engineers, academics, metallurgists, and inspectors alike have been engaged in uncovering the cause of cracking in welded beam-to-column joints in over 250 steel moment resisting frame (SMRF) structures throughout the Los Angeles area. As a result, thousands of dollars a day are being spent testing, analyzing, inspecting, and repairing steel connections using a variety of sharply contrasting methods and criteria. Despite the Interim Guidelines published by the SAC Joint Venture in 1995, the current approaches within the industry for the evaluation and repair of steel moment frame structures are largely governed by engineering judgement, costs, and tenant relations rather than systematic approach and protocol. As an aid to the structural engineer and building owner, this paper outlines several factors that should be taken into account when determining the scope of investigation for an existing SMRF. The evolution of FEMA 267 guidelines from 1995 to 1999 and the implications for SMRF investigations are discussed. Practical insights regarding the various components of an existing SMRF evaluation, such as connection preparation, visual inspections and ultrasonic inspections are discussed to equip the engineer and building owner for better decision making. Drawing on the lessons learned from investigating damaged SMRFs throughout Los Angeles, the authors discuss the differences between a post-Northridge initial evaluation with that of a more costly, yet complete investigation.

Forensics---the art of argumentative discourse suitable for use in courts or public debate or in the case of engineering, the application of engineering principles to legal problems. Herein lies the problem with forensics, as an attorney, who will not be named, aptly stated, "It's a sad state in the engineering profession when I can hire one of its members to say anything I want." This one statement illustrates the level to which engineers' status has fallen. This paper discusses in detail a natural disaster, which occurred as a landslide generated tsunami at Skagway, Alaska on November 3, 1994, resulting in one death and extensive property damage. The paper exposes government attempts to win at any cost by retaining cooperative experts dealing with selective information and giving polished presentations carefully worded to give the appearance of fact when only hypothesis is presented. Government neglect of contributory construction and government interference with agencies charged with investigation is discussed. The correct forensic approach to the Skagway problem, both scientifically and logically, is briefly reviewed. This is not a novel written for television, but if it were it could form the basis for interesting entertainment in the public forum.

Structural failures at the interface of different structural systems and materials are often caused by inadequate attention to the effects of the achievable construction tolerances and to the volume changes. Two case histories illustrate the importance of considering the overall construction tolerances in design and construction of concrete-steel framing connections.

The authors were retained to perform independent forensic investigations as a check on the work of other investigators at two distant, independent apartment complexes. Buildings at the complexes had experienced distress. In one case, distress was attributed to ground movement due to settlement of fill in a previously undetected buried creek channel, a conclusion based on the observation of asphalt concrete revealed in a deep test pit. An expensive repair scheme involving pressure grouting was proposed. In the other case, the various forms of structural distress, which included cracking of floor slabs, was attributed to excessive wind loads. Demolition and reconstruction of the distressed structures was recommended. The authors' investigations incorporated valuable information from fields of expertise other than engineering. Identification of the actual causes of damage to the apartments in both cases was critical for the development of appropriate and cost-effective repairs and remediation. One lesson learned was that there should be no reluctance to pursue apparently distracting leads when investigating the true cause of failures.

Design and construction consideration for preventing failures of precast concrete facade panels and their connections are presented. Discussion and recommendations concerning the panel design, concrete mix design, connections design and construction, and field modifications are included. Examples of projects where failures have occurred illustrate the concepts presented.

Over the last 15 years, the authors have investigated a variety of failures in metal and glass facades. While these facades, commonly referred to as curtain walls, have been utilized for over 35 years, forensic investigations have revealed that certain types of failures—such as joint sealant failures and glass staining—occur repeatedly. Other curtain wall failures involving the glass and metal materials, coatings/finishes, and insulating glass unit seals are less common, but may nevertheless result in costly remediation. There are measures that can be taken during the design, construction or maintenance of the facade to prevent each of these types of failures.

On October 22, 1974 a pedestrian walking in Chicago's Loop area was killed by a piece of terra cotta that fell from a building façade. A task force formed as a result of the incident determined that 45 percent of the facades surveyed had unsafe conditions. Consequently, a Façade Inspection Ordinance was passed in 1978 that required all Chicago buildings taller than six stories to undergo a close-up inspection of 100 percent of the façade surface area. The ordinance language mysteriously did not appear in the new 1979 City of Chicago Building Code and was therefore technically repealed. In August 1994 more pieces of terra cotta, brick and glass fell from three buildings in the city. Another task force was organized and recommended language for a city ordinance, which was passed by City Council on January 10, 1996. This ordinance provided for annual "Ongoing Inspection and Repair" programs as well as "Critical Examinations" for building facades. From 1996 to the present, the author has performed over 65 ongoing and critical inspections of building facades in Chicago. The exterior walls of these buildings were composed of various materials, and included terra cotta, brick, stone, concrete, metal and glass. The purpose of these inspections was to satisfy the new ordinance which was designed to prevent failures by identifying imminently hazardous conditions and repairing them before they could cause damage to life and/or property. This paper will provide an overview of conditions discovered on the buildings that the author inspected, as well as information and experience that was used in determining whether or not these conditions could be deemed "imminently hazardous".

The Ore Bridge was a moveable crane built around 1920. The main span was a steel box truss structure with a 365-foot span length that was supported by two 100-foot tall steel "legs". Its two supports or legs rested on platforms that traveled simultaneously down two parallel railroad tracks. The bridge suffered severe structural damage in 1991 during a windstorm when the brakes on one of its support platforms failed causing one end of the structure to continue moving down its track while the other end came to a halt. The resulting twisting and skewing of the structure caused significant inelastic deformations in numerous structural members and resulted in one of the bridge's support legs being pulled off its track. During repairs to the structure, the entire bridge and a 125-foot high support tower being used to lift it back into place collapsed. This paper evaluates several different (and rather contradictory) potential failure scenarios advocated by various eyewitnesses and engineers who investigated the collapse, and proposes a scenario which we believe represents the most likely cause of the collapse.

A forensic engineering analysis of the cause of collapse of a 3-story retail-clothing store that occurred on July 7, 1988 in Brownsville, Texas was conducted. This investigation included the reconstruction of as-built plans, a structural analysis of the building identifying potential collapse causes and triggers, an analysis including witnesses statements, and a discussion of the deficiencies in the construction process. The most over-stressed part of the structure whose failure is consistent with the witnesses' statements and physical evidence was Euler buckling of the second floor column "assembly". This assembly consisted of the second level columns and two supported steel beams. No web stiffeners or other bracing were located in the beams over the columns.

Heavy snowfall in the winters of 1993–94 and 1995–96 triggered numerous collapses in the northeastern part of the United States. This paper presents three case studies that were investigated by the writer's firm. Topics covered for each case study include specific climatological. circumstances, comparison to code provisions, results of structural analyses, and lessons learned. In each case, it appears that the snow load on the roof exceeded the design value given in the governing building code, by a greater margin than might be expected from the amount of precipitation alone. Issues needing additional research are also identified, such as accumulation on cold roofs, effects of freezing and thawing cycles, snow drifting on large roofs, and the effectiveness of bracing provided by standing seam roofs.

This paper discusses the problem of rotted wood piles and the forensic study undertaken to determine their cause. The piles had been supporting the rowhouses for more than 100 years, so why did their tops suddenly rot away? The investigation at first led to the obvious, but the development of the convincing evidence for legal actions was an arduous task that delved into construction records for a new dam and historical information on the drainage conduits prior to dam construction. The conclusion is that the impacts of remote construction may not be readily apparent and can be far-reaching.

As a result of construction, pitfalls sometimes await unsuspecting nearby and future landowners. In the case of one uncontrolled fill site, supplanted work seemed to be the catalyst used to bring the problem to life. Remedial action for a failing foundation was needed quickly, and compaction grouting provided the physical support needed. With investigations and disputes still pending, the identities of various parties and individuals in this incident have been withheld until a later date.

Foundation engineering in Jackson, Mississippi is complicated by the presence of Yazoo Clay. Yazoo Clay is a high plasticity montmorillonitic clay with a very high shrink/swell potential. Yazoo Clay has caused severe structural and aesthetic damage to many structures in the Jackson area. This paper will focus on light commercial and residential construction over Yazoo Clay and the common approaches to coping with the highly expansive clay. Shallow and deep foundation design and construction philosophies are presented. This paper will discuss common engineering practices which have been derived from long-term professional experience in Jackson, Mississippi.

Currently the roof structures on at least 1,000 low-rise mixed-occupancy commercial buildings nationwide are at-risk of extensive damage and possibly collapse unbeknownst to anyone in spite of annual visual inspection and customary maintenance. The cancer-like decay and corrosion that is destroying these roofs is caused by the use of green or wet wood during construction, reliance on sealants instead of flashing and counter-flashing of roof seams and penetrations, the hidden spread of small water leaks along the joints between roof panels, inadequate ventilation below insulated roofs, and seasonal roof inspections that fail to actually examine the roof structure and instead examine only the built-up roof membrane on top of the roof structure and the insulation on the underside of the roof structure. In terms of repair costs and lost rent for the average affected building, this represents a two-million dollar expense. In terms of potential injuries, the cost is incalculable. The forensic investigation of two such buildings is a lesson for all.

One of the primary functions of a building is to control the exchange of energy and moisture between the external environment and habitable spaces. Moisture intrusion, that is unwanted or unplanned moisture, is a long-standing problem that building owners and managers face daily. Unwanted moisture can be introduced into a building through direct and indirect means. Direct means include water intrusion through roof, flooding, permeation through foundations, leaks, etc. Indirect means include water vapor pressure differences between the outdoor environment and the interior of the building, and occupant activities of cooking, showering, and shampooing of carpets. Regardless of the means of moisture intrusion the results can be very serious not only to building materials but also to occupant comfort and health due to microbiological growth on environmental surfaces and within building cavities.

Most infrequent high profile failures occur due to natural disasters, and society is mesmerized by the destruction they leave behind. When events, such as Northridge, Kobe, and Andrew occur, the media coverage is dramatic and irresistible. Not only are we touched by the cost to human lives, but also we are staggered by the costs reported for property losses, generally into the millions and even billions of dollars. Yet, there is little mention of failures that occur regularly, costs for which, over time, can also reach into the millions and billions of dollars. Failures of building envelopes, such as roofing and wall systems and facades that are intended to protect structures, occur daily in industrial facilities. They are generally less dramatic, gradual failures, yet they can lead to deterioration of steel, concrete, and wood components in a facility and can be very costly to correct. Too often failures of building envelopes of industrial facilities are not viewed as failures at all, but as inevitable maintenance items to be addressed in time as budgets allow. The term maintenance suggests that a item will be kept in good condition; if an item has failed, the action required to address it is not maintenance, but repair or replacement, either of which likely would be significantly more expensive than true maintenance. If, however, reasonable procedures are used to identify failures before they lead to extensive, unplanned, emergency repairs, significant savings would be realized. Legitimate maintenance of industrial facilities is achievable. The paper proposed will describe a program that has been used in industry to identify, rate, and recommend action to address failures that have occurred, along with maintenance to be done to minimize future failures. The paper will present case studies of the program in use and the benefits that have been realized.

The post office building in Chicago, Illinois is a five-story tall steel-framed structure. The Architect/Engineer of the building designed the steel structure of the building including all connections and provided prescriptive structural steel and connection details on the contract drawings and specifications. After the construction contract was awarded, the steel erector changed the construction sequence of some of the beam-to-column connections to facilitate the construction of the connections. This change in connection construction sequence included the use of a temporary erection angle to temporarily support the beam while its permanent connection was being constructed. The design of the permanent connection of the beam was not changed by the change in the connection construction sequence. On November 3, 1993, while the structural steel frame of the building was being constructed, a 30 m (100 ft) by 32 m (106 ft) by five story tall section of the frame collapsed injuring several workers, some fatally. Our investigation of the collapse included: 1) Review of eyewitness descriptions and of the contractor's log on the collapse. 2) Review of structural design drawings, shop drawings, and specifications of the structural steel. 3) Inspection of steel members in the collapsed area, and inspection of erected steel members outside of the collapsed area.

Temporary bracing is often viewed as an unnecessary step in the process of constructing a structural facility. Unfortunately, many times this often-neglected step becomes the subject of avoidable litigation and lawsuits. This paper presents two case studies that were investigated by the authors of this paper. Included are failures due to wind and gravity resulting from inadequate temporary bracing. Topics covered in each case study include: investigative approach, analysis results, probable failure cause, and associated meteorological conditions.

A mid-size building is defined as single or multi-family residential, commercial, office, or industrial space not over 3 stories in height and of any lateral extent. This paper will address a definition of foundation failure in terms of the effect on the supported structure based on deformation criteria as opposed to physical damage to the foundation. A foundation is often deemed failed based on the opinion of the occupants, experts or laymen on a jury, often with statements such as "The slab has cracked, therefore the foundation must have failed." This paper attempts to answer the question, "When has a foundation failed and when is it still performing its function?" A concise review of published deformation criteria for different types of structures, ways of measuring and calculating the deformation ratios, and theoretical analysis of material tensile cracking will be presented. New methods are proposed for analysis of curvature of foundation surfaces and for quantifying distress levels to the super-structure. This information will be useful for forensic engineering studies to establish in a practical and in a legal sense when a foundation has "failed", utilizing objective criteria.

Every year billions of dollars are invested in residential and light commercial construction and resale. Often times, an engineer's evaluation of the condition of the property is required by one or more of the parties involved in the transaction. A significant portion of these evaluations will focus on the foundation and many will require the use of forensic methods. For this reason, forensic engineers are frequently selected as the engineer of choice to perform these evaluations.