Forensic Engineering (2006)

Under the Federal Rules of Evidence, and in accordance with case law, technical forensic evidence presented in court has to be valid and reliable—a judge may rule evidence inadmissable if it is shown to be invalid or unreliable. Engineering methods and processes operating in arenas other than litigation also must be valid and reliable in order that those methods and processes achieve their intended results. This paper discusses of types validity and reliability, and gives examples of expert witness evidence and of an engineering method that lacked validity and reliability.

The authors initiated a course in Forensic Structural Engineering at Portland State University two years ago. The main goal of the course is to learn from the past experiences of practicing engineers, thus leading the students to a more critical, creative, and cautious thinking process. The course introduces the students to the basic principles and approaches of forensic engineering, along with studying several case histories. A portion of each case study is devoted to outlining the ways to help minimize potential failures of similar nature, as the students embark on their journey to professional practice. The authors have observed that teaching students by examining cases presented by the forensic engineers who actually investigated the cases, is an effective way to accomplish the goals established for this course. This paper describes the authors' experience conducting the course in the past two years.

Recent series of unfortunate events resulted in thousands of damaged/deteriorated structures. To validate insurance claims and rehabilitation efforts and to assist disaster-worn citizens, a significant amount of forensic engineering work is currently on-going and will continue for a long time. In the midst of these activities, a significant amount of disputes/mis-judgements will occur and will cause further difficulties in settling claims and restoring normal operations. To ensure quality of forensic work, this paper attempts to address the more fundamental issue of current forensic science and engineering practices, which adopts an inverse engineering approach whereupon knowledge is accumulated from construction design and post-event observations. The reasoning process is based on pure deduction with very little in-between causality evidence. Current approach relies heavily on an engineer's interdisciplinary expertise, training, and reasoning ability, and lacks the fundamental scientific process of elimination of possibilities. It, therefore, often fails to produce complete multidisciplinary solutions to complex forensics problems. This paper attempts to establish quality quantification by suggesting forensic benchmarking such that the involved procedures can be standardized and eliminate the "guess work" still common in an otherwise rapidly developing and highly challenging field.

In this age of high technology, the expert consultant usually must state an opinion on what must be done to a building damaged by an earthquake or hurricane to bring it back to its pre-earthquake or pre-hurricane condition. This paper presents an approach for defining the pre-earthquake of pre-hurricane condition of the building in terms of the estimated expected damage to a natural hazard event. With this definition, it is possible to then determine what is required to return the building to its current post-event condition to that same level of expected damage, i.e., its pre-event condition.

Hurricane Katrina has been estimated to be the costliest storm in U.S. history, with total losses exceeding $100 billion. Hurricane Katrina was at Category 5 strength while in the Gulf of Mexico, and reportedly diminished to a strong Category 3 when it struck the Louisiana and Mississippi coast on August 29, 2005. The hurricane surge forces breached protective levees in New Orleans, and resulted in catastrophic flooding in the City. Although the flooding catastrophe in New Orleans drew world-wide attention and the media's focus during the reporting of the hurricane aftermath, the strongest winds and highest storm surge from Hurricane Katrina ravaged Mississippi coastal communities. The Mississippi coast was vulnerable to the destructive forces developed on the "right side" of the hurricane, and had little or no protection from levees, barrier reefs, or breakwater structures. Given the severity of this storm and resultant damages to the Mississippi coastal communities, the structural engineering profession has a unique opportunity to evaluate our approaches to hurricane damage assessment. The purpose of this paper is to provide structural engineers with lessons learned from building damages that occurred along the Mississippi coastline during Hurricane Katrina. The authors personally inspected and/or supervised the damage assessment of over 300 buildings and structures in Mississippi as a result of Hurricane Katrina. This paper presents an approach to assessing hurricane damages from this storm in order to provide answers to society so as to rebuild from this catastrophe. The insurance industry requires that specific questions be answered by structural engineers who assess hurricane damages, and we will address those issues in this paper.

Civil and structural engineers can provide crucial expertise following natural disasters, man-made catastrophes, and other accidents. In recent years we have experienced major terrorist attacks on buildings and on public transportation, devastating storms, and singular collapses of public structures. Even highly qualified engineers, when faced with a large disaster often feel overwhelmed and have initial difficulty dealing with the situation and knowing where to start. There is very little training on this topic that is targeted at the engineer. This paper discusses strategies from the author's experience. It is hoped that this will assist other engineers in coping with emergency situations, so that they can best apply their skill and knowledge for the public good.

This paper describes the work performed to determine the cause of out-of-plumb masonry veneer and horizontal cracks in a concrete foundation wall of an approximately ten-year-old single family residence. The investigation included a visual inspection of the property, measurement of the lateral movement of the brick veneer and concrete foundation wall and determination of masonry brick ties locations. The investigation was performed on behalf of the homeowner to resolve a construction defect dispute between the homeowner and builder. Based on the findings of the investigation, it was concluded the outward movement of the brick veneer was the result of an insufficient number of brick ties installed to secure the brick veneer to the building. In addition, the bricks used to construct the house were highly expansive. The horizontal crack in the east foundation wall was due to the unreinforced concrete wall not having sufficient strength to resist the applied earth load. In addition, the construction of the foundation of the porch adjacent to the east foundation wall on uncompacted fill material may have contributed to the stresses in the foundation wall as an eccentric load was applied to the foundation wall as the two-story brick enclosure was constructed on the porch foundation.

A patio under construction failed catastrophically, resulting in a back yard full of concrete blocks and rubble fused together with sand and cement. My assignment was to determine the cause of failure. A homeowner had laid concrete unit masonry blocks around the perimeter of the patio. A combination of flowable fill (a mixture of sand, cement, fly ash, and water) and debris were used in the center as a substrate for the slab which was to be poured at a later time. The patio failed during the final pour of flowable fill. The patio failed because the moment created by the fluid pressure of the flowable fill against the wall overcame the adhesive force of the mortar between the blocks.

One need only consult the local Yellow Pages under `Waterproofing Contractors' to appreciate the scale of the leaking basement epidemic in the United States. This paper draws from a detailed case history to look at its causes, financial ramifications, and ideas on mitigation. It concludes that most often the failures are systemic involving multiple factors, but that very significant among these is the role of the downspout drain, its frequent deterioration over time and consequent loss of functionality. This is compounded by poor design decisions that have resulted in walls unable to support the lateral loads that are created when hydrostatic pressures develop. Solutions range from proactive maintenance to strengthening of walls. However, there must first be more public awareness of the causes and liabilities involved, and this may best be accomplished through more focused attention when property transfers occur.

On Saturday, 9 March 2002 at approximately 1:45 p.m., a 100-ft long, suspended scaffold platform fell from the west face of the 100-story John Hancock Center in Chicago, dropping debris along an arc from the northwest corner of the building to the building's south face. The scaffold wreckage killed three motorists on East Chestnut Street and severely injured several other passers-by. In early 2000, the building's commercial and residential owners embarked upon a major facade restoration project. They engaged a prime contractor who contracted with a scaffold vendor to design and furnish the scaffold system. The scaffold rig involved in the accident consisted of a 100-ft long, aluminum truss work platform suspended from two outriggers on the roof of the building. On the day of the accident, the contractor determined that it was too windy to work from the platform, and, as had become their custom during off-hours, the contractor's workers moored the work platform on the building's west face at the 42nd floor. We investigated both the technical and procedural causes of the failure. We determined that under the platform's self-weight and down-draft wind loads acting on it, the cam followers (uplift rollers) and wire rope lashing holding the north outrigger to the building's roof track failed. Without this support, the outrigger overturned, and the scaffold platform dropped. As is the case in many catastrophes of this magnitude, there were many opportunities for the project participants to avert the failure. Many of those parties failed to meet their obligations to the project, and their shortcomings contributed to the accident.

This study presents the evaluation of reinforced concrete residential structures with a non-fixed connection between the first and second floor. In Puerto Rico, the construction of concrete second floor over the existing first floor is a common practice due to the high cost of the land and the increasing necessity of houses. The lack of appropriate connection between the existing structure and the new one produces the non-fixed connection. The structure consists of two floors with all rigid connections except the connection of the base of the columns of the second floor. This connection can be assumed as pinned or semi-rigid. A field survey was made to identify what engineers are doing in practice to connect the upper and lower stories. Finally, a vulnerability analysis was performed to typical reinforced concrete frames. It was concluded that the structural integrity of almost all the residence frames analyzed is compromised when subjected to loads specified by the UBC 1997.

The primary concerns for veneer systems are typically cosmetic (appearance) and the function as part of the building envelope, especially regarding moisture issues. However, the selection of the veneer system and the execution of the veneer support can become issues of public safety. This case study outlines issues of veneer-related safety on two public buildings with similar construction. Improper selection of the veneer materials during the design phase of the project and improper execution during the construction phase caused several safety concerns around the entire building perimeters. The safety issues were not caused by special or unique conditions imposed on the structure. Consideration and execution of fundamental issues related to exterior veneer material selection and the installation of a stone veneer system would have prevented all of the unsafe conditions.

Slope instability phenomena are frequently responsible for considerable losses of both money and lives. In view of above consideration, it is not surprising that slope instability phenomena are rapidly becoming the focus of major scientific research, engineering study and practices, and land-use policy throughout the world. The paramount importance of slope instability management is by and large recognized. Herein lies the guiding principle of the current paper; i.e., to describe slope instability hazard assessment and methods to mitigate the associated risks in an appropriate and effective way. Back analysis of failed slopes is one of the most effective ways to advance our knowledge in the field of slope stability engineering. This paper discusses procedures to back calculate soil shear strength parameters from slope failures and illustrates how these parameters can be subsequently used to design slope remedial works.

There is a dearth of information available in the literature and published engineering texts addressing the impacts of pyrite expansion in buildings. The texts have largely been silent, and the intersection of engineering geology, geotechnical engineering and foundation design has been lacking, with the exception of limited investigations related to highway engineering. Typically pyrite has been associated with shale materials when used as fill. Granite, as well as other rocks and soil can also contain sufficient pyrite to initiate the destructive forces associated with pyrite oxidation. In this case study paper, the insidious and destructive forces of pyrite expansion are presented. The investigation offered the opportunity to study the fill material manufactured and placed in 1998 in both an unaffected, or pristine condition, along with material subjected to varying states of sulfation. The long-term implications to the facilities, and strategies for remediation of the buildings are considered.

Distressed secondary riser pipes were discovered at a hazardous waste disposal facility during routine sampling. The riser pipes extended from a secondary sump, up a 10-foot high (vertical) intracell berm, turn 45 degrees through the primary clay and 80 mil geomembrane liner, and extend vertically through approximately 120 feet of hazardous waste to the surface. Video inspection of the 8-inch to 12-inch diameter riser pipes revealed that at four riser locations, the field-fabricated elbows had partially buckled. At one riser location, the vertical portion of the pipe buckled at two points. Investigation of the distressed riser pipes led to a unique and challenging repair approach.

This paper presents the findings of a structural engineering evaluation of earthquake damage to an 8-story reinforced masonry residential building in Los Angeles. The load in some of the upper level masonry walls of the building is transitioned at the 2-story subterranean parking garage levels through reinforced concrete transfer beams and columns. On-site damage investigation revealed severe cracking of the concrete transfer beams. The cracks were most significant in the mid-span of the beams as opposed to the termination point of masonry wall above closer to the beam ends where shear and moment transfer and consequent damage would be expected to occur. A staged finite element analysis of the building subjected to gravity loads, to replicate the sequence of construction, revealed that the walls had separated from the transfer beams during construction when the temporary shoring was removed. This is consistent with field observations of separations along the beam-wall interface. This separation was incorporated into a detailed computer model of the building for evaluation of the building's response to the 1994 Northridge Earthquake. The locations and sizes of observed beam cracks correspond well with the location of predicted large moment demands in the beam elements. Predicted regions of overstressed masonry walls also correlated well with locations of observed wall cracks.

In the wake of a hurricane event, the attribution of damage causation to "wind" or to "flooding and storm surge" is essential to the process of cost-recovery and the determination of insurance applicability. In such a catastrophic event, the damage left in the aftermath is often seen as chaotic and inseparable into these two categories. Knowledge of the storm dynamics and careful observations on the ground, however, can provide clues leading to an equitable attribution. In contrast to complete forensic analysis, for which there is usually insufficient time, a concentration on applied forces, observed damage, and debris geometry is often sufficient to arrive at a segregation of damage between the two or a determination of simultaneous action. Drawn from experience in Louisiana following Katrina, this paper seeks to set forth a series of guidelines for the conduct of such an examination and contains descriptions of commonly-encountered patterns of damage with the attributions suggested by each.

This paper presents a failure investigation case history of a partial roof collapse of a below-grade water storage facility during rehabilitation. The evaluation considers the original design and maintenance of the facility, rehabilitation design, and construction sequencing. The cause of the roof collapse was the failure of selected columns under approved construction equipment loading. The columns that failed were initially damaged by hydrostatic uplift of the base slab during a severe rainfall event and subsequently loaded repetitively by construction operations. Hydraulic and structural models developed during the evaluation accurately predicted the response of hydraulic systems, general crack patterns and specific crack locations; thereby confirming the failure mechanism.

The University of Colorado at Denver has been studying the relationship between wind loading and structural response in historic truss bridges adapted to pedestrian use. Currently, many historic truss bridges with traditional timber decks would be inadequate for pedestrian conversion using the traditional "skeleton" method of modeling and the current American Association of State Highway and Transportation Officials (AASHTO) Guide Specifications for Design of Pedestrian Bridges for lateral (wind) design loads (AASHTO 1997) on the windward bottom chord members (eyebars). An experimental and analytical study was completed on the Prowers Bridge over the Arkansas River, constructed in 1909, which is located near Lamar, Colorado. The experimental study utilized data from anemometers and clamp-on modular strain transducers to provide verification of an analytical deck model of the current Prowers Bridge. This paper presents the equipment, results with methodology, and engineering applications based on the experimental and analytical response to the lateral (wind) loads at the Prowers Bridge. The overall results indicate that increasing the dead load of the deck and accounting for the stiffening effect of the deck in the analytical model allows the windward bottom chord eyebars to satisfy AASHTO lateral (wind) loading requirements. In summary, this research provides useful applications to aid rehabilitation and restoration of historic vehicular truss bridges for pedestrian use.

The overall purpose of this research is to analyze an historic truss bridge called the Blue River Bridge near Dillon, Colorado under wind load to investigate the stiffening effect of the deck. The bridge, located in the Rocky Mountains has a timber deck with relatively high stiffness in the lateral direction. The traditional method of analysis is based on a skeleton frame with no deck and alternative load paths are neglected. Analytical modeling was completed using finite element software. The American Association of State Highway Transportation Officials (AASHTO) wind load of 75 psf was applied to the models to demonstrate the stiffening effect of the deck. The deck analytical model was verified by a field test under real wind conditions. In summary, Blue River Bridge was analyzed under AASHTO wind load for two different systems, skeleton frame and skeleton with stringers and deck and again under wind pressure determined experimentally for the skeleton with stringers and deck. The results were compared for critical members. Despite existing distress in the truss and abutments, it was found that the lateral stiffness of the deck was near its theoretical maximum.

Current AASHTO requirements for pedestrian bridges may prove some historic truss bridges to be under-strength when applying wind loads to simple skeleton models. The Rifle Bridge over the Colorado River at Rifle, Colorado, is a historic steel truss structure that was one of five in a study to analyze actual wind loads on existing structures. This paper discusses the effects of including stiffening elements in 3D models by comparing actual and calculated wind loads. During the six week wind study period, maximum wind loads measured were in excess of 60 mph, which resulted in easily measured strains. Analytical models include the metal deck with asphalt as a stiffening element, which is treated as plate elements with a modulus representative of the composite section. Recommendations for modeling the deck are provided.

The Civil Engineering Department at the University of Colorado at Denver has been involved in a bridge research project funded by the National Center for Preservation Technology Transfer and by the State Historical Fund of the Colorado Historical Society. The subject topic of this paper is the San Miguel Bridge, located in Montrose County. The lateral stiffness of the existing bridge was compared to a finite element analysis. The analysis accounted for the extra stiffing offered by the deck. The results are presented and issues with the data are illustrated and discussed.

The Ohio Strategic Highway Research Project (SHRP) Test Road, constructed on U.S. 23 about 25 miles (40 km) north of Columbus, Ohio, consists of forty test sections in the SHRP SPS-1, SPS-2, SPS-8, and SPS-9 experiments. During the summer of 2002, after the appearance of localized distress in Section 390103, a forensic study of this and Sections 390108, 390109, and 390110 in the SPS-1 (Asphalt Concrete) experiment was completed through a series of destructive and non-destructive tests. Distress surveys were conducted on these four sections in accordance with SHRP-P-338 "Distress Identification Manual for the Long-Term Pavement Performance Project." Non-destructive testing included Falling Weight Deflectometer (FWD), transverse profiling, and Dynamic Cone Penetration tests (DCP). Trenches were excavated at locations with various levels of distress to measure transverse layer profiles, and to obtain material samples for laboratory testing. Collected data was analyzed to determine the causes of localized distresses. The investigation revealed substantial variability in stiffness and high levels of moisture in the subgrade soil at all four pavement sections. These trends indicate that the severity of distress in Sections 390108, 390109, and 390110 would soon be similar to those in Section 390103 if the sections were left open to traffic. Despite the use of various base materials and the presence of edge drains in Sections 390108, 390109 and 390110, higher than anticipated levels of subgrade soil moisture reaching saturation were present in all four pavement sections. Excessive moisture was determined to be the underlying cause of rutting and cracking. While edge drains probably removed some moisture infiltrating down from the pavement surface, they provided little relief from moisture migrating up through the subgrade.

This paper describes work to provide civil engineering based arguments for the maintenance and repair of a harbor lakewall and breakwall system. A condition survey for three important harbor facilities was completed in an attempt to introduce some factual data into a discussion that seemed to be undefined and perhaps endless. Three concrete structures were inspected, their condition evaluated, and recommendations made for work that was needed and realistic. The results were introduced into the debate.

AASHTO has specified probability-based design methodology and load factors for designing bridge piers against ship impact and vehicular collision. Currently, no specific AASHTO design guideline exists for bridges against blast loading. Structural engineering methods to protect infrastructure systems from terrorist attacks are required. This study investigated the most common types of concrete bridges on the interstate highways and assessed the capacities of the critical elements. A 2-span 2-lane bridge with Type III AASHTO girders was used for modeling. AASHTO Load and Resistance Factor Design methods were used for bridge design. The girders, pier caps and columns were analyzed under blast loading to determine their capacities. This study determined the blast capacities of the AASHTO girders, pier caps and the columns, and the required standoff distance of explosion from the columns that may possibly protect the bridge from failure.

The purpose of the paper is to provide the historical background of Love Canal tragedy and the lessons learned from the environmental tragedy. In 1948, it was discovered that hazardous waste had contaminated homes and schools in the Love Canal area. During the summer of 1978, the Love Canal first came to international attention. On August 7, 1978, the United States President Jimmy Carter declared a federal emergency at the Love Canal, a former chemical landfill which became a 15-acre neighborhood of the City of Niagara Falls, New York. The Love Canal became the first man-made disaster to receive such a designation based on a variety of environmental and health related studies. As a result of grass roots and interest and media attention, the Love Canal provided an impetus for dramatic interest in changes to environmental concerns worldwide. The tragedy shows the importance of identification of hazardous waste and the proper disposal of hazardous waste for protection of public health.

The 1904 collapse of the Darlington Apartments during construction was a sudden and complete failure: eleven stories fell into a pile of rubble less than 15 feet high in a matter of seconds, killing 25 people. The collapse and forensic analysis were prominently reported in the newspapers and engineering press; thirty years later, the publicity was cited as a deterrent to structural use of cast-iron columns. This failure became permanently linked to the shortcomings of cast-iron structure. If completed, the Darlington would have been typical of an obsolete structural type: the high-rise cage-frame building. Cage frames, first built in the 1870s, had an iron frame supporting the floor gravity loads and surrounded by a self-supporting masonry wall that provided lateral stability to the building. The use of cast-iron columns in commercial buildings with cage frames had effectively ended by the mid-1890s; the structural engineers who were increasingly used as consultants in commercial high-rise design preferred wrought-iron and steel columns. Wrought-iron and steel were known to have lower allowable direct compression stresses than cast iron, but were ductile and could safely withstand accidental tension and moment. The gradual replacement of cast-iron with the ductile metals in the late nineteenth century was encouraged by fears of collapse caused by the brittleness of cast iron. Cage frames remained popular in high-rise apartment houses for nearly a decade after they were no longer used in commercial construction. Unlike tall commercial buildings, which were built in cities throughout the United States, tall residential buildings were concentrated in a few cities, especially New York. These buildings were typically designed by residential architects working without consulting engineers. Common practice was for the iron sub-contractor to provide "engineering services," often consisting of sizing steel and cast-iron columns from tables based on the span and floor load schedule. In short, lateral load analysis was not part of the design, so the deficiencies of cage framing were not made visible. This paper will describe the design and construction background to the failure, the forensic analysis performed at the time, a modern review of the failure, and discussion of cage-frame failures within the engineering community.

University courses in the areas of building performance and building failures can take a variety of successful formats. This paper describes a course in building failures and forensic techniques offered primarily to architectural and civil engineers at Penn State University. The course incorporates a broad architectural / engineering definition of failures concentrating on topics ranging from water penetration resulting from roofing defects and poorly installed building envelope flashing, to a review of both major and lesser known historic structural collapses. A discussion of the use of industry partnerships and various forms of student centered learning techniques used to enhance the educational experience is included. The paper also describes the incorporation of case history class examples as they relate to teaching failures topics in an educational setting.

Recently, cable-stayed bridges have become very common in the United States. However, the cables of many of these structures have experienced unforeseen vibrations causing significant damage to what were relatively new structures. The damage in some cases has cost state departments of transportation millions of dollars to inspect, maintain, and repair. Perhaps even more perplexing than the cost of the repairs is the question: why were the vibrations unforeseen? For many years, vortex shedding, occurring around the cables such as what occurred with the Tacoma Narrows Bridge (except around the girder deck system), was thought to have been causing the problem. Recently, another phenomenon termed rain-wind induced vibration was found to be causing the problem. But was rain-wind induced vibration really causing the problem or were there other factors involved that could have eliminated the problem from the beginning? This paper examines two such bridges that have experienced vibrational problems requiring major repair. These bridges are the Cochrane Bridge in Mobile, Alabama and the Talmadge Memorial Bridge in Savannah, Georgia. An understanding of structural vibrations and the importance of the need to properly design critical connections is vital, when designing and constructing cost effectively flexible structures, such as cable-stayed bridges.

Individuals sitting in the press box and suite levels of a college football stadium had noted significant structural vibrations during games, specifically when the home crowd sings their sports hymn. Synchronized side sway of tens of thousands of spectators during the chanting of the sports hymn appeared to be the prime reason of the vibrations. This reinforced concrete stadium has gone through several stages of expansions and renovations over the years. Walter P. Moore and Associates, Inc. (WPM) instrumented the various section of the stadium with accelerometers to evaluate the levels of vibrations during three games of a recent season. Our testing revealed that the lateral vibration levels in the press box and suite levels to be strongly perceptible, mostly occurring around 1.4 Hz.

Intolerable vibrations and damage to structures from construction and industrial dynamic sources are subjects of the investigations in forensic engineering. There are some typical vibration problems and different ways can be used to diagnose building conditions and understand the causes of high vibrations or failure. Analysis of the structural response and a choice of vibration limits are very important. Practical solutions are demonstrated in four case histories.

The protection of existing structures during adjacent construction is a common problem confronted by engineers and architects in urban environments. The problem is considerably more complicated when the existing structures are older, historic structures or structures in historic districts. This paper reviews the potential impact of adjacent construction on existing structures as well as published guidelines for the protection of existing structures during adjacent construction. Case studies are presented that show how these guidelines can be incorporated into construction protection plans tailored to specific projects.

In March of 2002, a construction company specializing in light steel construction was awarded a contract for the construction of a fire and rescue facility located in rural Virginia. The project was completed and put into service in October of 2002. Between February 15, 2003 and February 17, 2003, the site area experienced a snow storm resulting in measured snow accumulations of approximately 20 inches. On February 17, 2003, the roof structure of the building failed, collapsing the roof and portions of the second floor walls. The paper describes the process of analyzing the collapse from the perspective of three years later. A review of construction documents, site photographs, and communication documents were used to establish the mechanism and cause of the failure. The lack of available direct site evidence required that the analysis primarily utilize pre-failure information as a means of determining cause of failure.

On July 21, 2003, The Kinzua Viaduct, a 91m (300 ft) tall, 626 m (2,053 ft) long railroad bridge in northwestern Pennsylvania, located approximately 26 km (16 mi) south of the border of New York and Pennsylvania, collapsed during a severe wind storm. The fingerprints of the collapse were evident within the debris field which extended over a distance of 320 m (1050 ft). A Board of Inquiry investigation of this historic Civil Engineering Landmark was conducted on August 12, 2003 by a team of forensic engineers, metallurgical specialists, meteorological scientists and government engineers, given the assignment to decode the secrets of the collapse. The findings of this forensic investigation are presented in the final Board of Inquiry Report dated December 31, 2003. This paper will highlight the systematic processes employed in the investigation and present the specific findings attributable to the tragic collapse.

During the 2004 baseball season, instances of concrete falling from the upper stands of Wrigley Field were reported, generating local and national media coverage. Several engineering firms were retained by the Chicago Cubs to determine the cause of the falling concrete, develop appropriate remedial measures, and review the general condition of the stadium structure. This paper describes the investigation and structural analysis carried out by the authors. Structural analysis of the grandstands, on-site strain and vibration measurements during a crowded baseball game, and laboratory testing did not reveal any systemic structural deficiencies. The cause of the falling concrete was attributed primarily to corrosion of metals embedded in chloride-contaminated concrete near joints, thermal movements restrained by welded connections, and unintended concrete-to-concrete contact between precast sections. Recommendations for remedial action were provided. The case study underscores the value of forensic engineering techniques to isolate structural performance problems and to develop appropriate and practical remedial solutions.

Distress of building cladding is either a symptom of an underlying problem within the support structure or is a sign that the cladding is deficient in some way. Cladding distress typically affects the appearance of the building, may allow unwanted intrusion from the elements to affect and degrade interior materials, and/or may allow the potential for unsafe conditions to develop if conditions are left uncorrected. Like other building components that fail, cladding distress develops from a number of factors that often involves more than just a single cause. The reason why cladding fails and the extent of this failure is a continued topic of debate among engineers, architects, contractors, owners of buildings, and our courts. Presented herein is a case of exterior cladding distress at a building that includes a search for reasons why the distress occurred based on forensic engineering methods and evaluation. This search concluded that the likely causes of distress for the subject structure were related to corrosion of embedded steel bars, differential movement due to dissimilar materials, excess water infiltration in conjunction with inadequate drainage at the exterior walls, changes in the as-built construction not represented on the plans, and inadequate design coordination/supervision prior to and during construction.

The lateral strength of thirty-six, 7/16 in thick oriented strandboard samples taken from two existing multi-story apartment buildings deemed to be in a state of substantial impairment in Western Washington state, USA were evaluated. These samples, although stained and partially deteriorated, met the minimum requirements for structural wood panels set forth by governmental and industry standards. A discussion of imminent collapse and substantial structural impairment and their relationships to the 1997 Uniform Code for Abatement of Dangerous buildings and the 2003 International Existing Building Code is presented as well as discussion on the economic burden created by the complete removal (stripping) of exterior wall claddings to replace oriented strandboard sheathing that still meets the minimum requirements for a structural wood panel.

A small district library retained the authors' consulting firm to perform a condition assessment of a single story facility that had been renovated from a grocery store some eight years prior to the assessment. To perform the renovation, the library staff entered into a design-build arrangement with a local contractor and their affiliated architect. The document review uncovered evidence of design errors, code violations and a general lack of appropriate detailing. The condition assessment revealed improper material selections, incorrect system installations and overall low quality workmanship. The inexperience of the library board, coupled with a contractor-architect partnership that did not provide for checks and balances, fostered a situation where the owner's interests weren't represented and industry standards of care and quality were not met. Retaining an independent professional consultant to review project documents, assist with contractor procurement, and provide quality assurance during construction would have better served the owner's interests and likely saved them money in the long run.

This paper first briefly describes a method for using consensus-based publicly-available models and computer software to estimate earthquake-induced structural damage. Next, and the primary focus of the paper, is the presentation of a technique for quantifying and increasing the confidence in the damage estimate with the use of the professional structural engineering culture and the principles of probability theory.

Following reports of a "loud noise," the building engineer for a 20-year-old, 42-story high-rise in Chicago, Illinois, found the head of a sheared bolt in the mechanical room on the 42^nd floor. Structural engineers subsequently discovered a connection missing five of its six 7/8-inch (22mm) diameter ASTM A325 bolts. This paper provides an account of the events at the building and describes the analysis through which engineers concluded that differential elastic rebound between the concrete shear walls and the exterior steel framing was likely responsible for the connection failure.

Cast-in-place concrete joists at a high school building were severely damaged by an intense fire. Three of the joists exhibited spalled concrete, cracking indicative of shear and bending failure, buckled reinforcing, and a color change in the concrete. The damaged concrete was removed. The bending and shear capacities were reestablished by strengthening the joists with reinforcing steel encased in shotcrete and by clamping the cracked joists with threaded steel rods. The repairs were performed in a relatively short period of time with only minor disruption to the operations at the school due to the planning and teamwork of the school district, building department, contractor, and engineer.

This paper describes an investigation of the partial collapse of a structural steel frame during construction of a shopping mall in December 1999. The accident occurred when an assembly of a 36 ft tall steel column and an 80 ft long girder overturned in high winds and fell to the ground. Two ironworkers attempting to make a girder-to-column connection at the top of the column died in the accident. The investigation, as well as observations by others, showed substantial deviations in the failed column's base connection to the footing from the requirements of the structural design drawings. As fabricated, the column's baseplate was a different shape with a different configuration and fewer number of anchor bolts than shown on the design drawings. A setting grout pad, placed before erection of the column, was undersized for both the as-designed baseplate and the as-fabricated baseplate. Most significantly, the cast-in column anchor bolts were installed in the wrong configuration for the as-fabricated baseplate, and the contractor cut off these bolts and replaced them with adhesive-set remedial anchors. A unique aspect of the investigation involved testing and inspection of the anchor bolts from the base of the failed columns as well as concrete cores, which had been removed from the footing, containing the holes in which the adhesive-set anchors had been placed. We performed laboratory tests using CAT scans, materials analysis, and microscopy to examine the anchor-bolt-to-concrete bond interface. Due to several errors in installing the anchors, the anchors had no adhesive bonding to the concrete. The deviations in the column base connection from the requirements of the structural drawings grossly reduced the overturning capacity of the column. The accident would not have occurred if the column base had been constructed as required by the design drawings.

This paper presents an overview of the effective use of non-destructive testing at two evaluation and repair projects involving concrete structures with internal defects. Frequently, visual inspection is insufficient to locate the extent of known or suspected damage in concrete, such as in the case of concrete undergoing internal distress, deteriorated bond of overlays, underside damage on concrete placed on grade or on stay-in-place forms, or from poor concrete consolidation. This paper presents the application of Impulse Response (IR) testing to locate internal planar fractures and micro-cracking in an elevated viaduct and to locate areas of poor concrete consolidation and horizontal cold joints in a structural slab. This paper also presents an overview of the repair methods and explains how IR testing can be used to measure the success of the repairs.

Kyoto protocol proclaims major targets for the next decades: saving energy uses and not renewable resources, such as Cultural Heritage. In Italy the large amount of old and historic buildings requires to articulate different approaches in order to reach these goals. Priority to historic buildings preservation will ensure to also reach the energy savings. Planned conservation is based on the effective and real evaluation of residual performances of building elements and building system. Suitable diagnostics use images from different spectral bands to obtain information regarding damage distribution and materials. Among images analysis techniques, Infrared Thermography (IRT) has a prominent role because of the variety of applications on buildings and sourrondings, feasibility, real time results and non destructivity. Integration with quantitative tests and microclimatic monitoring allows to obtain necessary input for preservation project and maintenance.

In 2005, a lawsuit in excess of 6 million dollars was brought to trial pertaining to 31 single-family residences in Arlington, Texas. The basis for the lawsuit was distress related to foundation movement. An extensive forensic investigation was performed on each of the structures, and the results of the investigation indicated improper construction and inadequate design of the post-tensioned slab-on-grade foundation systems. Testimony given during the legal proceedings indicated that the foundation design methodologies used deviated from the governing Post-Tensioning Institute (PTI) Design Manual. This paper summarizes the construction and design defects observed during the forensic investigation and the reasons why industry standards were not followed in the design and construction of the foundation systems. The market pressure for the least expensive residential foundations is driving design engineers to compromise their ethics and ignore industry standards.

Our practice in forensic engineering includes wood structures. Over time, we have received many calls about buildings with metal-plate-connected wood-roof trusses (trusses). Trusses are used extensively, both within the housing industry and in commercial buildings, and their engineering is fine tuned and precise. At the Second Forensic Congress in 2000, and based upon experiences designing and investigating the use of engineered wood trusses, I presented a view of the problems I saw. Many of those problems grew out of the difference between how trusses actually work and how the builders using them understood them. Other problems seemed to grow directly out of the nature of the design and construction industry and in the way trusses and their design fit into the existing contracting process. This paper provides an update on the use of manufactured trusses, changes in legislation and codes that affect their design and use, and problems that remain.

Many factors affect the performance of structural roof framing, and if deficient components exist, the structural integrity is compromised. When a roof system is improperly designed, failure may result from under-design regarding net uplift pressures. Today's commonly used lightweight roofing products (EPDM, poly-isocyanurate) have made net uplift loads a more critical design load, and in some instances, the controlling case. In particular, a commercial warehouse building was under-designed for net uplift pressures, which in conjunction with unclear bridging spacing requirements per Steel Joist Institute (SJI) requirements, resulted in a roof collapse during a storm event. The net uplift design load for the steel joist roofing system should have been higher than what was specified on construction drawings. Additionally, a lack of clarity in the SJI requirement for joist bottom chord bridging resulted in excessive bridging spacing, which lessened the capacity of the roof framing considering uplift. Consideration of the lightweight roofing materials in the joist design and clarity in SJI uplift tables would have prevented the roof collapse.

This paper discusses a series of tunneling mishaps and related claims, which occurred during construction of the Hollywood segments of the LA Metro Red Line project. Forensic engineering was used as an important tool for evaluating likely failure causes in an effort to evaluate the merit of the construction claims, or lack there of. Since some of the failure causes remain controversial to this day, little has been published, and valuable lessons which could be learned are in danger of being forgotten. Even though all legal aspects eventually were settled, these events also created an atmosphere of public anxiety about tunneling in Los Angeles, which weakened the political support for future tunnel projects in the region.

The Duck Creek Phase III flood protection project presented the Corps of Engineers' Louisville District with numerous difficult challenges in the design, contracting and construction arenas. The purpose of this project was to lower flood elevations by eliminating an oxbow bend in Duck Creek, an urban stream located on the east side of Cincinnati, Ohio. The proposed long-span culvert, designed to carry flood flows around the existing creek channel bottleneck, was oriented parallel to and in several locations was nearly underneath the centerline of an adjacent, relocated roadway. The culvert alignment included two significant horizontal curves in order to snake around existing high-tension overhead power line towers. The culvert also had to be constructed with very little cover, presenting a challenge to the precast culvert designer and manufacturer including limited space within the contractor's work limits for the storage of overburden material from the culvert excavation.

Several different nondestructive evaluation (NDE) techniques were used to detect delaminations/flaws in a reinforced concrete tunnel liner. This case study involved three areas located in different parts of an abandoned streetcar/subway tunnel in Cleveland, Ohio. The tests were performed during the Summer of 2002. Four methods were used, and a comparison was made of the testing time and extent of deteriorated area detected. The Impact-Echo method provided the maximum amount of flaw detection, followed by Ground Penetrating Radar (GPR), Rotary Percussion (RP) and Visual Inspection (VI), respectively. The GPR and RP methods provided the minimum testing times. Based upon this study, the GPR method, along with a sophisticated data/image processing technique, has the potential for practical rapid NDE of subway tunnels.