Forensic Engineering 2012: Gateway to a Safer Tomorrow

The ASCE Technical Council on Forensic Engineering (TCFE) has announced the recipients of the 2009 and 2010 Forensic Engineering Awards, planned for presentation at the Sixth Forensic Engineering Congress in San Francisco, California, October 31 - November 3, 2012. The Forensic Engineering Award recognizes individuals for outstanding contributions to the field of forensic engineering. The award is not necessarily given every year. There have been 13 recipients since the establishment of the award in 1989. Past recipients of the award are John P. Bachner (1990), Jack R. Janney (1991), Joseph S. Ward (1992), Lev Zetlin (1993), George F. Sowers (1994), Kenneth L. Carper (1997), Narbey Khachaturian (1998), John M. Hanson (1999), W. Gene Corley (2002), Paul F. Mlakar (2003), Lewis L. Zickel (2006), Howard F. Greenspan (2007) and Henry Petroski (2008).

The Platte River Bridge, opened in 2004, is a cable-stayed pedestrian bridge, crossing the South Platte River between Commons Park and Commons West Apartments on the 16th street in Denver. Cable-stayed pedestrian bridges, like all bridges, must be inspected and maintained to limit the threat to life and safety. This paper presents a practical and stepwise approach for evaluating the health condition of this type of bridges, incorporating visual inspection, dynamic investigation, and structural reliability assessment. This approach is adopted to inspect and rate the Platte River Bridge. The visual inspection only finds the minor distresses and reveals that the bridge is in a good condition, but the dynamic investigation indicates excessive global vibration of the bridge. Fatigue cracking of the cables and cable connection welding are identified as the governing failure modes. The fatigue reliability assessment is recommended to be performed along with cyclic loading estimation, in order to assess the possible remaining service life.

A technical framework that uses a Structural Health Monitoring (SHM) system, which continuously measures bridge response to unknown ambient trucks, was proposed to calculate load ratings based upon finite element model simulations coupled with a statistical backbone. A steel bridge located in Iowa was selected to demonstrate this technical framework. Critical locations of the bridge were instrumented with a network of fiber optic sensors that collect real-time strain data from ambient trucks. As their characteristics were unknown, they were statistically characterized in terms of configuration and weight using Weigh-In-Motion (WIM) data collected in Iowa. Subsets of strain data were randomly selected to optimize computational models created with finite element software. The optimized models were used to determine distributions of load ratings following the AASHTO Load Factor Rating (LFR) methodology. Distributions were created for each strain set. The distributions, which account for variability in unknown trucks, can be used to evaluate the structural capacity of the bridge.

Changes in fundamental frequency in structures can reveal if a loss of stiffness has occurred, which may be an indication of critical deterioration. This paper presents a radar-based method that measures member deflection as a function of time - providing data which can be used to determine fundamental frequencies - for virtually all structural elements in the line of sight and in a non-contact manner. This paper summarizes interferometric radar theory, presents various applications, and reports on lab testing for verification of utilizing radar to monitor vibrations in cables. While interferometric radar has been used to monitor vibrations in light poles, wind towers, buildings, and other structures, particular attention is given herein to cable stayed bridges. Limitations are also discussed.

A highly efficient image processing technique can be used to document the status and damage/distress levels in bridges using high resolution images. The bridge deck images can be used to quantify deck distress conditions and deterioration progress. The paper provides insights about the important role of the image format in image processing techniques. The method can be extended for crack detection and quantification in roads. Using engineering models and analysis, we can evaluate the current performance level in terms of strength and life-cycle. Since the data obtained in these studies is static, or dynamic, the analysis depends on the quality and accuracy of the system used to capture the images. Consequently, the processing of this data needs to be done by looking into acquisition, enhancement and improvement, and later comprehension and interpretation so that it can be used in engineering analysis. These features are presented with diagnosis on the effect of damage in typical case studies done on some existing bridges.

The investigation into the causes of collapse of the I-35W Bridge in Minnesota required a vast amount of design, retrofit and maintenance data to be sorted prior to beginning the complicated work of analyzing the condition and loading of the bridge at the time of collapse. A Forensic Information Model (FIM) was created to store all of this data, as well as the geometry, as a 3-D visual database enabling the engineers to pinpoint possible trouble areas in need of further investigation. SAP models were built to evaluate the linear behavior of the structure. Components were modeled in Abaqus to study the post buckling capacity at a member level. The results were combined into a LS-DYNA model to capture the bridge's initiation of failure. The collapse simulation matched well with existing video of the failure. This paper will describe the interaction between the models, how the FIM was instrumental in guiding the numerical modeling to its conclusion, and the subsequent creation of a 3-D animation that allowed the client to better visualize the collapse mechanics.

On October 27, 2008, Span 1 of the Robinson Road Bridge, being constructed to cross over Interstate 84 in Nampa, Idaho, collapsed. The bridge was being constructed in a staging area on temporary falsework supports and, after completion, was to have been transported to its final location on completed abutments and piers by a self-propelled modular transport (SPMT) device. Fourteen construction workers were on the elevated span when it fell and they sustained various injuries. Wiss, Janney, Elstner Associates, Inc. (WJE) was hired to determine the cause of the collapse. This paper will focus on our investigation of the falsework collapse and present our findings of cause, which concluded that a critical lack of effective bracing of falsework transfer beams caused the collapse. A discussion of falsework bracing requirements and methods of analysis of effectively unbraced beams are presented.

Routine inspections lead to the discovery of never-before documented fatigue failure of reinforced concrete bridges in California. During bridge inspections on Interstate 40 near Needles, California, Caltrans inspectors observed movement along the horizontal cold joints between the decks and girders in several normally reinforced, cast-in-place, concrete, T-girder bridges constructed in the early 1970s. Inclined cracks and a fractured stirrup at one of the cracks were also found, leading to closure of the bridges. Later destructive investigations conducted just prior to demolition of the bridges revealed that many of vertical stirrup legs crossing the construction joints had fractured. With many similarly vulnerable concrete T-girder and box-girder bridges in service elsewhere in California, an investigation was conducted to determine the cause of the failures and develop recommendations to mitigate this type of failure in the future. Based on the investigation, it was concluded that the bridges failed due to cyclic degradation of the horizontal construction joint. This paper highlights important aspects of the investigation.

A total of 157 bridge collapses, not including the ones caused by earthquake, were collected from the public media report in China from January 2000 to March 2012. The information, including the cause, bridge type, bridge scale and location, were studied in statistical way. The analysis indicated that the bridge collapse is mostly caused by natural disaster. Especially the flood is a main cause besides earthquake. Unreasonable construction scheme is the main causes in artificial factors and the collapses of overload and collision has a large proportion in total. According to the bridge attribute information, arch bridge collapses more frequently than other types; the longer the bridge is, the more frequently the collapse may occur from this statistic; collapses in countryside are two times more than the ones in city. Based on this study, some suggestions are provided such as perfect safety assurance system, standardized bridge maintenance and management, more intensive study on new technology and the natural disasters.

Past earthquakes have highlighted the susceptibility of curved steel girder bridges to damage from seismic events in the United States. One major part of a regional vulnerability assessment of these bridges could be the completion of sensitivity analyses that assist with identifying their influential seismic response parameters. In this study, an available inventory of curved steel girder bridges was used as a basis to establish statistical characteristics for a sensitivity study. 3D finite element models were employed to capture critical seismic response information. In this study, statistical tools, including the Plackett-Burman, Pareto and Prediction profiler methods, were implemented to determine critical parameters. This paper presents the sample results for tangential bearing translations, which are one of the critical response parameters. The results revealed that, although the relative significance of the different seismic response input parameters may change for a given seismic response output variable; the same parameters, including span number, maximum span length, radius of curvature, girder spacing, and cross-frame spacing, were typically the most significant.

Nowadays, most of the bridge structures that use steel bars encounter corrosion problems with steel bars or tendons. This problem results in the early failure. The fiber-reinforced polymer as reinforcement enhances the durability in corrosive environments and refuse to reach the failure early. The purpose of this research is to investigate the maximum length of reinforced concrete girder in FRP bars as reinforcement by use of displacement, stress and strain by computer simulation. To avoid the failure, allowable displacement, stress bar and solid strain value were checked. In other words, steel bar in bridge concrete beam is replaced by CFRP and GFRP bars and the deflection is checked to find the maximum length. Seven various spans are tested by three specimens of CFRP, GFRP, and steel bars are utilized in each of the spans. This study can aid bridge designers and structure engineers to make decisions of selecting appropriate polymer materials for preventing early failure in bridges.

The Sherman Minton Bridge, constructed in the early 1960's, is a twin, double-deck, steel-tied arch bridge traversing the Ohio River along Interstate I-64 between the states of Indiana and Kentucky. The discovery of previously hidden surface cracks during a gusset retrofit warranted a comprehensive inspection program which revealed numerous cracks and weld indications along the fracture critical tie members, particularly at the vertical butt-welded joints. Following the closure of the bridge on September 9, 2011, a structural investigation was initiated to ensure that the bridge would reopen with three principles in mind: safety, schedule and cost. A forensic information model (FIM) of the weld testing inspection program was created to organize available data, illustrate all past and present inspections and to understand any trends. A 3D mathematical model was produced to verify the original design of the superstructure and to evaluate the adequacy of its capacity to support increased loads as a result of the necessary retrofits and repair. This paper will present the process used to evaluate the problem, develop solutions, and construct the retrofit.

In previous work, certain shortcomings of traditional design approaches against restrained bending fatigue of axially preloaded spiral strands used in cable-stayed structures (e.g. bridges) based on the extreme fibre direct stresses have been identified and subsequently resolved. Restrained bending fatigue life of such spiral strands clamped at the end(s), is shown to be governed by interlayer fretting fatigue. Interlayer fretting is found to be greatest near the so-called neutral axis and not the extreme fibre position, where, during tests, initial wire failures have invariably been found to occur. A new parameter has thus been developed for design against such rather common and often very costly fatigue failures. The reliability of any restrained bending design procedure is based on a reasonably accurate estimation of the minimum critical radii of curvature at the fixed end(s) with such values of curvature then used as an input into the fatigue design model. The present paper makes significant progress in resolving the longstanding debate in the literature as to whether the traditional method of assuming a constant effective bending stiffness for estimating such critical curvature(s) is a practically reasonable one.

The performance of glazing systems in past (mostly US) earthquakes is reviewed. The mechanism of glass failure in curtain walls and possible sources of seismic failure of glass is explained. In general, past earthquakes have revealed that glass held in punched window frames, storefronts, and curtain walls are vulnerable. Some approaches to reduce glass damage in earthquakes are also discussed. Such methods include the use of large glass-to-frame clearance, the use of safety film, and the use of structural silicone glazing. Recent research on innovative ways to mitigate seismic damage to architectural glass is also reviewed. Finally, current trends in curtain wall construction for improved seismic performance of architectural glass are discussed.

In the event of a blast, conventional window glasses break into numerous flying shards which account for most injuries to the inhabitants ranging from minor cuts to severe wounds and in many cases to death. As windows serve an important role in modern building design, balancing the safety and security with physical appearance and cost-effectiveness is essential for design of blast-resistant glazing systems based on proposed level of protection. For this purpose, explicit non-linear finite element methods are applied on three types of window panels ranging from annealed glass to thicker composite systems. The response of the window panels to different blast loading cases is dependent upon edge restraints and composition of the window. We have integrated brittle material failure theories into the finite element models to find the crack initiation and propagation patterns for each of the proposed conventional glazing technologies. This will make it crucial to develop a more comprehensive injury model to better address the threats during an explosion event. Merging failure mechanics' concepts along with the analysis of the window panes that incorporate different glazing technologies will result in developing more realistic models. These models will enable the decision makers to bring the appropriate structural, architectural and building perimeter choices together to ensure the safety of the building inhabitants and the community residents.

Glass is becoming an increasingly popular building material, particularly in its use for building enclosure systems. Spandrel glass is typically used in lieu of vision glass to conceal underlying building structure or equipment. Spandrel glass is typically heat treated to avoid breakage induced from thermal stresses resulting from the heat trap that develops along the interior side of the glass. This paper provides a case study of a high rise residential tower that experienced excessive breakage of spandrel glass as a result of thermal stresses. In this particular case study, the glass was designed and specified properly; however the placement of interior thermal insulation greatly affected the temperatures that developed within the spandrel glass. Instrumentation was used to monitor the spandrel glass surface temperatures and to show how the stress buildup in the glass as a result of the temperature differentials between the center of the glass and the edge of the glass contributed to breakage of the glass in the as-built condition where thermal insulation was installed too close to the glass surface. A trial installation of the "as designed" condition was then performed and monitored to show that had the thermal insulation been installed correctly, the thermal stresses that developed within the spandrel glass would have been within the expected range.

The WilTel Technology Center was a recently constructed 15-story building in Tulsa, Oklahoma. The structure had many green aspects and LEED certifications. One key feature was the solar well acted as the plenum for the entire building. Along the entire east elevation, the plenum was created by a glass curtain wall system supported by vertical steel trusses. During a windstorm on June 2, 2004, approximately 20% of the curtain wall structure buckled outward away from the building, releasing over 70 panes of glass upon the adjacent sidewalk and roadway. Subsequent forensic investigation revealed numerous fabrication and construction defects during construction that led to the failure. A tubular truss and strut frame provided the main wind force resisting system for the solar well structure. The joint design between components relied upon clevis and pin connections secured by snap rings. While the design intent was achieved as presented in the architectural drawings in the overall structural design and fabrication details, the design, fabrication and construction of the joints did not provide an acceptable structural system. Review of the construction documents revealed significant and unapproved changes in the fabrication of these joint components including dimensional and material selection changes. The failure investigation included the expertise of meteorologists, structural engineers, mechanical engineers, and metallurgists providing an all-encompassing investigation into the facade failure. The investigation findings illustrate the requisite review process that must be adhered to between the architect, structural engineer, and fabricator. The following presents the findings regarding the structural engineering aspects of the investigation.

Composite panels are increasingly common in roof applications. These panels are made by sandwiching a layer of rigid foam insulation between two facer materials. Advertised advantages include the speed of installation and the greater continuity of the insulating layer. When panels are applied to a sloping roof, the upper facing layer becomes the nailer, and the rigid foam core provides the insulation. If the insulating layer must also transfer the along-slope component of weight - roof dead load and superimposed live load - then the shearing force and compression within the foam core may lead to problems. Typically, the engineered building structure ends at the roof decking. The composite roof panels, or an assembly of insulation plus nailing layer, are specified by the architect, usually without the benefit of structural engineering. Details for attaching the composite panels usually include a fastener schedule sufficient to resist wind-induced uplift. However, the weight of the roof covering, nailing layer, and superimposed live load also includes an along-slope component which tends to induce sliding along the slope. There is not always explicit attention paid to how the upper nailing layer will be prevented from sliding. Further, where the nailing layer consists of wood panels, it is important to maintain a narrow gap between adjacent panels. Where the sliding resistance must come from shear and/or compression in the insulating layer, gaps between wood panels may close, resulting in problems for the roofing and insulation. This paper describes a case study where the rigid insulation was the only material available to prevent the wood-panel nailing layer from sliding. When they were installed, the composite panels were placed with the requisite 1/8 in. gap between the wood face panels. The gap was to be maintained by compression in the foam core along the joints between adjacent panels. Over time, however, the rigid foam core compressed, the nailing-layer panels moved down the slope, and the cumulative dimension of the closed gaps resulted in a significant separation along the ridge line. The shingle cap split, water entered, heat escaped, and the roof required significant repair.

The severity of hail damage to residential and commercial roofs depends on several parameters including the age and type of roofing material, the roofing assembly, hail size, and roof slope, among others. Asphalt shingled roofs comprise a large percentage of insurance claims submitted for roof-related hail damage. For asphalt shingled roofs, hail damage typically consists of radial/circular areas of granule loss, which constitute latent damage and may affect the future performance and lifespan of the shingles. The severity and extent of hail damage to asphalt shingled roofs is not as visually apparent as compared with some other common high-slope roofing materials, such as metal panels, wood shakes, and clay/concrete tiles. Assessing the extent of hail damage to shingled roofs and developing a scope of repairs can be difficult. Furthermore, guidelines for such assessment are not well established. Based on the authors' experience, we propose guidelines and procedures to assess the extent of hail damage to asphalt shingled roofs from which a scope of repairs can be developed. A cost analysis for the consideration of repair versus replacement is also presented.

The Hamptons at Metro West, a wood-framed condominium complex located in Orlando, Florida, has suffered extensive long-term large-scale structural wood decay. Framing members inside the stucco-covered exterior walls had rotted to the extent that they provided little or no structural support, and the walls had begun to sag away from the main structure. Large sections of stucco had become detached and begun to fall from the buildings. Exterior balcony floor framing was so decayed it could no longer provide adequate support. Problems with the construction of building envelope weather protection systems were ignored or poorly understood, leading to the long term underestimation of the causes, repair and extent of damage. It was not until a thorough forensic investigation was undertaken, beginning approximately eight years after construction was completed, that the causes for and the full extent of the structural damage was understood sufficiently for a repair protocol to be developed. This paper discusses the forensic investigation undertaken to identify the sources of water intrusion, the rot damage they produced, and the efforts to maintain the buildings safe and habitable during the four-year litigation process.

One of the most common complaints about buildings is water leakage through the building envelope. A well-planned investigation can efficiently uncover the root causes of water leaks, a critical step in designing effective repairs. Investigations for litigation often involve special protocols and coordination with more parties than for non-litigation situations. A successful investigation begins with a clear problem definition and a clear understanding of what the ultimate deliverable will be. Reviewing available documents, having a sound basis for testing, and understanding the requirements specific to the project will help the investigation run smoothly. Communication protocols will keep all parties informed of the planned testing activities. Understanding the ultimate deliverable will ensure that sufficient data is collected during investigation. For large scale investigations, coordinating efforts among a team of engineers is necessary to maintain consistency in documentation, which will translate easily into a report afterward. Clear reporting includes providing all information upon which conclusions rely, separating facts from opinions, and illustrating quantitative information graphically where appropriate.

The types of non-catastrophic failures in glazed architectural terra cotta masonry are a combination of those for stone masonry, brick masonry, and concrete. They include the problems created by the oxidation of ferrous anchors and ties, expansion and freeze-thaw problems associated with moisture in fired-clay masonry, and delamination. The challenge in assessing the condition of glazed architectural terra cotta masonry is to employ a single, cost-effective method that can quickly identify the various forms of non-catastrophic failures before they develop into imminent public safety hazards. Drawing from the author's experience with accessing mid- and high-rise terra cotta facades in Chicago and Los Angeles, this paper provides a detailed description of the nuances in using the three senses of sight, hearing, and touch - in conjunction with mechanical sounding - to thoroughly assess the condition of glazed architectural terra cotta masonry.

Façade repairs in city settings always pose logistical challenges. An 18-month, $7.7 million, NYC Landmark Preservation Commission-accepted façade repair program was performed at 230 Park Avenue, a 34-story, 1.4 million SF landmarked office building in midtown Manhattan. The program specified and administrated by Thornton Tomasetti (TT) focused on restoring ornate terra cotta elements that had been deteriorating since the building's construction in 1929. The building features many architectural façade elements constructed with terra cotta masonry, most notably 3-story tall, free-standing terra cotta columns with one story tall terra cotta bottom brackets and capitals. In order to correlate the degree of cracking evident at the surface of the terra cotta column enclosure to the amount of corrosion loss of the concealed steel column elements, impact echo, ultrasonic pulse velocity, infrared scanning, and invasive probing methods were performed. A finite element model was developed to analyze the behavior of cracks in the terra cotta brackets. Appropriate and cost effective repair techniques, including specially designed stabilization anchors and liquid applied fiber reinforced tension bands were applied. An impressed current cathodic protection system was also installed at certain locations to prevent and monitor steel corrosion. This was a robust repair program accomplished with sensitivity to preservation requirements and it demonstrated that state-of-the-art technology can be cost effective.

Exterior masonry wall construction evolved over the centuries from thick mass masonry walls to modern veneer systems with backup walls and cavities for drainage. Many early cavity wall systems of the 1960s and 1970s were designed with what turned out to be inadequate waterproofing and durability features. Consequently, many older cavity walls now require remedial work to extend their useful life. After completing a multi-million dollar interior renovation of a middle school, the school district became of aware of pre-existing, widespread and severe cracking and spalling of mortar joints in the exterior brick masonry. The deterioration significantly impaired the structural integrity of the walls. Extensive remedial work, required to address the deterioration, had to be implemented from the exterior and without significant disruption to the occupants and recently completed renovations. This paper describes the investigation, evaluation, and remedial strengthening of the exterior walls.

The bell tower of an historical church in Houston, Texas, was noted to be leaning. Long-term tilt survey over a period of approximately six years revealed that the bell tower movement was cyclical in nature but gradually increasing. Field investigation revealed that expansive soils under the bell tower foundation was the primary reason for distress. Structural analysis revealed that the tilt of the bell tower was unlikely to cause stability problems. However, physical evidence and additional analysis indicated that cyclical movements of the bell tower would continue to cause visible distress in less structurally significant parts of the bell tower if the movement was not arrested. Given the historical significance of the bell tower, the church officials elected to correct the tilt as well to stabilize foundation movement. Specialized foundation repair techniques were used to correct the tilt and stabilize the foundation.

Using recycled products to build green is rapidly gaining momentum in the construction industry; however, these materials must be incorporated correctly within building envelope assemblies to avoid potential pitfalls. In this paper, we address problems that can arise when an incompatible combination of materials is used and construction defects occur. This paper presents a case study demonstrating the detrimental effects of construction defects on a masonry cavity wall assembly that incorporated vapor retarders and cellulose insulation, a green building material.

This paper outlines problems with the current practice of designing and constructing stucco framed buildings. The where and why stucco wall assembly failures occur with today's standard stucco trim products is explained and illustrated using the casing bead as an example. The paper includes illustrations of the typical details using a casing bead around wall penetrations which are inadequate and lead to water intrusion. What designers and builders should know is illustrated with recommendations for independent flashings with a secondary function as stucco screeds. And included are recommendations and details to permit the use of casing beads as stucco screeds, as well as, effective flashings. The paper reviews and critiques the responsible parties, products and relevant industry standards regarding waterproofing stucco buildings. The few available sources for relevant and valuable guidance are identified to improve building performance.

Water losses from plumbing failures, accidental releases and appliance leaks are among the most frequent claims in the insurance industry. Key to the interpretation of any water loss is the duration of the event and whether the loss was continuous or repeated before it was reported to the insurance provider. Water exposure tests on composite wood products (i.e., faced particle board, medium density fiberboard and oriented strand board) provide insight into the physical and moisture content changes that occur following one-time and repeated water exposure events. The test results are used with information obtained during the claim investigation to interpret the duration and frequency of a water loss.

Research was undertaken to evaluate the current condition of asbestos-cement (AC) pipe and develop service life prediction model for the Alameda County Water District (ACWD) distribution system. Laboratory assessment of 47 pipe samples removed from the system revealed that, while pipe strengths were satisfactory, deterioration of AC pipe due to leaching of calcium from the cement matrix was progressing. Analysis of leak records between 1987 and 2006 demonstrated that pipe age and nominal size were the most critical factors affecting leak rates. A semi-empirical model developed for predicting future leak rates and cumulative number of leaks over time was individually calibrated for each grid cell in the distribution system to reflect unique leak rate history observed for the specific cell. The estimated remaining service life of AC pipe in each cell was determined by comparing the predicted cumulative number of leaks with a threshold number of acceptable leaks.

This paper reports the failure of a 20-m-long section of a 10-m high downstream-constructed dike on the perimeter of an ash pond in eastern India. In the incident the debris washed out rapidly to distance of about 100 m before getting deposited in a low-lying area immediately downstream to the failed site. An investigation into the possible causes of failure indicated that the dike failure was initiated because of increased pore water pressure within the dike body resulting from accumulation of decant water immediately upstream of the affected section of the dike and blockage of a decant structure nearby and the chimney drain within the dike body. The instability was initially triggered because of pore water pressure rise within the dike body followed by severe loss of shear strength of liquefiable fly ash with which the dike was partly constructed finally leading to a flow failure.

This paper presents a case study of a slide that occurred during the construction of the initial starter dam for a planned four-stage coal refuse impoundment located in Eastern Kentucky. During the installation of 1700 linear feet of 36-inch HDPE decant pipe, loading from coarse refuse placement on a side hill adjacent to the pipe alignment and future embankment initiated a slide in natural ground prior to the construction of the dam embankment. This slide caused a 300-foot section of pipe to displace laterally and vertically. This paper presents the lessons learned from the remediation of this slide and the repairs made to the decant pipe. It also presents the challenges that developed as construction progressed and operation commenced as well as challenges that developed as later stages were proposed and constructed. This paper also examines the economic, regulatory, and maintenance and inspection challenges created in later stages of the permitting and design process as a result of the initial remedial efforts and the course of action taken.

A closed-form solution is presented for the calculation of the stability of a wedge in the roof of a tunnel. The stability of the wedge is investigated using a two-stage relaxation procedure. A polynomial function is used to fit the horizontal induced stress along the axis of the noncircular tunnel based on the numerical results. The effect of the ratio K of the horizontal-to-vertical in situ stress on the internal horizontal force is investigated. The influences of the normal and shear stiffness and the far field stress on the stability of the wedge are investigated. The results indicate that the stiffness and far field stress have significant effect on the stability of the wedge.

Ingham and Biggs were in Christchurch during the M6.3, 22 February 2011 earthquake and Moon arrived the next day. They were enlisted by officials to provide rapid assessment of buildings within the Central Business District (CBD). In addition, they were asked to: 1) provide a rapid assessment of the numbers and types of buildings that had been damaged, and 2) identify indicator buildings that represent classes of structures that can be used to monitor changing conditions for each class following continuing aftershocks and subsequent damage. This paper explains how transect methodology was incorporated into the rapid damage assessment that was performed 48 hours after the earthquake. Approximately 300 buildings were assessed using exterior Level 1 reporting techniques. That data was used to draw conclusions on the condition of the entire CBD of approximately 4400 buildings. In the context of a disaster investigation, a transect involves traveling a selected path assessing the condition of the buildings and documenting the class of each building, and using the results in conjunction with prior knowledge relating to the overall population of buildings affected in the area of the study.

Post-earthquake reconnaissance typically yields voluminous information about structural failures and collapse. In some situations, the causes of failure and strategies for mitigation are obvious. On the other hand, sometimes these are clouded by uncertainties in the circumstances that precipitated failure. This may be due to (1) the lack of information regarding true ground motions, building response or material properties or (2) complexity due to nonlinear interaction of various effects. Within this context, a robust framework for forensic analysis of earthquake related fracture is presented. In this paper, the failure of Eccentrically Braced Frames (EBFs) in the February 2011 Christchurch earthquake is used as a case study to illustrate this methodology. Detailed drawings and material samples were obtained from the failed frames, whereas some data, pertaining to overall building response (such as soil-structure interaction and diaphragm/connection flexibility) could only be speculatively estimated. Thus, with the a posteriori knowledge of the location and occurrence of fracture, the "blame" for it may be apportioned among various underlying factors. The case study includes physical material tests from the failed frames, and finite element simulations at the component as well as the connection scale. Based on these, a comprehensive presentation of the framework is presented, along with a discussion of its limitations.

Recent earthquakes continue to show the vulnerabilities, as well as the resiliencies of natural gas pipeline systems to ground shaking, liquefaction and fault movement. Materials, coatings, piping configuration, and geologic conditions combine with localized peak ground acceleration (PGA) to create the primary drivers determining how the pipeline or network responds to seismic events. After a significant earthquake, engineers and researchers often evaluate pipeline failures through on-site visits with the pipeline system operators. The primary method of data collection is through the use of checklists. This is of particular importance since many individuals collecting data are not necessarily involved in the natural gas industry on a normal day to day basis, and thus need guidance regarding questions to ask and information to gather. Recent Federal requirements for ongoing evaluation of the integrity of natural gas pipelines is creating a significant database of individual pipeline attributes that can be useful in determining specific causes of pipeline failure due to earthquake. This paper presents an updated, comprehensive checklist for those involved with post-earthquake natural gas system evaluation. It takes into account data that will likely now be available due to federally mandated integrity management procedures. Use of this data will permit engineers and researchers to better identify the risk factors that cause pipeline failures during earthquakes. This checklist will also be of value to those evaluating earthquakes outside of the United States, since many of the items listed should be known to pipeline operators and gas companies world-wide.

The focus for engineers and those hiring engineers has historically been the quality of the engineering skills, and has not focused on the elements required to perform their engineering services safely and within the requirements of an ever increasing governmental agency reach. This paper focuses on the environmental and safety training and equipment that would be needed for those forensic engineers to enter into a scene and perform their services. A scene scenario is given that introduces hazardous conditions in the origin and cause investigation area, which requires environmental and safety training and equipment in order to enter the scene to perform forensic engineering services. The need for this paper is due to increased attention to dangers at these scenes in this industry and the truthful application of "you don't know what you don't know" at these types of scenes. The paper achieves "you now know what you didn't know" for engineers performing on-site forensic engineering services.

Following the collapse of an external self-climbing tower crane at 303 East 51st Street, New York, New York, on March 15, 2008, Ove Arup & Partners, PC (Arup) was hired by the New York City Department of Buildings (NYCDOB) to provide engineering and investigative services. Many government agencies were involved during the investigation, including NYCDOB, the NYC District Attorney, NYC Department of Investigations and the Occupational Safety and Health Administration. The investigation carried out by Arup will be described together with the limitations which were imposed as a result of the need to interface with these agencies. This description is with regard to our direct experiences and does not reflect any interpretation or application of law.

Digital photography and video technology are often used to process and document complex man-made disaster scenes, such as that of a crane collapsing during scene processing upon the area of potential origin. Better records of early and on-going origin & cause site documentation can be found with the use of laser scanning equipment based upon standard surveying techniques and principles. Laser scanning technology has been used for over 15 years within other industries. This paper explains how laser scanning of debris fields works, the deliverables it can create, its requirements and limitations, and other basic facts. It includes an overview of the equipment available for performing laser scans; important questions to ask laser scanning service providers; acceptance into the court system; the processes of obtaining site data and "parking" that data for potential use; "single scanning" and "progress scanning" processes of debris fields; and more.

Large scale cause and origin forensic engineering investigations present a wide range of unique and often-changing legal issues under the best conditions. The number and complexity of the issues dramatically increases when the forensic engineering work compromises the original integrity of the investigation being conducted. Paper will explore the various legal issues affecting forensic engineers from all sides when conducting a cause and origin investigation where the scene is compromised by the investigative work itself, namely when heavy equipment used to conduct the investigation collapses into the area of suspected origin.

Construction industry is ranked first for occupational risks and workplace incidents among all industries. Popular belief assumes most of these incidents happen due to structural failures or worker carelessness. However research shows a link between design and construction site incidents. According to the literature, considerable number of accidents can be linked to the design phase. However, designers usually avoid focusing on construction safety due to legal complications. There are very few risk analysis and control methods available which can evaluate the degree of safety risks for different design options. This study aims to recommend some appropriate measures to enable designers to assess potential risks in construction and deal with it in the design phase. Visualization tools, based on Building Information Modeling (BIM), can help designers to detect potential accidents and play a major role in safety planning prior to the construction phase. This article establishes the ways in which integrated design and collaborative features of BIM can be used in enhancing safety on construction sites. The main objective of this paper is to prioritize the ways in which BIM can be utilized in improving construction safety. For this purpose we classified the appropriate measures that help BIM be more practical in safety management. Based on analysis performed on responses to a survey, the two measures ranked the highest were as follows: 1. Incorporation and development of various levels of detail into the BIM model, as it pertains to construction equipment, material and labor at the design phase 2. Integration of hazard potentials and prevention strategies with the 3D BIM model

Transfer of information from one party to another along a chain of parties can be problematic. When communication between design professionals is not coordinated effectively, the message can be corrupted or lost along the way. If this happens on a construction project, the results will be costly. Large and/or complicated projects may require a variety of design professionals, and coordination among these professionals is essential. For many project types, coordination takes place under a primary design professional: as employees, subconsultants, or specialty contractors whose designs are reviewed and approved by the primary. However, there are projects where design professionals are separated and independently contracted under an owner or developer, such as with certain owner-build or construction management projects. The architect has a diminished role and communication among professionals may take place through intermediate parties who are not design professionals and may not realize the significance of certain design details. This paper presents three case studies of this kind of occurrence: ≤ A proprietary retaining wall system where the designer was unaware of structures that were to be placed within the surcharge area on top of the wall, leading to demolition and replacement of the wall; ≤ A three-quarter-acre courtyard designed to drain toward a trench drain at the entrance to an underground parking garage, with the trench drain not designed to accommodate storm water runoff, leading to flooding of the garage and installation of an unplanned-for storm water drainage system; ≤ An underground parking garage where miscommunication among design professionals and the contractor resulted in application of soil loading that exceeded the design capacity, leading to a partial collapse of the garage slabs. This paper will describe how the miscommunication occurred, the roles of the various parties involved, the results of the miscommunication, and the authors' opinions of what should have been done and what can be done to prevent repetition of these occurrences. Details of the authors' investigation of the issues will also be discussed. The authors highlight the inherent advantages of the engagement of a primary design professional on the project with responsibility to coordinate information among design professionals, regardless of project type. As each of these projects resulted in litigation, the names of the parties involved and locations of the projects will not be provided.

This paper will discuss the responsibilities of the structural engineer in designing and detailing conventionally framed multi-story structures. Specifically, this paper will identify the importance of a clear layout of intended shear walls, detailing for the transfer of design wall loads, and for the transfer of design diaphragm loads. The necessity for these design and detailing requirements, including the issues that result when the structural engineer fails to do its job properly, will be illustrated through a case study of a multi-family residential complex located in southwest Colorado. Structural deficiencies resulting directly from improper design and/or detailing of the lateral force resisting system, and the potential for, and consequences of, unintended construction deficiencies will also be addressed.

The State of California has developed a new program (S.B. 1608) to assist people with disabilities to gain greater access to businesses and, at the same time, help business owners certify the accessibility of their establishments to their customers with disabilities. This paper provides an overview of the current Certified Access Specialist program (CASp) in California, briefly describes how similar programs operate in other states and countries, and also discusses whether the program is fulfilling expectations for people with disabilities as well as for business owners. Finally, this presentation looks at case studies showing the important role civil engineers can play, either alone or in concert with architects and other professionals, to provide accessible constructed environments.

Budgets and safety of building projects are factors that both strive for attention. To use available budgets effectively, it would be helpful to know the factors in the design and construction phase that primarily influence the structural safety of a building -- the critical structural safety factors. This article mentions possible influencing factors on country level, organizational level and human level. An advantage of the method for determining the factors in this study is that they have not solely been based on the lessons from structural failures, but are also based on organizational and safety theories. Although additional research is needed to point out critical factors, this approach is promising to get insight into the factors that require special attention to stimulate structural safety.

The challenge of risk management is to reduce the harm that disasters cause to society, economy, and the lives of individuals and communities by decreasing uncertainty, calculating and comparing costs and benefits, and managing resources. This must often be accomplished more extensively and much faster than it is possible by traditional problem solving methods. Recently, intelligent agents have more and more been used in a variety of fields, as some scientists even consider them a new computational paradigm based on autonomy and social interactions. Agent-based systems can provide additional capabilities to help people understand the dynamic realities of a disaster more clearly by simulations of risk scenarios and can allow them to make better decisions more quickly by providing intelligent support for decision making. By using GIS-based visualization of geospatial data, the knowledge on structural seismic vulnerability for urban infrastructure can be further improved. In this way, stakeholders can increase the quality of their decisions for the management of possible emerging crises and/or for planning the rehabilitation programs. Modeling, simulation, and analysis scenarios based on linear or non-linear dynamic procedures are described, with applications to some different classes of buildings models from the Iaşi municipality, the second largest city of Romania. A set of artificial intelligence methods are used as tools for the awareness and monitoring of seismic effects taking into account possible future disasters.

For more than 30 years, the Federal Emergency Management Agency (FEMA) Building Science Branch of the Federal Insurance and Mitigation Administration has studied the performance of buildings affected by disasters of national significance, including flooding, tornadoes, hurricanes, and terrorist attacks. The Mitigation Assessment Team (MAT) program draws on the combined resources of the federal, state, and local governments and the private sector to quickly assemble and deploy teams of investigators following natural and manmade hazard events. The teams conduct field investigations at disaster sites to determine the causes of structural failure and success. Using the information and observations collected in the field, MATs work closely with local and state officials to develop recommendations for improvements in building design and construction, code development and enforcement, and mitigation activities that will lead to greater resistance to hazard events.

The Corps of Engineers conducts a variety of internal, external, and collaborative forensic studies. Herein we discuss the performance of hurricane protection in Katrina, the flow-induced vibration of a navigation lock gate, a safety review of the Boston Metropolitan Highway System, the distress of a tunnel beneath the space shuttle crawlerway, residential vibrations from mine blasting, and the 9/11 Pentagon crash. In each case we describe the problem, detail the forensic approach, and summarize the conclusions. The results of these studies have improved the performance of the built environment.

This paper introduces and discusses a number of teaching and dissemination topics, tools and techniques for engaging students and practitioners that show promise in the creation of an environment of active learning, and participation and enthusiasm as it relates to failures and forensic engineering education of all types. The context of the discussion centers on a course titled Building Performance Failures and Forensic Techniques (Building Failures) offered to graduate and upper level undergraduate students in Architectural Engineering (AE) at Penn State. Case studies of specific failures and categories of failures are integrated extensively throughout the course modules in multiple formats including self study, research and writing, conventional lectures, industry guest speakers, on-line discussion forums, and direct observation (aka The Campus is Our Lab). Of particular note is the success of the creation and use of an on-line failures dissemination wiki site, Failures Wiki and a resource and web-based discussion "blog" known as Building Failures Forum. Both of these on-line resources are failures dissemination and education resource efforts which are being monitored as outreach efforts related to committee activities of the Technical Council of Forensic Engineering (TCFE) of ASCE.

The history of the development of practice in many engineering disciplines is, in large part, the story of failures, both imminent and actual, and of the changes to designs, standards and procedures made as the result of timely interventions or forensic analyses. In addition to technical issues, concepts such as professional and ethical responsibility are highlighted by failure cases. Pilot studies have been carried out over several semesters to assess the use of failure case studies in civil engineering and engineering mechanics courses at Cleveland State University under an earlier NSF project. Student learning has been assessed through surveys as well as focus groups led by researchers from the Cleveland State University College of Education and Human Services. Students were asked specifically about the technical lessons learned, as well as their response to the case studies. Case study questions were included on homework assignments and examinations. Survey questions linked student achievement to learning outcomes. The focus groups identified additional benefits to the use of case studies. Students observed that the cases helped build engineering identity, and provided historical understanding. The cases made the technical information relevant and linked theory to practice. The project described in this paper will extend the work of implementing and assessing case studies from Cleveland State University to 11 other university partners, including using case studies in an Introduction to Engineering course for first year students, as well as the NSF Materials Digital Library for a total of thirteen universities participating in the project. The project is a work in progress, starting in the fall of 2009.

Engineering college students are educated to be able to apply mathematics, science and engineering knowledge for design, construction, and solving engineering problems. Civil Engineering programs in China usually introduce students to various mechanics and detailed design principles through the instructor-centered method. Although this knowledge is developed based on lessons learned by engineers of past generations, it is more effective to convey engineering philosophies if case-based teaching can be followed. This paper investigates the feasibility of improving educational functionality of case studies at the College of Civil Engineering of Tongji University, China. A sample course was introduced and suggestions for using research results to improve teaching were presented. Class designs for promoting failure case studies and involving students in laboratory research were described.

The recent Japanese earthquake and tsunami is one of several recent, destructive events that has provided critical engineering information regarding the performance of buildings, bridges, walls, roadways, etc. during intense loading. 3D laser scanning technology provides a valuable tool to acquire perishable information and preserve the scene digitally for post-disaster assessment. This paper discusses the challenges and benefits for use of 3D laser scanning on post-disaster reconnaissance efforts. This paper also focuses on special considerations when performing scanning work in post-disaster environments. Because of the limited time available to make critical decisions, it is important for personnel to know optimal procedures during planning, field reconnaissance, collaboration, data acquisition, processing, and analysis. Examples from recent events illustrate the power of this revolutionary tool in forensic investigations.

High resolution ground-based optical-photonic images generated from laser scans provide detailed geometric information about a structure and simple algorithms can be used to retrieve damage information from the geometric point cloud data. Also called terrestrial 3D LiDAR, the laser scanning technology has great potential for bridge condition assessment, in particular, for damage evaluations. This paper describes several studies on quantification of concrete material damages using 3D LiDAR including mass losses due to vehicle collisions, reinforcement corrosion and surface erosions. The computed information can provide engineers critical measurements for further damage analysis, which is not previously available using photogrammetry or plan photographic techniques.

Advanced nondestructive sensing techniques have been used for structural evaluation. However, measurements of most techniques are not valid when large deformations occur. The reason for the invalidity is the fundamental assumptions of elasticity in measurement technique and that large geometric distortion resulted in mismatching of damage data to surface topologic data. To address the mismatch issue, this paper reports the results of combining an internal stress measurement technique using piezoelectric (PZT) sensing, and a surficial topology measurement technique, 3D LiDAR scan. LiDAR uses rays of laser beams to measure position data that produces a point cloud. The PZT technique gathers data collected by an actuator/sensor network generating and receiving signals across the interior of the plate using unique wave properties. Since wave properties can be correlated to structural elastic properties, they can used to detect condition changes. The integration of the two results allows validation of nondestructive damage detection and concurrent large deformation quantification. Preliminary test results on a 16 inches-by-16 inches aluminum plate subjected to five damage scenarios are presented to demonstrate the potential applications of such technique.

Information collected by experts immediately following natural or man-made disasters is critical in understanding the causes of infrastructure and system failures. In many cases, such information not only helps identify specific causes of a failure but also provides critical insight into how future designs can be more resilient to similar events. However, there are instances where experts cannot get on location for a number of hours or days following an event and important perishable information may be lost or damaged during that initial period following a failure. Leveraging the capabilities of information technology to facilitate initial data collection represents an opportunity for future forensic engineering studies. This paper explores opportunities to engage the public in capturing such information while recognizing the limitations of technology as well as the manner in which it is deployed.

This paper describes the investigation of a chlorine gas release at a public swimming pool. Over one hundred patrons were exposed to the chlorine gas release. The chlorine gas was generated by the inadvertent mixing of sodium hypochlorite solution and hydrochloric acid. The accident investigation concluded that the release was caused by a combination of maintenance and design errors. The maintenance error was procedural: on the second day of the maintenance task the contractor did not follow the standard lockout-tagout (LOTO) procedure for isolating the chemical feeder. If he had followed the LOTO procedure, the accident would have been prevented. The design defect was related to the control logic and the physical arrangement of the equipment under control. The causal factors of the accident are discussed and lessons learned are offered to prevent a recurrence of similar accidents. A key feature of this accident was the failure to properly isolate the automatic control system during routine maintenance.

Recent changes to local, national, and international building codes include requirements for the installation of automatic fire sprinkler systems in new construction, including single-family homes. As more and more buildings are equipped with these systems, the likelihood of an inadvertent discharge (i.e. the accidental release of water from the system when there is not a fire) increases. The damage caused by water inadvertently discharged from an automatic fire sprinkler system can be substantial. Proper investigation of these failures by forensic engineers is critical to determining the root cause of the discharge. Based on prior forensic investigations of this type, six major root causes have been identified for inadvertent automatic fire sprinkler system discharges: (1) overheating; (2) freezing; (3) mechanical damage; (4) corrosion; (5) deliberate sabotage; and (6) manufacturing defect. This paper discusses these causes, examines historical loss data, and provides guidance for a forensic engineer performing a root cause analysis.

Civil/Structural engineers in the field of forensic engineering are often asked to evaluate residential and commercial buildings exposed to fire events. Typical concerns are determining the severity and extent of damage to various structural building components. The purpose of this paper is to characterize and describe fire damage that affects structural building materials typically used in residential and commercial construction. A general approach to the evaluation of fire-damaged buildings will be discussed, with a specific focus on concrete (both cast-in-place and masonry), steel and wood building materials. The paper will review inspection techniques and specific concerns related to the evaluation of key structural elements; and provide some discussion on indirect damage related to a fire event (such as water damage and saw-cut damage related to firefighting efforts, and physical damage from subsequent demolition activities). The forensic civil/structural engineer should find this paper to be a good primer on the subject of fire damage assessment, with valuable resources cited for future reference.

Automatic fire sprinkler systems are often considered the most significant component of a building fire protection strategy. When properly designed, installed, tested and maintained, they can control a fire and significantly reduce deaths, injuries, and property damage. However, mistakes during the design/installation phase and during periodic inspection, testing and maintenance activities can have a profound impact on the effectiveness of automatic fire sprinkler systems. This paper explores recent automatic fire sprinkler system failure data to identify current causes of unsatisfactory system performance, highlighting many specific root causes through the examination of past fire loss data across a broad range of occupancies. In addition, specific examples of recent fires where the automatic fire sprinkler system performed in an unsatisfactory manor are presented. By understanding the most common root causes and studying past examples, a forensic engineer can be better prepared to investigate and analyze future failures and losses.

As Civil/Structural engineers in the field of forensic engineering, we are often asked to evaluate residential buildings exposed to flood events. Whether the flooding is due to the storm surge from a hurricane, heavy rainfall events that result in riverine flooding, or failure of a levee, the effects on residential buildings have many common structural concerns. The purpose of this paper is to provide a primer on the evaluation of residential buildings exposed to flood events. Basic information regarding the National Flood Insurance Program will be discussed, including common insurance-related questions to be answered by the forensic engineer. An overview of flooding effects on structures will be provided, including considerations for hydrostatic forces, dynamic forces from flowing water, buoyancy, saturation of soils and related foundation movement, and environmental/contamination concerns. Case studies and selected topics will be examined as permitted by the length limitations of this paper.

Property damage attributable to hurricane-induced floods can be difficult to discern once flooding has subsided; however, flood levels can be estimated by measuring watermarks left by standing water on interior and exterior finishes including glass, gypsum board, exterior siding, fences, landscaping, etc. This paper illustrates how field measurements of watermarks can be used reliably, along with other field observations, to assess structure distress related to flood. A particular application of this can be seen in a dispute stemming from property damage related to Hurricane Katrina, in which the author was posed the task of determining if commonality existed to qualify for a class-action lawsuit. During site visits to putative class properties in the city of New Orleans, watermarks were field-measured to establish an estimated flood level, and the causes of various distress to each structure were analyzed including wind and flood. The field-measured watermark data were compared to the Interagency Performance Evaluation Taskforce (IPET) reported levels and revealed good correlation. The damage attributable to flooding was then compared across properties resulting in a conclusion that each property sustained significantly differing levels of damage, including some with no flooding above the finished floor; and thus did not meet commonality.

The National Flood Insurance Program (NFIP) requires that all new, below-base flood elevation (BFE) construction in the regulatory floodplain be constructed with "materials resistant to flood damage." To provide a quantitative approach to evaluating resistance to flood damage, the Federal Emergency Management Agency (FEMA) Building Science Branch has developed a pre-standard on evaluating flood damage-resistant materials. The pre-standard outlines procedures for identifying the flood damage resistance rating of building construction materials based on mechanical and aesthetic characteristics. The primary users of the standard will be manufacturers who will subject their materials and assemblies to the testing requirements and local building officials who will use the ratings to determine what is allowed in below-BFE construction. In an effort to evaluate the structural and health impacts of contaminated floodwaters on building materials and assemblies, FEMA Building Science is also undertaking a laboratory research task. The task sets out to develop a standard contaminated floodwater for use in evaluation and to evaluate the physical and environmental impacts of that floodwater on building materials and assemblies.

Lake Brownwood is a 7,300-acre reservoir located in the center of Texas, created by a dam on the Pecan Bayou, a tributary of the Colorado River. The shoreline of the lake and its three islands consists of approximately 90 miles of recreational waterfront property with nearly 1,000 floating dock structures. The dock structures at Lake Brownwood are similar in construction to those found at many lakes throughout the United States. This paper will discuss structural forensic investigations of twenty-two floating dock structures damaged by straight-line winds that occurred on May 8, 2009. Over half of the recreational dock structures on Lake Brownwood were damaged during this severe weather event. The primary focus of the case study will be the anchorage systems employed by the dock structures and an evaluation of their effectiveness in resisting dynamic wind and wave conditions associated with open-water exposure of large lakes. This paper will address common deficiencies of the observed anchorage systems, propose reinforcement of existing systems, and present a new paradigm for anchorage systems to improve the performance of future floating dock structures.

A commonly used standard to quantify finished quality of elevated and slabon- ground slabs is the ASTM Standard E1155. The procedure outlines the method of profiling concrete to determine the flatness (FF) and levelness (FL) of the concrete finish. This method is generally considered an improvement over the "straight-edge" method and has been adopted by the American Concrete Institute as the default method to determine concrete finish quality. Although the standard has been used successfully for many years by owners, general contractors, and concrete subcontractors, problems can arise if the standard is interpreted incorrectly. Data gathered from this standard is often used, or misused, to evaluate issues unrelated to finishing, such as lack of camber of steel beams, or deflection of elevated floors after concrete is placed. To further complicate issues, the technical basis for the method is not referenced in the standard and is very difficult to find, which can leave flatness and levelness readings open to various (mis-) interpretations. This paper begins with a presentation of the fundamental concepts of the FF and FL system. Also, with the help of case-studies and analytical simulation, this paper demonstrates that the length of a sampled profile has an effect on the FF and FL numbers. In addition, this paper demonstrates the problems associated with using widely spaced topographic survey points to determine the flatness and levelness of completed floor slabs, a common mistake used to determine floor surface quality "after-the-fact".

A commonly accepted standard to quantify finished quality of elevated and slab-on-ground slabs is the ASTM Standard, ASTM E1155. The procedure outlines the method of profiling finished concrete to determine the flatness (FF) and levelness (FL) of the concrete finish; this method is thought of as an improvement to the "straight-edge" method and has been adopted by the American Concrete Institute (ACI, 2004) as the default measurement system for concrete finish quality. Data gathered from this standard is often used in the forensics arena to determine the root cause of finish quality issues, such as using the profiles to determine the lack of initial camber of steel beams. Although the standard is very thorough and has been used successfully for many years by owners, general contractors, and concrete subcontractors, problems arise when the standard is interpreted incorrectly and the owner is left with no guidance on the quality of the sampled data or the quality of the finished surface. This paper will explore one of the major issues in the current standard: What to do when the number of samples does not meet the required minimum number of samples. The intent and meaning of the number of sample points is not clearly defined in the standard and has been commonly misinterpreted for years, without any changes to the standard. This leaves the owner questioning the validity of the data. In a statistical conceptualization, flatness can be regarded as a characteristic (parameter) of the constructed floor, defined as the FF value one would obtain with complete measurement of the floor (infinite sampling). For any calculated FF value, regardless of sample size, hypothesis tests—or, equivalently, confidence intervals— can be constructed to determine whether the constructed floor possesses the specified flatness with a high degree of confidence. Results from simulated floor profiles adapted from a case studies show that sampling at levels below the minimum requirements established in the ASTM standard may nonetheless provide sufficient information to reliably judge the flatness of constructed floors.

Carpet tack strips offer an excellent tool to interpret the occurrence and duration of a water loss. Water losses are among the most common claims in the United States. When a water loss occurs in a carpeted home, the carpet tack strips offer a precise method to evaluate the duration of the event based on various characteristics of staining and deterioration. Research studies compared the sequential changes that occur when carpet tack strips are exposed to continuous moisture for one week periods of wetting and drying over a period in excess of 2 years. Research using carpet tack strips exposed to continuous and cyclical wet-dry periods of moisture exposure revealed visual and microbial clues that prove effective in differentiating the duration of a loss and whether the loss originated from a single or repeated event. Forensic engineers and scientists will discover that a carpet tack survey will expose the water release history of a structure and guide them to more accurate and defensible evaluations of a water damage claim.

This paper presents an in situ and laboratory investigation conducted to diagnose unsatisfactory performance of new engineered wood flooring installed in an existing building. Shortly after installation, areas of flooring began to exhibit uplift and bowing (warp). Warp was more pronounced during the winter months, when indoor relative humidity was significantly below the flooring manufacturer's stated minimum. In addition to the correlation between low humidity and warp, other possible contributing factors were also considered; these included materials, construction of the finished product, installation, and end-use conditions. The investigation included detailed documentation of floor condition, building modifications, history of reported flooring defects, and apartment occupancy; plus laboratory environmental testing. An environmental test chamber was used to expose new flooring to a range of relative humidity regimes, including the full range permitted by the flooring manufacturer (35% to 65% RH), and the lower range experienced during the winter months (as low as 15% RH). Testing and analysis confirmed that the flooring performs satisfactorily within the allowable humidity range, and that poor performance at lower relative humidity was attributable to construction layup of the flooring product, the method of installation, and the building environmental conditions.

Ceramic floor tile systems can provide a durable finish; however, if internal stresses are allowed to accumulate in the tile system, fractured, buckled, and/or hollow-sounding tiles may develop. Using case studies of residential structures, this paper will discuss common perils that cause damage to ceramic floor tile systems and how these perils can be avoided through proper installation and maintenance. Testing and installation standards developed by the tile industry are used to discuss methods of site testing and evaluation of data. This paper was developed using quantitative and qualitative analyses of ceramic floor tile systems installed within multiple residential structures. The analyses indicate that failure of ceramic floor tile systems is often caused or exacerbated by installation methods that deviate from published standards. It is evident that increased awareness of accepted installation standards is essential to the service life of ceramic floor tile systems.

Many challenges confront owners, engineers, and contractors that elect to construct mechanically stabilized earth (MSE) retaining walls today. Owners select sites with difficult topography and less-than-ideal soils. Water-bearing utilities, natural water sources, or irrigated landscaped areas are located in close proximity to walls. A variety of MSE wall facings and reinforcing products are available, with different materials, geometry, connections, strengths, and behavior. Based on lessons learned from various failure investigations, the authors discuss frequent contributors to failures and common pitfalls in design and construction of MSE walls. With this knowledge, owners, designers, and investigators can more effectively focus their resources during design, investigation, and repair. Going forward, the authors suggest improvements to enhance design and construction practices of MSE walls.

The heave of underlying tunnel is considered as one of most important criterion to evaluate the stability and deformation of the new pit construction. Based on the superposition principle of corner point method and Boussinesq solution, the formulas of unloading stress at any depth below the pit are presented, in which the pit bottom plane is taken as the reference surface. The bending deformation of the tunnel and the rebound deformation of soil surrounding the tunnel are considered in these formulas. By combining the layer-rise summation method and Winkler's elastic foundation beam theory, the analytical solution is established to predict the tunnel heave. In addition, the formula modified by the time-space effect coefficient is applied to an engineering practice, and the results show that the modified fomrmula is reliable.

A building pad was certified for an allowable bearing pressure of 191.5 kilopascal (KPa). Subsequent to the pad certification, the site contractor had repeatedly driven across the building pad with heavy equipment. Due to this, the surficial soils in the building pad yielded in some of the areas. Subsequently, standard penetration test (SPT) test and laboratory unconfined compressive strength (UCS) tests were performed by others on the prepared pad and it was concluded that the bearing pressure should be significantly lowered to 71.8 KPa from 191.5 KPa. The UCS test used to estimate the shear strength of soils is the most common test in engineering practice. However, engineers often overlook one of the important soil parameters, the soil suction, which considerably affects the soil behavior. The increase in soil suction considerably increases the soil shear strength. A simplistic approach was adopted to measure the shear strength of partially saturated soils. A series of unconsolidated undrained (UU) tests were performed at different matric suction and by maintaining the same lateral confining pressure. Since the shear strength measured in the UU test reflects in-situ matric suction of the soil, an increase in matric suction significantly increased the undrained shear strength of a partially saturated soil. This in turn increased the bearing capacity of the soil and thereby the factor of safety. Based on the results from the test, it was concluded that the subsurface soils present at this site had adequate strength to support an allowable bearing pressure of 191.5 KPa. Further, it was also proved that the cause of pad rutting was not due to lower bearing capacity, but it was due to the trucks exerting 40% more load than the allowable bearing pressure of 191.5 KPa.

The long-short piles composite foundation, a new style of soft ground treatment during expressway embankment construction, possesses promising development prospects due to its reliability and economy. There is, however, no standard unified regulation about its design method in current Technical Code for Ground Treatment. Therefore, it is of paramount importance for engineering construction to study the load-bearing characteristics of the long-short piles composite foundation. Basing on the synergy that the long piles, short piles and soil mass are subject to the foundation deformation together in long-short piles composite foundation, this paper proposes a new method by introducing the concept of long piles synergy coefficient r and short piles synergy coefficient f. Employing this method, the load-settlement relational expressions for long-short piles composite foundation are deduced and the analytical formulas for complex modulus and pile-soil stress ratio of long-short piles composite foundation are derived. The in suit data measured by the history case from Lian-Hang part of Shen-Jia-Hu-Hang Express project, hence, were used to compare to the pile-soil stress ratio and complex modulus calculated by this method. The results highlights that, depending on the proposed method of r and f, values correspond well to the in situ values and meet the accuracy requirements in expressway embankment construction.

A heuristic approach was adopted to solve a time-dependent geothermal problem. Freezer floors in a cold storage were replaced due to frost heaving of subgrade soils. The failure of the previous heating system below the floor slab was attributed to the frost heave of subgrade soils. The heating system was fixed and the floor slab was replaced. Subsequent to the completion of the project, slab distress was soon noticed on the replaced slab. Several geotechnical investigations were performed (both prior to and after replacement of the slab) by others. Review of previous (pre slab replacement) geotechnical reports revealed that the incorrect estimation of thaw consolidation was the primary reason for the observed slab distress. A geothermal analysis was performed using TEMP/w to estimate the amount of time it would have taken by the frozen soil present at this site to thaw to the current condition. The settlement estimates from thaw-consolidation test and the time rate of settlement estimates from geothermal analysis correlated well with the observed slab settlement. In addition, it was also proved that the deformation (settlement) of frozen soils during thaw cycle is not completely reversible due to local soil consolidation caused by cryosuction forces.

In order to study the long-term deformation of Expanded Polystyrene (EPS) composite soil, i. e. creep behavior, a semi-empirical creep model was proposed. The elastic deformation was expressed by two Kelvin models and one Hook's spring which were connected in series, and the plastic deformation was described by two empirical models. Based on User Subroutines CREEP of finite element program ABAQUS, the proposed semi-empirical creep model was secondarily developed and was verified through triaxial undrained creep test. The results showed that the creep behavior of EPS composite soil could not be neglected and the secondarily developed semi-empirical creep model was reasonable and effective which can well reflect the creep behavior of EPS composite soil. The studies will provide powerful finite element approach to study the creep behavior of EPS composite soil in the future.

In the present study, the effect of sodium silicate stabilizers on the flowability and soil volume reduction are investigated. Two secondary additives are also admixed in order to assess their effects. Accordingly, a series of viscosity, shrinkage limit, and pH tests were performed to assess the effects of the mentioned cationic reagents as a suitable grout. It is observed that the sodium silicate grout has a viscosity higher than water and causes a very high soil volume reduction during the air curing. The reduction in the soil's volume was reduced significantly when secondary additives were used. The microstructure analysis performed to help understanding the reason of highly soil's volume reduction due to presence of sodium silicate reagent.

Recently the development of land reclamation in the eastern coastal areas of China has made a huge increase. It is estimated that the total area of reclamation will exceed 16 million acres in 2020. While the dredger fill is mostly hydraulic filled with super soft soil, it has high void radio as well as high moisture content. The soil is under-consolidated and with barely any structure strength. The improper foundation treatment would lead to large or uneven ground settlement, the failure of ground and some other serious consequences. It brings a great challenge to the foundation treatment and application. A modified multiple-vacuum preloading technique was proposed, which included the foundation treatments such as the floating bridge for construction detour on mud, the vacuum preloading with drainage pipes instead of sand cushion, and the optimized combination of vacuum preloading, surcharge preloading and electroosmosis method. The performance of super soft foundation under such method was tested in Wenzhou of China. The testing and theoretical analysis showed that the modified multiple-vacuum preloading technique overcame the deficiencies of the existing methods, shortened the construction period greatly, and met the design requirements effectively.

This paper presents an investigation conducted into the cause of collapse and the resulting subsidence and associated damage. The project is located in the East St. Louis area of Illinois. The study consisted of 3 subsurface investigations conducted into the old works over about a 30-year time period and numerous surface investigations. The old works are in the No. 6 Coal Seam in the Illinois Coal Basin, which is about 2 m thick, and were mined between the years 1900 to 1925. The depth of the old works is about 60m. At the project site there is up to about 50 m of soil overburden. Over the course of the 3-decade investigation period, extensive flooding of the abandoned workings was observed resulting in mine floor softening. Considering the softened floor condition, a bearing capacity of less than one was calculated and appears to be clearly the mode of failure. The paper discusses the floor stratigraphy and rock mechanics properties used in the analysis. The paper also discusses the resulting subsidence events and associated damage. As a result of the damage from one of the subsidence events, a state police headquarters building had to be razed. Also, the measured ground movements of the most recent subsidence are correlated with the rate of damage experienced by the recreational building. This structure exists in the tension zone of the sag subsidence and has consequently been subjected to hogging and tension related damage. The thick soil cover has significantly contributed to the draw zone width which has affected this building. In investigating the subsidence movements and the damage in this building, the measured ground displacements were quantified by angular distortion and compared to the damage over time.

The study on the stabilization of the dispersive soil has been quite intensive in the past two decades. Dispersive soils are highly susceptible to erosion and contain high percentage of exchangeable sodium ions. There are difficulties associated with reducing the dispersion potential of the dispersive soils. In the present research, changes in dispersivity potential and other properties of the dispersive soil samples were investigated. The reduction in the dispersivity potential was significantly changed upon the curing time and percentage of selected admixtures. The results clearly proved that adding pozzolan followed by curing reduces dispersivety potential of the samples. Furthermore, samples stabilized by pozzolan were found to have increased unconfined compressive strength (UCS), decreased plasticity index, decreased percent sodium, and increased electrical conductivity. The results indicate that the least dispersivity potential corresponds to the application of 5% pozzolan, and better results were obtained with increasing number of curing days. However the 90 days curing time was found to be the least amount required for the samples to achieve the non-dispersive status, that is, with dispersivity potential of less than 30 percent. In these tests, sodium cations may have been replaced by aluminum and calcium ions that have higher valences, causing a decrease in the thickness of the double layer. Consequently, the decrease in the thickness of the double layer causes a decrease in the repulsive forces between clay particles, resulting in a reduction of the dispersivity potential of soils.

Residential sinkhole-related claims have risen dramatically in Florida. Insurance companies are required to evaluate each case on a per-claim basis to determine if they are valid or if they are less than legitimate, as determined by the existence of sinkhole-related damages and/or by perceived damages as sometimes interpreted by misinformed homeowners and/or their representatives. Many sinkhole claims are initiated simply due to minor cosmetic issues, inappropriately categorized as damage from/or related to a sinkhole or sinkhole activity. In 2011, the Florida Legislature enacted revisions to the sinkhole statutes related to residential insurance contracts and property loss claims. Revisions and clarifications were deemed necessary due to the fact that sinkhole claims totals had risen so dramatically over the past decade. As technical consultants, professional engineers are often times asked to coordinate, manage, and investigate sinkhole claims for insurance companies, law offices and/or private individuals. Investigations typically follow the sinkhole investigation protocols set forth in the Florida Geological Survey (FGS), Special Publication No. 57 (SPN 57), "Geological and Geotechnical Investigation Procedures for Evaluation of the Causes of Subsidence Damage in Florida", (Schmidt, 2005, FGS SPN 57). The intent of this document is to educate the reader on sinkhole issues, on Florida sinkhole insurance intent, and to provide a discussion regarding the 2011 sinkhole statute revisions, their implications and their modified level of definition and clarity.

Wind erosion is a serious problem in arid and semiarid regions. Stability of earthen roadbed is seriously threatened because of droughts and easy wind erosion of roadbed filler in desert areas. So, evaluating the wind erosion resistance ability of roadbed filler is very important. Variation rate of shearing strength is regarded as the characterization of the wind erosion resistance ability for Aeolian sand soil roadbed filler through the field vane shear experiment. The results of the study show that the ability of roadbed filler to resist wind erosion increases gradually from the roadbed slope surface to its interior at a given height, and from the top to the base of the slope along the height. Based on the quantitative analysis of roadbed filler resistance to wind erosion, the stability of the wind-eroded desert roadbed has been simulated through the software ABAQUS. When wind erosion areas gradually expand from slope surface to roadbed interior and develop from the shoulder to the base of the slope, the slope stability is decreasing gradually.

The Church of San Giacomo at Spoleto, Italy, partially collapsed on November 23, 2010, during strengthening interventions. It was an ancient, unreinforced, masonry basilica that was completed in 1568 with the construction of two lateral aisles, an apse and a bell tower. The collapse involved the entire central aisle to the presbytery and the right lateral aisle. The author was appointed by the Judicial Authority to investigate causes and responsibilities of that structural collapse. This paper describes the collapse mechanism, the evidence emerged during site investigations and all phases of the investigation procedure. Graphical and photographical documents are reported and discussed to provide complete information on what happened and caused the accident.

A large Manitowoc crane mysteriously overturns while sitting idle for approximately 10 minutes after completing a lift. The boom falls on a nearby building, damaging property; but fortunately, no one is injured. Although the crane operator was accused of not operating the crane properly, a geotechnical engineer was called to analyze unusual occurrences that were noted prior to and immediately after the failure. Some factors in the tip-over were: (1) the crane was operating near an open excavation and (2) an underground waterline had ruptured a day or two before the crane was positioned for the lift. This paper explains how by considering various subsurface effects; it was possible to show that transient loss of soil strength resulted in a bearing capacity failure under the crane.

Compactness of the soil fill below the footing is an important criterion as it probes the chance of settlement of the structure. It is very difficult to estimate the degree of compactness of soil layer beneath the finished floor or footing using any conventional geotechnical testing as these testings are time consuming and random in nature. In this study an attempt has been made to investigate the homogeneity of the compaction quality of new soil fill below the finished floor slab using ground penetrating radar (GPR). This forensic investigation has been carried out to probe height and quality of compaction of soil layers below newly constructed industrial floor slab and machine foundation tilted and cracked site. The GPR survey has been carried out at identified three locations using ground coupled 500 MHz antennas capable of penetrating minimum depth of 6 m. Analysis of GPR radargram shows that electromagnetic wave characters and amplitude of wave traces are not uniform. Change in the wave characters are indicating heterogeneity in quality of compaction layers. Change in the wave amplitude in the same layer shows decrease in water content, which in turn reflects loose compaction. GPR results are compared with drilled borehole and measured soil strength in terms of standard penetration test (SPT) N values at distressed location.

Hurricane Irene made landfall as a sizeable Category I storm at the outer banks of North Carolina on August 27, 2011. Overland wind gusts associated with the storm measured nearly 115 MPH, and tide surge reached nearly 10 feet. The storm impacted numerous communities along the coast line and sounds, and it also damaged many communities and structures miles upstream in several larger river basins. This paper presents a summary of damages attributed to wind and storm surge for approximately 30 dwellings dispersed across eastern North Carolina. The analysis utilizes U.S. Geological Survey Storm Tide Mapper data and National Weather Service weather observations, both publically available, to develop storm tide and wind contours. The analysis categorizes and summarizes the structure types (e.g., foundations, framing, etc.) and ages, wind damage levels, and surge damage levels for each of the structures with respect to their wind and storm tide exposure. Lastly, the analysis compares wind and flood damages, where present, to the damage states or degrees of damage as outlined in the Enhanced Fujita Scale and the Wind and Flood Damage Scale for the corresponding structure types.

A low-rise, sloped-roof, steel storage building located on a canal between downtown New Orleans and Lake Pontchartrain experienced wall failures at two corners during Hurricane Katrina. At both locations the walls were blown outward. The insurance company asserted that the damage was caused by water, and not wind, and denied the claim. A modeling study was undertaken to investigate whether the strong winds could explain the damage. Because wind observations were not available at the height of the storm, the mesoscale meteorological model MM5 was used to estimate wind directions and peak wind speeds at the building. The Computational Fluid Dynamics (CFD) model FLUENT was applied to simulate wind fields and pressure forces on the storage building. The only two areas on the building walls with predicted strong outward pressures coincided exactly with the two areas of blowout damage. Calculations from structural engineers confirmed that these wind-induced pressure forces would have been sufficient to cause the observed damage. The study demonstrated the usefulness of CFD modeling in reproducing wind damage to structures during strong wind conditions.

Evaluating buildings to determine the causes of structural damage can be difficult under the best of circumstances. When buildings or other structures have been significantly or completely destroyed during a catastrophic natural event, such as a hurricane or tornado, the difficulty of this task increases exponentially. Failure modes and pre-existing conditions are largely concealed by the debris or by displacement of the debris during subsequent cleanup operations. These conditions were frequently encountered by forensic engineers and architects following Hurricane Katrina in 2005 and, more recently, the severe tornado outbreaks in the southeast in April of 2011. Determining pre-existing conditions and failure modes is critical to accurately evaluating the damages caused by a natural disaster. Such evaluations are vital to building owners and insurance companies alike. This paper presents several case studies from Mississippi and Alabama following Hurricane Katrina and the tornado activity in the spring of 2011. In these case studies, the authors will discuss clues found among the debris and areas surrounding the buildings that were used to identify causes of damages and conditions that existed prior to the event. In addition, the case studies will highlight the importance of using of sound engineering judgment and structural analyses in determining the causes of damages.

This paper presents the findings of an investigation of damage to a 12-story condominium building subjected to hurricane-force winds in south Florida during the passage of Hurricane Wilma. The building's structural system consists of reinforced concrete columns and flat slabs, with concrete masonry unit (CMU) infill walls at the building's perimeter. Most of the building's balconies were enclosed by aluminum-framed windows that were added subsequent to original construction. An investigation of hurricane damage to the building revealed that many of the sliding glass doors, including those protected by enclosed balconies, sustained damage either due to direct exposure to the extreme wind pressures after the windows were damaged and blown off, or due to buffeting of the balcony windows which transmitted vibrations through the balcony floor and ceiling slabs, which in turn subjected the sliding glass doors to wind-induced vibrations. This combined action coupled with the movement of the building during the hurricane compromised the enclosed sliding glass doors. The unreinforced concrete railing walls sustained damage in the form of cracking and spalled cement plaster due to direct exposure to the strong hurricane-force winds and the buffeting of the balcony windows to which the railing walls are attached. Wind pressures and movement of the building also caused separation cracks between the unreinforced CMU infill walls and the floor slabs. Structural engineering calculations showed that the wind speeds at the site during the hurricane were strong enough to cause the observed cracking in the unreinforced concrete railing walls and CMU infill walls. In addition to the obvious damage to the roof, doors and windows, this paper describes in detail the more subtle damages sustained by the building's structural and non-structural components and associated water damage.

On May 6, 2011, the Building Science Branch of the Federal Emergency Management Agency's Federal Insurance and Mitigation Administration deployed a Mitigation Assessment Team (MAT) to Alabama, Georgia, Mississippi, and Tennessee to assess the damage caused by an outbreak of tornadoes on April 25 through April 28, 2011. The MAT was then redeployed on June 1, 2011, to Missouri following the tornado on May 22 in Joplin. A report containing the MAT's observations, conclusions, and recommendations was published on the anniversary of the Joplin tornado on May 22, 2012. The MAT assessed residential (single- and multi-family) buildings, commercial buildings, critical facilities, infrastructure, tornado refuge areas, best available refuge areas, hardened areas, storm shelters, and safe rooms. The MAT also gathered information on the storms that spawned the tornadoes. This paper highlights the observations, conclusions and recommendations on building performance presented in FEMA P-908.

The results of a detailed damage investigation of the two tornadoes in Vaughan, Ontario, which were part of the 19 tornadoes in the outbreak of August 20, 2009, are presented. The bulk of the damage in both tornadoes consisted of structural roof failures categorized as F1 on the Fujita Scale and EF1 on the Enhanced Fujita Scale. However, multiple houses in both tornadoes suffered total roof failure, which is F2 (or EF2). It was observed that the total roof failures were all due to either internal pressurization and or weak (or non-existent) roof-to-wall connections. Since internal pressures are likely to be larger than external pressures for these single family residences, it is argued that the total roof failure occurred under wind speed conditions associated with a lower degree of damage, such that actual wind speeds are like those in EF1 in these particular tornadoes.

Years of continued investigation across several wind regions of the United States have provided a firsthand look at the performance of structures exposed to strong life-threatening wind events within tornado prone regions, including the area referred to as "Tornado Alley". Currently, there are no provisions in the design codes to address winds speeds in tornado prone areas; yet, recent events illustrate a need for some level of attention. Investigations and subsequent analysis of failure mechanisms of existing code compliant structures from life threatening strong wind events require development of adequate structural code recommendations. Through proper analysis, detailing, and strict implementation utilizing the knowledge of the maximum wind loads for specific strong wind event regions, it is possible to economically design the load path for a safe structural performance, providing protection for the inhabitants of structures as well as minimize damage to buildings. This study is intended to bring awareness of the life safety issues and economic impact resulting from actual documented deficiencies of in-service structures that were generally code compliant when they were constructed, but failed when exposed to the relatively common regional strong winds that were typically greater than code prescribed wind loading.

With residential homes serving as an integral indicator to ascertain storm wind speeds from their damage, an accurate wind speed-damage relationship needs to be established. Recent wind tunnel tests have suggested that well-attached building components can fail without flying from the roof. For complete failure of roofs, this suggests that we need to differentiate between failure of the structure and removal of the roof (i.e., flight) from the walls. This research serves to determine and differentiate representative wind speeds for both failure and flight of wood-framed roofs. In most test results to date, "chatter" and displacement of the roof mostly preceded flight of the roof structure, indicating that flight might follow from a different gust. The local flow field is influenced by the presence of the structure, leading to the conclusion that a both a spatially and temporally averaged wind speed, while difficult to ascertain due to the complex nature of the fluid interactions, is required to accurately describe failure of a structure or its components.

The maintenance and inspection of high-rise building façades and roof structures with panelized cladding may span over the course of many years and produce large quantities of information. Organizing what often contains decades of historical records for repairs and inspections alongside newly acquired data can become difficult and overwhelming. Recent changes in the building codes mandate more frequent and comprehensive inspections, pointing to an exponential increase in the amount of data to be managed. Incorporating a Forensic Information Model (FIM) can aid in the organization and representation of inspection data. FIMs are quickly becoming the state-of-the-art for presenting data associated with forensic investigations. Traditionally, FIM has been used for litigation and Building Information Modeling (BIM) software to tie a 3D model of a structure to results gained from analysis models and damage assessments. For façade and cladding investigations, FIM connects the 3D surface geometry to a back-end database of supporting documentation by way of a strict naming scheme. The result is a dynamic representational tool, which serves to highlight both geographical and chronological patterns in inspection or repair data. The database remains open-ended and customizable, making it applicable to a wide variety of projects. In addition, FIM can interactively communicate the investigation results to other involved parties in a uniquely visual way, thereby acting as a useful deliverable product. In this paper, we outline a flexible method for the management and presentation of façade investigation data. We present three case studies to illustrate the application of the method to a diverse range of projects.

It is essential that, when problems arise with structures, the facts are established by rigorous investigation, are fully published and clearly summarized and disseminated within organizations. For more important cases relating to safety, wider dissemination through publication and revised standards is appropriate. Initial press reports speculate, often wildly, and the myths created persist even when a full report is published. Full balanced published reports based on rigorous impartial investigations are rare. The complexities of reality revealed rapidly become oversimplified and distorted, often influenced by spin from interested parties. Then the lessons, which too seldom spread internationally, fade from the collective engineering memory, until the next time. This paper is based on the author's 45 years experience of the investigation of failures and his detailed reviews of published failure reports. In many instances the lessons from these investigations have led to changes in national and international design and construction practice. They have also been incorporated in the teaching of engineering design

The possibility of local structural failure to propagate into global collapse of the structural system has fueled the continued development of improved computational methods to model building behavior, as well as "best practices" engineering standards. In spite of these efforts, recent events are bringing the issue of collapse mitigation to the forefront and highlighting the shortcomings of existing design practices. The catastrophic nature of structural collapse dictates the need for more reliable methodologies to quantify the likelihood of structural failures and strategies to minimize potential consequences. This paper presents the results of a stochastic nonlinear dynamic analysis study of a simple structural model to predict catastrophic failure. The performed analysis indicates that, at the point of incipient failure, uncertainties associated with the analysis become increasingly large. Consequently, it is not be possible to accurately predict when (and if) failure may occur. Recognizing the need to understand uncertainties associated with risk and occurrence of low-probability- high-consequence events, this paper sets the stage to better understand the limitations of current numerical analysis methods and discuss innovative alternatives.

This paper discusses a proposal for a federally incentivized national "Strengthen America" program in order to prevent failures of buildings and reduce the loss of life, injuries and economic costs incurred from these failures. The paper presents the increasing number of federal emergency disaster declarations and their effect on the economy. In addition, the paper discusses the economic activity created by the program and how it could be structured similarly to the Energy Act of 1978 that established tax credits for energy conservation. The paper will also present the need for participation by private insurance companies to mitigate damage from natural or human caused disasters.

Imminent collapse due to wood decay has become an issue where large sums of money are expended to prevent imminent collapse where a structure's strength has been marginally reduced. Typically, collapses occur when a structure can no longer support imposed loads. The causes of actual collapses are normally easy to identify due to the combination of a weakened structure or element of the structure with a significant event such as a natural hazard (snow, wind, earthquake, etc.) exceeding the capacity of the structure, or a man-made hazard (improper use, construction activity, alteration). However, an imminent collapse when the structure is still standing and occupied can result in extensive studies in order to determine the extent of impairment. This paper presents a discussion of imminent collapse and substantial impairment.

The rate of decay in buildings, particularly of wood components and wood-based materials, is an issue that has become an area of focus in the construction and engineering industries, where estimating building performance and service life is becoming standard practice during construction litigation. While this may be a worthy goal, the technical data to allow for determining a specific time when wood decay began and to make statements about the rate of decay to a reasonable degree of scientific certainty generally do not yet exist. There are two primary means by which the rate of wood decay has been investigated: one is through experimental research such as in-ground stake tests, soil block tests, and wood exposure tests on various wood components and wood-based products. The second approach is through the development of service life prediction models. These models are based on data from experimental research, climate indicies, and other factors deemed to be significant in decay processes. The factors are used to make assumptions about the propensity of a certain wood component, configuration, species, or wood-based product to deteriorate over time. The focus of this paper is to present basic considerations when attempting to establish the rate of decay of wood and wood products used in construction.

Cracked, bulged, and displaced building facades are obvious indications that something is wrong and that repair, or at least an investigation, is needed. However, facades with no signs of failure may still be degraded or detached to the point of instability. Facade failures that are concealed from view are more concerning than those that are readily detectable from visual observations. Underlying facade deficiencies that rise to the level of life safety hazards can be difficult to detect from visual observations. However, certain characteristics or conditions of the facade may help us foresee hidden or potential facade failures. For example, a facade system with inadequate support redundancy, complicated connection details, or internal weak planes may be more vulnerable. Wall systems usually have hidden facade supports and internal flashings or moisture barriers that can be damaged or deteriorated without outwardly visible signs. The resulting failures may be dramatic, such as collapse of the facade, or subtle, such as water leakage. This paper does not offer a formula for identifying hidden failures, but instead provides insight to help recognize vulnerable characteristics that could result in latent building facade failures.

Every day structures are damaged and structural engineers are required to design repairs. When designing repairs, many engineers are unclear on how far to extend repairs into undamaged areas of the structure. Modern building codes provide direction on this. However, code requirements are somewhat ambiguous and can trigger significant costs. As such, it is important to have a good understanding of the code provisions and their intent. With a focus on how far repairs have to extend into undamaged areas of the structure, this paper presents a brief history of the building code as it pertains to repair of damaged buildings, and explains the current code provisions. Potential dilemmas created by the code are discussed along with possible solutions. Additionally, this paper examines a case study which highlights the drastic expenses a building owner or insurer can incur due to the most recent code changes.

The "standard of care" can be thought of as the boundary between negligence and non-negligence as defined by case law. This paper presents a brief, general description of the standard of care and discusses standardized jury instructions derived from case law defining the level of learning, care and skill a professional should apply, the degree of diligence and the quality of judgment the professional should bring to bear, and other duties the professional should fulfill to meet the standard of care. The paper examines and evaluates two specific standardized jury instructions concerning the duty of a professional.

This paper deals with Forensic Engineering (FE) practice in the field of Contract Management with special emphasis on infrastructure construction. The following failure case studies are discussed along with their contractual and post-contractual analyses: (1) FE applied in the judicial phase during contract performance and prior to possible contract resolution; (2) FE applied in the judicial phase after contract resolution or conclusion, aimed at reaching a transaction before the judge's decision; and (3) FE applied in the judicial phase after contract resolution or conclusion, aimed at clarifying unexpected technical issues of the contract to the judge and supporting his/her decision. It is shown that forensic investigations played a key role in all case studies, by reducing costs and ensuring benefits for both the construction companies and their clients.

Testifying experts have, on occasion, been known to invent tests or theories, or to stray from generally-accepted methods, to support their opinions. Since juries are composed of non-expert lay people, these newly invented tests and theories may have an aura of undeserved scientific validity. Provisions that exist in the law for challenging such work are intended to be used to shield juries from pseudoscientific or "junk-science" opinions and tests that have no proven basis in scientific theory or practice. Although rare, these challenges can be used to disqualify such pseudoscientific evidence so that it never sees the inside of a jury room. Specifics regarding how various experts have misapplied or strayed from published and commonly accepted principles and techniques to arrive at scientifically unjustifiable conclusions, and challenges to those techniques and conclusions in the course of litigation are provided. The court that heard the challenges concurred that these techniques and conclusions lacked sufficient scientific basis to be admitted as evidence and barred related testimony from being presented in the courtroom, dealing a devastating blow to the credibility of these experts and to the plausibility of their client's case. Adding insult to injury, not only was the testimony of these experts barred by the courts, but their client was eventually required to refund millions of dollars in opposing experts' fees. Experts reading this paper should consider themselves duly warned that "making it up" and using pseudoscientific techniques or tests can result in more than appearing foolish on the witness stand; you can actually hurt your client far more than might seem possible.

As professional engineers, we are required to uphold high ethical standards. These standards are imposed by national engineering organizations, state licensing boards, as well as various industry organizations to which we may belong. Serving as an effective expert witness requires a heightened awareness of professional ethics. The work of an expert witness is regularly scrutinized by professional colleagues and attorneys. Unfortunately, the desires of a client can sometimes influence an expert to take a position that is not founded upon established scientific, engineering, and/or industry standards. Depending on the position taken, the expert may violate professional ethics standards. This paper will provide background information followed by a discussion of the primary elements of a typical construction litigation case. The paper will present examples of potential ethical violations of expert witnesses. Specifically, this paper will discuss: 1) the first contact with a potential client; 2) performing and interpreting a conflict check; 3) document review; 4) performing an investigation; 5) preparing a written report; 6) preparing a repair scope; and, 7) providing expert testimony. Additionally, the paper will offer simple steps that can be taken by Professional Engineers to avoid violating professional ethics standards.

IABSE's Working Group 8, Forensic Structural Engineering, aims to examine and mitigate failures, improve the international professional practice of forensic structural engineering and to facilitate the application of failure information to design and construction. This paper gives a brief overview of the Working Group's first project: a survey of the forensic practices in the US and a limited number of European countries. A preliminary conclusion is that the forensic practices in the USA, followed by the UK, are more organized and structured than in the other countries of Europe that have been reviewed: France, Hungary, The Netherlands and Switzerland. The centralized registration and analysis of failures in France (Sycodes), the efforts in The Netherlands (ABCMeldpunt), and the UK (CROSS) with the accompanying initiatives to improve safety (e.g., Platform structural safety and SCOSS) are commendable, and other countries should consider following these initiatives in learning from failures.

An ongoing activity of the Committee on Education of the ASCE Technical Council on Forensic Engineering is the development of workshops for civil engineering faculty. The workshops are aimed at integrating lessons from failure case histories into undergraduate and graduate university education. These workshops have been successfully presented at seven locations throughout the United States to more than 100 college and university professors. The workshops encourage the use of forensic case histories in existing courses by providing easily adapted case modules, visual aids, and proven teaching strategies. Recently, the project has been extended to the international arena, with presentations in the UK, China, India, and Latin America. This paper reviews the background, intent, and content of the forensic engineering education workshops, with a focus on the international activities. Included are specific comments regarding the Latin American experiences in Costa Rica and Ecuador.

The first Indo-US Forensic Engineering Workshop (INDUSFEW) was successfully completed (December 15 - 17, 2010) at the National Institute of Technology at Tiruchirapalli (NITT), Tamil Nadu, India. Organized jointly by members of the ASCE Technical Council on Forensic Engineering (TCFE), the University of North Carolina at Charlotte (UNCC), and NITT, the Workshop included 23 technical presentations by both U. S. and Indian forensic experts including several speakers from the Structural Engineering Research Center (SERC), Chennai. The Workshop signified the international collaboration between India and U.S. in the area of Forensic Engineering. The specific outcome of the INDUSFEW workshop is the establishment of a forensic engineering curriculum and the proposal for the Center of Excellence for Failure Analysis (CEFA) at the NITT. This paper reports on the specific outcomes from the Workshop and the progress of the CEFA development.

A great interest in Forensic Engineering (FE) has been recognized in Italy and the rest of Continental Europe in the last decade. Amongst individual activities, such as short courses and lectures, the author is promoting FE by means of three primary activities: a post-graduate FE course at University of Naples Federico II, Italy; IF CRASC congress series including topics of both FE and collapses, reliability and strengthening of structures; and the institution of the Italian Association of Forensic Engineering (AIF). In this paper, the author describes all these activities with special emphasis to AIF of which he is founder and president. The main scope of AIF is to disseminate FE throughout Italy. To this end, an accurate selection and classification of AIF members is carried out through documentation analysis and its quantification based on training credits, as in the case of university courses.

Cracks in structures are often the source of litigation claiming some nearby atypical event, like heavy construction or an earthquake, caused the cracking. Current methods of determining crack age are subjective and limited in their scope. This body of research proposes to use accumulated biomass to evaluate the age of these cracks. A common bacterium, Pseudomonas putida was used to colonize various construction material surfaces to verify visualization using confocal laser scanning microscopy and quantification methods of sparse biofilms, developed with glass and mortar in previous work, for the purpose of crack dating.

This article presents use of radiographic imaging (X-Ray) in evaluation of existing reinforcing steel configuration of structures and development of steel retrofit and carbon fiber reinforced polymer (CFRP) repairs. A collapse of the driving surface in a precast concrete parking deck prompted an engineering evaluation and survey of the whole deck for damage assessment and repairs to distressed members. Distress was identified in decking members and perimeter spandrel beams. Repairs to the decking members involved supporting the distressed decking using supplemental steel brackets installed through the double-tee stems containing pre-stressing tendons. The precise location of the tendons in the stems needed to be identified to implement this repair in order not to damage the tendons during drilling. Radiographic X-ray imaging in this application enabled locating and avoiding the tendons in the stems to support and strengthen the decking member. The supplemental steel bracket also enabled continued operation of an existing expansion joint in the area of repair. The same technique was also used to identify steel reinforcement configuration in the spandrel beams exhibiting cracking at bearing locations for evaluation of existing steel configuration and implementation of CFRP repairs .

The FEMA Urban Search and Rescue (US&R) Structures Subgroup has developed standards for vertical shoring systems for temporary stabilization of damaged structures. While these shoring systems have been previously tested under vertical loading, the effects of combined vertical and lateral loading had not been investigated. A test program including two different types of vertical shoring systems was conducted at the University of Texas at Austin. The test program consisted of nine vertical shores under different combinations of vertical and lateral loading. The test results demonstrated the reduction of the vertical load capacity when lateral displacements were imposed on the shores. Nevertheless, the vertical load capacity of the shores was about twice the design working load at medium levels of lateral displacements. Furthermore, the shores were constructed with "boxed-heart" Southern Yellow Pine lumber, which has been generally considered not optimal for shoring applications. The tests demonstrated that the vertical load capacity of the shores was adequate and comparable to that of previously tested Douglas Fir lumber.

The aging and disengaging phenomenon of the elastic asphalt cushion between the isolated type cushion spiral case and its external reinforced concrete, which may lead to many serious hidden troubles, are very common. Based on the numerical analysis results of the stress characteristics of the spiral case structure of a 55-year old hydropower station, the effect of flexible filling materials on the structure was analysed, and a kind of bi-component, self-leveling and high-durability sealant (Hydraulic Structure Disengaging Filling Special Sealant) and a construction technology of filling and repairing the spiral case disengaging were developed. By comparing the geological radar method, impact-echo method, neutron detecting method and manual hammer knock method; the authors explored an appropriate detection technology of spiral case disengaging of the turbine. The study achievements have been applied to the repairing project of spiral case disengaging of the 1# turbine in the Xin'an River Hydropower Station, and achieved excellent effects.

There was no question that hail had damaged the copper roof of the only Dallas residential structure designed by the well-known architect, Frank Lloyd Wright. What began as a hail damage assessment on a historic house escalated to egregious claims that water intrusion and associated corrosion, wood rot and mold were the result of a single hail event that occurred in 2003. The author presents a case study that outlines the facts of the case including basic hail damage theory, the claims by the property owner, and completes with impeaching testimony provided at deposition and trial. A key trial exhibit is presented that illustrates that the information and assessment provided by the expert witness author was instrumental in revealing that the majority of the claimed damage existed prior to the hail event and developed due to long-term water intrusion.

This paper summarizes the types of damage that single-family dwellings experience under different hazard conditions. Available information on the performance of wood-frame, steel stud, structural insulated panel, concrete masonry unit, autoclaved aerated concrete, insulated concrete form, and adobe wall systems in natural disasters and fire is presented to develop an understanding of the damageability of the chosen wall systems. Lessons learned with regard to the vulnerability of damage due to high wind loads resulting from hurricane and tornado as well as missile impact, earthquake induced building deformations, flood water effects, and fire related effects are discussed. At the end, the paper summarizes the appropriateness of different wall systems for single-family dwellings in a simple rating form if the building is expected to experience any of the natural disasters or hazards discussed.

Cabinet damage following a water loss constituent is one of the most common and expensive property losses. This experiment compared the gradual changes that occur when vinyl-faced cabinets are exposed to a water source (i.e., a supply leak) and to a water source containing detergent (i.e., sink drain leak). The principal distinction between these two sources and the physical response observed in the cabinets was the difference in surface tension or penetrability exhibited by the detergent solution as compared to water alone. Two studieswere conducted using identical cabinets. Each study gradually discharged 200 millilters (mls) of either water or a detergent solution using a drip method onto the cabinet base over a period of several hours each day for an extended period of time (months). Temperature and relative humidity conditions were held under stable conditions. The test results showed a distinct difference between the response of cabinet bases to water and to the detergent solution. When water was discharged onto the cabinet base, it flowed to the nearest wall via gravity, swelled the exposed particle board joint until additional water releases began to flow elsewhere. The resulting affect was to create a "bowl like" appearance with the peripheral edges swollen and the cabinet center holding free water. The center of the cabinet base declined 33 millimeters (mm) but did not fall down following 152 days of continuous moisture. The discharge of the detergent solution onto the cabinet base over a period of 137 days caused a lesser decline (9 mm) in the cabinet base. The addition of surfactant allowed the water to penetrate into the vinyl-faced particle board base and prevented both the accumulation of free water and the formation of a "bowl-like" appearance. The study results allow the forensic engineer/scientist to distinguish whether the water source originated from a sink drain or the water supply and aid in the evaluation of duration of loss by taking measurements of the cabinet base drop.

On the evening of August 13, 2011 the Temporary Ground-Supported Structure Used to Cover the Stage Area and Support Equipment in the Production of Outdoor Entertainment Events located over the Grandstand Stage at the Indiana State Fair (the ISF Structure) collapsed while the audience was waiting for the headline act to begin. The incident resulted in the death of seven individuals and a multitude of serious injuries. At the request of the State of Indiana and the Indiana State Fair Commission, Thornton Tomasetti mobilized to perform a multi-faceted, highly detailed cause and origin investigation of the failure. The resulting investigation included the documentation, measurement and cataloging of thousands of components from the aluminum truss roof system and related suspended entertainment technology equipment, detailed site measurements, laser scanning, wind tunnel analysis, materials testing and analysis. Moreover, the study required the development of an as-built nonlinear finite element model based on field data and utilized site data to validate the analysis results and evaluate comparisons to the expected code-prescribed performance.

Improved structural robustness is expected for steel gravity load-resisting frames with double-angle shear connections as compared to single-plate connections, given the larger deformation capacity of the double angle. Detailed models of bolted double-angle beam-column connections have been developed for the purpose of evaluating the structural robustness, or resistance to disproportionate collapse, of steel gravity frames. The detailed models have been validated through comparison with available experimental data. Modeling of double-angle connections requires considerations not needed for single-plate connections, such as a reduced ductility in the "k-area" of the angle. Detailed models of two-bay gravity frames were analyzed under "push-down" loading to simulate a column loss scenario. Results for frames with bolted double-angle and single-plate connections show that the larger deformation capacity of the double-angle connection enables larger vertical loads to be sustained with correspondingly larger connection rotations.

The Roosevelt Island Tramway, constructed in the early 1970s, was the first Tramway built for routine commuter use in the United States. As it approached 35 years of continuous service, the Tramway's owner commissioned various engineering studies to define and evaluate the potential options for upgrading and modernizing the system. Thornton Tomasetti performed one of the studies, which focused on a multi-disciplinary condition evaluation of the Tramway's two stations and three steel support towers. That study concluded that, overall, the primary structural members of the Tramway system were in adequate condition and could remain in service with appropriate maintenance for the foreseeable future. The subsequent Tramway modernization project, however, included replacement of the Tramway's mechanical and electrical systems and Tram cars, with a new system that has significantly different structural loadings than the original. Because the project's budget and schedule did not allow for wholesale replacement of the existing support towers and stations, a detailed structural analysis was needed to evaluate how the new structural requirements could be accommodated, while minimizing structural alterations and reinforcement to the existing towers and stations. This paper focuses on the engineering team's solutions to the various engineering challenges faced in analyzing and designing the upgrade for the 35 plus year old structures to meet the new system's requirements.

This paper presented a study on the behavior of Carbon-fiber-reinforced-polymer (CFRP) strengthened steel beam specimens with square hollow section (SHS) under torsion. A set of tests on CFRP strengthened steel specimens under torsion was carried out in which several different strengthening configurations were used. CFRP sheet wrapping consisted of different configurations including vertical, spiral, and reverse-spiral wrapping were used. The results showed that using CFRP could improve the elastic and plastic torsional strength of CFRP strengthened steel beam specimens. The number of layers of CFRP and the strengthening configurations were important factors for the improvement. The failure modes and the amount of increase in the yield and ultimate torque for different strengthening configuration monitored and were presented in this paper. The results obtained can be useful in the design of the CFRP strengthened steel members under torsion.

Proprietary, modular steel space frame structures, commonly consisting of ball nodes and tubular members, are widely used in construction as an efficient method for supporting or covering long-span openings. Typical applications include support for roofs, atrium coverings, pedestrian bridges, and solar panel clusters. The subject space frame was located at the roof level of a four-story office building in a southwest U.S. desert. The space frame was covering a 120-foot by 120-foot triangular opening over an interior courtyard. The space frame consisted of ball nodes, steel tubular members, and steel panels attached to the tubes to provide shade. One morning in April 2011, after approximately 30 years of service, the building staff observed and heard the space frame fail along one edge of the frame. The redundant structure did not collapse, but suffered two complete bolt fractures, a number of weld fractures, buckled tubes, and exhibited large displacements. Emergency shoring and scaffolding was installed, and a visual inspection of all elements, nodes, and supports was performed. The space frame was analyzed using SAP2000 under in-service gravity and thermal loads. Fractography of the failed bolts revealed that the connections of boundary members to the supports experienced fracture due to fatigue. In parallel, the analyses results showed that the boundary constraints and panel configuration contributed significantly to the amount of axial load and bending stress imparted on the bolts and boundary members. The results of this case study highlight the consequences of insufficient consideration of thermal loading.

Structural steel is known to have a finite fatigue lifespan. This paper briefly discusses the concept of fatigue in steel structures and investigates the contribution of this phenomenon to the connection damage observed in steel moment frames after the Northridge Earthquake. A comprehensive fatigue analysis procedure is developed based on the Palmgren-Miner method and the S-N curves established for the high-cycle fatigue range are extended to the low-cycle region using the limited test results that are available. An analytical case study on a ten-story steel moment frame building is carried out and fatigue analysis is performed at critical locations of a representative moment frame using the established procedure. Finally, the pattern of cumulative fatigue at critical connections and the observed damage are compared. Results of this analytical study indicate that the effect of low-cycle fatigue may be significant in evaluating and predicting various types of connection damage similar to those observed in steel moment frames following the Northridge Earthquake.

Light gage steel framing, also known as cold-formed steel framing, continues to replace wood framing for low-rise commercial and multi-family residential use. It is used in load-bearing walls, non-load-bearing walls, curtain wall framing, and floor and roof construction. It has certain advantages over wood framing for some applications.

This paper addresses the concern that the current provisions in the code, on buckling and lateral bracing of steel moment frames, allows significant uncontrolled member distortions to occur, due to seismic events, which could lead to poor performance. The paper includes historical considerations on buckling and lateral bracing pertinent to the understanding of buckling and lateral bracing issues, relating to steel moment frames. Considerations and recommendations are given relating to the control of buckling. The paper also provides recommended alternative simplified procedures to evaluate lateral bracing of moment frame girders based upon the principles of mechanics.

An issue that sometimes arises and seems to produce varying responses from engineers is how to address the continued use of structures that have exhibited post-tensioning (PT) strand distress. That is, at what level of distress are repairs needed, and if they are, should the structure remain in operation until the repairs are implemented. On a number of recent projects, the authors have experienced engineers recommending immediate closure of PT two-way slab structures after discovery of distressed post-tensioning strands. In the authors' experience, reinforcement corrosion or other distress in mild steel reinforced slabs rarely elicit the same reaction, indicating that the tolerance for mild steel distress is significantly greater than that for PT distress. The assumption is, apparently, there is less reserve capacity and ductility in PT slabs relative to mild steel slabs. In addition, concerns are often expressed that the abrupt release of strain energy in a failed PT strand will result in sudden discharge of the strand and/or a corresponding sudden spalling of concrete presenting a life-safety hazard. This paper examines these safety concerns and presents findings related to evaluations of the expected reserve capacity of typical two-way PT slabs. Additionally, guidance to engineers for initial evaluation of a distressed PT system with due consideration to the relative risks is provided.

This article discusses the use of non-destructive and subsequent laboratory materials testing techniques in evaluation of extent of fire damage to a precast pre-stressed parking structure. The non-destructive and laboratory testing findings were used in determination of extent of heat damage to concrete and potential effects on the pre-stressing tendons. The in-situ non-destructive testing phase consisted of locating affected areas using ultrasonic pulse velocity through concrete members in the vicinity of the fire. Subsequently cores were removed and Young's Modulus of 25mm (1 inch) thick concrete disks was determined by utilizing non-destructive measurement of resonant frequency. Determination of Young's Modulus at small depth increments permitted assessment of the heat induced damage front into the concrete and more importantly at the level of the pre-stressing tendons. Based on the extent of damage identified, repairs were performed on the affected members.

Scientific crack dating can play a critical role in any litigation associated with claims from property owners alleging damage due to nearby construction or quarry activities or recent natural disaster events like earthquakes. This paper discusses the influence of surface treatments on the carbonation rates of fly ash concrete (0%, 25% and 50%) for the purpose of evaluating carbonation depths to determine the age of cracks within cementitious materials. Carbonation, a neutralizing reaction within the paste matrix, reduces the pH of cementitious materials from over 14 to less than 9. This reaction is a time-dependent process, which can be measured through various surfaces of both known and unknown age, then compared to determine a relative age and narrow down an absolute age so that such damage can be better linked to causation.

An engineering assessment was performed for a load-bearing, reinforced concrete basement wall upon discovery that multiple truckloads contained concrete with substantially low-strength concrete. In-situ testing of the wall consisted of Windsor Probes for initial in-place estimation of strength as well as zoning of substandard sections. Subsequently, stress wave based non-destructive evaluation (NDE) Impact Echo testing in accordance with ASTM C1383 was utilized, since the wall was accessible on one side only. Subsequently core locations were selected based on the areas identified by in-situ testing findings and cores were removed from areas with varying indicated properties. Laboratory testing of cores consisted of resonant frequency-based dynamic Young's modulus testing of cores (ASTM C215) and direct determination of stress-wave velocity (ASTM C597) on unconfined specimens removed from the wall. Both the in-situ impact echo and laboratory pulse velocity testing were effective in identifying the differences in the quality of the concrete across the wall. A comparison between the determined concrete compressive strengths and non-destructive Windsor Probe strength testing indicated in-situ and core test results were in agreement, but variability should be expected. Comparison of the dynamic Young's modulus with the American Concrete Institute (ACI) static elastic modulus approximation based on the compressive concrete strength indicated consistent results with approximately 15% higher value of dynamic modulus compared to static elastic modulus, as stated in the literature.

The expansion of an entertainment complex in the eastern US was under construction in 2003 when a portion of a multi-story parking garage collapsed during an 8th level concrete floor pour. This investigation was initiated to determine the cause of progressive collapse. Garage construction generally consisted of stay-in-place, precast, prestressed concrete formwork and cast-in-place composite floor system connected with mild steel reinforcing to cast-in-place concrete columns and shear walls. The collapse of an approximate 50 by 180 ft. area of the garage occurred during placement of cast-in-place floor system concrete at an upper level of the parking garage. A progressive failure of multiple levels of the stay-in-place precast formwork and cast-in-place composite floor system occurred, but nearly all perimeter columns and shear walls in the area remained standing. The authors were retained to investigate and evaluate the cause of the failure and study the progressive collapse. The investigation included site inspections of the garage collapse site and examination of garage structural components at an off-site location where debris was retained following demolition efforts. Visual inspection of the debris, review of eyewitness accounts, examination of construction documents, and structural analyses were used to evaluate the cause of the progressive collapse. Hand calculations and a three dimensional non-linear fracture mechanics model were also used to assess structural behavior of the composite reinforced concrete garage system. Strength of as-designed and influence of as-constructed connection conditions between the precast formwork floor system and cast-in-place columns and shear walls were evaluated. Results of the investigation were used to successfully assess the cause of the failure and make recommendations on how to avoid such accidents in the future.

The Halsey Street Teacher Village is a major redevelopment by the RBH Group of several city blocks in downtown Newark, NJ. New construction and renovation of existing buildings is contemplated to develop an entire complex of residential and commercial buildings centered on several new charter schools, also included as part of the redevelopment. As part of this project, Arup was requested to evaluate the Calumet Building, located at 17-19 William St., for potential rehabilitation and renovation. The Calumet Building is one of the original high-rise reinforced concrete buildings in the United States, constructed circa 1914, and the birthplace of the AA 12-step program. Due to the latter event, it is listed as a historic property with the state historic preservation office (SHPO). Years of neglect necessitated an evaluation to assess its viability for rehabilitation. Results of the evaluation indicated massive repairs and selective replacement of columns, slabs and beams would be required, in addition to complete removal and replacement of the two stairways.

Prediction of structural failure can occur when critical limit states are detected by engineering analysis during the design of the structure. In this paper, three case studies from the authors' forensic consulting experience are presented which highlight various ways in which simplifying assumptions in the analysis of reinforced concrete (RC) structures during the design process failed to capture key behavioral phenomena, resulting in significant damage, poor serviceability, and/or collapse of the structure. For each case, practical techniques using general purpose linear-elastic finite element analysis software are demonstrated which could have easily predicted each damaged state. Processes are explored to characterize the implications of simplifying assumptions in analysis of reinforced concrete systems. Improved understanding of structural behavior as exhibited in past failures such as these may aid engineers in determining when various phenomena need to be considered in future structural models of reinforced concrete systems.

Concrete structures rarely are crack free. Even properly designed and constructed concrete structures can develop cracks due to tensile stresses from restraint of volume changes and response to superimposed loads. Cracks in newly constructed concrete structures are typically the subject of some level of scrutiny as to their cause and their structural and durability implications. When cracking is not widespread or severe, the evaluation is usually a simple matter; however, when cracking is systemic and unusual, the evaluation is often not trivial. This paper presents the investigation and remedial strengthening of a podium-slab structure that experienced widespread and unusual cracking as the result of an unfortunate confluence of design and construction deficiencies.

This paper presents a study to evaluate the performance of single-story multi-family buildings' truss roof structures subjected to tornadic wind loads. This study was conducted to determine whether the roof structures of a condominium complex located in Florida were damaged by the storm event that occurred at the site. The investigation consisted of an assessment of the storm wind speeds and a detailed structural engineering analysis. The roof framing consisted of prefabricated long span wood trusses with metal gusset plate connections, supported on exterior masonry block walls and anchored to tie beams with hurricane straps. A challenge for this investigation was to determine wind loads generated by tornadic winds which are different in magnitude compared to wind loads produced by straight line winds for the same wind speed. This paper describes in detail the analysis performed which revealed that the primary mode of failure was at the truss connector plates caused by wind uplift forces. The failure pattern obtained from the analysis was consistent with the damage assessment noted from on-site observations which indicated that the majority of failures occurred at truss plates along the truss top chords.

St. John the Baptist Church in Hoboken, NJ, was originally constructed in 1852 and continues to function as Hoboken's oldest church. The structure consists of mass brick masonry walls supporting rough-sawn, scissor-type roof trusses. In June of 2010, WJE was hired to investigate the cause of two outwardly leaning masonry walls at the church. The Owner reported that the history of this condition dated back to at least 1902 when three metal tie rods were installed to restrain the spreading of the walls. The condition had reportedly worsened in recent years, including localized failure of the masonry and interior plaster wall at one of the tie rod anchorages. WJE performed an investigation and found severe distress and damage within the wood members of the roof trusses, causing them to exert an outward thrust force on the masonry walls. Cracking of the exterior stucco façade and damage to the masonry at the truss bearings were also noted. WJE then completed an analysis of the existing roof trusses to determine their capacity and to aid in the design of repairs. WJE provided and oversaw the completion of repair recommendations which included; immediate shoring of the existing roof trusses, installation of new upper tie beams and vertical members, installation of new tension rods between the bearings of each truss, masonry repairs at the truss bearings, and stucco repairs at the façade. These repairs were made more complicated by the fact that the building remained functioning as a homeless shelter each evening, necessitating unique repair methods and construction sequencing. This paper provides a unique perspective on the repair of historic wood roof trusses, as well as a brief overview of historic wood construction techniques and their inherent issues confronting today's engineers.

The moderate and humid climate of the southern United States provides attractive conditions for nature to damage wood framing. One destructive agent becoming more common in recent years is Formosan subterranean termites. Damage to wood structures from Formosan termites has been increasing since their introduction to the continental U.S. from Asia. It is estimated that Formosan subterranean termites cause in excess of $1 billion in property damage per year in the United States. The aggressiveness of Formosan termites and their ability to consume more wood in relatively less time has led to their label as a substantial destructive timber pest. Formosan termites often swarm in spring and early summer and have the ability to establish aerial colonies with no ground contact if a significant source of moisture is available above ground in a structure. Engineers are often asked to evaluate termite-damaged structures, design repairs, and provide expert testimony related to the extent of damage. This paper presents lessons learned from the structural evaluation of numerous termite-damaged structures. Two case studies are presented to demonstrate various conditions that may allow damaging termite infestations to become established in buildings.

While the wood nondestructive testing (NDT) community continues to offer and improve the technology and tools for identifying decayed wood in structures, our experience has been that the use of these technologies by design professionals has not kept pace with advancements. Rather, design professionals typically rely on rules of thumb and engineering judgment to specify the extent of wood removal. This paper presents a qualitative guideline narrative for design professionals recommending wood removal extents. The framework is based on the notion that the extent of wood removal should be commensurate with the level of confidence in the method used to determine the extent of decay together with the measures used to prevent future decay. While testing of new and developing NDT technologies may continue to be necessary to update these guidelines, the authors hope that this framework will serve for continued dialog between the research community, wood NDT equipment manufacturers, and design professionals.

The Dallas Cowboys Practice Facility (DCPF) was a large, fabric-covered, lightweight steel truss structure that collapsed in May 2009. News coverage of the event was quick to identify high winds as the cause of the failure, but in reality, there were a number of design errors which caused failure of the structure in winds far less severe than the nominal design wind speed. This paper presents the results of our failure investigation, including a comparison of the wind loads used in the original design to the provisions of ASCE 7, an analysis of the strength of the steel trusses, and the results of a 3D finite element model of the structure including the outer fabric covering. Portions of the original design that did not meet accepted codes and standards are highlighted and discussed. Based on these results and photographs of the collapsed structure, a likely initial failure mechanism and progressive collapse sequence is proposed. The results of our analysis and proposed failure sequence are compared to the investigation performed by the National Institute of Standards and Technology (NIST). Based on the design errors identified by both investigations, recommendations related to the design of lightweight fabric-covered structures are made.

Roof failures can occur at abutting lower roof structures which are susceptible to snowdrift loads. Snowdrift accumulation at abutting lower roofs is dependent on several factors including snow density, quantity of driftable snow, geometry of the lower and upper roofs, and wind directionality. Presented herein is a case study involving the partial roof collapse of an abutting lower roof structure as a result of snowdrift accumulation on the lower roof framing. While the authors' forensic investigation of the partial roof collapse led to the discovery of design and construction deficiencies in the lower roof framing, the authors determined that the code-prescribed design snowdrift height was less than half of the actual observed/measured height of snowdrift on the lower roof. These findings have led the authors to questions regarding the safety and adequacy of the current code-prescribed design loads as they relate to snowdrift at lower roof structures with similar roof geometries and ground snow loads to those presented in this case study.

Use of debris netting or screens is required by building codes and construction regulations in dense urban areas. There are no available calculations methods to assess the effect of wind on such fabrics. Following a series of accidents, wind tests were performed to assess the percentage of exposed netting area to be used in calculations. New York City Building Department design requirements were amended to include the results.

The collapse of industrial storage racks poses a safety hazard to building occupants and can result in costly property damage and subsequent business interruptions. Similar to building failures, storage rack collapses are typically caused by a combination of causative factors, such as: deficient storage rack design, construction, and materials; and/or improper maintenance and operational procedures. A forensic case study of failure of industrial storage racks is presented herein. This case study will highlight forensic investigation methodology, industrial storage rack installation guidelines; and how a combination of improper installation, maintenance, and operational procedures led to a catastrophic failure of a warehouse storage rack system. Methodology for, and results of, structural analysis of the subject rack system is presented. The authors will demonstrate that current installation guidelines do not provide for adequate stability of storage rack systems and propose that a change from guidelines to prescriptive requirements will provide a safer environment for building occupants and protect against costly property damage and business interruptions due to storage rack collapses.

The SoHo building was a 115 year old Landmark masonry building in New York City, SoHo district. After demolition, and during excavation at the adjacent lot, the ill fate of this building was set in motion. The building became undermined, tilted substantially, and needed to be evacuated. The building had to be shored and braced in order to prevent a complete structural collapse until it was subsequently demolished. Could this ill fate outcome have been prevented? Several factors lead to the building undermining and failure, including design and construction errors. The design team failed to fully investigate the existing conditions of the site and footings and they produced unclear, ambiguous and inaccurate construction drawings. Further, the contractor over-excavated the site and failed to properly protect the adjacent building. Additionally, the vacant, adjacent and excavated site remained open to the elements for a long period of time. This led to further deterioration of the foundation system below the doomed building. This presentation will discuss the events that caused the structural distress, damage and ultimate failure of the structure, with emphasis on lessons learned from this unfortunate failure.

During the construction of a five-story hotel building, up to 7 inches of settlement occurred around the southwestern corner of the building. Expecting that much of the settlement had occurred during construction, the Owner elected to complete the construction of the building without implementing any remedial measures. However, the building continued to settle after the construction was complete, resulting in wall tilt and floor cracks. Finally the Owner implemented a repair program that involved the installation of jet grouted piers under a significant portion of the building. The Owner brought claims in arbitration against the Contractor and a lawsuit against the Architect, the Structural Engineer, and the original Geotechnical Engineer. At the request of the attorney (i.e., the second author) on behalf of the Contractor, the first and third authors evaluated the likely causes of the building settlement and provided the assessment of whether the actions of the Contractor were contributory to the settlement. This paper is organized to provide: (i) an overview of the project history; (ii) the results of settlement calculations; (iii) an assessment of likely causes of the settlement and whether the Contractor's actions caused the settlement; and (iv) a description of the litigation process and results. The case study provides the geotechnical engineering profession an opportunity to understand both the technical and legal aspects of the issue.

The Plaintiff owned real property in New York City in the Chinatown area. This included two (2) four-story apartment buildings on one lot. The first was located on the front of the property and abutted the city sidewalk. The second was located at the rear the property. These buildings were best described as 100-year-old tenements located in New York's Chinatown that were "run down" and "poorly maintained". It was alleged that the rear building on the Plaintiff's lot sustained extensive property damage as a result of construction activities behind the property during November 2006. The Plaintiff's alleged damages include foundation cracks, cracks in the cellar floor, exterior wall cracks and cracks to the interior walls of the building. An investigation was instituted as to damages, allegations, and costs, proceeding to trial. The authors, Frank Giliberti, Esq., Jeffrey Migdalen, Esq. and James Cohen, PE, were, respectively, the attorneys and expert retained on behalf of the Defendant.

Demolition, excavation, and construction that are performed in close proximity to existing buildings and structures, and in particular those in an urban environment, may cause damage to the surrounding structures ranging from the loss of serviceability to complete collapse. In these instances, disputes often arise over the cause and the extent of the damage and also the roles and responsibilities of the contractors engaged in the work. A forensic investigation of the alleged damage, and in particular, the cause and the extent of the damage and a determination of new versus pre-existing damage after the construction has begun, or after it has been completed, can be challenging. One approach is to compare the alleged damage with those conditions, or the lack of conditions, identified in the pre-construction survey report. This paper surveys the industry literature on the code requirements for conducting pre-construction surveys, practices for conducting condition surveys used in the assessment and the rehabilitation of existing structures, and types of damage and the causes of that damage that are often alleged in construction claims arising from adjacent construction. This paper also compiles some of the best practices for conducting pre-construction surveys and for reporting the findings. These practices are taken from the lessons learned from actual construction claim disputes.