Forensic Engineering 2018: Forging Forensic Frontiers

Proper substrate preparation is critical for achieving adhesion, continuity, and durability of cold liquid-applied reinforced waterproofing membranes. Substrate preparation, including cleaning, surface profiling, removal of unsound material, and reduction of moisture, can be especially challenging with archaic masonry materials. This paper will present a case study of a roofing rehabilitation of a 1914 library constructed in the Beaux Arts style. The challenges encountered with designing and installing a new liquid-applied membrane over archaic brick masonry, concrete, and terra cotta substrates will be discussed. The preparation of these substrate materials was further complicated by a century’s worth of patch-work repairs involving numerous layers of coatings and built-up roofs that were entrapping water. This paper will be of benefit to investigators and designers contemplating waterproofing repair designs involving roofing membranes over masonry, concrete, and terra cotta substrates.

Forensic engineers commonly evaluate roof leaks for various buildings and structures throughout their careers. The typical scope is to determine the cause and source of the leak, as well as the extent of related damage. Such evaluations often consider direct damage from environmental effects such as wind, hail, and ice. Other considerations typically include breaches in the roof covering from improper/faulty flashing, unsealed seams/junctures, and long-term deterioration with neglected maintenance. In the authors’ experience, however, some of the most challenging roofing evaluations reveal moisture sources that are not at all due to breaches in the roof covering, but are caused by the effects of condensation forming within the building system. The purpose of this paper is to provide an overview of condensation effects within commercial roofing systems. The paper will include a discussion of causes, and provide an evaluation approach. The authors will present several interesting case studies collected over many years while working for a large forensic engineering firm. Practicing forensic engineers evaluating commercial roofing systems should benefit from information provided in this paper.

When a ceiling below a cold low slope roof assembly is not insulated or ventilated properly, condensation can form and cause extensive rot and deterioration of the roof framing members, leading to complete structural failure. This hidden condition can exist for many years before telltale signs become visible. Changes to the energy code have reduced the potential for moisture and condensation build-up to exist in newer buildings; however, based on the age of construction and geographic location, there are many buildings where these conditions continue to exist. This paper will discuss the telltale visual conditions, the method for destructive and non-destructive investigation, and the recommended method of retrofit and repair, including several case studies.

Single-ply roof membranes are an increasingly popular roof covering for low-slope roofing applications. A common installation practice for these types of roof coverings is to fully adhere the membrane to a layer of polyisocyanurate (polyiso) insulation, using an adhesive between the top of the insulation and the underside of the roof membrane to bond these layers to each other. When a hailstone impacts a fully adhered single-ply roof system, it is possible for the impact force to result in a discrete fracture to the top facer/surface of the polyisocyanurate insulation. Such a fracture may cause a localized disruption in the bond between the membrane and insulation, which in turn, may collectively be suspected of affecting the overall wind uplift resistance of the membrane. This paper documents an investigation into the effects that hail impacts can have on the wind uplift resistance of single-ply roof membranes fully adhered to polyiso insulation. This effect is analyzed through laboratory testing of fully adhered single-ply roof system mock-ups using a negative pressure vacuum chamber. The tested mock-ups contained varying amounts of bond disruptions simulating the effects of hailstone impacts. The performance of these mock-ups in a negative pressure environment is then used to establish a general characterization of the relationship between the extent of hail-created bond disruption and any reduction in wind uplift resistance of the roof system. This relationship can be used in forensic evaluations of roof systems to aid in the determination of whether or not hail has compromised a roof system.

The named storms of 2017 revealed the limitations of building envelopes’ water management and drainage systems, and even non-tropical rainstorm events have increasingly exceeded the capacity of constructed systems to prevent water intrusion. The severity of a storm may exacerbate existing conditions rather than being the actual cause of the leakage, and forensic building analysis must discriminate. Insurance providers focus on causal specificity regarding water intrusion damage, because their obligation for loss coverage is contingent upon those details. Water intrusion that results from impact or wind force damage may be covered under policy terms, whereas water intrusion through assemblies that were inadequately constructed or maintained may not be covered or could be grounds for subrogation. Ultimately, the detailed analysis and accuracy in stating the cause of water intrusion will be vital to corrective actions and repairs, and this aspect is relevant to all vested parties. Case studies from Hurricane Irma insurance claim investigations of commercial and large-scale residential water intrusion losses were reviewed to provide insight and specificity to the description of cause and origin. Each loss was purportedly the result of a single roof-related failure, but analysis revealed other contributory and causative conditions, and damage with more extended duration than initially reported. The case studies identified causation by deferred maintenance, drainage deficiencies, and fenestration and plumbing failures. These efforts and analyses provided insight and emphasized the value of critical thinking in forensic building science.

This paper presents an evaluation of wind-induced damage to rooftop solar array structures. Designed and installed just a few years prior to the storm, the rooftop solar arrays discussed in the paper, typically consisted of rows of fixed photovoltaic solar modules on inclined panels, supported by an aluminum framework with bracket bases, and ballasted pans that bear on low-slope roofs through protective slip sheets. Post windstorm investigation revealed that the solar array framework had displaced and the rubber slip-sheets below the bracket bases and ballast pans had slipped and no longer provided a protective bearing surface on the roofing below. Because of this slippage of the protective slip-sheets and direct bearing of the solar array framework on the roof surface, the roofing membranes sustained damage in the form of wrinkling, uplift, scrapes, and cuts. Analysis of the wind loads on the building roofs and rooftop solar arrays during the storm revealed that winds, though below design wind speed for the buildings, generated large uplift forces on the solar arrays that exceeded the array weight. The locations of calculated high wind suction zones correlated well with the locations of observed slippage of the rubber slip-sheets and damaged roofing. The evaluation recognized the load effect of design parameters such as solar panel geometry, array edge, and roof edge factors that will now be in building codes for the first time with the introduction of ASCE 7-16, with substantial differences from wind loads on typical building and roof components. The paper recognizes the need to implement the state-of-the-art methods that are now available in the wind design of solar arrays.

Recent changes in the building code helped fuel the current surge in mid-rise wood frame construction projects. Over the past several years, there has been an increasing number of water intrusion claims in relatively new mid-rise wood frame buildings. While the code requires the building envelope to provide protection from the weather, it does not provide the details necessary for designers and/or contractors to meet this requirement. Typical construction details, that have had limited success on 1 to 3 story wood frame buildings, are even more problematic on taller buildings. Specifically, vertical and lateral movements, caused by frame compression, shrinkage, external loads, and material incompatibility, can compromise the function of flashing and waterproofing details. Differential movements between the wood framing and exterior cladding components can cause physical damages to building envelope components that increase the extent of water intrusion. Once the water reaches the wood framing components, significant damages such as rot, corrosion, and mold can result. Additionally, once compromised, the effectiveness of products used to meet fire resistance requirements is unknown. If our design and construction of the building envelope does not incorporate “best practices”, mid-rise wood frame buildings may become the “black eye” of the construction industry.

The pace of development and advances in building enclosure and mechanical systems has been significant over the past few decades, with vast improvements in durability, reliability, and control over interior environmental conditions. Unfortunately, that development has been largely in parallel as opposed to in conjunction, with designers from one discipline rarely “crossing over” to better understand the other. In modern buildings, this lack of understanding can lead to significant problems in building performance—problems which can be difficult to solve due to the multiple factors that lead to their development. Even as little as 50 years ago, the design of both building enclosures and mechanical systems was relatively simple, with few governing codes/standards as well as fewer or less stringent expectations from building occupants. Modern energy codes have led to buildings that are more airtight and much better insulated than their predecessors, yet at the same time less robust and more sensitive to moisture and construction defects. Mechanical systems have evolved as well, improving in efficiency and providing much better control over interior environments. However, few codes and standards exist which take into account both of these advances, leaving it up to designers to understand how one system can affect the other. This paper describes how both types of systems have evolved and discusses the many ways the performance of one can impact the performance of the other. Case studies will be used to demonstrate the physical phenomena in play and develop basic guidelines for a more holistic approach to designing systems for positive and beneficial interaction.

The granite façade of a 41-story steel-framed building constructed in the early 1970s experienced multiple façade failures after 40+ years in service. A forensic investigation of the façade revealed that the approximately 3-inch thick granite façade panels were supported with a structural steel shelf angle detail similar to typical brick masonry support for cavity walls. The shelf angle support was poorly adapted for use with the granite clad façade and created reservoirs that trapped water against unprotected steel, resulting in corrosion of the steel and distress to the granite panels, and in turn formed hundreds of granite spalls that created a potentially hazardous condition around the building. In addition to the granite spalls, the window system contained significant air and water intrusion that led to staining at the window frames and moisture damage at the interior ceilings. Our work included the creation of a 3-dimensional analytical structural model to study building drift and movement; thermographic studies of the façade and windows to identify areas needing additional insulation and water management systems; and studies of both the solid granite wall areas and ribbon window areas to identify cause and origin of the granite and weather-proofing failures.

The author has evaluated hundreds of commercial and residential properties for insurance claims investigation purposes. This includes investigations related to nearly all major hurricane and tornado events that have occurred in the United States within the past decade. During the claims process, it is not uncommon for building owners to claim that excessive wind forces have cracked brittle finishes. This is especially true for single-family residential property owners. In the author’s experience, insurance professionals (claims examiners, adjusters, etc.) sometimes maintain that foundation movement caused the cracks and the cracks are unrelated to wind. This can be a major point of contention between the carrier and insured. Is it possible for wind pressures to crack brittle finishes, such as gypsum board? This paper will explore the answer to that question. A structural analysis will be performed on a representative residential wood-framed structure. In the analysis, the provisions given in ASCE 7-10 for determining design wind pressures will be reverse-engineered to determine the wind gust speed necessary to exceed the shear capacity of gypsum board wall panels. The findings from this analysis will be presented. The author recognizes that this is a static solution to the above posed question and several assumptions will be made. As such, the limitations of this analysis will be discussed. Additional testing and research that may be beneficial to this study will also be discussed.

For decades, waterproofing has been a major concern and a widely researched topic by building scientists and forensic engineers. Elastomeric coatings have been broadly used in different applications since the early 1950s. Manufacturer’s recommendations for the proper application of elastomeric coatings are often based on laboratory conditions (75 ^oF and 50% RH) rather than irregular conditions posed by the real world. This study examines the failure of elastomeric roof coating exposed to different environmental conditions of high temperature (150 °F) and water pooling caused by precipitation events. A qualitative comparison of exemplars revealed why roofing contractors must consider environmental conditions as an influential factor in determining the application range of elastomeric coatings. Test exemplars were made using different substrates (i.e., glass, asphalt, and metals) to test the behavior of elastomeric coating when applied to materials with different thermal expansion and contraction properties. Exemplars were prepared using modified methods from ASTM standards C 1375 and D 1640. After curing, test exemplars were exposed to extreme environmental conditions of high heat, constant submersion, and 180 repeated cycles of submersion for 2 hours followed by heating in a controlled high temperature chamber (140-170 °F) for 2 hours each work day. Elastomeric-coated specimens submersed continuously expressed bubbling, de-bonding from the substrate, discoloration, and shrinkage. Specimens that were either heated or submersed and then dried each day did not experience bubbling or shrinkage; however, specimens that were cyclically heated and submersed experienced discoloration and de-bonding on the glass substrate. The application of a primer beneath the coating offered competent adhesion to all test surfaces as compared to non-primer surfaces. Based on adhesion test results (modified ASTM D3359-09e2) the substrate that exhibited the strongest bond was rolled roofing and the weakest was metal.

A survey of design and construction practices of window and door installations is presented after 17 years of ASTM E2112 Standard Practice for Installation of Exterior Windows, Doors, and Skylights. It has been and continues to be the nationally recognized, consensus reference. Design professionals and construction industry leaders have the opportunity to avoid liability for leaky buildings following sound (but often ignored) drainage principles, avoiding common design mistakes, and including simple but basic specification requirements. This focus on window and door opening head flashing options will illustrate critical conditions and provide examples for detailed solutions to avoid moisture infiltration problems in frame buildings. Examples of various sheet metal head flashings will be used to show design principles, detailing recommendations and specification criteria for fenestration installations with different water resistive barriers and cladding types.

This paper investigates the cause of discoloration that has appeared along the interior glazing system in a State of Ohio public university building. The discoloration is evident in both the head and sill details and is evident adjacent to the glass pane in the glazing sealant as well as at the locations where the frame meets the adjacent concrete structure. These discoloration spots are located throughout the interior of the building, e.g. glass wall of the lecture hall, glass stair railing, windows, etc. By reviewing the architecture details, the top of the glass panels (1/2" or 13/16" thick) is anchored to a flush mounted aluminum frame and wood blocking supports the bottom and laterally anchored by two rolls in shims in a milled aluminum channel. The shims both on the top and bottom are sealed by a silicone caulk. The performance failure of discoloration may be caused by the corrosion of the shims due to the poor durability of materials, a reaction between the shims and the caulk, or poor craftsmanship of panel installation. The paper identifies the cause of the discoloration and discusses the potential economic loss. Through the investigation, the discoloration is surmised to be caused by a plasticizer leached out from a rubber shim. No performance data was provided for the rubber shim in the drawings or specifications. Additionally, this paper reconstructs the design, specification, and submittal process and identifies how and where the mistake was made, who should have known. The paper concludes with lessons learned from the failure of architects, engineers, and construction professionals to avoid similar failures in other projects.

This study examined the deterioration of carpet tack strips (CTS) exposed continuously and repeatedly to water over an eight-year period. CTS express gradual changes in the appearance of metal oxidation, microbial growth, laminate separation, discoloration, and physical deterioration by biological and chemical decay depending on the duration of moisture exposure. These changes constituted an instrument to estimate the duration of a water loss. The study examined 24, foot-long sections of two types of carpet tack (Halex and Roberts) exposed to two sets of conditions: continuous (wet set) moisture (water 1/4-inch-deep) and repeated (wet-dry set) moisture exposure (twice-yearly water addition) where the moisture was added and allowed to gradually evaporate. The CTS were incubated in closed plastic containers. Within the first days, metal oxidation of the steel tacks represented the first expression of moisture exposure. Small areas of wood discoloration adjacent to the tacks were followed by fungal growth that contributed to the degree of discoloration (describe the colors, rust, light brown, brown, black). CTS exposed to moisture continuously (wet set) deteriorated faster than those repeatedly wetted (wet-dry set). During the first 100 days, both sets exhibited gradual darkening from wood discoloration and microbial growth to a nearly black consistency. Ply delamination was first recognized within 75 days among wet-dry set. This finding was attributed to strain experienced by the wood in the wet-dry set. As deterioration progressed during month 24 through month 48, both sets of CTS retained their physical appearance with the exception of appearance from black to ashen gray. Exposure month 60 through month 96 resulted in continued layer disintegration of the continuously wet samples and shape retention by those exposed repeatedly. Documentation of the deterioration sequence will provide the forensic engineer an estimate of duration of loss for comparison to other quantitative observations when water releases encounter CTS.

This paper presents a case study of a two-story unreinforced brick masonry building that was adversely impacted by construction activity associated with the development of an adjacent high-rise building. One longitudinal exterior wall of the URM building was located along the property line where the construction activity for the new building occurred. The new construction extended several levels below grade requiring support of excavation along the property line. The excavation was shored with a system of soldier beams cast in drilled shafts, raker beams, and lagging that also served as the formwork for the basement retaining walls of the new structure. However, the excavation activity disturbed the equilibrium of the URM building and caused settlement of its longitudinal exterior wall foundation, which resulted in cracking of the exterior walls, settlement of the floor slab-on-grade, and other distress to the URM building. The potential for damage to the URM building was mitigated to some extent because of a prior seismic retrofit, which tied the second floor and roof diaphragms to the building walls. Photographs taken during a pre-construction survey of the URM building confirmed that cracking of the URM building occurred after commencement of adjacent construction. Details of the investigation performed to determine the cause of distress to the URM building are described in this paper. The intensity of vibrations induced by shaft drilling and their attenuation with distance was also assessed through a desktop study to complement the findings. The measures adopted to remediate damage to the URM building with the added constraint of adjacent construction are also discussed in this paper.

A successful response to structural damage requires attention to detail and the application of forensic engineering from the initial emergency response, into the repair documents through construction administration, and ultimately to project restoration. Sound forensic engineering is the heart of the life cycle of the structure getting back into service. This paper explores the full life cycle of a structural damage case and the role that solid forensic engineering plays throughout that life cycle. A case study will be provided to explore how the understanding of forensic engineering practices benefits all aspects of returning the structure back into service. Starting with emergency response services of the initial damage event, a strong understanding of forensic engineering practices will help in acting accordingly with damaged areas to correctly document the areas and protect evidence at the scene. Proceeding to utilize the forensic engineering findings into the repair documents through final restoration of the structure will help to assure that the cause of the initial damage is appropriately addressed.The benefit to those reading the paper would be to better understand the strong role that solid forensic engineering plays in all aspects of a structural damage case and the benefit of that understanding to the outcome and return to service of the structure.

This is a survey of design and construction practices of window and door installations after 17 years of ASTM E2112—Standard Practice for Installation of Exterior Windows, Doors, and Skylights as the nationally recognized, consensus reference. Design professionals have the opportunity to avoid liability for leaky buildings following sound (but often ignored) drainage principles, avoiding common design mistakes, and including simple but basic specification requirements. The focus on window and door opening sill pan flashing options will illustrate critical problem conditions and provide examples for detailed solutions to avoid moisture problems. Examples of various sheet metal sill pan flashings will be used to show design principles, detailing recommendations, and specifications for fenestration installations with different water resistive barriers and cladding types.

Opportunities to investigate residential structures supported over raised crawl space construction, above natural soils, after having sustained functionality failures in south Florida indicate that there is a shortfall in, or lack of understanding associated with the knowledge required by professionals such as designers, contractors, building officials, and tradesmen in the construction industry. Numerous observed failure mechanisms and resulting damages indicate non-compliance with respect to requirements documented in the industry standards such as the Florida Building Code, the Florida Weatherization Handbook, and the Federal Regulation 10 CFR Part 440. Case studies with associated deteriorations to be discussed include various forms of damage and failure associated with inadequate or incomplete construction techniques and a lack of required details. Industry standards that should have been followed and complied with during the design phase and/or construction process, but that may have been ignored, misinterpreted, or simply unknown by the responsible parties confirm a level of neglect and incomplete construction techniques, as observed during forensic investigations that have exposed substantial damage and failure. Deteriorated conditions noted within the observed crawl spaces include sagging, deflecting, and/or failed structural components, deteriorated wood subflooring and floor joists, extensive fungal growth, elevated relative humidity and condensation moisture levels, reinforced concrete component spalling, reinforcing steel corrosion, efflorescence staining on exposed masonry stem wall foundation surfaces, excessive floor slab deflections, etc. The historical Southern Standard Building Code and the subsequent South Florida Building Code were precursor codes and the basis for the current Florida Building Code. Prescriptive recommendations and requirements exist in the Florida Weatherization Handbook and the Florida Building Code-Residential, Chapter 4—Foundations, Section R408—Under-Floor Space. The Florida Building Code Energy Conservation also contains crawl space insulation requirements. Foundation venting and installation details include minimum opening sizes, geometry requirements, vapor barrier requirements, and floor insulation installation techniques. Subjects of importance include appropriate ventilation of the crawl space, vent opening size and quantity requirements, location and geometry of the venting, the crawl space area, vapor retarder requirements placed over unfinished dirt floors, insulation placed over the subflooring and floor joist components, crawl space access, etc.

Promoting student interest in forensic engineering will help support development of the next generation of industry professionals to serve this field. This paper details implementation of a student-identified failure case studies project in a junior-level undergraduate course in civil engineering technology and construction management. The final project requires students to identify a failure in a structural component, and implement the forensic process to identify, describe, investigate, and mitigate the failure. Forensic study of these small-scale failures offers an opportunity for students to learn technical concepts associated with design and construction of built systems, as well as the investigative and repair process associated with failures. Information on the lectures delivered prior to the project assignment is presented, along with the failure case studies assignment, assessment tools, and examples of student submissions. Learning outcomes are assessed, along with recommendations for implementation of a similar approach in other educational institutions.

This paper provides an overview of topics and delivery method of an innovative graduate level course focused on forensic engineering. The course provides graduate students practical insight into structural engineering practice and design through the examination of failures. The course is taught via a distance education format; that is, it is offered online in a real time synchronous format. Approximately half of the students are traditional in class students, while the other half are off campus, “distant learners”. During a given class meeting approximately half of the distant learners view/participate in real time while the others complete work at their convenience at another time. Forty-one, faculty prepared, case studies are examined with the examples ranging from infamous catastrophic collapses to little known examples of design criteria being violated. The case studies highlight the sequence of events that contributed to the engineering catastrophes and draw conclusions based on the evidence as to why these failures occurred and how they may have been prevented and what lessons were learned. Students are responsible for an on site investigation, either on campus or at a structure of their choosing, and a case study (presentation or report). This paper discusses the experience of the instructor over the 15-year development and execution of the course and the evolution to the current distance education version. Additionally, the paper provides the framework for delivering the course, assessment data, and student feedback.

The ASCE Forensic Engineering Division (FED) has been expanding the outreach of forensic engineering from the U.S. internationally. These activities have included the formation of an international activities committee to coordinate these efforts. Previously, these were coordinated largely by the education committee. Activities have included presentations at a number of international conferences, such as in Italy, Sweden, Portugal, Spain, and other countries. Other activities have been two day workshops presented by members of the FED, starting with Costa Rica in 2009, and continuing in the U.K., China, India, and Latin America. It has proven useful to develop long term ties with other countries. The exchange of ideas has been interesting. Good practices in failure investigations may be universal, there are important differences in societal pressures, codes of ethics, and legal systems from country to country must be considered. This paper reviews the past decade of work, and looks forward to developing future efforts.

This paper provides an overview of how forensic case studies are used in an introductory engineering mechanics course to demonstrate the importance of material testing of steel. Students often see demonstrations or videos on how to conduct material tests on engineering materials; however, they often lack a context of the importance of the material properties resulting from the tests. Forensic case studies have been successfully used in an introductory mechanics course to highlight the importance of the two most widely used tests on structural steel, the tension test and the Charpy impact test. The paper discusses how two different bridge design case studies are used as the backdrop for the importance of conducting the standard tests and the resulting data (elastic modulus, yield strength, ultimate strength, toughness, impact energy, and ductility measures). Background on the course, specific learning outcomes, the content of the lecture, case studies used, laboratory execution, and deliverables are presented. Additionally, the paper provides assessment data, student feedback, and recommendations for applying this format to other lessons.

Landslide is a complicated multi-hazard event that can turn into a great disaster; burying part of a city or village downhill the slope and causing a large number of fatalities. Landslide risk assessment and management (LRAM) process involves decision making to find an optimal loss-mitigation approach. A good, representative decision analysis process relies on reasonably capturing all possible scenarios that would happen in a landslide event and assessing the probabilities. This requirement for the evaluation of possible scenarios exists while there are multiple sources of uncertainties in such a problem and our knowledge of extreme events is limited. In our research, we showed that using the historical data and extending past knowledge to predict a future event is not completely applicable and reliable. Thus, it is important to consider the possibility of irrelevancy of historical data to the problem. The research shows that to consider extreme and rare events, it is required to use a non-informative prior probability in the Bayesian analysis. Such non-informative prior probability distribution is obtained by maximizing the entropy of possible events, which maximizes the lack of information. This paper includes a summary of our research to develop a new decision-based framework in order to reasonably capture sources of uncertainties in the landslide risk management decision analysis. In addition, a practical example of application of the framework to a landslide case study will be presented.

When investigating buildings for potential hail damage, determination of the approximate hail size is an important part of the investigation. Weather data resources, including free data made available by the government and fee-based reports from third-party weather analysis services, are often used to help evaluate the reported or estimated hail size in the vicinity of a given site location. In addition, data collected during a site investigation provides valuable, site-specific information regarding hail occurrence(s) at a site. The authors have investigated buildings, and especially roof coverings, for damages from numerous hail events. Based on this experience and published studies regarding damage profiles from varying hail sizes, observations and measurements obtained during an investigation for hail damage are utilized to determine an estimate of hail size at a given site. The purpose of this paper is to discuss the methodology used for on-site evaluation of hail size and to compare estimated maximum hail sizes determined from these on-site investigations with the available weather data. Data from multiple storm events affecting populated areas, which generally provides for a more comprehensive and more closely-spaced set of data, will be used. The comparison of on-site evidence with the available weather data will show that this weather data can provide information of varying accuracy with regard to the sizing of hail, and that the data collected during an on-site investigation is essential for the accurate determination of the approximate hail size which has occurred at a given site.

This paper illustrates industry opinion on railroad accidents, causes, and preventive techniques. It is a look at recent safety statistics and suggestions for improving them. Reports and studies from government agencies have indicated that the leading causes of railroad accidents are operator fatigue, poor maintenance of track, and associated infrastructure. Rail accidents occur when trains travelling on the same tracks collide or when trains derail because of technical faults in the rolling stock, the rails, or the security systems, or because of landslides, or objects obstructing the rails (possibly caused by deliberate actions of terrorist). The modern detection technology and computer simulation analysis can be used to narrow down the root cause of railroad accident. The railroad accidents could be minimized/avoided by taking strict preventive and protective measures (establishing regulations, intelligent signaling systems, training personnel) that minimize technical, human failures, and malicious attacks which involve installing a reliable alarm and security system and regular surveillance of rail installations and equipment. Based on the previous railroad accident investigation reports and findings, a preventive railroad accident plan can be developed and strictly implemented as a railroad organization policy instruction. The various innovative railroad accident prevention techniques via better practices along with technological tools can be used to find defects and faults before they reach the catastrophic failure stage.

The warehouse is located in East Multnomah County, a suburb of Portland, Oregon. Building roof dimensions are 384 ft long by 352 ft wide. Roof contains open web steel joists, 30 inches deep, 48 ft long, 8 ft on centers. The structure was designed based on 1997 UBC and completed in 2001. In December 2008, substantial rain and snow fell in the Portland metropolitan area. The accumulation of snow on the roof, according to some eye witnesses, was close to 3 to 5 ft at the parapets and about 2 to 3 ft on the interior sections of the roof. Late December, 2008, 24 roof trusses collapsed. Forensic investigation findings: 18 trusses failed in their connections by weld failure, and 6 by concrete breakout failure. Causes of failure were: snow load that surpassed the design load, wind direction that accumulated snow against the tall parapets (snow drift), construction defects, and each collapsing truss adding more load on the neighboring truss, i.e., a progressive collapse. The snow load requirements by ASCE 7-05 were higher than 1997 UBC, and if the trusses had been upgraded for the higher snow loads, failure most probably would not have occurred. As the requirements for snow load increases in subsequent building codes, it is recommended that the structural engineer of record advise the building owner that the structure be evaluated for the anticipated increased loads.

Three hangars constructed at a large airport in 2006 collapsed during a blizzard on February 6, 2010, causing significant damage to many private aircraft housed within the hangars. The authors investigated the cause(s) of the collapses at the request of attorneys representing the insurers of the aircraft owners. The authors’ investigation consisted of field investigations; review of the original design drawings, fabrication drawings, structural calculations, applicable design codes, and welding standards; structural analysis and calculations; and review of metallurgical testing and examination results. This paper presents the findings of the investigation including the cause(s) of the collapse and contributing factors. It also examines the roles and responsibilities of the various parties, such as the designers hired by the owner, the firm that designed and fabricated the hangars, the engineer that signed and sealed the structural design, and the shop inspectors. The paper also contains recommendations to reduce the probability of similar future collapses.

A forensic investigation of the failure of a building or structure typically begins with initial observations and data review that creates a first impression of the cause of the failure. While this first impression helps to start the formulation of an investigation plan, premature, incomplete, or biased initial assumptions of the cause of the failure can take the investigation in the wrong direction. First impression myopia describes a type of tunnel vision that can occur when initial impressions are formed before much of the supporting data is available. The preliminary investigation phase often begins with the client’s brief description of the failure during first contact with the investigator. An initial site visit is normally made to assess the circumstances of the failure, the building’s or structure’s characteristics, and the environment surrounding the failure. First impressions formed during this period will likely drive decisions on the type and scope of detailed inspections, sampling and testing protocols, analysis, and the investigation team makeup. First impression myopia may occur from incorrect or premature initial assumptions. If these assumptions are not adequately scrutinized and evaluated as the investigation unfolds, they can lead to investigation efforts that are either inadequate, inappropriate, or unnecessary. This paper discusses how a building failure investigation may be influenced by first impression myopia and provides strategies to guard against its detrimental effects. Case studies that demonstrate examples of first impression myopia pitfalls are presented. Overcoming the consequences of first impression myopia requires objective critical reviews by an independent qualified reviewer during the investigation. Periodic reassessment of investigation objectives, including rejection and replacement of the chosen failure hypothesis, is also required.

In early February 2017, near Yakima, Washington, snow accumulation on the roof triggered the collapse of a 125 foot by 85 foot single-story, steel building (Building 1) originally constructed in 2011. Two days later, about 100 feet away, a separate, similarly constructed building (Building 2), originally constructed in 2012, collapsed due to similar circumstances. The authors were hired to investigate the cause of the collapses for potential subrogation. Security video recorded the entire sequence of the Building 1 collapse. From the video, the snow depth on the roof was estimated to be 15 to 22 inches. Field investigation found that flange bracing for the steel column frames was not installed as specified. Each column frame was observed to have buckled at the same location as the missing bracing. The collapse was determined to be caused by the omitted bracing that reduced the column’s capacity to resist the imposed load.

High-strength steel reinforcement in new concrete structures is becoming more commonplace in practice. This reinforcement offers equivalent strength with less cross sectional area, which helps mitigate concrete consolidation concerns in highly congested regions. ACI 318-14 (2014) presently limits its applicability, as research is ongoing. High-strength reinforcement use requires verification that design and structural behavior assumptions embedded in the code equations remain valid for the higher steel grades. One important attribute of using high-strength reinforcement is its ability to be fabricated and bent into the shapes necessary for placement in a structure. The material must have enough ductility to be “cold-bent” without bar damage. ACI minimum bend diameters must be verified for a range of bend angles and pin diameters, and process changes may be required, as high-strength steel requires greater forces to bend. To achieve higher strengths, steel usually sacrifices ductility, and potentially fracture toughness, given the alloying elements and production process used to produce the reinforcement. This paper provides a case study regarding use of high-strength reinforcement in practice. A massive, reinforced concrete foundation element was designed with Grade 80 (552 MPa) reinforcement. These high-strength bars were bent into many different configurations. During cold weather construction, several #11 (~#35M) bars fractured at bends during normal bar placement. The author’s investigation identified the material properties, chemistry, bending procedures, and fabrication temperatures all contributed to the fracture cause.This paper analyzes the investigation into the fracture cause, including review and observation of the bar bending processes; conducting metallurgical examinations and bar mechanical testing; review of industry standards and literature; discusses the quality control/quality assurance testing protocol for the refabrication; and presents general conclusions.

This paper presents a fitness-for-service (FFS) evaluation of heavy structural steel weldments containing fabrication-related flaws, for the purposes of development of improved weld flaw acceptance criteria. In the high-rise construction industry, large welded nodes with complex geometries are becoming increasingly common. As such, these weldments, which may contain flaws such as material defects, welding irregularities, cracks, corrosion, or other anomalies, can weaken the structure making it susceptible to fracture at lower than design magnitude loading. The fracture mechanics approach presented herein can be used to evaluate this condition. First, a metallurgical investigation should be performed to categorize the severity of the flaw, and mechanical properties of the affected material should also be determined. This typically includes a review of the existing weld procedure specifications (WPS), preheating procedures, mill certificates, and some destructive testing, if possible. Once the size and type of the flaw are known, a fracture mechanics analysis incorporating a three-dimensional finite element model is performed to determine the maximum tolerable flaw size. The outcome of this assessment will directly determine the weldment’s fitness-for-service. These types of assessments can address the impact of residual stresses and potential fatigue crack growth, and are tailored to the weldment’s specific material properties and operating conditions. This methodology is very useful for structural engineers, contractors, fabricators, and building owners, as it directly establishes case-specific weld flaw acceptance criteria, which may result in the avoidance of unnecessary repairs.

Movable structures are becoming one of the new trends for large-span sports facilities. This structure typically involves retractable roofs which are supported by single- or double-line wheeled carts (called bogies) travelling along the steel rails on the runaways. Rail members, which are connected by thermite welding, are subjected to combined load conditions including the dynamic wheel loads during its operation and temperature change. This paper discusses the approach to evaluate the internal stresses in the rail section due to the combined effects of the service wheel loads, the anticipated in-service temperature changes, and the residual stresses due to both manufacturing cooling and straightening, and welding. The main factors that affect the performance of thermite welds are discussed, and techniques for in situ assessment of rail sections are illustrated. Finally, a case study on a rail failure is presented and the potential issues that defective thermite welding installations can raise are discussed.

Wood responds to changes in atmospheric conditions, swelling as it absorbs moisture under elevated humidity, and shrinking when surrounded by dry air. The affected wood, whether it is used for framing or applied as a finish, will move as it expands and contracts. Where the movement is constrained, or where the movement changes the members’ geometry, the result may be damage. As the symptoms of hygroscopic movement may resemble damage from external forces, understanding wood shrinkage can aid in correctly diagnosing the underlying causes of building damage. This paper provides two examples of damage that results from wood shrinkage.

The change in use of five stories of a 15-story vintage building to library usage appeared to have caused an increase in the settlement and tilt of the building. An investigative process is described in this paper to determine the cause and origin of the original tilt, as well as of the increased tilt and settlement, due to the change in use of some of the building’s space to library. It was eventually determined that the construction of an adjacent building many years ago had changed the groundwater profile and lowered it due to the deeper basements of the newer construction. This caused the deterioration of the timber piles supporting the building under investigation, and the consequential settlement.

Assessing and maintaining our critical infrastructure is challenging enough when we have physical access to the structures we are evaluating. Nevertheless, there are methods for determining the location and condition of underwater structures. The pipeline industry has maintained many thousands of miles of piping, however for many applications detailed assessment still requires divers and excavation. Lessons learned with underwater cameras will be discussed along with survey techniques including laser scan and sonar. A survey of helpful tools for assessment as built geometry, long-term deflections, and weld quality will be presented including suggestions for areas where future innovation would be helpful.

The author’s firm was engaged by an insurance company to perform an investigation of the cause and extent of reported damage to wood bowstring roof trusses at a large one-story commercial building in the northeastern United States. Prior to the recent report of damage, extensive repairs had already been installed on the trusses as part of a previous repair campaign reported to date back over twenty years. The current building owner had little knowledge of these repairs and, as such, no information on the repairs or the cause and extent of the damage that motivated the installation of repairs was available for the investigation. The claim of damage that the author’s firm was tasked with investigating was limited to damage that occurred subsequent to the previous damage that was addressed by the existing repairs. More specifically, the insurance company needed to know whether any additional damage to the building’s roof structure had occurred due to the weight of accumulated ice and snow over the most recent winter season. The subject investigation included site visits to observe the reported damage, identification of wood species and estimation of wood structural grades, a review of available weather data, and limited structural analyses. Using this approach, observed damage to the wood trusses was grouped into two different types, and the cause of each type of damage was assessed to determine whether the damage was caused by the weight of accumulated ice and snow during the time period in question.

Performance-based fire engineering (PBFE) has gained attention in recent years as a modern alternative to the conventional prescriptive methods for fire protection design. Acknowledged in the 2016 edition of ASCE-7 code, PBFE provides structural engineers with great flexibility to achieve more rational and cost-effective designs against fire hazards. In addition to applications in design optimization and performance evaluation of new structures under fire, PBFE can be an efficient tool for the assessment of existing structures, including renovation and fire protection, fire risk assessment, post-fire forensic investigation, and post-fire structural assessment. This paper outlines the key steps of the PBFE process to perform fire analysis for both new and existing structures, including simulation of fire scenarios with computational fluid dynamics (CFD) and finite element (FE) analysis of the subsequent thermal and structural effects. An example of a tall building façade subject to fire hazard will serve as a benchmark case to demonstrate how structural forensic investigations can benefit from each phase of the PBFE process. For example, it will be illustrated how fire simulation, complemented with traditional investigational data (e.g. photos, witness statements, etc.), can be used to reconstruct a fire event, or how thermal analyses can be utilized to determine the extent of fire-induced damage.

In September of 2017, a fire in a small commercial building partially collapsed the roof onto the portion of the building floor which was of interest in the subsequent fire origin and cause analysis. The building was a mixed-use facility with a “high-bay” shop area, offices, and a wood framed (internal) clean room. The tilt-up wall panels formed the primary structural elements in terms of gravity and lateral load resistance and were in danger of collapse after the roof was compromised. Engineering Systems Inc. (ESi) was retained for the fire origin and cause analysis, which also necessitated a structural engineering effort to shore the building and supervise the removal of the damaged roof. The fire analysis had to proceed immediately without compromising the safety of the individuals conducting the analysis and an emergency shoring plan and job safety plan was developed. Other topics of interest included hazardous material risk mitigation, working with municipal authorities, engineer-contractor relationships, and multi-disciplinary engineering.

Exposure of concrete members to high temperatures can affect the structural performance of concrete and embedded reinforcement in numerous ways including changes in material properties, loss of strength, and relaxation of prestressing forces in pre-stressed concrete members. The assessment of concrete members exposed to high temperatures follows both testing and analytical methods. A typical evaluation may include non-destructive testing, destructive testing, evaluation of fire intensity, determination of temperature profiles, and assessment of residual strength and prestressing losses. This paper includes the authors’ experience with the assessment of prestressed double-tee beams in parking garages that have been exposed to fire and high temperatures. The authors discuss both general information associated with the evaluation process (and review of relevant, published literature) as well as considerations specific to the presented case studies. These include consideration of effects of high temperatures on localized components of the double-tees, as well as potential remedial repairs.

When exposed to high heat and humidity conditions, as often found in unventilated attic/ceiling cavities, certain phosphate and sulfate chemicals used for fire retardant treated (FRT) lumber between approximately 1960 and 1980 can react with wood and cause unexpected failure. This condition caused a roof failure due to an enclosed attic cavity having no means of ventilation within the plenum. Similarly constructed roof trusses adjacent to the failure were open with no ceiling below. These were not exposed to elevated humidity and did not fail. This paper will discuss visual conditions, the analysis procedure used, findings, and lessons learned from the investigation of the failed roof trusses.

A shoring failure occurred while relocating a reinforced concrete column and footing supporting a structural roof system during a building renovation project. The steel shoring posts buckled, the roof slab structure exhibited significant cracking and vertical deflection. An initial condition assessment was performed to evaluate the stability and integrity of the existing structure and a more detailed assessment followed to assess the damage, examine the as-built condition of the structure, and develop the repair design. Visual observations, as-built field measurements, and non-destructive testing were performed to evaluate the condition of the structure and calculate the load capacity of the system. A series of finite element structural analyses were performed to investigate the structural behavior during the failure and to develop the repair design to remediate the damaged structure.

The Harmon Tower was a high-rise reinforced concrete building constructed as a part of the CityCenter development project in Las Vegas, Nevada. The tower was initially designed to be 47 stories tall but was constructed only to 26 stories. The discovered nonconforming construction was used as the basis for a lawsuit blaming the contractors, which resulted in a long and complicated litigation between the owner and the construction team. Brandow & Nastar, Inc. was retained as a structural expert for one of the main parties involved in litigation to investigate the impact of the reported nonconforming construction on the structural integrity of the tower and to determine required remedial measures. In the course of the forensic investigation, structural configuration conditions and design issues were discovered in the tower, which were more significant than the nonconforming construction conditions. The litigation ultimately settled out of court in 2014 and the demolition of the tower was completed by the end of 2015. This paper provides background information on the project, describes the forensic investigation performed, and discusses the decisions made during the investigation.

Performing repairs in the Arctic presents obvious logistical and environmental challenges. Geotechnical concerns must also be considered given the nature of permafrost and the effects of varying subsurface conditions. Many structures on the oil fields of the North Slope of Alaska consist of large modules housing various types of industrial equipment. The equipment often generates significant amounts of heat resulting in large temperature differentials between module interiors and outside arctic air. This temperature differential along with several other factors result in unique deterioration mechanisms throughout the buildings. Given the age and harsh environment of these structures, it is not surprising many are in need of structural repair. This paper is targeted at structural design and inspection professionals and will focus on the forensic study of a specific module located on the North Slope with a deteriorated roofing system. Before implementing repairs, identifying the root cause of the damage is of critical importance. A field investigation was initially performed to assess the structure’s condition. During the investigation, multiple buckled diagonal braces were noted throughout the lateral bracing system, potentially leaving the structure vulnerable to wind and seismic events. Forensic efforts to identify root causes of bracing failures and evaluations performed to assess the criticality of damage as it related to the roof repairs will be discussed. Ultimately, through the forensic study, the root cause of the damage was identified and an appropriate repair strategy is currently in process to mitigate potential instabilities resulting from the failed lateral bracing members.

The Kansas City Hyatt had been open for year. It was a fast track project with its fair share of problems, but the final project produced a functional and attractive building. A Tea Dance took place in the lobby of the hotel on July 17, 1981, with an estimated 1,500 and 2,000 people in attendance. Shortly after the dance began the suspended walkways above the lobby collapsed. It would be remembered for its tragic deaths resulting from the most catastrophic structural failure in the United States. The collapse resulted in 114 deaths, more than 180 injuries, and emotional trauma to many more. It served as a wake-up call across the engineering and steel fabrication community. This paper will focus on the evaluation of the box beam to hangar rod connection and the structural analysis that should have been completed to check the design. First, results of the National Bureau of Standards load tests on exemplar connection will be discussed. Second, an evaluation of the weld that was used to connect the two C-channels will be discussed. Third, an approximate structural analysis of the box beam under the concentrate load of the hanger will be described. Lessons learned for structural engineers of all experience levels will be included. This paper will be helpful to engineers in understanding the importance of analysis of the crucial details of a connection that may appear rudimentary on the surface.

Punching shear at concrete columns is a critical failure mode in a conventionally reinforced or post-tensioned concrete flat plates. Because shear failure is non-ductile, design deficiencies, unanticipated load conditions, and construction defects can result in catastrophic failure with limited warning signs. Therefore, investigation of potential problems in flat plate construction requires an understanding of the structural behavior at failure and the critical components to observe and document during investigation. Modern codes incorporate detailing requirements for continuity in order to reduce the risk of sudden collapse; however, structures constructed prior to these code modifications may represent a risk to occupants and property when the load conditions exceed the nominal capacity. This paper presents expected crack patterns at column to plate connections, relevant code provisions governing the design and detailing of these connections, and what to look for when investigating potential shear problems in these structures. Additionally, efficient methods for repair and retrofit of shear deficiencies in these structures are presented, based upon successfully completed and tested retrofits.

A 3-D printer was planned to be installed inside a one-story laboratory building. Manufacturer of the 3-D printer had specified the maximum allowable vibration of concrete slab-on-grade at the location of the 3-D printer to assure the accuracy of printing jobs. The laboratory building was located at about 100 yards from a set of highway and railway. An air conditioning unit, a bridge crane, and a drop tower were located near the planned location of the 3-D printer. A remote vibration monitoring system was utilized to monitor the vibration of the slab which was influenced by the ambient environment and machinery operations. Statistical analysis was performed to determine the probability distribution of the vibration data and estimate the probability of a vibration value exceeding the maximum allowable vibration value. In this study, the vibration of the floor slab met the requirement for the installation of the 3-D printer.

Construction of a megatall tower foundation was suspended in October 2016 over concerns related to concrete uniformity and the presence of surface water during construction operations. The foundation design consisted of a four meter thick reinforced concrete transfer mat set on a network of 136 drilled concrete piers. The authors were retained as third party advisors to independently assess the as-built conditions and assist the contractor and designer in the formulation of a repair plan. The investigation commenced in December 2016 and included documentation of cores extracted from the transfer mat as well as the development of procedures to effectively ascertain conditions within the core holes. Of particular concern to the construction team was the development of a sufficiently representative sampling plan, the relative shear strength and performance of concrete joints, and the evaluation of corrosion potential within the transfer mat. A plan to repair affected locations of the transfer mat was developed to address the nature and type of conditions identified during the investigation. The repair recommendations developed by the authors were widely approved by the construction team.

A bridge construction firm manufactured precast concrete slabs for the deck replacement of a major East Coast bridge. The slab segments were removed from the casting bed, transported to the lay-down site, and supported on dunnage. Cracks started to appear soon after. The authors were retained to determine the cause of cracking, feasibility of repair, and potential repair methods. Based on our analysis, cracking was due to excessive tensile stresses caused by the configuration and differential settlement of temporary supports at the laydown site. Assessment of concrete quality, crack type and size, and expected service level stresses identified that a gravity-fed methacrylate or epoxy repair, combined with crack injection, would restore intended serviceability of the slabs. This case study illustrates the importance of carefully considering temporary construction loads on structural members, including the significance of structural assumptions such as perfectly rigid support conditions. The study also identified sensitivity of the bridge slabs to fit-up tolerances in the likely to be encountered during permanent installation of the slabs.

This study examined the scientific basis for the tile tap method by comparing the results obtained using the human ear to sensitive auditory equipment. The study was composed of six tasks: (1) create a representative non-bonded tile, (2) identify the best tapping instrument, (3) evaluate tapping on different tiles, (4) identify the predominant sound frequencies from bonded and non-bonded tiles, (5) determine whether distinct frequencies could characterize non-bonded areas of tile above and below the thin set, and (6) determine the detection limit for increasingly smaller portion of non-bonded tiles. This study examined six types of floor tile (ceramic, travertine, marble, porcelain, limestone, and sandstone) and used wax paper beneath the tile to provide the best non-bonded sound. Among these tile types, marble exhibited the most modest difference between bonded and non-bonded areas. In general, the sound frequencies were lower and louder among portions for non-bonded tiles when tapped. Among the 18 different tapping instruments tested, a 2-inch steel ring produced the most distinctive sound for human ear perception to both bonded and non-bonded tiles. Microphonic analysis, unlike the human ear, was capable of distinguishing the difference in sound frequency produced between the non-bonded areas above and below the thinset. Finally, the detection limit for the tapping could distinguish area separations of approximately 9 in². The study concluded that the tapping method supported the non-bonded versus bonded distinction by the scientific method though some tapping instruments were shown to be better than others.

The American Concrete Institute (ACI) is generally recognized as the authority on concrete in the United States, including materials, analyses, design, and repair of new and existing structures. ACI recognizes two different load test protocols that may be used to evaluate the strength of existing concrete structures, understanding that one protocol may be better aligned with project parameters than the other protocol. The two test protocols are the cyclic and monotonic (or 24-hour) tests. Each of the protocols, their application, and acceptance criteria are outlined in ACI 437.2-13, a code-level document titled Strength Evaluation of Existing Concrete Structures. This document is directly referenced by ACI 562-16 Code Requirements for Assessment, Repair, and Rehabilitation of Existing Concrete Structures and Commentary. In addition, adoption of 437.2-13 provisions (including cyclic test protocol and test load magnitudes) is being considered by ACI Committee 318, the committee that produces the Building Code for Structural Concrete. As engineers use the relatively new repair code (ACI 562) more often and gain familiarity, they should also be aware of available load testing provisions cited by the code. The monotonic test protocol has been a part of ACI since the first half of the 20^th century. The cyclic test, on the other hand, has only been recently introduced to ACI committee documents, beginning with ACI 437.1R-07 and now in ACI 437.2R-13. Although the two load test methodologies are now both available to engineers, the use of the cyclic test within the U.S. has been limited, in large part due to familiarity and code acceptance of the test. Differences in the application of each of these test protocols lend each to being better suited to specific project applications. In addition to presenting the recent history of the load test protocols, two case studies will be discussed in which the selection of the test protocol was based on its suitability to the respective project.

This paper presents a fitness-for-service (FFS) assessment of wind turbine towers currently in service. The turbines had been in service for several years before the manufacturer determined that the towers were inadvertently manufactured with crack-like defects that were not identified during quality control. This revelation resulted in the possibility of crack propagation over time, which could remain unnoticed in between infrequent visual inspections during routine maintenance. Cracks could grow long enough to threaten the serviceability or even the survivability of the towers. While it was possible, using the principles of deterministic fracture mechanics, to determine the maximum allowable crack length before fracture is expected to occur, and hence the remaining life in years, these types of calculations may be excessively conservative, depending on the material properties, and loading parameters assumed. A much more definitive quantification of failure risk was determined, by evolving deterministic fracture mechanics into probabilistic fracture mechanics. This approach runs tens of millions of individual fracture calculations by addressing the inherent spread in material behaviors with return periods of turbine specific load cases, culminating in the determination of a probability of failure over time. The manufacturer could then compare these probabilities with industry allowables, helping to manage their risk. These risk measurements also helped determine appropriate frequencies of inspection, helping to further alleviate manufacturer and owner concerns. This paper will benefit the engineering community by introducing them to state of the art analytical tools available for determining the status of damaged infrastructure, helping to make informed repair/replacement decisions.

Defects in a building’s water-resistive barrier (WRB) and veneer drainage systems are in direct conflict with modern building codes, industry standards, and manufacturers’ instructions and create avenues for water intrusion and/or the accumulation of moisture within the building envelope system. The effects of the damage resulting from these defects are not always readily apparent and are often concealed in the form of deterioration of the structural sheathing and framing systems. Moisture intrusion through the building envelope and deficient discharge of the moisture from the veneer drainage system may result in moisture distress to the structural framing over time, ranging from latent to severe and unsafe conditions. The authors have investigated hundreds of water intrusion cases and have found over the course of these investigations that evidence of the moisture intrusion and damage to the structural systems may not be revealed by distress at the interior finishes or manifested at the exterior façade. The lack of reliable correlation between exterior and interior distress and framing deterioration necessitates the removal of exterior finishes to determine the condition of the structural framing. This paper is case study-driven and provides examples of both positive and negative correlation between visible interior and exterior distress and the extent of underlying structural damage observed through destructive testing.

Vertical pressure vessels and storage tanks are among vital structures that may undergo significant degradation over their life span. The current study investigates fitness-for-service (FFS) of steel methanol tank. The tank is composed of six courses of plating along the height of the tank. Upon inspection, significant corrosion and deep pitting was identified at various locations in the tank with severe and extensive metal loss near the bottom of the tank. The aqueous chloride environment coupled with tank operating scheme is responsible for the corrosive damage. The mechanism for the concentrated metal loss in the tank bottom and the decreasing impact proportional to elevation is the same. This study discusses the probable corrosion mechanism focusing on the tank components that may limit the remaining life of the tank and recommendations to address the limiting components in the tank. Due to the severity of the deterioration, detailed Level III FFS analysis per API 579, which requires detailed 3-D nonlinear finite element analysis, has been performed to gauge the remaining life of the tank. The results of the analysis indicate that the likely failure mode is buckling in shell course 2. Repair recommendations have been made, the repair strategy was to add reinforcing steel to the deteriorated shell course bands that are susceptible to buckling, which consisted of steel plating seal welded to the existing cylinder. A parametric study to determine the corrosion thresholds and minimum tank thickness required to preclude buckling under normal operating conditions has been performed.

The forensic engineer recognizes the importance of metal corrosion as a diagnostic tool when conducting a building investigation. This study advances the scientific community’s use of qualitative analysis by reporting the results from three long-term moisture exposure studies. The study was divided into two tasks: 1) creation of a moisture exposure chamber that would allow repeated exposure of study exemplars to fresh water and salt water mists repeatedly over extended periods of time (months), and 2) documentation of the gradual changes that occurred in the specimens as they experienced surface oxidation, discoloration, and the presence of advanced surface corrosion. The study was conducted over three test periods. The first and second test periods were conducted over 244 days and 461 days, respectively. These tests documented qualitative changes to galvanized steel pieces (i.e., corner bead, framing, sill plate, electrical conduit, metal lath, galvanized pipe, and brass fitting). The third study was conducted over 122 days and documented changes to metal components commonly found in the plumbing/building materials for bathrooms and kitchens. These components consisted of stainless steel water supply lines, angle stop valve handles, escutcheon plates, under sink mount brackets, concealed and face cabinet door hinges. The components were exposed to fresh water and seawater using modified methods from ASTM Standard B117. Controlled tests were conducted within an acrylic and polycarbonate test chamber equipped with a recirculating solution system. Frequent time-lapsed photography documented the corrosive effects facilitated by continuous fresh and salt water exposure. The test procedure enabled evaluation between both wetted, humid, and un-wetted (control) specimens. The photographs document qualitatively equivalent exemplars that were compared to “real world” component installations affected by a water loss. These comparisons facilitate determinations of loss duration under conditions of a worst-case, water exposure scenario.

Forensic engineers and scientists often encounter water damage associated with copper tubing leaks. This article examines the use of galvanized piping and the reasoning behind the transition to copper tubing materials during the years between the 1930s and the early 1960s. A brief description of the proper technique to prepare solder joints following ASTM B 828-00 methods precedes the primary objective of the paper, explaining examples of the two primary categories of copper tubing failure: non-uniform and uniform corrosion. Case examples accompanied by photographic documentation will help guide an investigation into the origin and cause of failure. The paper discusses non-uniform corrosion derived from installation-related errors using both hard and soft copper tubing materials. Examination of installation procedures with accompanying case histories demonstrate an effective interpretation of various types of copper corrosion. Failure related to the application of “poor plumber’s hygiene”, excessive flux, improper tubing preparation, improper joint cleaning, and “cold solder joints” will be presented. The occurrence of uniform interior copper corrosion is presented in terms of water quality, sulfur-reducing bacteria, aggressive soil conditions, and antibacterial additives. Finally, the placement of copper tubing through concrete slabs and the historical evolution of various pipe sleeving techniques to minimize galvanic action will be described. The paper will conclude with investigation methods and analyses that will help lead an effective investigation of copper tubing failure.

The present paper begins by briefly discussing research on construction failures caused by computer-related errors. The failure of the Sleipner A Platform serves as a detailed case study to point to the dangers inherent in computer-related errors. Next, the paper discusses the two broad categories of computer-related errors: system errors and user errors. The paper continues to discuss the main factors affecting user errors: analysis novelty, complexity, and experience. Typical modeling errors are listed next: wrongful structures and loads, erroneous or omitted failure modes, inadequate finite element types, and deficient meshing. Proper meshing requires attention to convergence, curved boundaries, and local mesh refining. To prevent computer-related errors, the steps of a comprehensive analysis validation are presented. An integrated framework to prevent system and user errors encompassing the following components is derived: software validation, factors affecting user errors, analysis evaluation, and lessons learned.

Engineers and other design professionals are held to “the standard of care” when the possibility of their negligence is being assessed. If it is determined professionals failed to meet that “standard,” they can be liable for damages arising from that failure. This paper is intended to explain what the “standard of care” is, what might a forensic engineer do to assess and to testify regarding a practitioner’s actions relative to the standard of care, and what the standard of care of a forensic engineer might be.

Florida is known for the phenomenon of sinkholes. Homeowners submit claims to insurance companies when they observe minor signs of distress such as cracking in their walls or floors, doors or windows that stick, and sinking or differential settlement of their driveways, patios, and interior floors. While these signs may indicate the potential for sinkhole activity, they are not conclusive evidence. Further investigation and monitoring is required. Insurance coverage applies only if structural damage to the covered building was caused by sinkhole activity. Florida Statutes do not have clearly established criteria and situations arise where the homeowner’s engineer argues for and the insurer’s engineer against sinkhole activity. Ethical ambiguity arises when one party argues definitively for and the other against, and yet, the homeowner continues to live in the home. As engineers, we are required to uphold a high ethical code to “safeguard the life, health, property, and welfare of the public.” If the engineer truly believes there is sinkhole activity, the occupants should be relocated and proper remediation implemented. Several case studies will be presented with continued occupancy.

Construction documents are the written and demonstrative representation of the expected finished structure. The expectation of design professionals is to provide clear, unambiguous documents for the construction team to follow, i.e. the GC/CM, their subs, and fabricator. Two case studies will be presented that illustrate construction projects where contract documents and/or shop drawings were alleged to be deficient resulting in misalignment in construction, a structural failure, and subsequent personal injury and property damage. The purpose of this paper is to provide a basis for discussion by structural engineer professionals after the presentation of factual evidence with respect to relevant construction documents, as-designed and as-constructed details, and resultant incident. Questions will be posed to promote thought and further discussion regarding current design and construction practices in the industry, specifically with respect to each party’s responsibilities and the standard of care. Specific incidents include a failure of a temporary weld connection of an ornamental stair steel stringer resulting in an iron worker falling over 20 feet, and ambiguous design documents and factory assembly resulting in misalignment of connection during erection of box girders.

Experience shows that in review of design and construction documentation, design errors are sometimes present. Very often, the errors are inconsequential to the service life or performance of the constructed facility. Unfortunately, in other cases, design error often brings about eventual failure or misbehavior of the built environment resulting in damages to property or injury to persons. While most designers successfully engage in daily practice without mishaps, designers sometimes render inadvertent mistakes or step outside their realm of competency in producing their design product. While a study of the historical aspects in the education and training of engineering practitioners might be of benefit to the practice, this paper deals more simply with a number of cases in which design errors, some of which were seemingly insignificant, yielded considerable liability for the designer of record. A background for each case is supplied, the respective error identified, and the consequences conveyed. Finally, observations of how the designers might approach their work to avoid similar errors are listed.

In developed urban areas, many sites have near surface materials described as urban fill (brick-bat, concrete rubble, and debris/garbage) which are hidden from the design team. Urban fill materials are variable in composition and density and therefore often result in slab settlement/movement and cause millions of dollars in damages/repair costs and impacts to operations. A solution is to both properly identify urban fill and properly remedy the subgrade. For loose urban fill, permeation grouting is one of the solutions that has exhibited success. In one case, the project team selected compaction grouting which in fact made slab settlement worse, due to the presence of compressible soft soils below, insufficient overburden pressure and extra weight of grout led to new settlement of soft soils below the urban fill. Two case studies are presented. An existing apartment building experienced wall and slab distress issues. The distress included floor slab settlement/cracking/movement, sloping of the floor slab, buckling of the metal framing in the interior walls and ceiling due to forces applied to the interior walls, and damages to below slab utility conduits. The apartment building floor slab-on-grade settlement/cracking/movement and interior wall distress were related to the long term consolidation/compression of loose urban fill that was likely placed as backfill during demolition of old structures at the subject property or used to raise the grade from historic ravines. Permeation grouting of the loose urban fill and reconstruction of the concrete floor slab-on-grade were performed to remediate the problems. A school floor slab had settled several years after construction as a result of consolidation/settlement of loose urban fill. A preliminary recommendation from a structural engineer recommended compaction grouting. The settlement recurred a few years later after compaction grouting.

Forensic engineering is a widely used term in engineering practice. Forensic engineering is often confused with having the resources to perform testing as opposed to having a thorough understanding of the different possible mechanisms that may affect a structure. The true challenge of forensic engineering is to be able to identify the cause of a problem among the many other damaging mechanisms or distress affecting a structure. Performing field testing may be an obstacle to solving a problem unless the testing is well defined based on an understanding of the problems and goals of the investigation. Being part of the solution does not mean identifying what was not correct, but being able to identify the technically correct solutions to a problem. This paper discusses case studies highlighting the benefits of the cooperation between concrete petrography and structural/materials engineering in identifying the actual cause of problems which had been previously misdiagnosed.

ASCE defines forensic engineering as the application of engineering principles to the investigation of failures or other performance problems. While notoriety is often gained for the investigations and case studies following large catastrophic failures, smaller scale investigations using these same principles occur almost daily on construction projects in the form of non-compliance, incident, and near-miss reports. However, these data are often rendered inaccessible upon project completion, and the learning opportunity to the wider community wasted, only remaining as tacit or experiential knowledge. Additionally, these data are predominantly captured in written prose, an unformatted style, therefore analysis is hindered by the lack of techniques to deal with data of this type. This results in restricting learning to fewer significant cases to avoid inundating people with constant minor alerts or updates. This paper will determine how recent research can be leveraged to implement learning from everyday forensic engineering by presenting a framework that uses recent developments in both the data analytic and natural language processing fields. It will demonstrate a hybrid natural language processing and knowledge discovery framework to transform everyday forensic engineering data into a valuable resource exploitable for learning.

Precast structures are a preferred method for the construction of parking garages in the United States. These garages often employ precast double tee beams for the garage deck system. The pre-topped precast double tees of a finished wearing surface, serve as part of the lateral force-resisting system as well as gravity support for vehicle loading. The vehicle loading imposes both static and dynamic loading on the double tees. To transfer the repeated or cyclic loading from one double tee to the adjacent member, shear connections are provided near the ends of the flanges at routine intervals over the length of the tees. Over the past fifteen years considerable research has studied the flange-to-flange shear connection details. While improvements have been made during this time period, several precast garages have shear connections that have failed due in large part to fatigue induced distress within the connection assembly. While industry advances the state of practice with regard to shear connections, several garages have been constructed with older shear connection technology that remain in service and are prone to shear connection failures. The paper provides a case study of an existing parking garage with pre-topped double tees using steel plate connecting hardware that was popular in the late 1990s through early period of the current decade (T-108).

Precast concrete double-tee (DT) beams are used extensively in parking garages due to their relatively ease of construction and low cost. Three case studies will be presented of different projects in which the stems in DT beams were damaged. The processes for evaluating and repairing those stems will be discussed. In the first two case studies, a stem was damaged by impact from vehicular traffic. A full-depth repair of the impacted stem was chosen as the repair method for both case studies, but considerations to ensure a sound repair, such as shoring, preloading, and venting, will be discussed. In addition, the two case studies will be contrasted to identify why one was more successful than the other. In the third case study, investigation and repair of DT stems that were cracking and spalling in a precast yard and during transportation to the project jobsite will be discussed. Field load tests were conducted to confirm the mechanism of the distress as well as develop an appropriate repair strategy. The use of a mild reinforcing bar that did not extend the full length of the beam was concluded to be the culprit: unintended compressive stresses developed near the ends of the mild reinforcement as a result of the prestress eccentricity. The repair strategy to address the cracking concerns will be presented.

Silos are most often constructed of steel panels or reinforced concrete; and are typically used to store bulk solids such as food, fuel, and feed for livestock. Because the stored bulk material is flowable, silos are subjected to complex load scenarios requiring unique design considerations. In the spring of 2013, a recently constructed reinforced concrete silo storing solid biomass material suffered a catastrophic failure resulting in displacement of the stored material and complete loss of the structure’s use until it was repaired. Additionally, multiple neighboring silos, which were of comparable construction and design, manifested similar distress patterns to those observed at the subject silo just prior to its failure. The objective of this paper is to explain the investigative methodology and conclusions drawn regarding the failure mode of the subject silo. The investigation revealed that the failure initiated at a concrete keyway cast into the silo wall at the silo’s elevated concrete floor; and that the failure was caused by construction defects.

Silo structures are utilized in many industries (e.g. energy, mining, cement) throughout the world to store granular bulk solids such as coal, cement, raw materials, and mineral ores among many others. Every year the news headlines about structural failures are alarming and, in many cases, not only economic loss is involved but also loss of human life. These failures usually occur due to inadequate design, poor construction, improper usage, and/or lack of maintenance. In this paper we will discuss the first item: silo failures due to design errors. Certainly, if the silo design is inadequate, the life and performance of the storage structure will be affected. A catastrophic collapse may occur when the structure is first loaded. Even if this doesn’t happen, signs of distress can appear over time. This has a lot to do with the stored material behavior and the loads (e.g. normal pressures and shear stresses) exerted on the silo walls, and how the silo’s structural system reacts those loads. This kind of interaction is often not well understood at the design stage. Engineers in charge of the design and construction of concrete silos will benefit from this paper as they will be able to understand the structural implications of concrete silo design as well as the loads imposed by the stored material. Forensic engineers will be able to identify areas of distress in concrete silos caused by different loading scenarios commonly observed in silo structures. This will allow them to make more educated decisions during their engineering work.

Service life estimates in the context of forensic engineering provide information valuable to quantify the observed (or alleged) damage. However, service life estimates are often a single, deterministic value despite recognition of the variance in the parameters used for the estimation. This paper evaluates the sources of variance in service life estimates and their consequence on the final life estimate through an example of initiation period of chloride induced corrosion of reinforcement in reinforced concrete structures. The effect of industry standard variances, including variance allowed within ASTM test procedures, and ACI tolerances, on the uncertainty in the corrosion initiation period were explored. The analysis helped identify the parameters that play a dominant role in the variance of the initiation period estimate. The paper highlights the value of this probabilistic information to the involved parties in properly estimating the scale and impact of the observed (or alleged) damage.

Over the last century, researchers have continuously improved concrete mechanical properties, including toughness. Despite substantial improvements in engineering properties, brittleness and low toughness still are two weaknesses of cement-based composites. Reinforcing cementitious composite with carbon nanotubes (CNTs) is an effective method to address both problems. The main objective of this experimental investigation was to assess the effect of synthesizing multi-walled carbon nanotubes (MWCNTs) and cement matrices on the toughness of cementitious nanocomposite. In this research, 0.2 wt%-0.6 wt% of MWCNTs with a water-to-cement ratio of 0.4 were utilized to make a cementitious nanocomposite paste. The drop-weight impact test was used to measure the toughness of the specimens. The results indicated a significant enhancement in energy absorption of the cementitious composites. Additionally, MWCNTs additive decreased crack propagation and debris spatter of the specimen subjected to the impact load. Moreover, the failure mechanism showed less brittleness throughout changing the radial-to-diagonal failure pattern.

Alkali-silica reaction (ASR) is a deleterious internal expansion in Portland cement concrete caused by the reaction between alkali from the cement and/or pozzolans and reactive silica aggregates in the presence of moisture. ASR has resulted in significant damage to concrete infrastructure throughout the United States and worldwide. This paper discusses ASR with a focus on the evaluation and repair of existing wastewater concrete infrastructure. This infrastructure is particularly susceptible to ASR because much of it is used to convey and contain water, which raises the internal humidly in the concrete over extended time periods. Since the expansive ASR reaction requires water, high internal humidly in concrete can contribute to the development of ASR under the right conditions. Additionally, a case study is be presented which illustrates the evaluation of existing wastewater infrastructure for ASR and how a structure affected by ASR can be repaired and its service life extended in a cost-effective manner.

Alkali-silica reaction (ASR) in concrete structures is a well-known damage mechanism. The mechanism of near-surface ASR (NSASR) differs from traditional ASR in that the reaction occurs relatively quickly, occurs only near the top surface of a concrete slab, extrudes gel onto the surface of the slab, and does not result in widespread cracking of the slab. Evaluations of residential and commercial structures in Central Texas have determined the presence of this mechanism. Through recent case studies, this paper will discuss factors that cause and/or exacerbate NSASR and the patterns of NSASR distress. These case studies involve slab-on-grade foundation systems with many similar conditions, but with some important variation in the factors which contribute to NSASR. This paper will also discuss in situ testing and material testing performed for the case studies and how the results of these tests correlate with some common theories related to the causation of NSASR in slab-on-grade foundation systems. Finally, the paper will discuss potential future laboratory testing to study the NSASR mechanism and the effects of specific causation factors.

A full-scale, in situ load test was performed on a composite canopy structure. The canopy structure is characterized by 3-3/8-in. thick composite panels composed of stainless steel and aluminum sheeting with an aluminum honeycomb core, bonded with adhesive. Embedded aluminum tubes act to provide additional flexural capacity and stiffness, allowing the canopy to cantilever up to approximately 15 ft. from the building. Shortly after construction, excessive deflections were observed, and upon review of conditions, retrofits were specified by the engineer of record. A load test was recommended to verify that the canopy could support code-prescribed loads, subsequent to the installation of repairs. Our team was called upon to develop and implement the testing and instrumentation program. Following the load test, our team was tasked with designing additional structural retrofits to strengthen and stiffen the canopy. An analytical model of the canopy was developed using CSI SAP2000 software, and results of the load test were utilized to verify the relative accuracy of the modeled behavior. Upon consideration of several unique variables, including material nonlinearity, panel delaminations, and loose, missing, and sheared fasteners, the results of the analytical model were compared to the load test results under various loading increments and were deemed to be reasonably accurate. The validated analytical model was subsequently used to analyze the effectiveness of a series of proposed retrofits.

Dual-temperature secondary water piping for perimeter HVAC systems became ubiquitous in mid-20th century urban construction, for both commercial office and residential high-rise buildings. Proper design and water treatment have allowed for decades of service. Many of these systems, however, have reached the end of their designed service lives. Failure analysis case studies involving secondary water piping systems will be presented, detailing a variety of root causes, including under-deposit pitting corrosion and insulation degradation. Discussion will also include non-destructive inspection techniques, the realities and limitations of current water treatment options, and the imminent HVAC system replacement decisions that will become more prevalent in the next decade.

This paper presents a study of the snow load requirements per governing New York State (NYS) codes since the 1990s to present day (particularly the transition to adapting International Code Council codes in 2003), and discusses maintenance requirements for air supported structures during major snow events as outlined in various standards and by a manufacturer of air supported structures. This paper also presents a case study of a collapsed air supported structure in New York State and the snow loads for which it was designed. The author found that the design snow loads met the manufacturer’s requirements and the requirements of an ASCE standard, but that they did not meet the current NYS building code requirements.

Occasionally, in forensic engineering there are claims of damage to buildings from the vibrations caused by construction or vehicular traffic. The first steps in investigating these claims includes a condition evaluation of the structure to observe any damage. An evaluation would be conducted of any damage to hypothesize the cause of the damage. To validate the hypotheses, an evaluation of the conduction of vibrations from the source may be made. This may include instrumentation of the site and replication of conditions causing the alleged vibrations. In the absence of instrumentation, the use of formulas that approximate the conducted vibration can be used. Comparison of the measured or calculated vibrations to established thresholds for damage can be used to validate the hypotheses. This presentation will provide a description of a case involving claims of vibration damage to a 100-year old brick residence from buses and large trucks hitting an un-topped, 3-inch deep construction area in the street. A description of the investigation, observed damage, and analysis will be included. A description and comparison of the published damage thresholds will also be included. Additionally, a description and comparison of three approximate methods to calculate vibrations will be provided. These include the Federal Transit Administration (FTA) generalized ground surface predication method, the Watts method, and the Caltrans method. A discussion of the difference between felt vibrations and damaging vibrations will also be included.

Wind, and rain combined with wind can induce unwanted vibrations in bridge stay cable that have not been aerodynamically enhanced. Both of these phenomena have been identified and aerodynamic or mechanical devices have been deployed to enhance the intrinsic damping in these typically lightly-damped cables in order to minimize the susceptibility of stay cables to vibrate. Unintended vibrations can lead to short- and long-term issues with fatigue. The authors of this paper were involved with an assessment of a set of stay cables in order to analyze the propensity of these cables to vibrate; to identify the phenomenon that could potentially excite the cables; and to determine the need for any supplemental damping to mitigate the vibrations. Initial analysis of the sources of wind-induced vibrations was based on an assumption of mechanical damping in the cables and was informed by previously reported estimates of damping in similar cables. The inherent damping in bridge stay cables is quite low and is heavily dependent on the cable anchorage and finished surface of the cables. A good estimate of this inherent damping is critical in understanding the likely response of stay cables to wind-induced excitation. Therefore, a program of in situ measurements of the frequencies of vibration and damping in the stay cable was also conducted. The paper will describe the analytical assessment of stay cable vibrations, field measurements, and design of the supplemental damping systems.

During the life of a structure, there are many service loads that can create disruptive vibrations. These vibrations may not create a concern for the strength capacity of the structure but, due to the frequency, amplitude, and occurrence interval, may be disruptive to the building’s occupants and operations. Further, the problems caused by these vibrations can seem insurmountable to building owners. This paper discusses best practices for investigating complaints of floor vibrations within a structure. A three-stage process of dynamic testing, load and structural modelling, and remediation performance predictions is described. This paper presents results that are encountered for a variety of potential scenarios and structures. Several types of floor loading are considered including impulsive loads, harmonic excitation caused by human occupants, and periodic excitation from machinery. Various design standards including ISO 10137, AISC Design Guide 11, and CRSI’s Vibration Design Standard will be discussed and the recommended loads, analysis procedures, and acceptance criteria will be compared. An illustrative example will be discussed along with general remediation options.

While tall buildings are being constructed at an increasing rate worldwide, a number of new and older structures have experienced excessive wind-induced vibrations. Tuned mass dampers (“TMDs”) can effectively mitigate wind-induced vibrations. Traditional TMDs are however difficult to post-install in existing buildings because they require significant space near the top of the structure and impose large concentrated gravity loads. Thornton Tomasetti has developed a modular TMD system with the objective of simplifying TMD design and installation. The modular TMD consists of off-the-shelf plastic pipes filled with air and water and interconnected to create a resonant system. In an existing structure, the mass of the system can be distributed to occupy space that is already available while minimizing the gravity loads imposed locally. This paper describes the modular TMD system and presents a case study on potential retrofit applications.

Exposure to coastal flooding has traditionally been studied by estimating the likelihood of flooding at a single location using return level curves. While a cornerstone of flood risk analysis, this approach neglects the spatial impact of flood events capable of affecting assets over large areas simultaneously. Understanding the joint likelihood of flooding at multiple locations is important when studying critical infrastructure systems comprising interdependent networks of energy, fuel, and water systems. Recent events such as Superstorm Sandy (2012), which led to power outages to over 8.5 million customers and severe fuel shortages, highlight the devastating consequences of cascading failures both within and across infrastructures systems due to flooding. In this study, a bivariate copula is used to estimate the joint return period of storm surge flooding at two locations flooded during Sandy (the East 14^th Con Edison electrical substation and the Port Reading Hess refinery). The analysis is based on simulated storm surge from a database of 566 synthetic cyclone events.

Located in the tropics, the Republic of Mauritius is exposed to a number of natural disasters such as cyclones and torrential rains commonly causing flash floods. The World Risk report 2016 ranked Mauritius 7^th on the list of countries that are more exposed to natural hazards. Early warning systems (EWS) are recognized in both the Hyogo Framework for Disaster Reduction (2005-2015) and the Sendai Framework for Disaster Risk Reduction (2015-2030) as an important element of disaster risk reduction. When disasters strike, first responders need to understand new situations on the ground. They require timely, validated information that can be integrated into information products for efficient communication, situational understanding, and ultimately for better decision-making. Communication technology play an important role in disaster management, especially in the preparedness phase. This study assesses the status of EWS of floods in Mauritius, key gaps and challenges, and will propose a framework for a people centered early warning system using big data for flash floods in the country. The study is useful to professionals and policy makers involved in disaster management at all levels in applying early warning information for use in disaster management and mitigation. Currently, real time warning does not exist for flash floods in Mauritius. This research would be significant in enhancing awareness about incorporating big data generated from mobile phones for real time evaluation of the situation and importance of spatial data infrastructure.

The FEMA Mitigation Assessment Team (MAT) Program is managed by the Building Science Branch at the FEMA headquarters. Following natural disasters, the team conducts field assessments and makes technical observations on the performance of buildings subjected to the effects of natural hazard events. MAT observations are used to recommend changes to building codes and design standards, prepare recovery advisories, gather information to improve guidance and influence construction practices during repair, support the integration of hazard mitigation measures into the repair process, provide technical assistance related to code and standards, and contribute to research efforts. FEMA deployed a MAT to Aransas, Refugio San Patricio, and Harris Counties, Texas, following Hurricane Harvey. MAT investigators evaluated building systems to determine the effectiveness of various construction practices and ascertain the effect of code adoption and enforcement for reducing damage. To improve resiliency in future events, lessons learned from MATs can be incorporated into retrofits when mitigation measures are applied to existing buildings and when new buildings are designed. This paper provides a summary of the damages and the lessons learned related to building performance, focusing on the building envelope and dry floodproofing. Representative building envelope topics include roof systems, rooftop equipment, soffits, wall coverings (siding and veneer), and garage doors. With respect to dry floodproofing, it is anticipated design, construction, planning, and implementation considerations will be addressed. Dry floodproofing observations illustrate successes at sites retrofitted since Tropical Storm Allison and failure modes observed. The overall purpose is to communicate lessons learned to help improve building performance moving forward and demonstrate best practices that help reduce damage and prevent failures.

Estimating the load on a reinforced concrete retaining wall is very important and if not evaluated correctly can lead to damage or failure. The evaluation of the failure of three retaining walls and their repair is discussed. The first retaining wall failure consisted of a concrete wall retaining fill at a spillway for a lake. The influence of puddled water behind the wall and inadequate weep holes was evaluated. Because a highway was also located in the influence zone behind the wall, methods were investigated to temporarily retain the fill while the repair was completed. The second and third concrete retaining walls were part of two different grain storage buildings. Both failed due to inadequate design. One failed due to improper evaluation of grain bin loads and the other because an engineer did not design the wall. An evaluation of repair methods for both is discussed. This paper will demonstrate to engineers the important role that retained load determination has in the analysis and failure of retaining walls. Additionally, the role of temporary walls and repair methods will be helpful to structural engineers.

While the interior renovation of a 1970s mixed-use, cast-in-place concrete building seemed straightforward, complications quickly presented themselves. The work required trenching the existing lightweight concrete structural slab to accommodate new design features for the hotel’s lobby and gathering space. However, the demolition revealed unknown penetrations adjacent to existing columns, reducing the effective shear critical section perimeter by 35% to 65% depending on the location. The investigation included reviewing original drawings, documenting existing conditions, and conducting material testing to confirm concrete material properties. This investigation informed a finite element analysis that determined the shear stresses around the column while taking into account the effects of openings and unbalanced moments. Analysis indicated the openings compromised the two-way shear strength of the flat slab around three column locations. Design finishes constrained the strengthening measures, and operational and access restrictions caused work below the slab to be minimized. Design concepts were implemented using two solutions: the first using through-slab shear rods at the two columns with the less severe reduction in critical section perimeter, and a second using structural steel outriggers above the slab that support a hanging frame at the column with the most severe reduction in critical section perimeter. The findings will highlight the evaluation of existing lightweight concrete flat slab construction, shear stresses due to moment transfer between the slab and the support, and the impact of openings adjacent to columns. The strengthening demonstrates minimally invasive and innovative measures, as well as the application of research and testing findings.

WJE performed a structural analysis and designed splint shoring repairs for a parking garage at a university in Connecticut. The garage was built in 1974, and the original design specified a steel framed structure with nonstandard girder-to-column moment connections. The girders laterally brace the columns in the north-south direction at each slab. Lateral stability in the east-west direction is provided by ‘K’ bracing. During a routine inspection, WJE observed deformation of the column webs and flanges at the moment connections, a significant tilt in the columns, and severe corrosion of many steel members throughout the garage. An assessment of all steel columns and girders was performed, which included section loss measurements. To better understand the behavior and stresses in the garage, representative areas of the structure were modeled in CSI SAP2000 and Autodesk Simulation Mechanical finite element analysis software. The finite element model of a typical moment connection served to locate points of high stress in the connection, particularly at the bolts and welds. In combination with the finite element model, the SAP model provided better understanding of the behavior of the gravity system and the utilization ratios of the columns. Columns with critical utilization ratios and severe section loss were selected to receive atypical splint shoring repairs. WJE’s repair design accounted for significant axial loads in the columns and moment transfer at the existing beam-column connections.

Many well documented failures of post-tensioned (PT) strands have occurred and the potential seriousness of corrosion induced failures of PT is well recognized. This paper presents two non-destructive methods for investigating corrosion of post-tensioned structures. Also discussed are methods of mitigating corrosion and extending the service life of in situ post-tensioned tendons. The principal causes of corrosion of un-bonded (un-grouted) or bonded (grouted) high strength PT tendons is the presence of moisture (high humidity), voids, air (oxygen) contamination, and the presence of corrosive constituents adjacent to the PT steel. Moisture infiltration can occur during initial construction or from water leakage. Voids can result from poor quality grouting. Early identification and mitigation of corrosive conditions significantly reduces the cost of repairs and the risk of failure. Un-bonded PT cables are used primarily in parking and other commercial structures. The first section of the paper describes an effective method for identifying the corrosion potential of un-bonded PT cables. Methods to mitigate corrosion in un-grouted PT cables are then discussed. Problems with grouting techniques and grout materials used on thousands of bridges have resulted in voids, chloride contamination, and soft grout which has resulted in premature corrosion failure of bonded PT tendons. This portion of the paper describes the use of state-of-the-art nondestructive testing methods and an innovative corrosion mitigation technique specifically developed for grouted PT tendons. Field demonstrations and case histories confirming the effectiveness of these evaluation and corrosion mitigation methods are presented.

Structural assessment and evaluations were performed for the boathouse storage facility located at Lake Ridge Marina. The Lake Ridge Boathouse facility is a single-story wood framed structure. While the project was initiated from the wood decay observed at several wooden posts, the scope expanded to the other primary structural members including footings, floor framing members, roof trusses, exterior walls, and even the global structural stability of the structure due to the lateral loads. A series of structural analyses were performed to evaluate the capacity of the structural members due to the gravity loads and the lateral loads. Numerous repair and strengthening methods were applied to the existing structure. These included footing and wood column replacements, floor strengthening, new shear wall construction, steel rod cross bracing, roof truss strengthening, roof truss bracing, mezzanine railing, and reconstruction of the storage units.

Renovation of a restaurant in a suburban shopping center revealed numerous fractures in the prefabricated wood roof trusses. The building was constructed in the mid-1980s, and was about 30 years old at the time of renovation. The fractures were consistent with progressive strength loss attributable to fire-retardant treatment (FRT) chemicals that were commonly used in the 1980s. Several repair and strengthening schemes were considered, leading to the conclusion that the compromised trusses needed to be replaced in their entirety. This paper describes the discovery, diagnosis, and documentation of the FRT-induced distress, as well as the analysis and decision process that led to full replacement in lieu of retrofit. Additional background information on FRT lumber is provided, including a similar case study and prior laboratory testing performed by one of the authors. Unique characteristics of this case included a variety of service environments that ranged from conditioned space in an open-ceiling portion of the restaurant to un-conditioned attic space. Additional notable details of the retrofit are also discussed including the need to bring the roof into compliance with current energy code requirements, and challenges faced during replacement of the weakened roof structure.

Two recent structural failures in California resulted in fatalities, casualties, and subsequent changes in state building code regulations. Both failures were associated with wood framed construction and structural timber appurtenant assemblies, which are now identified as timber-framed exterior elevated elements, or EEEs. The California Building Standards Commission developed emergency changes to California Building Code regulations to address EEE issues identified as contributing to both failures. The “as-built” construction of the Berkeley balcony utilized three (3) layers of wood structural panel (WSP) horizontal sheathing nailed to the top of the cantilevered timber joists. Despite an exhaustive literature search, the authors were unsuccessful in finding research relevant for psychrometric evaluation of the multi-ply “as-built” construction of the Berkeley balcony. This paper presents the findings from the authors’ testing program developed and conducted to specifically evaluate wetting and subsequent drying rates of multi-ply assemblies of near-horizontal WSP.

Wood truss members that have been in service for decades can sometimes fracture unexpectedly under normal service loading, often with little more than the dead load of the truss and supported building elements. When wood members are subject to relatively high stresses over long periods of time, a reduction in strength of the wood member can occur, especially when the imposed dead load is high relative to the allowable design load. Creep rupture occurs when load duration effects cause a sufficient loss of strength to result in fracture. This paper examines the following: 1) The basis for load duration failure models and what they predict. 2) How allowable design values are derived, how they have changed, and how load duration is accounted for. 3) How time to failure under sustained loading can be predicted. 4) Example case studies of wood truss elements that have fractured due to load duration effects.

Historically, Oklahoma has not experienced earthquakes. This has changed over the last few years, with the state experiencing an exponential increase in earthquakes. This development correlates with an increase in oil and gas industry wastewater injection well activity. Fortunately, to date there does not seem to have been any loss of life, but some have caused significant structural damage, with buildings condemned and demolished. Adjustments to earthquakes, however, have been minimal, both at the state and individual level. Given that most of the focus within the state has been on wind events, practices have focused on mitigating that risk. Questions have been raised, however, as to whether strengthening structures against high winds and tornadoes may also add mass and vulnerability for earthquakes. This paper reviews the recent history of earthquake activity as well as some of the reported damage. A new reality of earthquake activity in Oklahoma presents significant engineering, insurance, risk management, and public policy challenges.

Reinforced concrete shear walls are part of the lateral force resisting system for many low- and medium-rise buildings. Such reinforced concrete walls will likely be damaged in design basis and maximum considered earthquake shaking. Engineers tasked with evaluating an earthquake-damaged building must determine whether the lateral strength and stiffness of the building has been compromised. A structural repair may not be necessary for a damaged wall if the earthquake-induced displacements are less than the displacement associated with peak shear strength. However, there are no quantitative data in the literature that correlate crack widths and lengths, and extent of spalled concrete, with the peak shear strength of a wall. A correlation of damage observed at zero lateral loading to peak shear strength would be beneficial to the design community for informing post-earthquake repair strategies. In this paper, the damage sustained by 12 squat reinforced concrete shear due to fully reversed cyclic loading is presented, enabling the reader to judge whether peak shear strength has been achieved using crack widths and lengths, and extent of spalled concrete, measured in the post-earthquake (unloaded) condition.

In November 2017, a 7.3-magnitude earthquake—the deadliest in 2017—happened 30 km southwest of Halabja, near the Iran-Iraq border. It was a shallow earthquake with its focus located at 11.8 miles below the ground surface. The death toll rose to 530 with nearly 7,900 wounded mainly in Iran’s western province of Kermanshah which was very close to the epicenter. The shockwaves were also felt in Turkey, Kuwait, and other neighboring countries. The earthquake left nearly 70,000 people homeless and in need for shelters. It caused damage to many buildings and devastated large areas in western Iran and eastern Iraq with majority of the lives lost and property damage to be concentrated in western Iran. The earthquake caused total or partial failure to many residential and commercial midrise buildings. It damaged a hospital and a few emergency response centers in nearby towns. The earthquake triggered major geotechnical failures that, in turn, made rescue efforts difficult. The Iran-Iraq border region is located above a highly active seismic zone where Arabian and Eurasian tectonic plates collide. Many houses in these rural regions are made of adobe and masonry and never certified or tested to withstand a seismic event. This paper aims to investigate the main reasons for building collapses and factors lead to such tragedy. It studies the lessons learned from emergency preparedness and crisis response efforts as well as the role of increased consciousness of natural disasters among all stakeholders—the agencies and the public.

To promote failure literacy of professionals in the sectors of architecture, civil and architectural engineering, and construction, and to reduce risk to the general public, the Education Committee of ASCE Forensic Engineering Division has published two editions of the Failures in Civil Engineering book since 1995, covering fifty short case studies of structural, geotechnical, environmental, and hydraulic failures. Eight additional case studies of steel structures failures, including the West Gate Bridge Collapse, I-35W Bridge Collapse, Pittsburgh Convention Center Expansion Joint Failure, and others observed between 1970 and 2013, are covered in the first volume of a new Failure Case Studies Series, to supplement the previously published case studies. Each case study briefly outlines the failure, summarizes lessons learned, and provides a list of references for further in-depth studies. This paper discusses the contributions of forensic engineering education initiatives to the technical and professional development of architecture/engineering/construction management (AEC) students and AEC professionals to learn from both successes and failures of civil engineering projects. It offers guidance on the use of case studies to recognize root causes of failures, which often are a result of multiple factors, including design errors, construction defects, material deficiencies, and others. Finally, the paper demonstrates how failure case study publications are an effective way to promote failure prevention based on lessons learned from previous failures.

This study aims to understand the conditions and the mechanisms that led to aboveground storage tank (AST) failures during Hurricane Harvey. First, a detailed survey of the damage suffered by ASTs is performed using aerial imagery and governmental incident databases. Analysis of incidents identifies to two main failure modes: flotation due to flooding and floating roof failures due to rainfall. Next, fragility models are developed to assess the structural vulnerability of ASTs. An existing fragility model for the flotation of ASTs is improved to include hydrodynamic effects, while a new model based on buoyancy and drainage calculations is proposed for the failure of floating roofs. Finally, the fragility models are coupled with empirical data to ascertain the conditions that could have led to the observed failures during Harvey. Results indicate that in preparation for a storm, ASTs should be filled with product to prevent flotation and improve floating roof drainage. Results also highlight the importance of adequate terrain drainage to avoid water accumulation around ASTs that can lead to AST flotation or to inefficient roof drains.

Hurricane Maria hit the island of Puerto Rico as a category four storm on September 20, 2017; just two weeks after Hurricane Irma had already affected the island. Maria caused extensive damages in almost every aspect of the infrastructure and the natural and human-built environments. This paper presents an overview of the damages to the energy infrastructure, highway signs, traffic signals, luminaires, steel roofs, wood and concrete homes, multistory buildings, and bridges. Two case studies are presented: a highway sign, for which estimates of wind speed based on backward calculations are presented; and a reinforced concrete roof that was damaged by wind loads. Recommendations about updating the Puerto Rico Building Code are given.

On February 28, 2017, an EF3 tornado caused widespread damage to the little town of Naplate, Illinois, and the neighboring town of Ottawa, Illinois. In Naplate a large glass manufacturing plant was in the direct path of the tornado and sustained significant damage to portions of several buildings including tearing off or damaging over 390,000 sq. ft. of roofing, peeling off metal roof deck and structural steel purlins, twisting and deformation to multiple steel plate girders up to 40-inch deep and heavy wide-flange steel columns, and pulling steel column base plate anchors out of the concrete foundation. The equipment needed to be protected and serviced concurrently as the structure repairs and plant operations were performed around and above them. Engineering Systems Inc. (ESi) was retained to have a team of engineers evaluate the damage, prepare repair design, and provide onsite field engineering to create solutions for the ongoing issues as they developed. This paper will discuss the methods used to evaluate the damage to the building including the use of drones to evaluate roofing damage. Additionally, discussion will be provided regarding temporary protection methods to facilitate a compressed schedule with multiple trades literally working on top of each other and around plant activities while partially in operation, analysis of existing structural steel, and design of repairs to the structural steel and building envelope. Several existing plate girders required advanced analyses to resolve code compliance issues which were justified given the cost saving considerations of rehabilitation vs. replacement.

In 2017, Hurricanes Harvey and Irma wreaked havoc with civil infrastructure systems, primarily due to flooding caused by rainfall and storm surge. Damage data were collected using online resources such as power company outage websites, the reports provided by the Energy Administration Information (EIA) branch of the U.S. Department of Energy (DOE), and the cell tower outage reports provided by the Federal Communications Commission (FCC). Geo-statistical data for wind speeds, rainfall, and storm surge have been identified for Harvey and Irma in Texas and Florida, respectively. In this paper, models for system-level electric power delivery and cell tower fragilities and recovery over time have been fit using previous published models. Comparisons with combinations of individual system-level fragilities are made.

Hurricane Harvey made landfall August 25, 2017, near Rockport, Texas. With maximum winds of 130 mph, Harvey was the first Category 4 hurricane to make landfall in the U.S. in over a decade and the first storm of this intensity to hit Texas since 1961. Four sub-teams were assembled to document damage in the landfall region in three coordinated waves from September 8-17, 2017. A pair of teams worked sequentially to conduct door-to-door Damage Assessments in Rockport, Port Aransas, Aransas Pass, and Bayside, supplemented by unmanned aerial surveys (UAS) of select residential areas. These teams were flanked by a Coastal Scout Team measuring high water marks as far east as Palacios. These damage assessments were followed by block-level scans of these same neighborhoods using a mobile LiDAR van. 3D point clouds were acquired for select structures obtained using portable LiDAR/imaging laser scanners. This study will present a summary of the observed damage, correlated by age of construction and roof characteristics, followed by illustrative examples highlighting the performance of wood-framed, single-family residential construction, and metal-framed buildings to underscore common failure modes observed.

Hurricane Irma made its first landfall in the continental U.S. at Cudjoe Key in southern Florida on September 10, 2017, with Category 4 winds. Irma made its second landfall later that afternoon on Marco Island on Florida’s Gulf Coast, as a Category 3 storm, weakening further as it moved north. Reconnaissance teams respectively dedicated to the Gulf Coast, Atlantic Coast, and Miami/Florida Keys carried on a first wave of rapid reconnaissance from September 15-20, 2017. A second more exhaustive campaign was then conducted in the Florida Keys on September 22-25, 2017. These investigations employed primarily door-to-door damage assessments to classify buildings and evaluate component damage levels using a Fulcrum mobile smartphone application for data collection in a unified assessment framework feeding into a quality assurance/quality control process. At select locations, unmanned aerial surveys generated aerial imagery, 3D point clouds, and 3D textured meshes. This study presents the geospatial distribution of observed damage, correlated by age of construction, typology, construction materials, and estimated wind speed. Specific case studies highlight common failure modes observed in different construction classes and editions of the Florida Building Code.

Hurricane Harvey struck the Texas coastline on August 25, 2017, as a Category 4 hurricane. Wind gusts over 233 km/h and storm surge as high as 3 m caused widespread damage to buildings and critical infrastructure in coastal communities including Rockport, Fulton, Port Aransas, and Aransas Pass. Over a 12-day survey period, a study team led by the authors assessed the performance of more than 1,000 individual, geo-located residential buildings. This study presents an initial evaluation of empirical wind fragility functions for single-family residential structures impacted by Hurricane Harvey. The fragility functions are constructed using 3-second gust wind speeds adjusted by local ground surface roughness as the demand parameter. The analysis finds that the local terrain is a significant factor in determining the level of damage for structures. High variability is observed in the wind speed to damage relationship.

Hurricane Maria has been termed the worst natural disaster on record in Puerto Rico, as the third consecutive major hurricane to threaten the Leeward Islands in a two-week period. The storm caused catastrophic damage and numerous fatalities across the northeastern Caribbean, creating hurricane force winds on St. Croix in the U.S. Virgin Islands, less than two weeks after Hurricane Irma caused extensive damage in St. John and St. Thomas. Maria made its U.S. landfall on September 20 near Yabucoa, Puerto Rico, as a strong Category 4 hurricane. As part of a wider coordinated effort for the 2017 season, a regional node was established in Puerto Rico to organize local reconnaissance efforts between October 6 and November 18, 2017. A separate reconnaissance campaign was organized for the U.S. Virgin Islands, November 9-14, 2017, to document the impacts of Irma and Maria. Investigations on all four islands employed primarily door-to-door building damage assessments using a customized Fulcrum smartphone application. At select locations, additional unmanned aerial surveys were conducted. This paper will introduce the overall reconnaissance effort, followed by case studies highlighting common failure modes with a particular emphasis on topographic effects.

This paper presents a methodology for quantifying the cumulative probability of failure for a natural gas pipeline in the northeastern United States. The pipeline comprises approximately 21 miles of API 5L X42 seamless line pipe with diameters from 2 to 12 in. and contains roughly 3,600 circumferential welds. Some segments of the pipe date back to the early 1960s, while the newest segments were installed as recently as 2010. Six pipe samples were provided, from which 50 tensile specimens and 510 Charpy V-Notch (CVN) specimens were machined. CVN impact energies were converted to fracture toughness using two-stage CVN-K_1d-K_1c and temperature shift correlations and the master curve approach. Statistical inputs (i.e., mean, standard deviation, minimum, and maximum) for yield strength, flow strength, and fracture toughness were calculated from the mechanical test results. Nearly 700 weld radiographs, taken during installation, were reviewed by a Level III ASNT qualified inspector. The length and width of each discontinuity were used as the data population for the initial flaw size distribution inputs. Rigorous three-dimensional finite element analysis was performed for all diameters with a variety of geometries and considered pressure, thermal, soil bearing, vehicular traffic, and seismic loadings. A probabilistic fracture mechanics evaluation was performed for each pipe diameter considering the worst-case geometry and loading combination from the stress analyses and random samples based on the distributions of the statistical inputs. Cumulative failure probability over a 100-year period was calculated for each pipe diameter, enabling the prioritization of pipe segment replacement based on failure risk.

In recent years, the distress of large magnitude cracking has been observed in Denver’s Green Valley Ranch (GVR) neighborhood and this distress was assumed under the effect of exceptional climatic and geographical conditions in Colorado. Hence, it is necessary to monitor real-time environmental factors in situ within the pavement soil layers. The field-monitoring system on the East 49^th Avenue was developed in order to simultaneously monitor seasonal and daily pavement temperature, the volumetric water content in the soil, and crack width change. The data was recorded during six months and collected on a bi-weekly basis. The results indicated that the temperature variation (the difference between highest temperature and lowest temperature during this period) at the pavement surface was 56 °C (100.8 °F), which was 1.4 times higher than that at the pavement bottom surface. The temperature difference through the thickness of the pavement during the period was in the range of -9 °C (-16.2 °F) to 20 °C (36 °F). During the same period, moisture content readings reported that the highest value was 0.443 and the lowest value was 0.348, which significantly exceeded the historical database of precipitation in the weather station.

In this study, an array of nondestructive testing techniques including live load testing, strain monitoring, and acoustic emission monitoring were conducted on a section of I-235 bridge located west of the state capital, in Oklahoma City, to assess the performance of repairs on a section of a post-tensioned box-girder bridge. The goal of this study is to comparatively assess the performance of repair in situ between locations where ungrouted tendons were repaired and similar known locations, which were originally deemed to be structurally sound. The structure’s strain response at critical positions, for example the midspan location and the location of the structural supports of tested span, were recorded during the bridge live load test over the entire span of the bridge. In addition to strain monitoring, acoustic emission (AE) monitoring was implemented as a supplemental test method to the standard load/deformation analysis. This study demonstrates results which indicate an elastic behavior of the tested bridge span under three different load levels utilizing strain response combined with acoustic emission parameters.

This paper presents the results of an investigation into the total collapse of a 100-foot-long span of a bridge during demolition. The bridge was a steel-framed structure with a composite concrete deck. At the time of the collapse, the deck had been sawcut transversely and longitudinally, and a large excavator was hammering the deck to release it from the steel girders. The entire span collapsed, causing the excavator and the operator to fall with it. The operator was injured, the bridge replacement project was delayed, and litigation followed. This paper presents the deficiencies in the demolition plan and execution, which led to the collapse. It also discusses the legal proceedings that followed, focusing on the various expert opinions and their basis. This paper also provides recommendations to owners, engineers, and contractors to prevent the occurrence of similar bridge collapses and also recommendations related to performing investigations that are used for litigation.

Ellis shore posts have been used throughout the United States since the 1940s for shoring of formwork for concrete deck construction. In California, Cal OSHA (2017) does not require civil engineer approved design calculations or working drawings for vertical shoring unless a noted condition, such as installation is greater than 14 feet in height. However, ambiguity exists as to the applicability of this height limit for cases of multiple levels of vertical shoring with working platforms in-between. Further ambiguity exists in cases of shoring installation on a sloping grade as no specific guidance is provided by the manufacturer. This paper will present a case study of a shoring collapse during concrete placement in which Ellis shore posts installed on a ramp supported two levels of vertical shoring. Recommendations are developed as to specific issues to be addressed when Ellis shore posts are used with two levels or on a sloping grade.

During the concrete placement of the elevated slab in a two-story building, excessive deflection in the un-shored composite steel supported concrete flooring system caused the contractor to place additional concrete in an attempt to satisfy project requirements for flatness. When the placement was suspended, the concrete deck thickness was approximately 7 to 10 inches in select locations compared to a specified thickness of 5-1/2 inches. The structure consisted of a concrete slab supported by metal decking on I-shaped steel beams. The authors will discuss the factors contributing to the overpour, such as the flexibility of the system and camber of individual elements, as well as the impact of the overpour to the structure in terms of strength, serviceability, and the structure’s intended use. The authors will discuss methods to mitigate issues in the future. As composite steel systems become more efficient through the use of higher strength steels, the concerns with the overall flexibility of the steel frame increase. This project highlights for the professional community the issues associated with concrete placement of an elevated composite slab system and methods to mitigate issues in the future.

On October 30, 2003, the Tropicana Parking Garage, for the Tropicana Casino and Resort in Atlantic City, New Jersey, collapsed. Four construction workers were killed and 21 others were injured. The structure was a 10-story reinforced parking garage, which utilized filigree wide-slab (composite) concrete construction. This was a sudden and progressive collapse, which occurred during construction. Investigation revealed that failure to properly install steel reinforcing along with failure to provide adequate shoring and reshoring triggered the initial collapse. Although the technical cause(s) of failure were not difficult to understand, the loss emphasizes the need to carefully comply with drawings and specifications and to follow proper construction proceedings and sequencing. It also shows the need for redundancy in design.

The peak particle velocity (PPV) threshold limit for damage of structures due to ground vibrations has been a topic of great interest and engineering debate throughout the years. However, the most accepted industry standard since 1980 regarding the PPV limit for damage of structures was established through a series of studies sponsored by the United States Bureau of Mines (USBM). Since then, other researchers and government agencies have conducted studies to establish the damage limits due to ground vibrations from other sources, including traffic, construction, demolition, pile driving, and geophysical exploration. Presented herein, is a summary of the most common standards utilized by various governing bodies and industries when ground vibrations are a potential cause of distress.

Oil refineries are among the harshest environments for structures and associated equipment due to the temperature and pressure differentials, continuous operating cycles, potential impact and blast loading scenarios, and highly corrosive materials. This paper will provide a detailed case study for a Midwest refinery coker structure wear plate system where multiple wire ropes failed within a short time span. Wire ropes were used to suspend a steel plate used to protect a concrete chute structure from material impact. Failed wire ropes were analyzed by metallurgists and various conclusions were derived to the cause of failure, including temperature, fatigue, and corrosion due to exposure to the aggressive environment. Based on the forensics and analysis results, a solution was designed to improve the reliability of the wear plate system by addressing the causes of failure, while maintaining the required strength. The solution was also designed considering the geometry, connectivity, and flexibility benefits gained from using wire ropes. The improved system was installed successfully, and the coker unit is currently in operation.

The paper details the investigation of a recreational vehicle explosion, the risk from using propane cooktops without a flame safety feature, and remedies to prevent similar reoccurrences. The trailer was inspected. All propane appliances with the exception of the cooktop incorporated flame failure devices (FFDs) which shut off the flow of propane if a flame is not present. All of the propane appliances were tested and found to operate normally. One burner on the cooktop was on, indicating it was the source of propane. The lack of a positive propane shut-off mechanism in the absence of a flame led to the explosion. The propane was tested for odor, and one of the cylinders was shown to have de-odorized the gas. Odor fade is a known phenomenon, and likely occurred in this case due to rust in the cylinder. The propane detector was tested and found to be working. However, it did not warn the occupants of a leak before the explosion. A review of applicable standards showed that flame failure devices were not required in cooktops for the recreational vehicle industry. Several manufacturers supplying valves with FFDs, and which were in compliance with ANSI Z21.15 were identified. These stovetops were available to both the RV and marine industry as early as 1993, and were adopted as requirements by the marine industry. Two commercially available valves were tested on an exemplar RV cooktop and found to work seamlessly with the existing hardware. Flame-out conditions were simulated, and both valves shut off the flow of propane in under 12 seconds.