Forensic Engineering 2009: Pathology of the Built Environment

Common failures that occurred in the past continue to replicate themselves even though the analysis, design and construction phases have become more sophisticated and specialized. The mundane issues that designers and constructors may consider unimportant or uninteresting due to their low cost, visibility or low technical level can become huge factors in a constructed facility's performance and a tremendous drain on the nation's economy. This paper discusses ten common types of failures with examples and provides general recommendations to prevent or reduce these types of failures. The failures discussed herein vary from analysis and design consideration to construction practices and techniques.

This paper will present the methods of evaluation utilized, as well as the results, of several forensic investigations involving the building envelopes of three different buildings. These case studies will present the conditions known regarding the original design and construction, as well as the storm circumstances that led to the observed failures. Where appropriate, discussions of the construction and workmanship realized for each project will be provided. It was determined during the investigations for each building that internal pressurization most likely played a part in the cladding or roofing failures, increasing the wind pressures incurred by these structures to levels exceeding the original design and the capacities of the various construction assemblies.

As the use of more sustainable building products is incorporated in the designs for both new construction and as well as building renovation, proper water/moisture management becomes a critical design consideration. Likewise, the understanding of moisture dynamics in and through the building envelope has become more important for the forensic engineer. Sustainable products generally do not have the same capacity to store moisture as traditional construction materials such as brick, block and concrete. Sustainable products also contain more organic matter, which make them more susceptible to mold growth. This paper will explore the various pathways of moisture intrusion; discuss strategies to investigate buildings to determine sources of moisture intrusion; and, provide calculation methodologies for predicting moisture intrusion. The paper will also describe the effects of leaking, condensation, and water vapor for their respective contributions to water damage and provide practical solutions to minimize the moisture damage to building materials.

During a recent northern California earthquake of magnitude 4.4, a newly-built hilltop home experienced no structural damage, but some unexpected nonstructural damage. The golden sandstone veneer covering the top portion of an exterior wall dislodged and fell to the ground. The owner hired a consulting engineer to investigate why the damage occurred and how to repair the wall. Given the extent of the stone veneer throughout the house — cladding both exterior and interior walls; in the bedrooms, living room, and kitchen — it became important for the engineer to also determine the extent of the problem throughout the house. The cause of the failure was the contractor's omission of steel wires and dovetail anchors, and the poor bond between the stone and mortar. Repair recommendations consisted of providing supplemental out-of-plane anchorage for the stone veneer.

In many buildings, thermal inefficiencies result in condensation problems. Some of these problems are readily visible, such as condensation on window surfaces, but some occur within our wall and roof systems. Condensation problems occur for several reasons, such as elevated humidity and stagnation of air. We will discuss condensation related moisture problems, their cause and proposed remedial options. We will focus on presenting investigative approaches and tools used to evaluate these inefficiencies such as visual observation, tracer smoke testing, infrared thermography as well as thermal analysis. We will discuss specialty building considerations using examples from past investigations. We will discuss considerations for structural retrofits for buildings such as blast resistance, seismic upgrades or structural retrofit for stabilization where the structural elements used form thermal bridges. We will discuss considerations for architectural features on buildings such as light shelves and sun shades and methods to reduce thermal bridging at these elements.

Building envelope failures resulting in water intrusion distress are well documented in the literature. Weather-resistive barriers underneath siding systems are often installed in haste by subcontractors or workers that do not understand lapping sequence to achieve the desired water-shedding installation. This paper documents a case study whereby a simple detail around a roof drain scupper caused significant damage to a residential house located in Denver Colorado. Non-destructive inspections and destructive tests were completed in order to determine the origin and cause of the damage. Economic ramifications as a result of the litigation are also discussed.

Composite multi-wythe walls for exterior walls, especially those that combine brick units and concrete masonry units (CMU), are vulnerable to certain special problems. There are a considerable number of existing structures that were built using this type of construction, and it is still occasionally used for new construction. These types of walls are prone to certain problems, and these problems are not generally well known among engineers and architects. The result is that existing buildings that show symptoms of these problems may be misdiagnosed, leading to inappropriate or expensive repairs, and that design professionals may not be fully aware of the pitfalls when they use this system for a new design. This paper discusses the vulnerabilities of this type of construction, surveys the available literature on the topic, and illustrates the issues with a case study

Early building walls were usually constructed of stone or masonry and were intended to support the structure and to shelter the building occupants. Over the past 100 years building walls have become lighter and thinner. While they still serve to keep the weather out, these newer walls no longer support the structure. They often contain complicated interdependent components which can increase the likelihood of failure. Facade failures are not just limited to collapse, cracks, or excessive water or air infiltration. Building facades that do not comply with project specifications, governing building codes, or industry standards have also failed. Even facades that do not meet aesthetic standards or the desired appearance may also be considered to have failed to the owner or architect. Considering the complexity of contemporary wall systems, understanding why they fail to perform as expected is seldom an easy task. Failures can originate from a wide variety of influences; such as accumulated differential thermal or moisture expansion, inadequate wall cavity drainage, or material incompatibility. Complicated internal leak control systems or intricate connection or support mechanisms further increase the probability of facade failures. Special diagnostic techniques and tools are needed to properly identify facade failures to enable effective remediation (Beasley 2001).

The Litton Reaves facility is a multi-use laboratory and classroom building for the Animal Science Department of Virginia Tech. Constructed in the early 1980s, the facility had been in service for almost 20 years before symptoms of distress began to appear in the exterior cladding of the building. The severity of the distress was punctuated by the partial failure of a section of oolitic limestone panel that fractured and had to be removed from the facility. This case study offers an overview of the evaluation performed on the exterior cladding system of the building and discusses the mechanisms that led to the problems in the brick and limestone veneer. The paper discusses the repair program and highlights several structural repair and sequencing challenges that were encountered due to the redistribution of forces within the veneer. Correction of nagging water penetration and air infiltration problems were sequenced and performed in conjunction with the structural repairs in order to improve the building's interior conditions while meeting the University's "design-to" budget.

An 80-year-old school building in Brooklyn, New York, with pervasive water leakage and deteriorating brick exterior walls was a potential candidate for a treatment to stabilize and seal the surface. The building continued to experience extensive water leakage despite the recent installation of a new roof and flashing repairs. An investigation was conducted to evaluate the cause of the leakage and to evaluate the potential effectiveness of four prospective surface treatments to seal or consolidate the brick. Each of the four products tested was a commercially available proprietary product specifically marketed for use on brick masonry. This paper presents the findings of our field and laboratory studies, which identified critical defects in the extensive recent repair work, and indicated that surface treatment of the brick masonry was inadvisable.

On March 14, 1887 a Boston bound train, near full capacity and after departing Roslindale Station, crossed an iron frame bridge. The locomotive along with the first three cars safely crossed but the remaining six cars fell to the street below as the bridge collapsed. Failure of two iron hangers was the cause, however contract mismanagement on the part of the railroad company was an underlying factor. This paper presents an overview of the Bussey Bridge collapse, its historical background, the engineering and construction.

Structural failures, such as the MacArthur Maze I-880 overpass in Oakland, California and the I-35 bridge in Minneapolis, Minnesota, are recent examples of our national infrastructure's fragility and serve as an important reminder of such infrastructure in our everyday lives. These two failures, as well as the World Trade Center's collapse and the levee failures in New Orleans, highlight the national importance of protecting our infrastructure as much as possible against acts of terrorism and natural hazards. This paper describes a process for evaluating the vulnerability of critical infrastructure to large blast loads using a fully-coupled finite element approach. A description of the finite element software and modeling technique is discussed along with the experimental validation of the numerical tools. We discuss how such an approach can be used for specific problems such as modeling the progressive collapse of a building.

Successful but time-intensive use of high-fidelity computational capabilities for shock loading events and resultant effects on and within enclosed structures, e.g., tunnels, has led to an interest in developing more expedient methods of analysis. While several tools are currently available for the general study of the failure of structures under dynamic shock loads at a distance, presented are a pair of statistics- and physics-based tools that can be used to differentiate different types of damage (e.g., breach versus yield) as well as quantify the amount of damage within tunnels for loads close-in and with standoff. Use of such faster running tools allows for scoping and planning of more detailed model and test analysis and provides a way to address parametric sensitivity over a large multivariate space.

On, July 6, 2003, the Wimer Covered Bridge, an historic covered wooden bridge located in southern Oregon, collapsed shortly after a pickup truck crossed over it. A local resident and his two grandsons were on the bridge at the time and sustained serious injuries. The bridge was originally built in 1892 and substantially rebuilt in 1927. The bridge underwent major rehabilitations in 1962 and 1985. The 2001 bridge rating concluded that it was safe to keep the bridge open to restricted traffic loads. The bridge collapsed due to extensive decay in the bottom chord at a panel point on the upstream truss. Engineers involved had numerous opportunities to identify the critical nature and deteriorated condition. Mistakes were made in both the analysis and in the inspections of the bridge. This paper addresses standard of care and the importance of assessing wood decay when analyzing a timber bridge structure.

Wood construction is common for low-rise buildings, including residential and light commercial structures. For these types of structures, vertical structural members may consist of multiple wood studs, called built-up columns. As wood-framing becomes increasingly common for multi-story structures, concerns of both structural strength and stability of the wood members should be of paramount importance to the engineer. Specifically, the engineer must have knowledge of the type and extent of bracing present to properly determine the capacity of each member. Most commonly, wood studs in low-rise buildings are braced in the weak direction by fastening wall sheathing to the face of the stud of the narrower dimension. The use of gypsum board wall finishes to brace wood stud walls (and for lateral shearwall diaphragms) has become common in the design of wood structures. However, engineers must remain aware of the limitations of gypsum board when designing heavily loaded, non-repetitive members such as columns. These limitations are particularly important for the design and detailing of built-up columns. Design and construction defects related to wood columns in a wood-framed townhome project are presented herein. The subject three-story structures utilized built-up wood columns that depended on gypsum board for stability bracing. The columns did not satisfy the National Design Specification requirements for built-up columns. The proper design of the columns and the implications of using gypsum board for bracing will be discussed.

Mold growth in ductwork is an abnormal, but not an unusual condition. One of the prerequisites for mold growth to occur is that the interior surface of the duct must become wet. Moisture in ductwork can occur for a number of reasons, including, but not limited to: water can be stripped off cooling coils and carried down the ductwork; operation of the equipment can result in condensation inside the ductwork; or, a fog could be created inside the duct. This paper will describe the causes of moisture inside ductwork, the factors allowing mold growth to occur, and strategies to correct or avoid these problems. After the moisture problems are resolved, mold will cease to grow; but microbiological debris will be left in the ducts. The pros and cons of duct cleaning to deal with this debris, as well as alternative duct cleaning methods, will also be discussed.

In August 2008, the Federal Emergency Management Agency (FEMA) released the Third Edition of FEMA 320, Taking Shelter From the Storm: Building a Safe Room For Your Home or Small Business, and the Second Edition of FEMA 361, Design and Construction Guidance for Community Safe Rooms. First released in 1998, FEMA 320 is the benchmark publication that provides prescriptive designs to be used in the design and construction of residential safe rooms (shelters) to protect occupants from hurricanes and tornadoes. Originally released in July 2000, FEMA 361 provides technical guidance for design and construction of community safe rooms to protect larger groups of occupants from hurricanes and tornadoes. These FEMA documents were the basis for the development of the new ICC/NSSA Standard on the Design and Construction of Storm Shelters (ICC-500) released in August 2008. This paper presents the criteria and levels of protection from the FEMA documents and compares them to new ICC-500.

This paper will present case studies and assessment of collapses of tall, free standing residential masonry chimneys resulting from windstorms in North Texas. The case studies will outline the assessment of the causes of the collapses and a discussion of design and/or construction defects. A review of limited and highly lacking documentation on design, construction and code requirements governing the architectural and structural "design" and construction of residential chimneys will be conducted. The paper will provide a discussion of the lack of design standards and poor construction practices used for residential load-bearing masonry chimneys. This paper will illustrate how the lack of design, construction, and code requirements results in chimneys lacking sufficient capacity to resist below design wind loads leading to unsafe conditions. It is only a matter of time before the collapse of one of these elevated masonry chimney "missiles" results in severe injury or death of an inhabitant.

As civil / structural engineers in the field of forensic engineering, we are often asked to evaluate roof coverings for storm damage. Of the myriad of roof coverings available for the numerous types of buildings, roofing types used for residential applications comprise a substantial portion of this wide spectrum. The purpose of this paper is to characterize and describe storm damage that affects roof coverings typically used in residential construction. It will address damage induced by hailstorms and windstorms to asphalt composition shingles, wood shingles and shakes, and slate and clay tile roof coverings. The paper will also discuss the typical steps involved in this type of forensic investigation, including obtaining and analyzing weather data, safely performing a physical inspection, and providing repair or replacement recommendations. It will also touch on the common material defects, installation problems, and reparability concerns encountered when evaluating these roof coverings.

Distress to asphalt roof shingles due to high wind events, beyond obvious physical dislocation, might not be evident and is often overlooked, improperly evaluated and/or is a source of debate among insurance adjusters, roofing contractors, building inspectors, and design professionals. This paper presents an overview of asphalt roof shingles including material composition, style, grade, and installation, and their impact on wind resistance. A practical non-destructive method for identifying, quantifying, and categorizing wind distress is presented. Distress not related to wind is briefly considered including installation deficiencies and manufacturing defects. Recommendations for repairing or replacing a damaged roof are also discussed, considering material properties and type and extent of distress. Finally, this paper highlights the role of the builder and/or design professional regarding the proper specification and application of shingles based on the geographical region and climate in which they are installed. Regulation which correlates with existing guidelines needs to be specified and enforced.

Poor roof drainage can cause accelerated deterioration of a roofing system and in extreme cases, roof collapse. It is the authors' experience that roof collapses related to poor roof drainage are almost exclusively limited to low-slope roofs with parapet walls that prevent drainage over the roof edge. For roofs with parapet walls, the proper function of the primary and secondary drain systems is essential for roof performance and safety. However, many buildings with parapet walls do not have adequate drain systems. The authors consider this to be an "epidemic", akin to the much-publicized deficiencies in public infrastructure. With this study, we propose to discuss common roof drainage issues and to offer a set of conditions for the oversight and approval of roofing projects. For both new construction and existing buildings undergoing roof repairs, compliance with these roof drainage conditions should be mandatory and specifically enforced by the local building officials.

Problems arising from subsidence pose danger for future land development above abandoned coal mines and are challenging to forensic engineers to substantiate these damages and differentiate the effects due to mine subsidence from other possible non-mine related damages. Forensic investigators commonly asked to provide evidence that the structures-of-interest are in fact above or close to the coal mines by associating the structures to possible mine activity sites, such as within the angles of draw to the underground mine. This paper discusses the problems and errors associated with abandoned mine mapping using Google Earth^TM and historical mine maps. Analyses of dimensions are performed to validate the results of error analysis.

Determination of the causes of structural damage that can result from sinkhole activity is a difficult process requiring consideration of many arcane factors. Most investigations are directed to analysis of subsurface conditions as they relate to signature conditions known to occur when sinkhole activity is present. Missing in many sinkhole investigations is a thorough analysis of structural damage as it relates to causal subsurface conditions. Several case studies are presented where careful analysis of site conditions and structural damage has provided valuable clues to subsurface conditions responsible for structural distress. Also presented is an outline of the typical phases of a sinkhole investigation that will help the investigator adequately consider failure analysis in understanding how subsurface conditions interact with the structure.

A commercial structure in western Colorado constructed circa 2001/2002 began to exhibit drywall distress within a few months of completion. The foundation consisted of a monolithic, cast-in-place footing and structurally connected slab-on-grade bearing on 0.3 to 0.8 meters of lime-treated, clay soils. The clay soils were documented to have low expansion potential and high sulfate contents. A survey of the building in 2004 showed an elevation difference of 27.9 centimeters over 15.2 meters. A Scanning Electron Microscope showed the presence of ettringite beneath the foundation. Sulfate induced heave is caused by the volume change associated with the formation of ettringite. Water entered the lime-treated soils beneath the foundation and was the catalyst for soluble sulfates to react with calcium in the lime to form ettringite. This reaction resulted in the structure's distress.

Land affected by a legacy of industrial and commercial activities including domestic and accidental contaminative spillages is termed contaminated land. Recent research estimates there are approximately 325,000 contaminated sites in the UK with an annual spend of approximately £1.2 billion on regeneration and remediation. Following the `polluter pays' principle, those involved in pollution are liable to take appropriate action and return the land to its original form. Where the polluter cannot be identified, remedial and regeneration costs are borne by the public exchequer. Alternatively, forensic engineering can be applied to identify persons liable of polluting air, land, groundwater and surface waters and also to assist in recovering remedial costs through litigation. This paper describes effective and practical methodologies for the forensic assessment of contaminated sites with regard to determination of polluter responsibility and allocation of associated liabilities under UK and European legislation.

Tropical peat soils are considered as extremely soft, wet, unconsolidated deposits. These kinds of soils are geotechnically problematic due to their high compressibility or high settlement and low shear strength. Cement columns may be used to improve the settlement problem of these soils. This paper describes the results of the effects of cement columns on the compressibility of fibrous tropical peat soils. Coefficient of consolidation, compression index, coefficient of secondary compression, and coefficient of volume compressibility were obtained by a Rowe cell test for both, untreated peat soil and peat soil treated with cement column. The results indicate that installing cement columns and increasing cement ratio could reduce the compressibility of peat soils and decrease its settlement dramatically.

A method of three-dimensional slope stability analysis is presented here based on the energy consideration to obtain the ultimate bearing capacity of rectangular foundations located near the slopes with coaxial nonassociated flow rule. Taking the eccentrically loaded foundation into account, a rotational failure mechanism consisted of several lateral surfaces is considered. The stress distribution along the rupture surface, needed to obtain the rate of dissipation of internal energy for the nonassociated flow rule, is established on the basis of extended Bishop's method and boussinesq theorem. The bearing capacity of rectangular foundations in different conditions is obtained using the proposed method and the effects of dilatancy angle are investigated. The results indicate that for the nonassociated flow rule materials, the bearing capacity of slopes reduces with decrease in the dilatancy angle. These influences increase in the case of mild slopes in frictional.

This paper presents a case study of a forensic investigation and subsequent geotechnical and structural remediation of an operating 5-story hotel experiencing large differential settlements. The hotel construction consists of concrete masonry unit (CMU) load bearing walls and concrete hollow-core plank (HCP) floor framing founded on shallow strip and spread footings bearing on variably thick structural fill over sloping residual soils. Survey data 4 years following construction showed maximum settlements of 11 inches over the thickest fills, with trends indicating the potential for continued settlements. The building had experienced significant distress and concerns about its structural stability and life safety were raised. By working closely with the owner and each other, the geotechnical and structural consultants developed an effective and feasible approach to stabilize the foundation system and repair the structural elements while allowing the hotel to remain operational. This case study highlights the benefits of joint geotechnical and structural participation throughout the forensic and remediation process, and stresses the need to identify the full extent and root causes of building distress and to identify potential construction defects or omissions that may affect the available remediation options.

Six multi-family residential buildings consisting of wood frame structures founded on post-tensioned slabs-on-grade were constructed in approximately 1995 in Basalt, Colorado. Collapsible soils had been identified at the site, in geohazard evaluations, as early as 1976 and a pre-construction geotechnical investigation indicated that the silty clay soils at shallow foundation depths could have high collapse potential when wetted. The buildings experienced between 4.8 and 13.0 cm (1.9 and 5.1 in.) of differential settlement between 1995 and December 2006. Compaction grouting test pads were constructed and pre- and post-grouting analyses of the soils were conducted to quantify changes in moisture content, density, compressive strength, and collapse potential of the soils. Introduction of water into the soils prior to grouting played a significant role in the improvement of soil conditions under the buildings. The grouting methodologies are summarized, and the resulting soil improvement at the test pads and stabilized buildings is discussed.

Waterproofing for subsurface structures long has been accomplished using standard practices that typically are determined by cost and routine practice, regardless of the potential ramifications of poor functioning or failure. Repair measures for waterproofing often also follow faulty procedures that attempt to control water flow. Experience with evaluating seepage problems has revealed inherent flaws in many of these standard procedures. Numerous projects involving seepage in areas with heavy groundwater flow have led to the conclusion that sump pumps and trench-type drain systems do not provide suitable control of water and often are relied upon with disastrous results. A new approach to waterproofing proposes using crystalline concrete and various bentonite-based materials to prevent water from penetrating subsurface structures or to prevent water from seeping from subsurface structures. More advanced methods have been developed to arrest seepage where flow is heavy and cannot be stopped long enough to install waterproofing materials.

The measurement of building floor or foundation levelness using floor level surveys can be an important tool in construction quality control and engineering analysis and design. The processed results of floor level surveys are often used to evaluate conformity to construction guidelines, to form professional opinions regarding causation of distress and for selection of appropriate repair methodologies. In this latter case, the interpretation of results requires a great deal of judgment and experience. This paper focuses on the application of floor level surveys in forensic geotechnical investigations. Following a brief discussion of required fieldwork, data acquisition, and data processing, three case studies are presented. These case studies serve to illustrate the importance of the adoption of an integrated approach in forensic geotechnical investigations by combining the floor survey results with other site observations and published and historical records.

Structural vibrations in a proposed fitness center area and the existing computer server room located on the third floor of multi story building was evaluated. Natural frequency of the concrete floor was evaluated in the proposed aerobics area. Aerobic activities were simulated by people spot jogging on the bare floor as well as the existing raised floor for 120, 150, 180 BPM metronomes. Vibration levels were monitored inside the computer server room, the proposed aerobics area and at a location close to the proposed treadmill area. Natural frequency of the concrete floor found to be not susceptible to structural resonance during aerobic activities. However, the vibration levels due to simulated aerobic activities in the computer server room were significantly above the published threshold for a computer equipment room. It was recommended that the floor system be modified to reduce floor vibrations in the server room.

This paper presents outcomes of a blast effect on power transmission structure study, which mainly include discussions about considerations for blast plan establishment. The ultimate goal of this study is to provide scientific data and a systematic research procedure that would allow power companies to determine the best blast plan to secure power transmission assets during blasting. Through this study, the importance of peak-particle velocity, airblast, flyrock, fracture and mudseams in blast planning has been identified. Factors such as blast distance and velocity, structure type and area geology should be included in the blast planning. A design example is included to demonstrate the procedures recommended herein.

The existing vibration limits were developed for 1–2 story houses surrounding coal surface mines, and these limits are applied for ground vibrations as the criteria for the possible crack formation in structures. However, other blast design, soil conditions and structures require different vibration limits. There are no regulations for multistory building vibrations from blasting and there are no limits to assess possible dynamic settlements of soil and structures triggered by ground vibrations from blasting. Nevertheless, numerous case histories are available in technical papers which describe tolerable and unacceptable soil and structural vibrations measured for different soil conditions and structures. These case histories are valuable sources of information to evaluate vibration effects on structures, analyze vibration levels that do not produce damage to structures, determine the areas of application of the existing regulations and assess tolerable vibration limits for various structures during blasting operations.

Liquefaction can significantly increase the deformation of soil around underground structures but at the same time, the stiffness and internal stress of soil are also dramatically reduced. Therefore, it is questionable that if it is really essential for the structure to accommodate all the free-field ground deformations as the conventional design approach currently requests. In the present study, a typical subway tunnel is subjected to earthquake excitations using dynamic Finite Element method coupled with soil and pore water considering the nonlinearity of both structure and soil foundation. The simulation is carried out in both drained and perfectly undrained conditions to clarify the effect of liquefaction on seismic response of the structures. The computational results imply that the required ductility of RC ducts can be moderated provided that the liquefaction risk is high. Furthermore, the effect of sheet piling on various types of tunnel damages such as uplift or shear deformation is also investigated. It is found that installation of sheet piles can cause the structure to suffer more damage due to the increase of relative stiffness between the structure and the soil.

A busy shopping center department store was suddenly brought to a standstill because of the collapse of the structural roof support system. This paper will explore the reasons leading up to the collapse. Those reasons include overloading the roof structural support system during re-roofing operations, design errors within the building structure, construction errors, and lack of maintenance of the building structure. Various roof loading conditions assumed during the re-roofing operations will be analyzed with the assistance of a computer structural analysis program. A torsional analysis will also be performed to determine if the structure collapsed by way of torsional overturning under load. Other modes of failure investigated were lateral buckling, web crippling and sidesway web buckling. The paper concludes that the structure failed due to under-designed cantilever beams, no weak axis bracing, excessive welding of joists to structural beams, poor maintenance of the building roof, and poor supervision of the Roofing Contractor.

Bow truss 13 failed during construction of the David L. Lawrence Convention Center in February 2002. Bow truss 13 was designed to withstand the gravity loads and horizontal tension loads from the roof suspension system. The truss itself required stabilization during erection proceedings to prevent it from toppling over. During construction a change order was introduced directing that the bow truss be temporarily supported by a tension strut in lieu of the originally designed compression strut. In addition, no clear erection procedure was given in the shop drawings for the tension strut. During construction, the connection fastening the tension strut to the foundation block failed. Bow truss 13 rotated forward and then to the side, landing on the ground killing one steel erector/iron worker and injuring two others. To prevent this kind of failure of a non-self-supported structure in the future, proper and clear erection notes should always be provided during construction.

This paper proposes a quantitative measure and mathematically reproducible definition of structural robustness as it pertains to a structure's ability to minimize the potential for structural progressive collapse. Structural robustness is defined by the structure's ability to withstand any unforeseen loading as well as initiating damage scenarios without a disproportionate response. Presented here is a study that finds that in the absence of the specific progressive collapse load scenarios and unknown location and extent of initiating damage, progressive collapse potential can be minimized by employing the concept of structural robustness as well as safety and reliability, which are all interdependent qualities of a structural system. This study also concludes that structural robustness represents a structure's ability to absorb small structural failures (perturbations) without affecting the overall structural integrity, and can be measured as a standard deviation of the progressive collapse dynamic resistance probability density function.

On June 2007 the corner part of an ancient masonry building realized in the 20's of the last century at the centre of Salerno (Italy) fell down suddenly. The collapse occurred at the sunup, but no victims or injured people were caused only because that part of the building contained living rooms of apartments, rather than bedrooms. The building, made up of tuff masonry and having six storeys, was one of the most beautiful palaces of the town for its location and the beauty of the façades. During restoration works at the ground floor, retrofit interventions on masonry walls were been proposed and alarming cracks appeared along the masonry piers few days before the collapse. Despite these clear signs of alarm forecasting the disaster, no shoring structure was realized to avoid it. In this paper all the investigation phases that allowed to define the mechanics of the collapse and to identify its causes are discussed.

A pedestrian bridge near Marcy, New York collapsed during construction on October 12, 2002, injuring nine workers and killing one. The authors were retained to investigate the reasons for the bridge collapse, and whether the actions or omissions by the key players contributed. The pedestrian bridge was designed as a straight, single-span, composite box girder composed of a trapezoidal steel tub with stay-in-place forms and concrete deck. The collapse occurred while the concrete deck was being placed. Based on eyewitness accounts and the position and orientation of the debris, the mode of failure was consistent with lateral-torsional buckling of the entire girder cross-section. While conventional engineering training would preclude lateral torsional buckling of a beam bent about its weak axis as a potential failure mode, computer simulations using nonlinear analysis and eigenvalue buckling analysis confirm eyewitness accounts, that is, a point of bifurcation is reached during concrete placement on the torsionally flexible steel tub girder. Since this failure, which was slightly predated by a very similar failure in Sweden, the State of New York and AASHTO have appended bridge design specifications to explicitly require diagonal bracing between the top flanges in order to suppress this buckling mode. A discussion of the collapse and the failure mode follow, highlighting the lessons that the engineering community has learned from the collapse.

The development of new products is essential for the continued progress of the building industry. New products can improve the performance and efficiency of building systems; however, they must as a minimum maintain the same level of public safety provided by proven existing products. This paper presents a case study of a new cold-formed steel joist roof framing system/product. The manufacturer designed and manufactured the product, taking it from the concept stage to implementation as a product sold for use in building structures. One of the buildings with this new roof framing system experienced a roof collapse during a rainstorm. Investigation of the collapse led to the discovery of design errors of the joist product and defects in its fabrication, leading to questions regarding the safety of this product and its suitability for use in a roof system. This case study also highlights the role of the design professional with regards to the selection and verification of new building systems and products.

Crib walls are a form of gravity retaining walls that are constructed of prefabricated interlocking concrete units. The space between the interlocking units or "crib" is filled with soil to provide weight and stability before the adjacent backfill is placed. In recent years, crib walls have been used in greater numbers and heights to solve varied retaining problems. This has resulted in an increasing number of failures. This paper discusses common problems with the design and construction of crib walls by summarizing five crib wall failures ranging in height from 20 to 40 feet that occurred recently in Southern California. The laboratory test procedures and test results performed during the forensic analyses of these failures is presented. Single and multiple assemblies of drycast crib elements were tested to destruction under laboratory conditions. Proper and improper construction procedures are also discussed and a crib wall design specification section is presented for inclusion in model building codes.

A section of the roof for a warehouse structure collapsed after a rainstorm event during the summer of 2006. Given the location of the building, one may be surprised to find that such a roof would collapse after a rain event rather than a snow event. Was it an unusually heavy rain event? Were there errors in the structural design of the building? Were there problems with the fabrication/installation of the roof joists, girders and columns? Were there errors in the design and installation of the roof drains and associated plumbing? Surprising, none of these issues proved to be the culprit. This paper steps through our forensic evaluation of this case, and briefly reviews roof drainage design considerations. From the collection of weather data, through our consideration of various failure hypotheses, we will show the forensic methodology that led us to a very interesting conclusion.

St. Peter's Catholic Church in Charlotte, North Carolina, commissioned artist Ben Long to erect a fresco in the church sanctuary. The fresco was erected on the gabled south wall of the sanctuary. The work of art commenced in 1988 and it was completed in 1989, with assistance of apprentices and consultation of building professionals. In February 2002, the buon fresco partially collapsed from the wall of the sanctuary, which was constructed c. 1893. Coincidentally, the church was surrounded by ongoing construction activity for a large multi-use development, and the collapse reportedly occurred during removal of concrete pavement close to the structure. The church alleged, as did some investigators, that the collapse ensued because of adverse vibrations associated with the construction activity. This paper presents the evaluations of the author, including observations, analysis of vibration activity, and laboratory testing, which revealed the fresco failure commenced prior to surrounding construction because of inherent defects in the fresco installation.

Collapses of a number of roofs in Europe during the winter 2005/2006 initiated discussions concerning reliability of the roofs exposed to snow loads. Presented overview of extensive investigations of structural failures is focused on causes and consequences of failures. Main observed causes may be subdivided into human errors and insufficient code provisions. Collapses developed from local failures particularly in cases of insufficiently robust structures. Probabilistic reliability analysis reveals that the model for snow loads in the Eurocodes should be modified. Obtained experiences provide valuable background information for future revision of current standards and for forensic assessments of failures of structures exposed to snow loads.

Philadelphia's Wagner Institute has a long-span roof completed in 1864, consisting of wood-and-iron arched trusses supporting wood purlins. The plaster ceiling below the roof is extensively cracked, and gaps in truss joints are present in some locations. The truss structure that supports the roof can be analyzed in several different ways, and this ambiguity makes interpretation of the signs of damage difficult. This paper includes a review of the possible mechanisms that could have been used at the time of construction incorporating the visible materials, including various forms of truss and tied arch. This review provided the key to analysis and interpretation of the damage.

This paper presents the analysis used to demonstrate how load duration affects the time required to cause failure of overloaded wood structures. A bowstring roof truss of a commercial building partially collapsed two months after remodeling. During remodeling, several industrial HVAC units and a new suspended ceiling were attached to the roof structure. However, failure of the truss did not occur immediately after the introduction of the new loads; it took approximately two months for the truss to collapse. A computer model of the roof trusses was created and a linear-staged analysis was performed. The load duration curve of wood developed by U.S. Forest Product Laboratory was used to determine the time-to-collapse after application of additional loads. The analysis showed it would take approximately two months for the truss to fail. The calculated time-to-failure closely matched the actual time of collapse of the bowstring trusses. Load duration curve shows that when the stress level in a member exceeds 60% of the ultimate strength of wood, failure is imminent.

Structural Engineers have a duty to their clients and the public to provide safe designs. Typically, the Structural Engineer of Record is responsible for the structural design of the overall project, including specification of the design loads, issuance of design documents, and review of submittals. When structural components are used, the engineer for the Component Designer/Manufacturer is responsible for the design of individual structural components. This can constitute a significant portion of the structural design on ae project. Structural Engineers must understand their duties and must also be aware of the extent to which structural component design is (or is not) being performed by a Professional Engineer. In the subject case study, the Component Designer/Manufacturer's licensed engineer was not familiar with the project layout and only reviewed the design output for the individual components, without regard for the framing layout and the resulting loading conditions. As a result, the project was built with structural inadequacies, which necessitated extensive repairs.

Temporary stability bracing is required to hold wood trusses true to line and dimensions, plumb, and in a stable condition until permanent truss bracing and other permanent components necessary for the overall stability of the structure are completed. Industry guidelines provide prescriptive recommendations for temporary bracing of metal plate connected wood trusses to inform truss installers, contractors, and builders of record about handling and stability considerations for wood trusses. This paper presents a case study involving the collapse of an 11,000 sf wood-framed warehouse during construction and includes the procedures used to investigate the technical and procedural causes of the collapse along with an overview of industry guidelines for temporary bracing of wood trusses during construction.

Various organizations publish and promulgate Codes of Ethics which are intended to guide practitioners in their relationships with their clients, with their colleagues, and with the general public. Structural computations are intended to substantiate the judgment of the engineer and present the engineer's design intent. They also depict, for the purpose of explaining to others, the modeling and analysis of the intended structure, and its anticipated response to the demands which it must withstand to provide intended performance over its intended useful life. This paper examines the correlation between the ethical responsibility of the engineer and the modeling and mathematical computations used by the engineer. Examples will be presented where there has been a disconnect between the structural computations and the ethical responsibility of the engineer.

Forensic experts are asked to provide testimony concerning technical issues in disputes involving failures and defects. Among the most critical of the areas of testimony, certainly from the perspective of an engineer defendant, is the presentation of opinion concerning the "standard of care" and whether a defendant met that level of performance. The evaluation of an engineer's performance, the definition of the duty the defendant owed the plaintiff, and the comparison of the defendant's performance with that "standard" are all questions of fact addressable by an expert witness. This paper discusses necessary components of a valid and reliable method an expert can use to support testimony concerning the standard of care.

A 2^nd level university Master degree on Forensic Engineering coordinated by the author has been instituted at University of Naples Federico II in the present academic year 2008–2009. It is the first Master of Science degree regarding this field of engineering in Italy and in the rest of Europe, with exception of United Kingdom. Professors of the Faculties of Engineering and Law are involved in the Master degree and teach eighteen courses of engineering and five of law, respectively. The programme is aimed to create two different professional figures: the Civil Forensic Engineer and the Industrial Forensic Engineer. Only graduates in engineering are admitted to the Master courses and its duration is one year. This paper describes the subjects, the contents of the courses, the main objectives and the great interest showed about the Master degree. On 25 available positions, as many as 53 civil and industrial engineers made application in time.

Education of construction professionals for a dynamic and challenging industry requires a sea change in how we educate. The traditional didactic methods no longer engage the student who operates in a world of instant information, instant messaging and instant coffee! The student body are no longer prepared to be drip fed information in discrete modules on diverse civil engineering topics. Furthermore, at the end of a bachelors degree, these modules will not necessarily coalesce to produce a competent well rounded graduate ready for training in the practice of engineering. The traditional lecture based method is, at best, challenged to produce graduates with the skills needed in a 21^st century economy. Therefore, engineering education needs a unifying student led approach to direct their learning. Many professional bodies have recognised the need for change and accordingly commissioned vision reports to chart the skills demanded by the environment in which we now operate. To this end, the following paper summarises how forensic engineering can be used as a means of promoting problem solving skills in undergraduate students. I argue that forensic engineering case histories provide the means of developing these skills and others without impacting on the technical rigour demanded of an accredited engineering programme.

The intent of the paper is to instigate a discussion on the adequacy of wind design and construction practices for temporary installations such as scaffolds, formwork or sidewalk sheds. The paper presents data collected on incidents ranging over a period from January 2006 to July 2009. It describes patterns of collapse for various types of installations following gusts in the range of 40 to 60 mph, significantly lower than the code specified wind speeds. Some of the collapses led to worker and pedestrian injuries. Two cases involved a fatality each. In all the cases, the forensic investigators determined without difficulty that accidents were due to improper contractor practice and/or lack of engineering design. The author suggests that the accidents could have been avoided by some basic rule of thumb instructions. The relative low wind pressures that led to the collapses might also require clarifications and reevaluation of some wind design requirements for temporary installations.

One of the major reasons for disasters during construction of massive concrete structures is the failure of weak and defective scaffolding systems. During the construction of Bojnourd cement factory, the failure of forming system related to the concrete slab of the bypass clinker silo led to collapse and crush of the fresh concrete slab and death and injury of some labors in the site. In this paper, using in-situ and numerical investigations, the main causes of the accident are studied. So, by making use of Finite Element Method, the forming system including scaffold grids has been modeled and analyzed respected to common and extra loading applied on the elements. Various analyses were carried out in existence and absence of the proper lateral bracing system considering P-Delta effects in scaffolding elements. Based on the current study, application of improper connections in vertical elements of scaffolding piers, weak lateral bracings in two orthogonal directions, and discontinuity in scaffolding performance were distinguished as the main reasons for occurrence of this destructive event.

Wind farm towers are the steel lattice or tube towers serving as the support structures for large power-generating wind turbines. This paper presents a variety of wind farm tower problems encountered over two decades of practice in the wind energy industry. Wind towers are subject to turbine operational loads that cause very high-cycle fatigue loading and can give rise to unusual tower problems requiring special repairs. Problems unique to wind towers include: structural damage or collapse from turbine overspeed ("runaway" condition); tower resonance with turbine operational frequencies; turbine fires; and excessive localized member vibrations. Further, wind towers can suffer from construction-related problems: fabrication and weld defects; design deviations; accidental dents and gouges during transport; construction errors during tower erection; and wind-induced vortex shedding oscillations. Each tower problem is discussed in terms of its cause, evaluation method, mitigation strategies, and repair options with special consideration for high-cycle fatigue.

The recent rash of crane accidents across the United States, and even internationally, has raised the public's awareness of the potential hazards posed by crane use in the construction industry. This paper will provide a broad overview of the rapidly changing regulations relating to crane operations, as well as review crane accident statistics, the causes of milestone crane accidents, and summarize new regulations at local and national levels.

This paper describes an investigation of the collapse of a 250+ ft tall, hammerhead, freestanding tower crane during a Category 2 hurricane at a construction site in southeast Florida. The investigation showed that the technical cause of the collapse was a tensile failure of the anchor bolts connecting the lowest tower section to the expandable legs cast into the concrete foundation. A subsequent independent study revealed that the out-of-service design-base wind speed for the tower, originally designed and manufactured in the mid-1980s under the Rules for the Design of Hoisting Appliances by the European Handling Federation (FEM 1.001), to be inappropriate for the expected wind conditions in southeast Florida during hurricane season. Our work showed that the collapse during this specific hurricane event would not have occurred if the tower crane in this configuration were more appropriately rated to resist wind conditions consistent with SEI/ASCE 37: Design Loads on Structures During Construction.

This paper addresses methods of assessing damage to buildings and houses based on an engineering approach that utilizes forensics along with codes and standards to determine the extent of the damage. The various causations of the damage include wind, fire, floods, earthquakes and blasts. A general approach to the examination of the risks is outlined, and the elements that a report should contain are addressed. Emphasis is placed on the decisive role that corroborating information plays in determining the extent and the proximate cause of damage.

This paper presents a literature survey of roof and floor slab systems constructed of assembled concrete blocks as manufactured in the 1940s, 1950s, and 1960s with a retrospective on load capacity considerations and serviceability. Assembled concrete blocks were formed by assembling a row of lightweight hollow core concrete blocks into a prestressed plank. The most common system, which came to represent the industry, was Dox Plank named for its inventor Bernard A. "Doc" Vander Heyden. Mr. Vander Heyden patented improvements in the planks and the methods of constructing them in 1954 and 1965. This survey of United States patents, manufacturers' design data, and design theory will aid the forensic engineer in an investigation of the load capacity and serviceability of existing systems. This survey identifies the original design parameters, such as the allowable unit stresses, area of embedded steel, material properties, etc.

In India, natural disasters can cause considerable amount of damage in terms of lives and financial investments. The after effects of disasters in mitigating the effects to repair and rehabilitation can take considerable amount of time as experts visit the site to get a personal assessment. The information flow is language independent and it is possible to communicate with persons on site either in visual or oral manners. In this paper, the role of uncertainties in visual and oral communications provided by the various groups of visitors is addressed. A methodology is proposed in which the statistical nature of the input information relating to damage parameters like location, spread and intensity are translated into engineering inputs that enable the modeling of the problem, which is followed by assessment, diagnostics and possible rehabilitation measures.

Architectural heritage objects exhibit a vast variety of damage and failures which is difficult to categorize for the sake of designing general preventive or repair and conservation measures. The authors studied sensitivity of historic structures and elements to weather and disasters within several international research projects using their personal experience and research as well as records of damage and failures gathered in literature and special databases. It should be emphasized that any historic structure or element cannot be dealt with unless its material characteristics and a general environmental situation, (e.g. hydro-geological conditions), have been taken into account, which must be reflected in evaluating results and designing mitigation strategies. This paper presents selected examples from a developed information system containing data on typical damage and failures related to weathering effects and disasters action, namely wind, floods and landslides. In specific cases, not the historic structure but its surroundings and supporting structure are prone to failure, which can adversely affect their behaviour and response and cause damage to cultural heritage objects. The approach is documented by preventive strategies and measures and accompanied with life expectancy and repair cost estimates.

The paper discusses methods of nondestructive testing used in masonry and concrete evaluations. Many of the methods discussed were first used to evaluate concrete structures and have been adapted for use with masonry. Test methods discussed include: Infrared Thermography (IRT), Surface Penetrating Radar (SPR), and Impact Echo (IE) testing methods. These test methods can be used as evaluation tools for existing construction and as quality assurance tools for new construction offering advantages over visual inspection alone. The paper addresses the basic technical aspects of the test methods so that the audience has a general working knowledge of the test methods and understands the limitations of each.

Ground penetrating radar (GPR) continues to gain use as a non-destructive investigative tool for existing reinforced concrete structures. Structural engineers conducting a flexural strength evaluation as part of a condition appraisal can use GPR to identify the relative positioning of reinforcement within the concrete element for use in their calculations. Different techniques can be used to convert the recorded time signals from the GPR into depth measurements. These techniques could include implementing an equipment-based default for the dielectric constant for the surveyed concrete, selecting a user-defined dielectric constant for the surveyed concrete, or creating a site-specific calibration using depth measurements recorded at destructive exploratory openings. Ultimately the usefulness of the GPR information to the structural engineer is a function of the accuracy of the technique used to convert the recorded time signal to an estimated depth. This paper presents a case study on the implementation of several conversion techniques, and compares how these techniques affect the estimated depths to reinforcement to be used in the strength calculations.

Nondestructive test methods (NDT) are available for the assessment of many types of defects in existing structures including: the evaluation of reinforcing steel corrosion, determination of defect location, accurate assessment of the member sizes, and reinforcement locations. The use of these methods has increased as engineers and owners become aware of their capabilities. However, recent experiences have suggested that the integration of the NDT results into the evaluation process is lagging, and often the results of the NDT program end up as little more than report filler. Worse, the lack of NDT verification can result in incomplete or erroneous conclusions about the structure. Integration of NDT results into the evaluation process requires an understanding of both the output of the test methods and how the results impact structural performance. The successful integration of NDT results into the evaluation process is described.

Settlement of subgrade resulting in poor performance of slabs-on-grade is a common problem in structures. On a recent project, significant amounts of soil slurry infiltrated the basement of a large manufacturing warehouse. The washout of the underlying soil and resulting settlement was sufficient to cause visible dynamic deflections when subjected to routine forklift traffic. These observed conditions indicated the void space beneath the slabs would be moderately deep and widespread. This paper discusses the application of surface penetrating radar (SPR) to identify the locations of subgrade voids and provides a comparison to other nondestructive test (NDT) methods. Impulse response and impact-echo can be used to locate these voids; however, these methods have inherent limitations and often require more destructive testing for confirmation of results. Due to its accuracy and ease of use, SPR is an ideal NDT method for this application.

In-situ load testing is commonly used to assess the safety or the serviceability of an existing or new structural system or part of its elements for a particular external load condition. The most frequently used load testing procedure includes the in-situ load test method described in Chapter 20 of the ACI 318 - Building Code Requirements for Structural Concrete and the Cyclic Load Test method in ACI 437 and ACI 437.1R. This paper describes the load testing programs used for two field projects to evaluate the load capacity of existing and upgraded structural components. The main objective of this paper is to describe the process for determining the test load level, loading procedure, instrumentation, evaluation criteria and load test outcomes. The first case study is for the evaluation of the sidewalks for a historical steel bridge in which the supporting beams lost up to 70% of the original cross-section due to extensive corrosion. The load test was performed in order to assess whether the sidewalks were able to safely support the pedestrian load. The second case study is for the evaluation of a typical bay in an old reinforced concrete (RC) pan-joist floor system. The floor was being considered to support new telecommunication equipment that required an increase in the capacity of the floor system. Load tests were performed for typical existing members and members upgraded using externally bonded FRP reinforcement as well as bonded RC overlay.

A detailed damage survey of a single, wood-framed, structure, which had a complete roof failure during the passage of a gust front in southern Ontario, was performed. Radar data was used to estimate upper level wind speeds associated with the gust front. Details pertaining to the structural failure, including the debris field, were obtained. Wind tunnel pressure time histories, in a simulated atmospheric boundary layer, were used to establish the roof height, gust wind speed at failure. This speed was smaller than the upper level speed found from the analysis of the radar. The flight of the roof was also examined, and confirmed the wind speeds obtained from the analysis of the failure. The study illustrates that detailed damage surveys, which incorporate the use of wind tunnel test data and debris flight in the analysis, can shed considerable light on the details of the wind speeds at failure, reducing the uncertainty caused by the many assumptions in such analyses.

An industrial facility near Baton Rouge, LA experienced significant damage from Hurricane Gustav. Observed damage patterns indicated that a localized gust resulted in damage to sections of the facility that were disproportionately higher than to the remainder of the facility. One of the wind speed data sources available was a local meteorological tower which measured an equivalent 3-second wind gust of 70 miles per hour (mph at 10 meters). The National Oceanic Atmospheric Administration (NOAA) — Hurricane Research Division experimental product H*WIND estimated a 3-second gust of 62 mph for the site. However, after a careful examination of all the data sources and structural analysis, it was estimated that the probable peak wind speed experienced in a section of the facility was at least 80 miles per hour. The latter implies that the damage observed at the facility was produced by a gust factor that was on the order of 15% larger than the average gust estimated for non-hurricane regions.

On the evening of April 2, 2006 a severe wind storm passed through the downtown of a major Midwest urban municipality. This event resulted in distress to a 36 story high rise structure with approximately 10% of its curtain wall visibly missing and unknown damage to the balance of the building's cladding and structural systems. This paper will present the authors' involvement with the initial emergency response to the property where they immediately worked with contractors to stabilize the remaining curtain wall, designed and erected temporary enclosures and shoring systems, and began an assessment of damage. Moreover, the paper will discuss the 3-dimensional analytical model of the building's cladding and structural frame that was developed for the purpose of determining the extent of damage, in addition to the wind tunnel analysis, field instrumentation, tuned damper study and other analysis that provided critical data for the design of the curtain wall over clad to be installed at the building.

The Enhanced Fujita (EF) Scale was developed specifically for the estimation of wind speeds based on damage caused by tornado winds. Recently, the question has arisen as to whether or not the EF Scale can be reliably used in reverse to predict the amount of wind damage based on measured or estimated hurricane wind speeds, particularly when wind action is co-mingled with severe storm-surge action and evidence of the exact level of wind damage is obliterated. In considering such use of the EF Scale, we examine separately its two major components: (1) Degrees of Damage and (2) ranges of tornado wind speeds associated with these damage levels. Our experience suggests that, in general, the EF Scale properly describes the overall progression of damage with increasing wind speeds in both tornadoes and hurricanes; however, the wind speeds associated with various degrees of damage are generally expected to be different for structures exposed to hurricanes and tornadoes. Use of the EF Scale to predict hurricane damage based on peak wind speeds is therefore discouraged.

Tornados often create and transport large amounts of debris that can be ejected at high velocities. There have been empirical and theoretical studies conducted on missile transport and impact, but ground damage from tornado-borne projectiles has not been well documented in the field. This paper summarizes the evidence and extent of ground damage from tornados and proposes a method for field data acquisition and assessment. Impact velocities of projectiles can be estimated using field measurements of ground deformations coupled with projectile and soil properties. Ground damage has the potential to adversely affect subsurface infrastructure if the penetration is deep enough to strike a buried pipeline or if the ground impact transfers sufficient energy to induce local settlement around a buried pipeline. With reliable data, ground damage assessment can be considered for inclusion as part of the Enhanced Fujita Scale for tornado classification.

The original Fujita Scale (F Scale) was introduced as a means of estimating the intensity of tornadoes and hurricanes by relating appearance of damage to wind speeds. The relationships were based on the extensive experience of Dr. Fujita but were never independently verified. Furthermore, the importance of construction quality was not recognized, and the number of damage indicators was limited. The Wind Science and Engineering group at Texas Tech University agreed to lead an effort to improve the original scale. The improved scale, known as the Enhanced Fujita Scale (EF Scale), defines 28 damage indicators and a number of degrees of damage for each one. A process of expert elicitation was used to relate estimates of expected, upper and lower bound wind speeds for each degree of damage. The Enhanced Fujita Scale was then correlated with the Fujita Scale by means of a regression equation. The National Weather Service implemented the Enhanced scale in February 2007. In its present form, the EF Scale is applicable only to tornado intensity.

This paper addresses methods and guidelines for assessing damages and distinguishing between damages caused by wind, flood and storm surge to homes and buildings from a hurricane event. These methods are based on an engineering approach that utilizes forensics, engineering science along with codes and standards to determine the extent of the damages and various causations. A general approach to the examination of the risks is outlined, and the elements that a report should contain are addressed. Emphasis is placed on the decisive role that corroborating information plays in determining the extent and proximate cause of damages.

In 1983, Hurricane Alicia caused extensive glazing damage to high-rise buildings in the Central Business District (CBD) of Houston with fastest-mile winds reaching 80 mph (∼94 mph 3-second gust). Twenty five years later, Hurricane Ike also passed near the Houston CBD causing significant glazing damage despite 15–20% lower wind speeds. Straightforward kinetic energy calculations of hurricane Alicia and Ike show that Ike can cause comparable or even more damage than Alicia if cladding components start failing at 60 mph (1-min) winds. While both hurricanes followed virtually identical headings, Alicia passed west of the CBD and Ike to the east, providing a unique opportunity to understand extreme wind environments in an urban area for different angles of attack. This paper discusses post-Ike glazing and rooftop appurtenance damage observed in sixteen high-rise buildings within the Houston CBD, including those affected during Alicia

This paper will discuss structural forensic investigative procedures used to assess wind storm damage, tornado damage, and methods to differentiate between hurricane wind and storm surge damage. Several structures or facilities are considered on a case study basis to determine commonalities and differences in the types and extent of wind-related damages. In several cases, comparisons to storm surge-related damages were conducted as part of the investigation. This paper will address the factors impacting the types and degree of wind-related damages exhibited by each structure. Wind forces related to hurricanes, tornadoes, and wind storm events vary in strength, duration, and directionality; however, common wind-related damages were observed as a result of the differing wind events. Though commonalities in the types of damage were observed, the extent of damage varied depending on the type of construction, quality of construction, age of the structure, and orientation of the structure to the wind forces.

In June 2004, thunderstorm winds caused significant structural damage to a downtown Tulsa, Oklahoma 15-story building. Damage was concentrated on the east facade of the building's multi-story glass atrium. The atrium is constructed with a framework of vertical steel trusses and horizontal struts. Eyewitness accounts from inside the atrium described a shaking or pulsing of the exterior glass curtain wall while wind gusts of up to 56 mph were recorded at a nearby weather station. On the building's sixth floor, the alternating wind pressures caused the failure of several horizontal strut connections. Without the horizontal support, the vertical structure deformed outward dislodging approximately thirty glass panels and damaging much of the surrounding structural support. In the ensuing investigation, a number of structural deficiencies and construction defects were uncovered in the curtain wall framework. This paper describes the sequence of events that led to the damage and summarizes the investigation's findings.

Reinforced Concrete (RC) overhead reservoirs are important water-supply systems that may fail due to aging and other durability problems. To maintain the integrity of these structures, proper inspection and repairs are necessary. A case study on a near thirty-year old overhead water reservoir, located in Tiruchirppalli, India, is presented. An important lesson learned in the case study is the need for frequent inspection and proper repair and rehabilitation schemes to prevent further deterioration. This paper discusses the issues associated with the maintenance of the water tank and describes in detail the repair process.

Imagine that a hurricane or an earthquake has occurred. Your assignment, either for an owner or for an insurance company, is to recommend what rehabilitation, if any, is needed to bring the building back to it pre-event condition. There are two parts to this rehabilitation: Building Lateral Force Resisting System and the Building Envelope. This paper will only address the former and will focus on concrete buildings even though the concepts apply to all buildings. This paper shows that the concepts presented in recent publications by FEMA and ATC (especially ATC-63) and the experiences of the authors that it is scientifically possible and practical within reasonable budget constraints to complete the above defined assignment.

The rehabilitation of a 17-story, concrete framed residential building presented an interesting and under-documented technical challenge in the design and execution of structurally complex, effective, and durable repairs. The case study is located on the southern New Jersey shore in which numerous columns within the exposed parking levels were structurally debilitated from on-going marine exposure, poor original construction, and previous improper repair attempts. Initial investigations of the deteriorated elements indicated that conventional localized concrete repairs would require significant concrete removals that could undermine the structural stability of the building as a whole, and an alternate remedy was implemented.

Load bearing structure of a new department store consists of flat (double ribbed) reinforced concrete slabs supported directly on columns within span distances 12 x 12 m. Slabs above the first and second storey cantilever out beyond the edge columns by 3 m. After few years in service, serious performance deficiencies concerning cladding as well as interior partitions and other secondary elements were observed. Analysis of load effects showed that although the structure was safe (with respect to the ultimate limit states), the large span cantilevered slabs had insufficient stiffness. Serviceability deficiencies of the department store were primarily caused in design by lack of consideration of deflection due to permanent load and shrinkage. Several construction faults and overloading of the structure enhanced unfavorable deformation defects. It appears that causal (Bayesian) network may provide valuable insights into causal links between observed deficiencies, overall performance and utility of the building.

This 20 year-old, 75' x 120' concrete structure, originally built for landing four medical helicopters, was presented to Torello Engineers with serious structural deficiencies, a deteriorated landing slab and structurally insufficient safety outriggers. Torello Engineers was charged with investigating the extent of repair needed and redesigning the structure. Among the challenges of this project was the need to keep Life Star Helicopters operational during rehabilitation of the landing surface and no disruption of other hospital services. Because the height of the heliport being more than 150 feet in the air, it was difficult to provide access for future repairs. Construction materials that will provide a long life but require little maintenance were used including stainless steels, polypropylene fibers and epoxy coating systems. The new design eliminated deficiencies and provided upgrades to the facility to accommodate landing of larger helicopters including Marine One, in the event of a Presidential emergency.