Structures Congress 2020

Active shooter scenarios can potentially inflict physical and psychological harm to the public making such attack scenarios attractive to would-be assailants. Recent history indicates that such attacks might target the public at their most vulnerable facilities, including public schools, houses of worship, commercial centers, and residential dwellings. Normally, these facilities are not designed for direct fire attacks. This article will highlight the inherent ballistic rating, if any, for conventional residential construction materials used in the USA. Furthermore, ballistic damage assessment methodologies using analytical and experimental techniques will be presented, and finally cost effective mitigation strategies will be highlighted.

Vehicles of all types are increasingly being used as a hostile threat in public and urban environments. While vehicle barriers have been designed, manufactured, and installed for high-security applications in the government, military, and energy sectors, there is a growing need to provide hostile vehicle mitigation for commercial property. Though there are many suppliers of vehicle barriers in the U.S. and abroad, impact test certification is typically only applicable to a single configuration. Oftentimes there are site constraints that prevent barrier installation in the tested configuration. One specific and common variance that arises is the use of surface-mounted barrier systems installed atop an existing, elevated structural slab. Though the need for a deep foundation is avoided with this barrier type, there remains a strong assumption that the barrier is continuously supported by the soil beneath. When barriers are mounted above basements or in parking structures, the existing structural slab is vulnerable to failure from vehicle impact loads and providing an anchorage design can be challenging. The aim of this case study is to evaluate the performance of typical elevated, reinforced-concrete slabs for surface-mounted vehicle barrier designs currently available for procurement. Finite element analysis is employed to assess the load transfer to and behavior of the slab and anchorage in the event of an impact. Key implications and design challenges are documented.

Terrorist organizations have advocated conducting vehicle ramming attacks against crowds, buildings, and other vehicles in recent years. These attacks are becoming more widespread across the world. One common method for preventing these attacks is the deployment of vehicle barriers. The field expedient non-lethal vehicle arresting barrier (FENVAB) is an active vehicle barrier designed and patented by the U.S. Army Engineer Research Development Center (ERDC) to prevent unauthorized vehicle entry in urban and austere environments. The FENVAB does not include anchors and was designed to absorb the kinetic energy of the aggressor vehicle and convert it into frictional energy by forcing the vehicle to slide once it impacts the barrier. Additionally, this barrier design includes only basic steel materials and requires limited engineering support, equipment, or specialized tools. Multiple experiments have been conducted by ERDC to analyze the performance of the FENVAB against small vehicles. To prevent penetration of large vehicular threats, multiple FENVAB units can be linked to form an array. ERDC recently demonstrated the ability of the FENVAB array to limit penetration of a Class 6 Freightliner box truck. A computational model was also established using LS-DYNA to simulate the impact of a large aggressor vehicle into the FENVAB array. This research will provide government and private agencies with critical information regarding mitigation of large aggressor vehicles using innovative and expedient vehicle barriers.

In the wake of recent events where vehicles have been turned into weapons of mass causality, our vision of urban landscape has changed forever. Urban public spaces are designed to be open and hospitable to encourage usage by crowds of people. However, these are the same reasons why such spaces are attractive soft targets to would be aggressors, and would require vehicular barriers. This article will discuss pre-engineered and engineered vehicular barriers, and how these systems can be integrated urban landscaping. Engineered systems will be highlighted specifically in light of analytical modeling advancements. Challenges associated with vehicular barrier systems in urban areas will be highlighted. Engineered and pre-engineered systems will be discussed. In addition to pedestrian and traffic flow requirements, underground conditions and aesthetic requirements are among the main drivers for barrier selection.

Design and construction errors and material deterioration can lead to concrete elements being subjected to high levels of sustained stress well exceeding typical service levels. These high levels of sustained stress have led to structural collapses in the United States and around the world. However, the performance of shear-controlled concrete elements (beams and slab-column connections) under high sustained stress is not well understood. Under high sustained compressive stress (greater than 0.75 fc’) concrete will suffer tertiary creep characterized by accelerated permanent strain, leading eventually to a failure. The bond of the reinforcing bars to the concrete is also affected leading to slip. This research presents the results of experimental tests on shear-controlled RC beams that were loaded to 81, 86, and 92 percent of their short-term capacity and observed for about four weeks. Deflection and strain measurements were recorded for each specimen throughout the sustained load test. Under high sustained stress the specimens showed continued deflection with time, with most of the deflection occurring shortly after the application of load. The failure of the specimens exhibited more flexural response than that of the control specimen. The test results show that high levels of sustained stress (up to 92% of their short-term capacity) can be sustained for a prolonged time; however, the deflections and cracking are increased and the ultimate failure mode may be changed. This information will help engineers identify elements nearing failure under high levels of sustained stress.

The prevailing analysis approach in the field of disproportionate collapse of structures is the alternate path method (APM). This method adopts the notion of a complete removal of a key load-bearing component of the system, such as a column or a shear wall, and investigates the capability of the remaining structure to bridge over the loss of this component. Though it offers a practical and efficient tool for the assessment of structural robustness, the complete column loss scenario is a rather unrealistic idealization of damage initiation. This study expands on previous work done by the authors in the field of structural robustness and applies a partial distributed damage method (PDDM) in 3D multi-story steel framed and concrete composite buildings. This method assumes that damage is being distributed in more than one components, as a common output of real-case extreme events. Using advanced nonlinear finite element modeling, this work applies a PDDM scenario in a prototype structural system and evaluates its mechanical performance, making direct comparisons with the APM with regards to the governing collapse mechanism, structural capacity, and damage progression path.

Progressive collapse is a global failure in a multi-storey frame. All stories above the removed column will help to redistribute the loads initially resisted by the removed column together. However, due to time and cost saving, majority of existing experimental studies on progressive collapse is based on single-storey beam-column substructures. To date, how to use the results from single-storey substructures to equivalently investigate the behavior of multi-storey building is still unclear. Thus, for this purpose, in this study, a series of planar multi-storey RC beam-column substructures are modeled using high-fidelity finite element software LS-DYNA. The validated models were used to capture the difference of mobilization of load resisting mechanism in different stories.

In addition to gravity and lateral loads, there is a broad range of events that may impact a building during its service life. Amongst these, extreme events such as accidents and natural catastrophes can cause significant damage with a risk of propagation through the structure that can lead to disproportionate collapse. Current standards and guidelines that give direct and indirect approaches to ensure structural robustness are limited to concrete, steel, and light-frame wood structures. Mass timber buildings, however are a new method of construction, and existing advanced analysis techniques which are generally not adopted by practitioners. This paper uses linear static alternative load path analysis to investigate the performance of a six-storey post and beam mass timber building following different column loss scenarios. The approach enables to identify possible collapse resistance mechanisms and load distribution of the system after element loss. The results help improving typical connection detailing designed for gravity and latera loads, hence preventing disproportionate collapse.

Ground floor reinforced concrete columns are vulnerable to blast loading of close by distance (i.e. less than 3$\text{m}/{\text{kg}}^{1/3}$). In this work, a 25-story commercial building was designed in low-seismic and high-seismic regions respectively to find the typical column dimensions and reinforcements. A finite element model was developed to simulate above mentioned blast loading scenarios and to evaluate effectiveness of FRP retrofit. The model was found to be adequate in capturing the trends of deformation and damages as expected and effectiveness of FRP in providing additional confinement. The qualitative results thus obtained are presented.

Meshfree methods such as the reproducing kernel particle method (RKPM) are well suited for modeling materials and solids undergoing fracture and damage processes, and nodal integration is a natural choice for modeling this class of problems. However, nodal integration suffers from spatial instability, and the excessive material deformation and damage process could also lead to kernel instability in RKPM. This paper reviews the recent advances in nodal integration for meshfree methods that are stable, accurate, and with optimal convergence. A variationally consistent integration (VCI) is introduced to allow correction of low order quadrature rules to achieve optimal convergence, and several stabilization techniques for nodal integration are employed. The application of the stabilized RKPM with nodal integration for shock modeling, fracture to damage multiscale mechanics, and materials modeling in extreme events, are demonstrated. These include the modeling of man-made disasters such as fragment-impact processes, penetration, shock, and blast events will be presented to demonstrate the effectiveness of the new developments.

Blast wave interaction with structures is a complex phenomenon. Not only are the fluid mechanics and combustion physics involved in the blast wave dynamics difficult to correctly model, but also the interaction with a structure, the structure’s response to the dynamic loading, and the structure’s influence on the blast wave propagation itself. Clearly, blast waves propagating on nearby structures fall under the category of three-dimensional scenarios featuring highly time dependent fluid and solid mechanics responses. In addition, the high strain rates imparted onto the structure make it difficult to extrapolate a low strain rate response of the structure. Here we present a novel small-scale experimental setup to study blast wave-structure interaction in a three-dimensional setting in which a cityscape is subjected to a dynamic blast wave event. The experimental turn-around time is very fast: less than two minutes per experiments. Experimental data is obtained via ultra-high-speed schlieren photography and local strain gages attached to the structure(s) of interest.

Improvised explosive devices (IEDs) used by terrorists frequently contain significant quantities of primary fragmentation packaged around the explosive device. When detonated, this fragmentation is ejected from the device at high velocities, fully or partially penetrating victims in the nearby area. This paper undertakes a comprehensive literature review of the various tools and associated equations and provides a methodology, with underlying assumptions, for an algorithm that generates an estimation of the severity of injury based on fragmentation from an IED. This methodology is expected to allow organisations to develop mitigation measures and advise on preparedness for emergency response and supplies for injury from primary fragmentation.

Fatigue tests on steel-concrete composite specimens with different shear connection arrangements are presented in this paper to evaluate the cyclic incremental deformations, deflection and slippage, and cyclic incremental strains in the shear connectors. The full shear connection between the concrete decks and steel beams was achieved by two sizes of shear connectors in two arrangements, one row and two rows. The fatigue tests were conducted to one million cycles under a four-point bending test. Shear connectors’ arrangement played a major role in controlling longitudinal fatigue cracks in the concrete decks. Shear connectors with large diameter can be arranged in one row over the centerline of the steel beam web to achieve the full shear connection, freeing up most of the top flange width, and enhancing safety conditions for construction workers. However, a concentration of the shear force transferred between the concrete deck and the steel beam occurred, which led to a high level of fatigue damage in the concrete around these connectors. This high level of damage caused more incremental deformations, deflection and slippage, and incremental strains in the shear connectors relative to the two-row arrangement during fatigue loading.

Steel-concrete composite (SCC) bridge superstructures are widely used today extensively in highway bridges. Post-tensioning (PT) has been commonly used in this type of structure as a repairing or strengthening technique. As bridges are typically subjected to cyclic loading, understanding their performance under fatigue is vital. In this paper, two specimens were tested to study the performance of SCC beams with external post-tensioning under the effect of fatigue loading. Because the external PT is mostly added to existing bridges as a retrofitting technique, one of the specimens has undergone some damage prior to experiencing fatigue loading. The strains in the shear connectors as well as the midspan deflections were monitored during the fatigue tests. The results show that as the number of fatigue cycles increases, both the deflection and strain in the shear connectors also increase. The pre-existing damage decreased the effectiveness of the PT to enhance the fatigue behavior of the SCC beam. For the pre-damaged specimen, the increase in the shear connector strain and the midspan deflection was 4.5 and 1.4 times those for the undamaged specimen, respectively.

Seismic performance evaluation of a structurally deficient as-built reinforced concrete bridge bent and a comparison to a retrofitted bridge bent was conducted. The as-built bridge bent had deficient seismic details and was retrofitted with a carbon fiber-reinforced polymer (CFRP) donut, which included a CFRP shell, eight headed steel bars, nonshrink concrete, and a steel collar around the column; CFRP composite jackets were also employed to increase column shear capacity. Detailed design guidelines of the rehabilitation method by using a simplified strut-and-tie model (STM) were presented which could be applied to rehabilitate similar reinforced concrete bridges. A fiber-based model was developed in OpenSees; in addition, soil-structure interaction (SSI) was considered using simplified springs; the bridge bent model was validated using experimental results from previous research of an existing bridge. A comparison of the as-built and retrofitted bridge bents under nonlinear static pushover analysis, incremental dynamic analysis (IDA), and fragility analysis using 22 far-field ground motions, showed that the rehabilitation method improved the seismic performance in terms of load capacity and structural stiffness.

Accelerated bridge construction (ABC) technologies are being adopted by state departments of transportation. ABC increases the public’s and workers’ safety by lowering exposure to construction activities and also increases mobility and economic opportunities by reducing traffic interruptions and delays. As an alternative to ultra-high performance concrete (UHPC), Idaho Transportation Department (ITD) is interested in the suitability of high-early strength (HES) concrete Class 50AF with polypropylene fibers in closure pours between bridge deck bulb-T girders. The advantages of this alternate material are the reduction in costs and construction time. In the first phase of the project, an optimum concrete mix with good material properties was identified through a series of standard laboratory experiments and tests on larger specimens. In the second phase, field performance of a closure pour mix similar to the optimum mix found in Phase 1 is examined by placing the material in the closure pours between deck bulb-T girders in the SH-36 Bridge over Bear River near Preston, Idaho. Despite some deviations from the standard construction practices, the strain data in seven out of eight sets of gages (four sets of concrete and four sets of steel gages) shows low strains. The finite element computer model of the bridge shows that, if properly installed, the HES Class 50AF concrete with polypropylene fibers in the ITD’s 10-in. closure pours performs well under the AASHTO design truck loading.

Applications of accelerated bridge construction (ABC) methods have been limited in moderate-to-high seismic regions because of concerns about the adequate performance of the connections. Recently, the Idaho Transportation Department (ITD) proposed a precast pier system in seismic regions. The proposed pier system incorporates the use of steel pipes at the column-to-footing. Similar to the connections with grouted ducts and grouted reinforcing bar couplers, the new connection is intended to emulate the traditional cast-in-place behavior by forcing the formation of plastic hinges in the pier during an earthquake. The benefits of this new method are: (a) elimination of precise alignment of the pier reinforcing steel bars (rebars) with those of the footing, and (b) avoiding damage to the rebars protruding from the precast pier during transportation and handling. To validate the concept, large-scale experimental testing is carried out on cantilever piers at Idaho State University (ISU). The specimens include cast-in-place and precast piers that are tested under quasi-static cyclic loading with increasing drifts. This paper focuses on developing analytical models for the piers using the open system for earthquake engineering simulation (OpenSees) software. The cast-in-place pier is modeled with OpenSees’ “Conceret01” and “Concrete04” for unconfined and confined concrete, respectively. “Steel02” material is used for the rebar steel. Bond-slip “ZeroLength” elements are used at the interface of column-to-footing connection to provide better results. Low-cycle fatigue is incorporated in the model. For the precast pier, similar material models are used with appropriate properties. The steel pipe in the ITD’s proposed connection is modeled as circular “patch” sections with the steel pipe properties. Experimental and analytical efforts to date are presented. Results show good agreement between the analytical and experimental data. The analytical modeling in this paper is aimed to provide a practical tool for bridge engineers when considering new connection details.

In this study, a new type of connection is proposed between precast elements in a bridge substructure system. The connection uses structural steel pipes at the column-to-footing and column-to-cap beam connections. For the column-to-footing, the steel pipe is placed inside the column during precasting. During on-site assembly, the other end of the steel pipe slides inside a larger pipe that is placed inside the cast-in-place foundation. Steel plate fins are welded to the column pipe to serve as guides inside the footing pipe. The gap between the pipes are then secured using high strength grout. For better seismic performance, an unbonded length of the pipe is left inside the precast column just above the column-to-footing interface. The unbonded length aims to achieve a higher ductility of the pier system and prevent low-cycle fatigue and strain concentration near the interface. For the column-to-cap beam connection, a similar approach is used. However, in this scenario, both the cap beam and the columns are precast. The pipe connection aims to emulate the conventional cast-in-place behavior, such as the formation of plastic hinges in the columns during an earthquake. It offers good advantages compared to other types of emulative connections such as grouted ducts and splice sleeve connections. The advantages include better tolerance in construction, avoiding damage to the rebars protruding from the precast columns during transportation and assembly, and preventing cracking to the columns during a small earthquake. The experimental program in this study includes testing of large-scale pier systems under quasi-static cyclic loading. Two specimens represent a cantilever pier system and another two represent a bent system. One cantilever and one bent specimen incorporate cast-in-place construction and are intended as a benchmark to compare seismic performance. The other two specimens are constructed using the proposed pipe connection. The paper presents the concept, design, and construction considerations for the proposed pipe connection. Experimental results from testing of the cantilever and bent specimens so far are presented. Based on the outcome of testing, the Idaho Transportation Department (ITD) is planning to use the proposed pipe connection in the construction of an actual bridge on I-15 in southeast Idaho in 2020.

Shallow structures are often required in highway bridges when an underneath clearance is critical. Use of shallow bridges allows to avoiding a more expensive bridge system such as arch or truss bridges. Through-girder bridges are categorized as one type of girder bridges and are more receptive to the majority of the contractors as compared to other sophisticated bridge systems. When conventional concrete is used in through-girder bridges, relatively large and heavy edge girders are necessary because they need to carry all dead and live loads. Recent advancement of ultra-high performance concrete (UHPC) allows to leveraging this exceptional material in various types of structures and results in increased structural capability and performance. The use of UHPC in shallow bridges can reduce the sizes of the structural members or increase the span capacity. This paper addresses a through-girder system that involves the use of UHPC in primary members and connections. It describes various components of a through-girder system, including the transverse beams, edge girders, and longitudinal and transverse connections. A numerical example is presented to demonstrate the analysis and design of a through-girder bridge. Both high-performance concrete (HPC) and UHPC options are described for comparison purpose. A UHPC through-girder system is expected to facilitate bridge construction due to the reduced girder weight and simplified prestressing and reinforcing details. It also allows to enhancing the structural performance and increasing the service life of the bridges.

Potential continuation or acceleration of climate change could increase the risk of failure of critical bridge components or bridge systems. This paper present preliminary results of ongoing study investigating the impact of extreme climate loads, on the safety and serviceability of a curved-continue composite box-girders bridge. A four-span curved box-girder bridge was designed according to the Canadian Highway Bridge Design Code and simulated by a 3D nonlinear finite element model. The bridge is investigated for the effect of different levels of temperature and ice accretion combined with other gravity loads. The results show significant increases in the moments, high levels of stresses, and very large increase of longitudinal and vertical displacements at critical sections of the bridge superstructure. More research investigations are required to further investigate the safety of the bridge elements, connections, and the integrity of the bridge system.

Long span and wind critical structures often require a wind tunnel study for determining the critical wind speeds which could potentially cause instabilities in the structure. This wind tunnel test is often cumbersome and expensive and therefore should only be used for the final design stage. In this study, consideration is primarily focused on numerically determining the fluttering effect. The critical flutter wind speed of a bridge superstructure is computed through the use of computational fluid dynamics in conjunction with finite element analysis of the full bridge model. Upon evaluation of discrete vortex method, flutter derivatives are determined which are then used to describe the full dynamic equation. The quadratic complex eigenvalue solution of this response equation is solved to find the critical wind speed of the given cross section. This critical wind speed allows the engineer to have a preliminary justification of whether the chosen shape is within a reasonable aeroelastic response given wind design speeds at the project site. This is especially important because, for large bridge projects, the industry is trending towards design-build projects where it is beneficial to fast-track the design process. This study is focused on the Abraham Lincoln cable stay bridge in Louisville, Kentucky, with comparison to wind tunnel results done on the structure.

The Bayonne Bridge, which spans the Kill van Kull Channel connecting Staten Island, New York, and the city of Bayonne, New Jersey, was opened for traffic in 1931. When opened it was the longest arch span in the world with a main span of 1,675 feet, a total length of 5,789 feet, and a mid-span vertical clearance of 150 feet. In the early 2000s, the owner of the bridge, The Port Authority of NY and NJ, decided to raise the bridge deck of the arch to provide a minimum clearance of 215 ft and build new, taller approaches. The new navigation clearance allows neopanamax ships access to the port of Newark. The new approaches are precast-segmental built with the balanced-cantilever method using an overhead gantry. The crowded urban site required construction over residences and active businesses within the footprint of the existing bridge without major traffic interruptions. Consequently, permanent works, temporary works, and construction staging were constrained by the existing bridge. This paper presents an overview (from the independent checker’s perspective) of the construction engineering required to accomplish this task.

Infrasound is an emerging remote sensing technology related to low-frequency acoustics. This paper provides a state-of-the-art assessment of infrasound’s ability to detect and monitor a diverse array of infrastructure, including a discussion of best practices for use and potential limitations. This paper follows field experiments where researchers were focused on a single bridge source with infrasound (remote monitoring) and on-structure instrumentation, in which the on-structure data validated infrasound data. After completing the assessment of the bridge of primary interest, the question of wide-area infrasound monitoring was raised. While the original experiment series focused on a single bridge source, further evaluation of the data set identified multiple sources within the area of study via infrasound, allowing investigation of the feasibility of multiple-source monitoring. These additional sources included hydraulic features, bridges, industrial activity, and a dam. Some of these features were detected via infrasound while others were not.

Sustainable building materials are the future of the construction industry. Specifically, eco-friendly cementitious materials that are mechanically sound and durable are desired as the majority of the world’s infrastructure, including roads and bridges, are made with concrete. Since the durability of cementitious materials can greatly affect the performance of a structure, it is important to evaluate the properties of these new materials. In this study, cement mortar overlays containing recycled glass aggregates were investigated. Particularly, the focus of this study was to determine the benefits of using glass in reducing early-age cracking of mortar overlays. The rate of plastic shrinkage crack formation and overall crack area was quantified for specimens subjected to set environmental conditions. In addition, the rate of absorption, which influences the serviceability and structural performance of a structure, was also evaluated. The findings of the experimental study suggest that glass aggregates are effective in reducing the rate of crack formation by 98% when full glass replacement is used. Furthermore, at full glass replacement, the initial and secondary rate of absorption was found to decrease by 31% and 63%, respectively.

Deterioration of our infrastructure cannot be totally avoided due to severe conditions to which they are exposed to. A significant number of steel structures, especially bridges, undergoes deterioration due to corrosion as they are situated outdoors and subjected to moisture and other deleterious chemicals. Due to economic and other constraints, replacement of all these deteriorating structures is not feasible. Therefore, their effective rehabilitation is paramount. One of the effective ways to rehabilitate steel structures is with the use of fibre-reinforced polymers (FRP). This paper explores the effectiveness of rehabilitating corroded webs in steel I-shaped beams with unidirectional basalt fibre reinforcement polymer (BFRP) fabric. The structural deficiency was induced to the web of the beam by cutting a circular shaped area out of the web. The section loss was repaired with BFRP fabric using the wet lay-up technique. Overall, seven beams were tested utilizing a 4-point test setup, including a control (undamaged) beam, control corrosion (damaged) beam, and five rehabilitated specimens. Two patterns of rehabilitation were performed by attaching BFRP fabrics in horizontal and vertical orientations. The study concluded that the BFRP fabrics were effective in restoring elastic stiffness, yield load, and ultimate load capacity of rehabilitated beams to that of an undamaged steel beam. The tests also showed that there was a direct correlation between the improvement of structural behaviour and thickness and orientation of the BFRP fabric. Nonlinear finite element analysis was successfully used in this study to determine the optimum pattern of rehabilitation with BFRP fabrics.

Distortion-induced fatigue (DIF) cracking in steel bridges accounts for one of the most common types of fatigue damage in steel bridges in the United States. Many methods have been developed to repair DIF; however, most available repair methods require concrete deck removal, which is expensive and disruptive to traffic. This paper describes an experimental study aimed at investigating the fatigue behavior of steel bridge girders repaired with a novel CFRP and steel retrofit. The retrofit addresses an important need in repairing distortion-induced fatigue—creating a load path from the connection stiffener to the girder flange without requiring bolting or welding to the flange. To evaluate the performance of this combined retrofit, fatigue tests were conducted using a half-scale 2845 mm (9 ft) long steel girder-to-cross-frame subassembly. The girder was cyclically-loaded to produce realistic DIF crack patterns, then a retrofit that engages three surfaces: the web, the flange, and the connection plate, was added. Five trials are described; two of the trials were performed in the unretrofitted condition while the other three trials were performed in the retrofitted condition. The retrofit performance was examined for different crack patterns, up to a 4 in. crack length. The experimental results showed that the CFRP-steel retrofit was effective in preventing distortion-induced fatigue crack propagation for all the tested crack patterns and lengths.

The magnetic flux leakage (MFL)-based assessment is used to detect corroded regions of steel prestressing strands in pre/post-stressed (PS) concrete girders. The MFL instrument includes two blocks of DC magnet to create a powerful magnetic field in the vicinity of the steel within the concrete girder. Hall-effect sensors are used to acquire the resulting magnetic field signals in the vertical and longitudinal directions while the MFL instrument is moved along the length of the girder. To characterize corrosion-related signals, a correlation-based analysis is implemented. This approach helped to identify the position and intensity of the corrosion in the steel. Using the correlation analysis with an idealized corrosion signal, the effects of other steel in PS concrete girders, including the conventional shear reinforcement, are removed from the test signal. An approximate percentage of section loss and length of corroded regions are estimated using this signal analysis.

The I-78 mainline bridge over Schuylkill River in Hamburg, PA, is an example of a bridge built during the 1950s. This bridge is in the need of major rehabilitation owing to the increase in truck traffic and the condition of the existing structure. Additionally, the state government also moved it to the top, in the list of structures that need rehabilitation, due to several traffic related crashes on this roadway. This paper presents the review and analysis of the approach spans for the bridge and a discussion of how the scope evolved from a rehabilitation design to a complete structural replacement design, including the technical challenges and, the steps taken to mitigate them. The paper concludes with the most economical option for the proposed structure, based on the comparative evaluation among the various structure options reviewed for this project.

Alkali-silica reaction (ASR) occurs when the reactive siliceous aggregates (coarse or fine) are used in concrete with a high alkali content and exposed to high levels of moisture. In the long-term, ASR exhibits itself in the form of expansion, cracking, and ensuing degradation in mechanical properties, which may affect the functionality of structures. ASR has been extensively observed in dams, bridges, and power plants. In this study two mixes of concrete were prepared using fine aggregates from one of the most reactive siliceous aggerate sources in the United States located in El Paso, Texas. One of the concrete mixes was dosed with additional alkali content to bring the total alkalinity level to 1.25% by weight of cement to accelerate the ASR (compared to 0.1% in the other concrete mixture due to alkalinity from the cement only). Over a period of 18 months concrete cylinders, and plain and reinforced concrete prism samples from these two concretes were conditioned in different environments: indoor laboratory, outdoor in Los Angeles, and in an environmental chamber at 50°C and 90% relative humidity (RH). The ASR expansions and the corresponding changes in the compressive and tensile strength, modulus of rupture, and modulus of elasticity were monitored. Results showed that concrete tensile strength is more susceptible to degradation due to ASR. Additionally, the expansion caused by ASR in the prism samples reduces as the ratio of reinforcement increases. The results were used to develop relationships between ASR expansion and reinforcement ratio in a one-dimensional problem with an internal restraint.

The Jefferson Barracks Bridge is a fifteen-span structure that carries I-255 over the Mississippi River, in St. Louis, Missouri. The 910-foot main navigational span consists of a steel tied-arch superstructure, approximately 190 feet tall. In May 2019, during a routine and fracture critical inspection of the main span, inspectors discovered a six-foot crack at the toe of a weld in the steel tie girder. Further investigation revealed that crack extended at least 5/16 inch into the steel web plate. Because the cause of the steel crack was not known and the potential for bridge collapse if the crack were to propagate, the Missouri Department of Transportation (MoDOT) elected to close the three westbound lanes of I-255 on the structure. Several similar cracks were subsequently found at other locations throughout the tie girders. Working together with MoDOT and the Illinois Department of Transportation (IDOT), the inspectors responded quickly to evaluate the extent of the cracking at similar locations, obtain steel core samples, and perform laboratory testing to determine the cause of the steel cracks. Within approximately four days, the team documented the extent of this critical finding, determined the cause, began emergency repairs, and reopened the bridge to limited traffic. This paper/presentation discusses the decision-making process for the emergency response and presents the findings from the inspection, the results of the laboratory testing, the cause of the steel cracks, and the approaches used for repair.

Also known as the Great River Bridge, the US-34 Burlington Bridge is a signature stay-cable structure spanning over the Mississippi River between Gulf Port, Illinois, and Burlington, Iowa. Opened to traffic in 1993, the main river crossing span is supported by stay cables connected to two 305-foot tall reinforced concrete pylons. In 1992, prior to the bridge being opened to traffic, vertical hairline cracks were observed on the interior and exterior faces of the concrete pylons. The width of the cracks continued to increase slowly and consistently over time. The size and location of the cracks suggested that they may be structural in nature. Extensive investigations performed between 1999 and 2004 could not completely identify the cause or significance of the cracking. A more recent investigation was performed after the crack widths had grown to 1/4 inch wide. This follow-up study utilized instrumentation, material sampling, laboratory testing, and computer analyses, which determined the cause of the crack growth to be due to an alkali-silica reaction (ASR) in the concrete pylons. This case study will discuss the results of the investigation and why the cause of the crack was so difficult to identify. In addition, potential approaches to mitigate ASR deterioration in existing concrete structures will be presented.

Distortion-induced fatigue accounts for the majority of fatigue cracks in aging steel bridges in the United States. Departments of Transportation primarily use visual inspections to locate and characterize fatigue cracks, but recent studies have shown that visual inspections fail to consistently identify realistically sized fatigue cracks in highway bridges. Developing an inspection technique that does not rely on human visual inspection has the potential to reduce the risk of injury for inspectors and the traveling public, decrease the time and cost of performing inspections, and increase reliability, benefitting both bridges owners and stakeholders, as well as the traveling public. Digital image correlation (DIC) has the potential for detecting and characterizing fatigue cracks. The authors developed a methodology for crack characterization on fatigue specimens loaded in-plane which was then applied to out-of-plane distortion-induced fatigue cracks. The work was performed in the laboratory with conditions ideally suited for DIC data collection. Field implementation will require a robust system able to function in spite of numerous physical obstacles. These obstacles include non-ideal lighting, variable levels of camera focus, and inconsistent material surface quality. To understand how the DIC crack characterization methodology performs under non-idealized conditions, the effects of each of these physical obstacles must be examined. This paper describes an experimental study in which the developed DIC crack characterization methodology was applied to data obtained under non-idealized conditions. Of particular interest are the influence of lighting and camera focus on DIC data quality and its corresponding applicability to fatigue crack characterization. Preliminary results indicate that DIC may be feasible under non-idealized conditions, allowing for potential field application to in-service structures.

This research aims to develop a new bridge inspection approach using unmanned aerial vehicle (UAV) coupled with digital image correlation (DIC) system. The DIC system incorporating UAV images can measure displacements or strains by analyzing patterns of reference and deformed images. As part of this research, a commercially available UAV, DJI Matrice 210, was integrated with the DIC system using a 3D printed mounting plate, and the joint UAV-DIC system was utilized to inspect a timber bridge girder in the Structure Lab. Then, the UAV-DIC system inspected an existing timber slab bridge in Pipestone, Minnesota, but the system was not able to efficiently identify critical damage due to its instability caused by windy conditions. Therefore, only the UAV equipped with a gimbal camera was operated to perform the bridge inspection. A significant number of images from the UAV were used and analyzed through a conventional image analysis algorithm within ImageJ software for damage quantification. The major conclusion from this research was that the UAV-DIC system was only able to detect and quantify damage (i.e., crack) on the considered girder under almost zero ambient wind conditions, and the UAV integrated with the image analysis algorithm was capable of damage identification and quantification for the inspected bridge.

Failure of roof-to-wall connectors in residential buildings, in the form of metal clips, during strong windstorms and hurricanes are often reported as a major cause of roof failures. Non-intrusive fiber reinforced polymer (FRP) connections are considered useful replacements or retrofitting alternatives for intrusive metal connectors for roof-to-wall connections (RTWC) in residential buildings. FRP connections are advantageous as they are nonintrusive and corrosion resistant as opposed to metal connectors. To investigate their wind performance, FRP connections in a large-scale low-rise building were tested at the wall of wind (WOW), a large open jet wind testing facility capable of simulating hurricane winds at different speeds and up to 70 m/s, which represents a Category 5 hurricane. Prior to the WOW experiments, the FRP sheets were individually tested in the structures lab to determine their pull-out strengths. Based on the results, FRP sheets were used as RTWC in a 1:4 scaled model of a typical wooden residential house with a gable roof. The model was exposed to wind speeds ranging between 27 m/s and 54 m/s at the mean roof height. Initial results showed that the uplift load capacity of the FRP connection is adequate for resisting wind induced loads at high wind speeds (up to 52 m/s, Category 3 hurricane). In addition, the WOW tests were also used to experimentally estimate the failure wind speed of the connection in comparison to the theoretical calculation. A close agreement was obtained between the theoretical and experimental failure wind speeds. It was concluded that theoretical failure wind speeds, obtained from the strength equation of the connection, for a given roof configuration can be accurately estimated from component level testing for the uplift capacity of the connection and aerodynamic loads calculated based on current building standards (such as ASCE 7). The effective design and development of non-intrusive roof to wall connections can significantly reduce property losses in tropical storms and hurricanes, thus positively impacting the economy of the U.S. and the safety of its citizens.

Since its invention by the Romans, concrete has been cast into all manner of formworks whether temporary or permanent. Concrete members have traditionally been cast using a rigid formwork and engineering analysis has been on prismatic members. All rigid formworks including rubble, brick, and wood have become the containment form of choice for our modern concretes and an industry standard practice ever since humankind first sought to contain these early forms of mortar and “concrete” in their structures. But, since the 1970s there has been a renewed interest in using modern fabrics as part of concrete member forming systems. This type of forming system is not easily engineered and its analysis is very complex and requires nonlinear analytical procedures. Could this be a hindrance to its everyday use and acceptance? This paper explores the question of whether there is a future for the use of fabric as a material practical for forming concrete members.

A tension-only V-braced frame (TOVBF) is a new braced frame system with V-braces in heavily loaded girders above the first floor. This system utilizes gravitational potential energy, in addition to conventional strain energy, to balance input seismic energy. When subjected to lateral seismic loads, gravitational potential energy is mobilized because weight on the girders will be lifted through the tension braces. Theoretically, the system is in stable equilibrium, because the gravitational potential is at a minimum before it is displaced laterally. Analogous to a ball at the bottom of a hemisphere, if perturbed laterally, the ball will be restored by gravitational force to its original position. The system differs from the traditional V-brace in two ways: no brace at the first floor, and no compressive strength in the brace. In addition to its sound theoretical basis, the system enables highly ductile behavior, higher lateral stiffness, and economical construction, and it is an excellent seismic force-resisting system.

The evaluation of the seismic vulnerability of historical masonry buildings is a difficult task due to the uncertainty regarding structural characteristics and construction techniques, mechanical properties, and pre-existing damage. Hence, there is a need for an efficient computational technique for analyzing such structures and providing reliable results for a large number of buildings within a reasonable time frame. The present work describes the study of the seismic vulnerability using the applied element method (AEM) for high fidelity nonlinear structural analysis. The work is part of activities undertaken within the European Union funded project “INACHUS” (7th framework programme “Technological and Methodological Solutions for Integrated Wide Area Situation Awareness and Survivor Localization to Support Search and Rescue Teams”). Recently published studies highlighted the capability of AEM to overcome the limitations of the current structural analysis techniques, both in terms of results accuracy and in terms of use of computational resources. The paper reports the results of the seismic simulations, analyzing the effects of the implementation of different structural details, such as presence of arches and vaults and interaction between structural elements with different types of connections. The modelling of these details requires prohibitively expensive computational resources in the common modelling techniques based on FEM, due to the significant increase of the number of elements and the need to maintain the nodes compatibility. Moreover, in many cases historical buildings suffered significant damages due to detachments between different structural parts even with low seismic acceleration. The paper demonstrates the application of the AEM method implemented in the software Extreme Loading for Structures (ELS) for performance based design of these kinds of historical structures by subjecting the structure to multiple levels of seismic acceleration and evaluating the performance for each case. The study starts with a single building and then develops to studying multiple buildings at the same time. The objective is to detect extent of collapse for buildings, then road interruption and additional damage to the surrounding structures. A case study was performed by simulating and assessing a whole portion of the historic center of the city of Roquebillière, France. The study identified retrofitting actions, and demonstrated the practicality of using this technique to evaluate the accessibility of strategic roads for the purpose of reliable emergency planning.

The goal of repairs to existing concrete structures is for the repaired concrete structure to return, as closely as possible, to its original design strength and stiffness. At the repair surface, the bond between the original and new concrete layers is of primary importance and must provide a continuous transfer of the design loads at a minimum and preferably approach the original concrete strength. Although studies since the mid-1800s to the present day have not resulted in an accepted standard test to verify the bonded concrete shear strength, many studies suggest that actual shear strength at the bonded concrete interface is on the order of 5 to 10 times, and sometimes more than 10 times, the values currently adopted in present standards. This paper summarizes the results of selected historical studies, and recent research at the University of Colorado Denver, revealing shear strengths much higher than the current ACI 562 for repairs and rehabilitation might mandate. Structural engineers would benefit from an improved understanding of shear strength at a bonded concrete interface and, should the existing standards be more realistically revised, be able to design more efficient and cost-effective concrete repairs.

Many buildings in St. Louis and other cities in the United States are concrete-encased steel frame buildings designed and constructed in the early 1900s. The unreinforced concrete encasement for these steel frames was historically used to increase the fire resistance of the structure. The research in this study focused on a novel approach to increase the strength of the riveted joints in these concrete-encased moment frames using fiber reinforced polymer (FRP) applied to the concrete near the moment-resisting connections. A nonlinear finite element analysis of a concrete-encased joint in a historic steel structure, the Syndicate Trust Building in St. Louis, Missouri, was performed to investigate the possibility of improved performance in the riveted joint. Moment-rotation (M-θ) curves and load-deformation relationships of the joint before and after the application of the FRP retrofit were obtained. The FRP retrofitted connection used in the analysis showed improvement in the load and moment carrying capacity of the riveted beam-column connection compared to the unreinforced concrete-encased model.

Considering soil-structure interaction (SSI) effect in the design of structures would affect their seismic demands. Design codes, such as ASCE 7-10, usually allow engineers to reduce the design base shear accounting for SSI effect. ASCE 7-10 methodology is based on modeling the underlying soil using a set of dashpots and springs that approximate the actual nonlinear behavior of the soil through an equivalent linear model. In this study, we aimed to study the effect of different approaches for modeling of soil nonlinear behavior on the response of the superstructure. We employed two types of soil-structure systems using 1) an equivalent linear model suggested by most of the design codes, and 2) a beam on nonlinear Winkler foundation (BNWF) model for the beneath soil. The results show that the difference between the structure’s response in the two models might be negligible for structures located on soil type C. However, for structures built on soil type D, this difference could be quite considerable. The results clearly show the structure experiences less inelastic deformations when the soil undergoes more inelastic deformation; in addition, the soil experiences less plastic displacement for more ductile structures.

This research study presents the experimental results of using basalt fibre reinforced polymer (BFRP) fabrics to flexurally strengthen reinforced concrete (RC), structural members. The purpose of this study was to determine the viability of using BFRP fabrics to strengthen RC members in situ. Using BFRP fabrics to externally strengthen RC structural members is a promising alternative to current RC structural repair and strengthening methods. BFRP fabrics, when compared to alternative fibre reinforced polymer (FRP) materials, are cheaper, exhibit better durability characteristics, and have a much higher fracture strain. Five full-size concrete specimens, with an internal steel reinforcement ratio of 0.77%, were studied. The test matrix contains one control specimen, and four additional specimens externally strengthened with an increasing number of BFRP layers. Increasing layers of two, four, six, and eight layers of BFRP fabric were used. This strengthening method showed significant strength increases in all the beams when compared to the control beam. Increases of up to 37% and 92% were observed in both yield and ultimate beam load capacity respectively. At the same points, the beam displacement increased by up to 5% and 54% at the yield load and ultimate load-deflection points respectively. This study did, however, determine a maximum number of layers of BFRP fabric which could be used to strengthen these RC beams before the failure mode changes. At the maximum limit of eight layers of BFRP fabric, the beam experienced brittle shear failure. All beams strengthened with six layers or less of BFRP fabric experienced a ductile flexural failure. The use of BFRP fabrics as an external strengthening member was found to provide excellent strength increases over the control specimen, while still maintain beam ductility. This novel method of maintaining and strengthening existing RC structures in situ provides a major cost and environmental benefit to countries that are trying to upgrade and maintain the existing ageing infrastructure.

The current vibration serviceability assessment (VSA) criteria for wind-induced vibrations in tall buildings is based largely on human perception threshold which is not necessarily translatable to human ‘acceptability’ of vibration. Therefore, issues such as the effects of wind-induced motions on occupants comfort, work performance, motion sickness, and sopite syndrome are not taken into account in current VSA guidelines. This paper provides an overview of the characteristics of wind-induced vibrations, state-of-the-art VSA guidelines, and the current understanding of occupants’ acceptability of wind-induced motion in tall buildings. The VSimulators facility in the Universities of Bath and Exeter to assess the effects of motion and environment on human is introduced. This facility enables in-depth research in this field through controlled simulation of structural motion and the environment and multi-modal measurement of human reactions.

Unbonded posttensioned precast concrete (UPPC) structure has shown its excellent aseismic performance in laboratory tests and earthquake investigation. However, the progressive collapse behavior of UPPC subjected to column removal scenario is still unclear. To fill this knowledge gap, two 1/2 scaled UPPC beam-column sub-assemblages were tested under a penultimate column removal scenario. The dynamic test results indicated that UPPC sub-assemblages have desirable load redistribution capacity to mitigate progressive collapse. The failure modes of the sub-assemblages observed in dynamic test were quite similar to that in static counterparts.

The current state of practice for seismic design of typical buildings consider only a single design level event. The recent 2010–2011 Christchurch earthquake sequences have shown the devastating effects of sequential strong ground motion events for building structures that have not been repaired post-mainshock (MS). These events highlight the need for building structures that can be rapidly repaired while also showing the critical need to consider the seismic response of these structures for cascading large seismic events, when post-MS repairs have not occurred prior to a large aftershock(s) (AS). In recent years there has been a high interest in the development of alternative seismically resilient seismic-force resisting systems (SFRSs) that offer self-centering and rapid reparability characteristics. However, compared to conventional SFRSs, these alternative SFRSs are potentially more vulnerable to large MS-AS sequences as the energy dissipation of the replaceable structural fuses are typically substantially less than those used in conventional SFRSs. Although seismically resilient SFRSs have shown to provide excellent performance under a single design level MS, their seismic performance under cascading large earthquake sequences is not well understood. This paper presents nonlinear response history analyses results of the seismic performance of two distinctly different seismically resilient SFRSs that are expected to provide frame recentering and concentrate inelastic damage to only the replaceable structural fuses. Specifically, one frame system is detailed with post-tensioned beam-to-column joints that rock about the top flanges only with a steel plate infill web plate structural fuses. The second system is detailed with post-tensioned beam-to-column joints that rock about the top and bottom flanges with tension-compression steel structural fuses. The results presented provides some insight on the system performance and seismic resiliency of these alternative SFRSs under large MS-AS sequences.

Unlike other naturally occurring loads such as wind-induced or earthquake loads, design snow loads are generally the result of a series of events including precipitation, temperature variations, and wind that occur over an entire winter. Further variability to the snow loading is introduced as building designs evolve in terms of geometry and energy performance. Physical and numerical modelling techniques exist which can be useful in providing insight into the snow loading on a structure beyond the generalized provisions of building codes and standards. Wind tunnel or water flume particle studies provide refinement on the accumulation conditions considering independent storm events, while computational time step approaches consider the cumulative effects of multiple storms over the course of a winter. While each modelling technique has definite strengths, each requires relaxation of certain scaling and snow accumulation parameters. This paper outlines these modelling techniques with their strengths and limitations. Examples are given highlighting how these modelling techniques have been used to investigate the variables used in deriving design snow load distributions.

Many reinforced concrete (RC) buildings built before the adoption of modern seismic codes in high seismic regions need to be retrofitted to perform well in a major earthquake. This study introduces a new retrofit method for code-deficient reinforced concrete shear walls that are vulnerable to non-ductile failure modes due to improper detailing or lack of well-confined boundary elements. The retrofit method combines weakening of shear walls with a base cut and self-centering of the walls with the addition of external unbonded post-tensioned strands. The retrofitted walls are expected to have controlled rocking behavior as opposed to the original walls that undergo shear and flexure and are expected to have minimized damage caused by earthquakes resulting in shorter repair times and lower repair costs. Three-dimensional finite element models of pre- and post-retrofit shear walls under cyclic lateral loading were used to identify working details of the retrofit method. To transfer shear at base and minimize shear slip, shear keys and other non-straight wall base cut shapes were explored. The contribution of shear, flexure, and rocking to the global response were measured and compared for pre- and post-retrofit walls. Results of analysis showed that rocking is the governing behavior for the retrofitted walls and contribution of shear to displacements decreased due to retrofit. Changes in residual displacements, energy dissipation, strength, and secant stiffness due to retrofit were documented.

There is growing consensus that the future of structural engineering is in employing humans as creative problem solvers who understand a situation, and its structural behavior. To this end universities are encouraging applicants with a wide range of skills to consider engineering, yet course entrance procedures still focus on math and physics requirements. However, there is no methodology for assessing applicants with a wider range of skills if the applicant has not already learnt a basic engineering communication language of shorthand, diagrammatic notations, and jargon. This paper discusses the development of a short multiple-choice online quiz—based on the principles of the Brohn test and the International Mathematical Kangaroo—designed to assess engineering understanding amongst students unfamiliar with the structural engineering language as it is later formally taught at university. The development of the quiz aims to stimulate discussion and reform in the way we teach engineering, and who we teach it to.

Automation is changing the definition and allocation of jobs in most engineering fields including civil engineering. This digital disruption of civil and environmental engineering (CEE) could potentially result in the extinction of the traditional role of structural engineers. In response, educators must strive to provide students with an evolving skill set, nurturing their creativity and engineering judgment. Students will have to design resilient and sustainable solutions for the built environment in a dynamic, virtually connected setting where clients, architects, and contractors are stakeholders with shrinking budgets but public safety remains paramount. This requires a paradigm shift, not only in the methods of teaching or the equipment used, but actually, in the way the students interact and employ such tools and how they swiftly adapt with a dynamically changing set of objectives. The paper is presenting a case study aiming to improve the civil engineering design process through running a mock classroom experience. This class is mimicking the introduction to engineering design (IED) course, offered at Rensselaer Polytechnic Institute’s School of Engineering (SOE), taught to undergraduate students mentored by senior undergraduate teaching assistants, and supervised by civil engineering professors. The educational module experimented through the mock class proved to revolutionize the way CEE students are introduced to the design process, by radically changing the design methodology and the classroom technology, with respect to the general SoE IED. The new CEE IED offered students the opportunity to brainstorm their designs through cloud-based modeling software, hold client-contractor interactive meetings through a flipped classroom setting, hold prototype analysis and shape optimization meetings through both cloud-based meetings and classroom team discussions, 3D print prototypes, and mechanically test these prototypes. Direct feedback and exit surveys showed that the participating students were able to put in practice what they have learned in their introduction to civil and environmental engineering courses. The current version of the course will help future CEE students to apply the skills that they have learned from CEE introductory courses taught in the semesters prior into IED class.

Forensic opportunities to investigate various failures involving commercial structures, transportation structures, residential/condominium structures, etc. many times provide opportunities to work closely with computer video animation staff for direction of how the key points or topics of merit may be communicated and produced for a specific audience. This activity will provide the necessary clarity for understanding of the failure scenario. Four case studies will be discussed that include various forms of failure mechanisms associated with human error, negligence, improper design, and/or construction, and that will describe the resulting damages.

A dome-shaped structure consisting of arched steel trusses and a tensioned fabric membrane collapsed during a winter storm in 2016. The dome was constructed circa 1977 and was strengthened in 2011 to support the addition of fans installed at two truss crowns. This study presents an investigation of the dome’s collapse, which included site visits, review of available design drawings, analysis of weather data, and finite element modeling of the dome truss. The investigation indicated that wind and snow loads at the time of the collapse were significantly less than their code-required design loads. Stresses due to addition of the fans were negligibly small, and the fabric membrane and its steel cable tensioning the fabric had significantly deteriorated prior to the collapse. As a result, the authors concluded that the collapse was most likely initiated by a sudden change in the dome geometry caused by membrane failure leading to overstressing of the steel trusses. This study concludes with recommendations for the analysis, design, and maintenance of dome structures.

Tank foundations within secondary containment dikes require special detailing from engineering professionals as well as specific chemical resistant coatings to ensure proper environmental containment and structural integrity. Many existing deficiencies due to lack of maintenance and improper detailing of current foundation and dike systems at industrial facilities create vulnerabilities for improper containment and infiltration of chemicals into structural components and the surrounding soil. At a Midwest chemical plant, after an event resulting in the spill of high concentration sulfuric acid into the secondary containment structure, an in situ partial destructive investigation and laboratory analysis were performed to assess the spill’s effect on the existing foundation and surrounding soil. The existing system was protected by a robust, acid resistant coating throughout the entire containment, which had deteriorated over its lifespan, resulting in widespread cracking and exposure of the concrete slab on grade. The existing foundation-to-containment slab interface was an isolation joint with a flexible sealant. Similar to the protective coating, the joint sealant had deteriorated over time due to weather and UV exposure. Concrete cores were sampled and demolition windows adjacent to the foundations were removed to examine the effects of the sulfuric acid spill. Information resulting from the inspection and laboratory results provided the basis for the evaluation of the existing structure. Due to acid infiltration through the deteriorated containment slab joints, concrete surfaces of the foundations exhibited significant chemical attack with up to 25 percent effective section loss. Based on these results, the foundation system was de-rated, and the facility operated the tank at partial capacity until repairs could be completed. Conceptual repair plans and detailing included removal of contaminated concrete, installation of a robust isolation joint around the repaired foundation, new concrete design and crack bridging procedure, as well as a new coating system providing adequate chemical resistance and durability. Ongoing maintenance and inspection programs were recommended to provide means to repair and restore the integrity of the secondary containment systems and foundation joint interfaces on a continuous basis. The engineering detailing of the new foundation system as well as the ongoing maintenance and inspection program provide the client with means to provide proper environmental compliance and structural integrity.

Waterway vessel collision is an accidental load case that is an integral component of the structural analysis and design of bridges and other marine structures spanning a navigable waterway. This paper presents the procedure followed during the analysis and design process of a pile supported fender system protecting a new major multi span bridge with several piers in the waterway. The design of any fender system is an iterative process based on energy absorption as per AASHTO specifications. In this case the total kinetic energy for the impact was calculated based on the vessel parameters to be a total of 44,200 kip-ft. There are two approaches used for the design of these fender systems: one is based on strength and the other is based on ductility. In the strength design method, the impact force is resisted while keeping the structural elements within the material elastic range limiting any permanent structural damage and deformation. This results in insignificant system deflections. The other procedure takes advantage of the ductility of the system to absorb the impact energy by allowing material yielding to occur while maintaining global stability. Since the fender system is designed as a sacrificial system, a decision was made to go with the ductility design approach to achieve considerable construction cost savings. A finite element analysis model (FEM) is developed using ANSYS APDL software. In this model, the piles are modeled using 3D beam line elements supported on non-linear spring elements representing the soil (Beam on Winkler foundation). The spring behavior is derived using Ensoft L-PILE analyses. This method of representing the soil is used instead of the computationally demanding solid continuum elements that require sophisticated calibrated material models. The FEM considers the full non-linear stress-strain behavior of steel, P-delta effects, pile-soil interaction, and global buckling of the piles. Local buckling analysis is also performed separately and explained in detail throughout the paper. After validating the single pile model with L-PILE, a full FEM model for the entire fender system is built. Push over analysis is performed and the total energy absorbed is calculated by integrating the area under the load-deflection curve. Different load cases are considered for different impact angles and vessel speeds. The performance acceptance criterion of the system is established to ensure that enough energy is absorbed to avoid any contact between the fender system and the bridge pier under vessel collision loading. To reduce P-delta effects, the final design is comprised of a hollow pre-cast 12 ft x 12 ft box pile cap supported on twelve 48 inch diameter 1.5 inch thick steel piles filled with low grade concrete to prevent the piles’ local buckling. This paper also addresses the structural detailing aspects implemented to ensure satisfactory performance of the system in the post yield stage. Construction challenges associated with the erection of this system is also discussed.

With an anticipated completion in the summer of 2020, the new LA Stadium is an iconic structure and an example of ingenious engineering that is a result of integrating design solutions with construction from conceptual designs to project delivery. The stadium’s location below the flight path of the Los Angeles International Airport required the lowering of the overall structure with the field of play being constructed approximately 100’ below existing grade. The complexity of the site and project requirements offered many challenges for the design team including nearby seismic faults, a 9.0 magnitude design earthquake, a massive excavation, and an aggressive construction schedule. Design elements including a 100’ tall MSE wall around the bowl, an innovative and intricate layout of vertical and horizontal post tensioned elements, a seismically isolated foundation system, hollow precast columns with external PT, and seismic isolators were required to support the iconic structure.

Petrochemical facilities frequently have large equipment supported by equally large nonbuilding structures. Examples of stacked nonbuilding structures in petroleum refineries include coker structures, vacuum tower structures, and fluidized catalyst cracking reactor and regenerator structures. Some of these stacked nonbuilding structures have a supported structure with a fundamental period that is larger than the fundamental period of the supporting structure. Examples are provided that show that when the ratio of fundamental periods is greater than two, then the supported structure can be decoupled and analyzed as if it were supported on a rigid base. In other stacked nonbuilding structures, such as elevated compressors supported by a reinforced concrete tabletop structure, the fundamental period of the supported structure is low compared to the fundamental period of the supporting structure. An established trigger for combined analysis of stacked structures is when the ratio of the supported structure weight to the combined weight of both structures is greater than twenty percent. Examples are provided that show that when the ratio of fundamental period is less than one half, then the supporting structure can be decoupled and analyzed as if there were a rigid mass on top of the supporting structure. The provided examples illustrate that decoupling triggers based upon natural frequency ratios are reliable for stacked structures.

Fatigue design for offshore modularized facilities is an established part of the design process. Such facilities are subjected to cyclic fatigue loading during initial transport as well as during the facility’s operating life after installation. Fatigue design for onshore modularization is different in that fatigue loading primarily applies only during ocean transport to the jobsite. This and other differences lead to the need for a different approach in dealing with fatigue. This study expands on the simplified fatigue analysis approach and how it can be specifically applied for the structural design of onshore modules. An implementation procedure and an example calculation are described to indicate how published guidelines can be applied. The results of the analysis can be used to validate whether a module’s structural design is adequate, whether design changes need to be made, or whether a more comprehensive fatigue analysis might be warranted.

Over the past two decades, pre-assembled units (commonly known as PAUs), including truck transportable equipment skid, piperack, and industrial building modules, have become more frequently used in oil and gas, petrochemical, power plant, and other industrial onshore modularization projects. Pre-assembled units require unique design and construction planning to overcome logistical challenges, from fabrication, transportation, and lifting to their final setting locations. While some design guidelines were established by structural engineers on large onshore modules during marine and land transportation, established guidelines on design criteria for onshore pre-assembled units are currently lacking. The lack of standardization in such criteria has the potential to cause omissions of structural design checks. This can result in either unnecessarily costly or unsafe designs. The consequence of adopting offshore module design practices for pre-assembled units without modification can be an overly conservative design. A review of published standards and documents, current industry practices, and internal company standards was conducted. The purpose of this paper is to provide modular design professionals an understanding of various available truck transport and lifting design criteria for pre-assembled units based on this review. History of these collected criteria and their limitations of application are summarized. The findings revealed that a standardized approach to design pre-assembled units for truck transport and lifting should be included in the ASCE state-of-the-practice engineering report on Onshore Modularization for Heavy Industrial Applications. The findings of this industry research study on various criteria provide practicing engineers with adequate design resources and guidelines to design onshore pre-assembled units for truck transport and lifting.

Quantifying the performance of retrofitted and un-retrofitted single-family wood-frame dwellings has become increasingly important in California due to the high seismicity of the state and the poor seismic resiliency of some portions of the housing stock. From field observations of past earthquakes, it has been found that inadequate lateral bracing of cripple walls and inadequate sill bolting are the primary reasons for failures of residential dwellings even in the event of moderate earthquakes. While methods to retrofit weak cripple walls and improve sill anchorage have been developed, the performance benefits of these changes have not been experimentally quantified. In addition, little knowledge is available to quantify the performance of existing dwellings. To address this limitation, a multi-university experimental investigation was undertaken as part of a collaborative PEER project funded by the CEA, with the ultimate goal of supporting numerical model validation and ultimately loss modeling of older residential dwellings. Particular emphasis was given to characterizing the performance of cripple walls retrofit using the recently published FEMA P-1100 guidelines: Vulnerability-Based Seismic Assessment and Retrofit of One- And Two-Family Dwellings. This paper focuses on presenting select test results from cripple wall component specimens tested under reversed cyclic quasi-static loading. Results in the present paper emphasize comparison amongst like existing and retrofit specimens with stucco and stucco over sheathing exterior finishes. Overall, results from these tests indicate that the FEMA P-1100 prescriptive retrofit design provides a large increase in strength, stiffness, energy dissipation, and in many cases also increases drift capacity of older, vulnerable cripple walls.

The current North American standards, AISI S240 (2015) and AISI S400 (2015), provide information that can be used to design cold-formed steel (CFS) framed steel sheet shear walls which meet the seismic demands for a low-rise to mid-rise (3–6 story) buildings. However, experimental data to support code guidelines for taller mid-rise (>6 stories) and high-rise buildings (>10 stories), where large lateral load resistance is required, are lacking. Moreover, most of the experimental research so far has involved testing shear walls under quasi-static monotonic/reversed cyclic loading. In the current research project, shear walls placed in-line with gravity walls were tested at full-scale first under a sequence of increasing amplitude (in-plane) earthquake motions, and subsequently (for select specimens) under slow monotonic pull conditions to failure. Experiments were performed at the NHERI Large High-Performance Outdoor Shake Table at UC San Diego. Selection of wall details was motivated by the design of a CFS archetype building (4 and 10 story) using available experimental data. This paper explains the design details and discusses the experimental response of a baseline wall specimen pair in the test program, which uses compression chord stud packs with a steel tension tie-rods assembly, is unfinished and designed with a symmetric configuration.

Despite calls to adopt performance-based solutions, the structural fire engineering community continues to embrace a classical stance to tackle the problem of fire. In support of these calls, this study showcases the merit of integrating computational intelligence (CI) as a modern technology to assess performance and fire resistance of structures. This paper sheds light on the proper use of CI to develop novel approaches that outperform traditional as well as currently use advanced calculation methods. The proposed CI-based approaches are specifically developed to comprehend the complex temperature-induced physio-chemical changes to properties in construction materials; i.e., thermal, mechanical, deformational, and special, and as such do not require input of such properties nor a complex and lengthy un/coupled thermal-stress analysis. The proposed CI-based approaches can serve as simple and efficient tools to advance the practice of structural fire engineering as well as to provide researchers and practitioners with alternative means to assess fire response of structures. The outcome of this work demonstrates the merit of utilizing CI to modernize fire resistance evaluation, together with performance-based methods, given that the developed CI-based models have high degree of perception (i.e., learn from past behaviors) and ability to improve their prediction capability through independent and unsupervised learning.

Elastomeric bridge bearings are widely used in bridges in order to allow deformations caused by temperature variations, traffic loading, shrinkage due to prestress or aging, and construction misalignments. However, manufacturing imperfections in these bearings (such as deviations in rubber layer thickness and non-parallel steel plates) affect their structural performance. Currently, quality control of these bearings involves destructive testing, which is costly and time consuming. This paper presents an alternative, vision-based approach for assessing the internal structure of elastomeric bridge bearings, which eliminates the need to destroy them. Three-dimensional digital image correlation (3D-DIC) is used to estimate the thickness of different rubber layers and any shim rotation or distortion based on deformation patterns on the surfaces of the bearings during compression testing. 3D-DIC provides full-field measurements of displacement and strain on the surface by tracking the distribution of grayscale values of pixel-based subsets in the sequence of stereo images. The presented approach enables engineers to efficiently evaluate bearings for quality control purposes.

Standard fire resistance curves such as ASTM E119 have been used for so long in structural fire practice. The issue with use of these curves that they do not represent real fire scenarios. As a result, the alternatives have been to either conduct experiments or find other tools to represent a real fire scenario. From this perspective, computational fluid dynamics (CFD) models developed to simulate a real fire scenario and to understand the structural responses on steel beams under elevated temperatures. The results obtained from these analyses were compared with those obtained in cases that used standard fire curves for its fire scenarios. A comparison of those models showed that relying on such standard fire curves might lead to a non-conservative design as compared to a real fire scenario; therefore, more research is required to determine the efficiency of using such standard curves in the field of fire protection engineering.

This paper presents the outcome of a study of the behavior and strength of plain and steel-reinforced concrete shear walls including carbon fiber-reinforced polymer (CFRP) retrofitting. This study uses near-surface mounting of CFRP strips to retrofit a steel-reinforced concrete shear wall. Experiments were conducted on a plane concrete shear wall and another steel-reinforced one and the performance compared with that which had steel reinforcement and CFRP retrofitting. A gradually increasing horizontal quasi-static lateral load was then applied at one of the shear wall top end corners until the ultimate load was reached. Load-deflection curves were obtained, and both concrete cracking patterns as well as failure modes were recorded. The study shows that although steel reinforcement provides a significant enhancement of the shear wall ductility, the CFRP retrofitting results in a substantial strength increase.

The response of reinforced concrete shear walls, when used as a lateral force resisting element in concrete buildings, may vary according to their detailing and geometry. In the present paper, comparison of the global response and damage distribution of three full-scale reinforced concrete shear wall specimens subjected to simulated seismic loading is presented. One slender and two squat full-scale shear wall specimens of the same wall length were designed and tested as cantilever walls to assess their performance during in-plane simulated seismic action. Axial load was also provided in the amount of about 7% of the wall section capacity to both the slender and one of the squat wall specimens. The second squat wall specimen was tested without axial load to evaluate the effect of compressive force on the walls’ lateral behavior. Cross comparison of these three specimens indicates that, despite common misconception, properly detailed squat walls can develop displacement ductility consistent with slender, flexure-dominated walls.

As low- and mid-rise construction design objectives push cost-efficient engineering practice to the forefront, cold-formed steel (CFS) has been increasingly used as structural or nonstructural components. The main lateral force resisting system in cold-formed steel construction is shear walls, comprised of chord studs, field studs, all capped in tracks and sheathed or strapped. This study aims to introduce and validate a computational approach capable of demonstrating how oriented strand board (OSB) sheathed CFS framed shear walls behave during lateral loading. A robust three-dimensional finite element model of wood sheathed CFS shear walls is introduced by numerically simulating three different shear wall configurations. The focal points of this work include fastener-based modeling approaches that account for the variability of CFS-to-sheathing fastener behavior. To inform the computational work and address the inherent variability in CFS connection behavior, 30 identical stud-screw-sheathing specimens were tested. The numerical results are validated by recent experimental studies, assessing the efficiency of fastener-based models to accurately capture strength, stiffness, and failure modes of CFS shear walls.

As the prefab modular construction is gaining more popularity, there is a growing need to accurately predict the performance of the “modules stack” and their interconnectivity under extreme loading conditions such as strong earthquakes or high winds. Due to the uniqueness of the assemblies and connections used in the volumetric modules, especially in a high-rise context, it is essential to establish a framework in which both experimental and analytical models are used in tandem to fully evaluate the overall structural system’s performance. Together they can help the engineering team gain more confidence in the structural system’s integrity under severe excitations. In this case study, a full-scale test program is discussed which was integrated into the design process of a thirty story prefab modular highrise in Oakland, CA. Twenty-two story residential floors over eight-story podium. Monotonic and cyclic tests of several structural sub-assemblies were carried out in collaboration with independent structural testing laboratories. Once the full-scale test results were gathered and processed, analytical models in high-fidelity FEA software packages were calibrated to accurately represent the experimental results. The “acceptance criteria” for the modular system’s performance was established on multiple levels. Using the “sub-structuring technique” a typical modular level was isolated from the superstructure to conduct analytical simulations on module stacks. This approach helped with reduced computational runtime and enabled faster module design iterations without losing accuracy. The sub-assemblies were modeled using combinations of line elements and semi-rigid hinges. Utilizing performance based design (PBD) in conjunction with full-scale testing of critical structural components helped to verify the capability and performance of modular assemblies to withstand 2.75% inter-story drift under MCE and their continuous elastic behavior under extreme building deformation.

Data-driven modeling’s recent rise has opened a new frontier of predictive modeling techniques for today’s engineer. Data-driven models are often divorced from the underlying physics of a given problem which leads to trepidation among many in the engineering community to embrace them as reliable tools. Traditional physics-based simulation models generally receive higher confidence within the engineering community, but they too have limitations in capturing the underlying physics. This is especially true in cases involving high model fidelity, complexity of the underlying physics, or system sensitivity. This paper has two key objectives. First, to demonstrate that selection of data-driven and/or physics-based simulation models is not a zero-sum game. Although each method is imperfect, both possess great utility when both employed to reinforce one another. Second, to demonstrate that the shortcomings of each can be overcome through V&V procedures already utilized within the greater engineering community. The V&V procedures from ASME V&V 10-2006, Guide for Verification and Validation in Computational Solid Mechanics are presented in the context of data-driven and physics-based simulation models to achieve confidence in the reliability of each method.

The need for resilient infrastructure continues to increase due to evolving environmental demands and the recognized economic benefits of increased lifecycles. Greater lifecycle expectations require consideration of a structure’s resilience in the face of uncertainties that are not always known, or readily quantifiable. This paper proposes a method for assessing the reliability of structural systems where sources of variability cannot be readily defined, and traditional methods of uncertainty quantification are inadequate. The proposed variability-based framework utilizes machine learning, L2-norm, and proximity indicators to assess the sensitivity of the structure’s expected performance due to minor perturbations in its conditions. The utility of the proposed method is demonstrated through its application to a simple truss bridge, where the loci of conditions that produce a robust performance prediction, as well as disproportionate changes in structural response, are sought in the face of variability.

This paper describes the evolution of deck shape of long span bridges since the Tacoma Narrows collapse trying to avoid undesirable aerodynamic behavior under wind flow and the trend in the last decades to increase the length of the main span of suspension and cable stayed bridges. The necessity to use advanced technologies to help the engineer to obtain the best possible design is highlighted and the advantages of applying optimization methodologies is encouraged. It is explained that this approach requires to use only numerical tools and hence to eliminate experimental studies, as wind tunnel tests using reduced models of full bridge of a segment of the deck, and their substitution by computational fluid dynamics (CFD) simulations. After doing so, the current capabilities of this approach are presented and, finally, the problems that need to be solved to have a fully operational methodology able to be implemented in real structures are outlined.

We present two recent projects at Skidmore, Owings, and Merrill, LLP that feature large canopy elements designed, analyzed, and optimized by an interdisciplinary team that consists of architects, structural engineers, and enclosure specialists. Through an integrated computational approach, structural optimization and material efficiency are achieved with an iterative form evolution facilitated by dynamic relaxation techniques. The integrated workflows further accommodate the extremely ambitious design and documentation schedules of both projects by incorporating major design-to-fabrication parameters in the information-rich models; thereby facilitating immediate geometric rationalization, constructability analysis, and documentation through numerous design iterations; as well as the seamless digital exchange of data between the various disciplines. The computational workflow presented herein offers a potential prototypical process for the design and construction of novel optimized structures.

Optimization techniques have demonstrated their capability to obtain economic and sustainable designs while meeting the performance and safety requirements in a number of engineering disciplines. In the bridge engineering field, the increasing main span length of super-long span bridges makes the wind-resistant design a top priority. However, it has been traditionally conducted following heuristic rules based on experimental analyses. Alternatively, the last advances in CFD and metamodeling techniques enables the development of optimization frameworks. The right conception of the aerostructural optimization problem is crucial to achieve noticeable reductions in the required amount of material and comprehensive safe designs. This paper reports the last advances in the authors’ line of research that pursues the definition of a numerical methodology for the full aerostructural optimization of long-span bridges considering shape and size design variables. The capabilities of the method are presented, and the necessity of considering uncertainty in the process is discussed.