Structures Congress 2019: Blast, Impact Loading, and Research and Education

In recent years, increasing attention has been paid to the safety of bridges affected by vehicle-pier collisions. Up to date, the vehicular impact demand, dynamic responses, and damage characteristics of reinforced concrete (RC) piers under vehicle collisions have been studied, but few studies discussed the damage quantifications of RC piers in this circumstance with full consideration of their specific damage characteristics. This study aims to provide a framework used to quantify and classify the damage of RC piers under vehicle collision, where a damage index is proposed taking both the shear and flexural damage into account. Finite element (FE) simulations are further conducted to study the section-level deformation and damage characteristics of a three-column type of RC piers under vehicle impact. The simulation results reveal that the vehicular impact energy, stirrup diameter, and the bottom constraint location of the piers all affect the damage of the piers. It is found that the damage features of RC piers observed from the FE simulations are generally consistent with the damage indices, although future work is also required to make them more accurate and effective.

In the present study, the 3D elasto-plastic finite element models of prototype pier column under impact loading are established by using LS-DYNA and validated against the observations from a field impact test in literature. The effect of essential parameters including impact velocity, impact mass, axial load ratio, and impact elevation on the impact response of RC columns are also discussed in detail. Then, a novel damage assessment method based on the sectional damage factor is put forward to quantify the damage level of RC columns, and the resistance mechanism of RC columns in the impact process is explored. Results show that when the initial kinetic energy of the impactor remains constant, the different combinations of the impact mass and velocity can lead to a significant discrepancy in the damage mechanism of RC columns. The damage assessment method proposed in this study can visually describe the damage distribution along the length of RC columns. Furthermore, the system impulse in the impact process is slightly larger than the initial momentum, whereas the energy absorbed by the impacted column is about 90 percent of the initial kinetic energy.

In this paper, the residual properties of sandwich panels with flax fibre-reinforced polymer (FFRP) faces which have been subjected to impact loading will be investigated. The sandwich panels tested in this study were fabricated using a closed cell polyisocyanurate foam with a density of 64 kg/m3 and faces made of a balanced bidirectional flax fabric (nominal areal mass of 400 g/m²) and an epoxy resin with an approximate bio-content of 30% after mixing. Each specimen was 1,220 mm long, 150 mm wide, and approximately 80 mm thick. The sandwich panels will first be subjected to an impact of 100% of the impact energy resisted in previous tests using a drop weight impact test. The span length of the tests will be 1,117 mm and a drop weight (10.413 kg) with an impact surface width of 150 mm will impact each specimen at midspan. For these tests, the top face strain, bottom face strain, and deflection at midspan will be sampled at a rate of 25 kHz. After the impact, the panels will be tested under quasi-static three-point bending to failure. During this test the load, midspan deflection, and top and bottom face strains at midspan will be sampled at a rate of 10 Hz. The results of the post-impact quasi-static flexural test will be compared with similar flexural tests performed on intact specimens to determine the effect of the impact on the flexural behavior of the sandwich panels. It was determined that the properties of these sandwich panels are not adversely affected by an impact event. There is potential that the impact increases the static capacity of the sandwich panels, however more research is required. This research is part of a larger on-going study and more results will be available at the time of the conference.

Deeply buried bunkers offer a level of protection that is unmatched by conventional, above-ground, construction methods. The construction of the bunker itself, as well as ingress/egress and ventilation for the completed bunker, requires substantial digging. Thus, deeply buried bunkers are usually located within a mountain and accessed via tunnels. In order to better predict the response of tunnels and bunkers to an average design blast load, computer simulations were performed. First, a simplified groundshock numerical code based on an assumed geology and buried depth was used to predict the demand. Then, analytical methods were utilized to design the tunnel wall and bunker slab geometries and reinforcement details. Finally, high-fidelity models were developed to predict the structural response. Physical tests on scaled specimens validated the baseline simulations. Additionally, three concrete materials models are compared.

This paper presents an analysis approach developed for estimating internal blast pressures, and approximating the extent of damage in a complex internal building structure. An example application of design for progressive collapse in a below-grade concrete parking garage structure is demonstrated. Parking garage blast is a common threat scenario and is based upon real world events, such as the terrorist attacks in Barcelona, Spain, (1987) and at the World Trade Center, NYC (1993). The postulated scenario for this paper involves an internal blast from a passenger vehicle parked in a representative parking garage structure. A pragmatic analysis approach, which makes use of a commercially available finite element analysis (FEA) code, was developed to predict blast pressures, evaluate structural response, and assess levels-of-damage in an economical manner. Based on the resulting damage to the building structure, an assessment of the potential for progressive collapse was performed to assist structural engineers on the building design to ensure occupants can safely evacuate.

Blast pressures can cause severe damage to building structures. Moreover, in numerous occasions, the affected structure will experience a significant fire ensuing from a blast event. It is therefore imperative that key facilities that may be exposed to these multi-hazard scenarios are properly designed against their actions. Besides, current structural fire design methods are restricted to smaller compartments. Nevertheless, the travelling fire methodology which considers a more realistic evolution of temperatures can be used for the assessment of larger compartments. In this study, a series of non-linear finite element analyses were carried out on prototypical office steel frames. Parametric analyses were conducted to determine the effects of blast pressure, fire size, direction of fire travel, and maximum compartment temperature on the steel frames. The study revealed that increased blast pressures decreased the resistance of the frame to the travelling fires. Also, the response of the frame may be different for different directions of fire travel. The results also showed that smaller fire sizes with longer total fire durations can result in higher structural deformations and damage. The study demonstrates the importance of considering travelling fires in multi-hazard scenarios.

The accidental vehicle collision has increasingly posed a threat to the existing reinforce concrete (RC) bridge pier. To reduce the damage of pier, appropriate measures to protect existing RC piers from this event should be developed. This study is intended to apply two types of protective techniques around piers to achieve this purpose. One is the full wrapping with fiber reinforced polymers (FRPs), and the other is to install a composite protective device with fiber reinforced polymer (FRP) skins and aluminum foam core. Finite element numerical simulations are carried out to investigate their effectiveness on the protection of piers against vehicle impacts. The numerical results show that the increase of layer number of FRP wraps significantly reduces the deflection of pier but has little influence on impact force, whereas the FRP-foam composite device can significantly reduce the impact force on piers and dissipate the kinetic energy of vehicle by the deformation of aluminum foam, and then mitigate the damage of piers. The increase in the thickness of aluminum foam has an obvious effect on those.

A pair of decommissioned thirteen-story reinforced concrete buildings were demolished via controlled implosion at the University of Nebraska–Lincoln in December 2017. The implosion consisted of controlled charges at select columns on alternating floors throughout the buildings, which initiated the collapse of the two buildings. This controlled implosion provided the rare opportunity to monitor and characterize the collapse progression of the buildings as well as the response of nearby and adjacent structures to both the remote blast loading and the subsequent building collapse. To this end, sacrificial accelerometers were placed throughout the two buildings before the collapse to record the buildings’ motions and load redistribution. In addition to these sensors, additional accelerometers were placed in the free-field and within three nearby structures, including two immediately adjacent structures as well as one high-rise at an approximate distance of 0.25 mile. These sensors monitored the adjacent structures before, during, and after the collapse to understand the impact of the collapse. While no noticeable damage nor shift in the natural frequencies was observed in the adjacent structures, each exhibited observable response to both the blast sequence as well as the collapse sequence of the buildings, with accelerations on the order of 0.08 g at the ground outside the closest building and 0.002 g at the furthest structure. In this paper, this unique experimental dataset obtained from the adjacent structures will be introduced alongside key observations of the performance of these adjacent structures during the blast and collapse of the two buildings.

Progressive collapse, a chain reaction or disproportionate propagation of failures following damage to a relatively small portion of a structure, has drawn attention from researchers and the public because it may lead to severe loss of life and property. Progressive collapse data are difficult to observe in situ and expensive to produce at large scales in laboratory testing. Because of the large deformations involved in structural collapse, lateral constraints at the beam ends exert variable axial forces on beams, which then provide extra collapse resistance known as compressive arch action and catenary action. In this paper, the absolute nodal coordinate formulation (ANCF) is combined with the fiber element method to build a finite element beam formulation for nonlinear dynamic progressive collapse simulation of reinforced concrete Euler-Bernoulli beam-column elements. ANCF is a non-incremental nonlinear finite element formulation proposed to describe the large deformation of moving bodies in multibody systems. Compared with traditional formulations, ANCF uses position vector gradients to describe the rotation of the body and strain state, thereby keeping the mass matrix constant and avoiding the need for interpolating non-vectoral rotation parameters. The explicit central difference method is applied to calculate the dynamic response of collapsing structural systems, and an example is presented in this paper.

Although extensive studies had been carried out on behavior of reinforced concrete (RC) structures to resist progressive collapse, the majority of existing studies assume the loss of the column is clear and no residual resistance remains in the damaged column. Moreover, the damage of surrounding components, such as beams and slabs, are ignored in their tests or numerical analysis. However, the above assumptions are unrealistic if the loss of column is caused by terrorist attack. Therefore, a physics-based finite element model is generated to investigate the effects of blast pressure induced by contact explosives on progressive collapse resistance of RC structures. The model is validated by extensive dynamic and blast tests. Parametric studies are also carried out to study the stand-off distance, charge weights, and damping ratio on the dynamic response of the structures.

Simulation of structures under collapse requires accurate prediction of extreme limit states associated with material (tension necking) and/or global (buckling) instabilities. While spring or hinge models, fiber models, and continuum finite element models have been used to evaluate the behavior of a collapsing structure, each of these methods have definitive drawbacks when attempting to simulate the post-peak behavior. An alternative method is proposed in this paper, which consists of a one-dimensional single line element that includes the effect of localization. Cylindrical steel samples of different lengths were tested in tension and their response recorded with a DIC system to evaluate the evolution of localization. The experimental data were then used to develop a simplified one-dimensional line element that can capture the effect of localization on the overall post-peak structural response to tension. The proposed model defines the pre- and post-peak stiffness of the line element, respectively, through a quad-linear curve. Of particular importance is the introduction of the bifurcation point which defines when unloading in the member occurs. This tension model was employed in a simple truss structure to evaluate its effectiveness in evaluating the post-peak response as compared with other conventional methods. The reported research results lays the groundwork for developing simplified models for other types of loading such as flexure.

The recognition of wood as a viable and sustainable alternative for construction has promoted the use of mass-timber panels in mid- to high-rise residential and commercial buildings. To safely expand the application of mass-timber constructions as post-disaster, military/federal, and high-rise buildings, studies with respect to disproportionate collapse prevention are required. Being a new method of construction, however, such studies are scarce and to date limited to numerical investigations. This paper presents the methods for experiments that evaluate possible catenary action as a resistance mechanism for disproportionate collapse preventions for mass-timber floor systems. Testing is performed at component level, with conventional and novel timber connection detailing to estimate the load-carrying and deformation capacities, in order to ensure adequate load distribution while undergoing large deformations without failure. The work will provide practical economic collapse-thresholds and define disproportionate collapse acceptance criteria for mass-timber floor systems to ensure structural safety after extreme load events.

The findings of a comprehensive study involving the static and dynamic investigation of seventy unretrofitted and FRP retrofitted glulam structural elements are presented in this paper. Key observations made in the experimental program regarding material properties, effect of combined axial and out-of-plane blast loading, and strengthening strategies using FRP are used as foundation for design recommendations. Based on the experimental results, unretrofitted glulam beams and columns were shown to have no significant post-peak resistance and thus it is recommended that such members be modeled using a linear flexural resistance curve with a ductility ratio of unity. A dynamic increase factor was found to only be present in beams with no continuous or closely aligned finger-joints. In cases where the finger-joint distribution is not known, a DIF of unity is recommended. Fibre-reinforced polymers (FRP) were shown to only provide significant post-peak resistance when bidirectional fabrics were used as confinement.

The principle of balanced design was developed to control the manner of failure in window systems such that the glass would fail before more catastrophic and damaging failure of anchorage or building substrate. When static loads are considered, determining the capacity of a pane of glass is straightforward. However, when dynamic loads are considered the capacity of the glass is a function of peak pressure, load duration, and load shape. All of these parameters vary with charge weight and standoff. Blast-resistant criteria and design specifications frequently require a balanced design for window systems, in particular. The response of a window system can change significantly depending on how the capacity load of the window system is determined and defined. Based on a review of representative blast-resistant windows evaluated analytically and through explosive testing, key factors are provided for consideration by designers and specification writers to improve balanced design of window systems while maintaining the level of protection required for blast-resistant projects.

Current design standards provide methodologies to analyze and design structures against disproportionate collapse, colloquially referred to in instances as progressive collapse. While these standards generally improve the overall robustness of structures, it is not known with a high degree of certainty how these structures will perform directly against blast loading. There is a need for blast and structural engineers alike to incorporate disproportionate collapse mitigations that adequately address specific design basis threats (DBT), such as blast. This paper tests the tie-force collapse prevention methodology outlined in UFC 4-023-03 (2013), against a vehicle borne improvised explosive device (VBIED) detonated within an internal basement. Consideration is given to a typical multi-story structural steel building frame where the tie force method has been applied. Empirical methods are used to determine the applied blast loading and finite element analysis (FEA) is used to analyze the highly transient structural response under these loads. Expected levels of damage and the limitations of using a standardized approach to collapse prevention are summarized within this paper. The purpose of this paper is to provide blast engineering practitioners an understanding of considerations in applying general collapse prevention provisions in lieu of an assessment where a blast DBT is modeled explicitly.

Conventional unreinforced masonry has minimal ability to resist high-energy hazards such as those created by blast loads. Consequently, blast mitigation is essential for unreinforced masonry structures. This paper will summarize research conducted for the Department of Homeland Security (DHS) by the U.S. Army Engineer Research and Development Center (ERDC) and Lawrence Livermore National Laboratory (LLNL) relating to retrofitting unreinforced masonry for blast resistance. The objective of this research was to determine the most effective mitigation scheme capable of resisting blast-induced damage due to near-contact detonations to unreinforced masonry. Sub-scale masonry test specimens were fabricated to test three mitigation concepts subjected to the same explosive threat. These damage mitigation techniques were evaluated based on their ability to prevent breach and reduce deformation in unreinforced masonry. Based on this evaluation, a mitigation concept was selected and validated using full-scale field experimentation and computational modeling. These experimental data were used to validate predictions of the computational models. Experimental results are compared to numerical predictions for both sub-scale and full-scale experiments. This research will provide critical information regarding mitigation schemes for unreinforced masonry and assist agencies in determining the most efficient way to harden masonry structures against blast loads.

In high threat environments, it is challenging to provide blast protection for building occupants while financial resources, construction materials, and labor skills are poor or in limited supply. An important hazard to consider is the failure of window glazing, which is one of the leading causes of injuries during a blast event. One mitigation method is to apply anti-shatter film to the glass and a catch system consisting of wire rope cables spanning floor-to-ceiling directly behind the windows. This approach allows for a simple implementation with materials generally available in high threat regions with limited installation skills required. The purpose of this paper is to introduce typical failure mechanisms for this type of hazard mitigation based on experience, provide a recommended design approach, and discuss the results of an open-air blast demonstration performed on window and glass specimens backed up with a cable catch system.

A major petrochemical entity in Australia desired to assess the potential impact of blast and fire related hazards associated with the placement of liquid petroleum gas (LPG) and diesel storage tanks located within a site that is required to support and house the operations workforce for the main LNG project and contains several buildings in the vicinity of the storage tanks. This article outlines the siting studies and recommendations to mitigate the fire and blast hazards.

Often, students arrive to their engineering classes day after day unprepared. When taking a course without reading quizzes, they are almost guaranteed to come to class without cracking open their textbook for even a cursory reading of upcoming material. When taking a course with reading quizzes, they might take the time to skim through the reading in hopes of catching a glimpse of a basic concept or key definition, since reading quizzes are typically not worth a significant percentage of their final grade. The authors surveyed students at the end of three semesters of engineering courses and discovered that well over half of the students in the course completed assigned readings prior to a given lesson less than one quarter of the time. The authors were determined to motivate students to read prior to class in order to provide students with an orientation of the material, encourage students to think critically about the subject matter, and contribute to student learning. Thus, the authors implemented an “In-Class Assessment” policy in their steel and wood design course. For the duration of the course, students sat in their self-selected project teams, each of which consisted of three students. Based on a roll of a dice, one person from each project team would stand up in class and answer a question from their instructor. If the student answered the question correctly, the entire project team earned their point for the day. If the student answered the question incorrectly, the entire team did not earn the point for that day. Key to implementation was removing anxiety for receiving low end-of-course grades for incorrect answers and ensuring the assessment was not perceived as a “haze” by the instructor, as the natural peer pressure for students to appear “qualified” in front of their peers provided incentive for students to prepare for class. Effectiveness of this verbal assessment procedure was assessed using both student course-end feedback and course assessment from the instructors (grades and time surveys). This paper will make the case that this pedagogy benefits the structural engineering profession by: getting young engineers in the practice of what engineers already do (prepare for work), increasing student understanding of a topic, and improving the ability of future structural engineers to communicate explanations clearly and effectively.

In October 1998, ASCE’s Board of Direction adopted Policy Statement 465: First Professional Degree (FPD), which supports the concept that the master’s degree or an equivalent would be required for a graduate engineer to practice civil engineering at the professional level. In this author’s opinion, this requirement has not been implemented because there is no clear vision of how to put together a curriculum and a mechanism to bridge the gap between the existing curriculum and requirements to satisfy the first professional degree. A model curriculum is presented for the development of a process that will lead to the entry-level degree of professional civil engineer or a master degree in civil engineering. This degree will carry with it not only a pure academic component, but also requires a full summer of professional experience which exposes the student to the practice in the field whether it being a site experience and/or an office experience. The duration of both degrees would normally be five academic years with an obligatory summer semester for the professional experience requirement. The deciding factor whether a student could pursuit a graduate degree or the professional degree would be the cumulative and/or the major GPA at the end of their junior year. Students pursuing the graduate degree would be awarded a BS at the end of their senior year and an MS in a minimum of one year after their senior year. Meanwhile students in the professional track would be awarded a professional degree at the end of the fifth year.

Base isolation has proved to be among the most effective technologies for earthquake hazard mitigation. Nevertheless, due to its implementation costs, the adoption of this earthquake protection strategy is generally limited to large and expensive infrastructures including chip factories, nuclear power plants, hospitals, and emergency response centers. The research described in this work, aims to verify the applicability of low-cost base isolation devices to residential buildings in developing regions of the world. This study focuses on recycled rubber-fiber reinforced bearings (RR-FRBs). These devices can be produced using simple to implement manufacturing procedures at a fraction of the cost of conventional isolators. The design of RR-FRBs for a benchmark building located near the city of Pelabuhan Ratu in Southwest Java, Indonesia, is discussed in this work. This is based on closed form solutions that were developed in early stages of the research program. Finite element analyses have then been adopted to verify the results obtained using the theoretical findings available in literature and to determine the lateral response of the devices under cyclic loads. Nonlinear response history analyses (RHAs) have been performed to assess the seismic response of the benchmark building when isolated at the base with the low-cost devices. Different hazard levels have been considered for the analyses. Results of the analyses confirm the advantages of adopting RR-FRBs as base isolators of ordinary buildings. It is hoped that this work will contribute towards the real implementation of the technology and its application to residential buildings in developing regions of the world.

Due to the challenges in numerical simulation of wind-structure interaction, the dynamic response of long-span bridges or high-rise buildings subjected to wind loads has been primarily evaluated through wind tunnel tests. The wind-tunnel tests, especially aeroelastic tests, require calibration of springs, masses, and the damping properties of an experimental specimen which takes considerable time and efforts. In hybrid simulation, where a numerical model and a physical specimen are tightly integrated, a component that is difficult to be represented with a numerical model is represented experimentally, while the rest of the structural system is represented numerically. In this paper, designs of two configurations of experimental apparatus for real-time wind-tunnel hybrid simulation are presented: one for section model tests of bridge decks and another one for high-rise buildings. The experimental apparatus for section model tests, which consists of four linear motors, is for aeroelastic tests of section model of a long-span bridge. The experimental apparatus for buildings consists of two linear motors to test aeroelastic response of scaled high-rise building model. The rational on the selection of the design configurations is discussed which is followed by configuration of the experimental setup and a potential strategy for running real-time hybrid simulation.

Concrete-filled steel tube (CFT) columns have been widely used in low and high seismic regions. These elements combine the high strength and ductility of steel with the ability of concrete to efficiently carry compressive loads. Numerous experimental studies have been performed to examine the behavior of CFT columns under pure axial or combined axial-lateral loads. Due to testing difficulties, however, limited data is available on the response of CFT columns under complex time-varying six-degrees-of-freedom (6-DOF) boundary forces during seismic events. In this paper, experimental studies are conducted to investigate the three-dimensional seismic response of CFT columns from the onset of damage to the state of complete collapse. The experiments include a series of large-scale quasi-static cyclic and hybrid simulation (HS) tests carried out on square and circular CFT columns. In the quasi-static (QS) tests, the specimens are subjected to bidirectional lateral deformation reversals that follows the hexagonal orbital pattern suggested in FEMA 461, combined with varying axial load. Hybrid simulation (HS) is then used to provide more insight into the response of these elements under realistic scenarios of seismic events. In the hybrid model, each test specimen serves as the first-story column of a symmetrical 5×5 bay 5-story framed building that is subjected to sequential biaxial ground motions with increasing intensities to collapse. The hysteretic response behaviors obtained from the QS and HS tests are then used for calibrating the analytical models employed in a comparative fragility analysis.

Steel-concrete sandwiched components have recently gained popularity as efficient and cost effective blast resistance systems because of their larger energy dissipation capacity compared to that of conventional reinforced concrete systems. For these sandwiched systems, the shear stress transfer mechanism between steel face plates and surrounding concrete through shear studs, and the resulting shear slip, play an important role in determination of resistance and deformation capacity. This paper presents a performance evaluation of beam-column sandwiched element with partial bond-slip explicitly considering softening and enhancement of compressive strength of concrete material under tensile-compressive and compressive-compressive biaxial stress state respectively based on potential energy functional; and proposes a new two-field mixed-based sandwiched element where independent interpolation functions for the nodal displacements, relative shear slip, and beam section forces are considered. The nonlinear coupled flexural-shear behaviour of the sandwiched element derives entirely from the constitutive laws of the steel, the concrete, and the shear connectors. Shear deformation is considered through the Timoshenko based section kinematics. Distributed inelasticity at the element and section levels are considered through section integration points along the length of the element and material fibre discretization across the cross-section respectively. Multi-axial stress state due to crack-induced anisotropy in concrete fibres is simulated through a fixed crack smeared softened membrane model which is based on the stress equilibrium, the strain compatibility, and the constitutive relationships of materials. The accuracy and efficiency of mixed-based variational principles over widely used displacement-based formulations are assessed by numerical studies of steel-concrete members comparing various response variables such as distribution of shear slip, section forces, and deformations along with capacity-deformation plots, which will in turn pave the way forward for developing performance-based design methodologies for steel-concrete sandwiched structures.

Typical strengthening of concrete structures is currently achieved with fibre reinforced polymers (FRP), which uses organic resin (epoxy) in the process of application. But towards the end of the last century, an upgraded system was introduced as an alternative for FRP for the rehabilitation of historic and damaged concrete and masonry structures known as fibre reinforced cementitious matrices (FRCM). FRCM systems are made from different materials like glass, steel, and carbon fibre meshes that each has a different strengthening capacity and temperature resistivity. The mesh of this system is formed from fabric grids and cementitious matrix components that are functioning as a matrix and binder. The inorganic cementitious mortar used by FRCM systems can be advantageous in harsh environments due to its excellent thermal behaviour and binding characteristics. Several small and large size beams were initially strengthened with FRCM systems and tested mechanically under four point bending. One and two layers of FRCM, as well as steel net material were used, and compared with a control beam. The observed results confirmed the higher flexural capacity and stronger bond when FRCM system replaces FRP composites in strengthening of concrete beams. In addition, several concrete specimens reinforced with FRCM and steel net were tested under a combination of mechanical loads representing gravity and controlled elevated temperatures. The results confirmed the specimens strengthened with FRCM outperformed those using typical FRP composites, mainly because of the superior thermal performance of the cementitious inorganic resin. Further, a new numerical finite element model was developed to investigate the structural response of FRCM-strengthened specimens under thermo-mechanical loads. The model was validated against the derived experimental data. The model was then used to investigating the different parameters affecting the behaviour of FRCM systems, especially at higher temperatures. The study demonstrates the viability of using FRCM systems as the strengthening and replacement material for FRP composites, particularly under elevated temperatures.

The connection between shear wall and floor slab is an essential link in the lateral load resisting mechanism of slab-wall systems. By modifying the joint detailing pattern, performance of the connection under lateral loading can be improved to a great extent. For this purpose, novel ductile detailing with additional shear reinforcement in the joint core region has been proposed. This paper analyses some experimental results, relevant to three sub-assemblies’ units tested under static lateral reverse cyclic loading, to evaluate the effect of the proposed joint detailing on the behavior of shear wall to floor slab joint region. Successively, three-dimensional nonlinear finite element models of the wall-slab joint sub-assembly were developed and analyzed using ABAQUS/CAE software. The provision of reinforcement in the core region of wall-slab joint for the construction of shear wall structures has been proven to be effective from the measured and computed results under cyclic loading. This paper thus verifies the viability of using the proposed type of joint detailing system in construction.

Rural communities are home to millions of people and small businesses, and are found in a wide range of geographic locations across the United States. As such, these rural areas are routinely subjected to extreme loads and natural hazards including earthquakes, tornadoes, and hurricanes. It is an enormous challenge to quantify the scale and extent of natural hazards’ damage on rural communities, particularly when considering the various components such as destroyed feed supplies, livestock losses, damage to barns and other structures, etc. This challenge is exacerbated by the lack of knowledge regarding the response of many rural systems to weather and climate disasters. Therefore, as a first step towards understanding the impacts of natural hazards on rural communities, this paper first presents the results of a digital/virtual reconnaissance of rural communities that have been subjected to a natural hazard during the first seven months of 2018. The results of this digital reconnaissance, in combination with traditional reconnaissance, highlighted that large steel grain silo structure is particularly susceptible to windstorms. To gain further insight into this problem, a numerical model of this structure in LS-DYNA is presented and used within a parametric study to identify the key geometric and load properties that lead to failure of the structure.

Composite construction including composite columns are widely used in structural design. In the transmission towers’ industry, composite columns are replacing the old timber and steel adopted designs. Research on the capacity and behavior of these traditional columns has been previously performed, yet few researchers investigated the behavior of hybrid composite columns, such as concrete filled steel tube (CFST) with embedded steel section or embedded steel tube (double skin column) and studs. Besides the non-homogeneity in concrete composition, choosing the right geometry for embedded steel components and their distribution pattern in the column section presents a challenge in achieving maximum section capacity. This study focuses on developing the P-M Interaction diagrams for different geometrical column shapes highly used in the industry such as hexagonal, octagonal, decagonal shapes, and the effect of adding headed shear studs on such diagrams. Three-dimensional non-linear finite element models were built using ABAQUS to compare and validate the behavior of the transmission towers against experimental work. The models include detailed analysis and investigation of the concrete and steel components behavior up to failure using concrete damage plasticity (CDP) and bilinear elasto-plastic model respectively. Good comparison between the FE results of such sections and previously studied columns has been achieved which leads to studying and investigating multiple forms of composite transmission towers. P-M Interaction diagrams were constructed for the proposed shapes for various diameter-to-steel thickness ratio (D/t) beyond AISC code limitations. Further extensive study was performed to investigate the effect of number of studs, studs’ dimensions, and studs’ arrangement in the cross-section and along the column length on the capacity of the columns. It was concluded from this study that certain arrangement and a smaller number of studs can give the desired capacity which is more economical and requires less efforts.

In this research, a new generation of metallic dissipaters has been proposed and experimentally validated. The dissipaters can be either in the shape of a brace or mini dissipater. The dissipaters offer advantages such as cost-efficiency, simple fabrication, replaceability, lightweight, ductility, strength, improved fatigue performance, redundancy during a large earthquake, option for self-centering, and compactness. The brace type dissipater can be used in buildings and bridges to absorb seismic energy. The mini dissipaters can be used in dissipative controlled rocking connections as external seismic energy absorbers. The paper presents a summary of existing metallic dissipaters. It discuss some common types followed by presenting the concepts for the innovative dissipaters. The concepts were experimentally validated using several prototypes which were tested under cyclic loading. Experimental testing showed stable and good performance of the dissipaters. None of the dissipaters showed any failure during the testing. The energy dissipation capability remained almost intact under cyclic loading. Furthermore, the mini dissipaters were tested in a precast bent with dissipative controlled rocking connections to validate implementation in a precast bridge substructure system.

During the design and installation of rooftop solar systems, it is often desirable for architectural reasons to support the solar panels without anchors attached to the structure, depending on friction for lateral resistance. This scenario has previously been studied with shake table tests and analysis in OpenSees and SAP 2000, resulting in the publication of a SEAOC standard. This paper contributes closed-form equations and fast-running code that will allow the development of simple design equations and probabilistic approaches. The proposed governing equations are presented then validated by comparison to an equivalent analysis with SAP 2000. Once validated, the equations are used to produce parametric plots of slip as a function of friction coefficient, roof slope, and intensity of roof shaking. This study is a proof of concept using a single earthquake record scaled to various intensity levels; other limitations and planned future work are detailed.

Precast concrete structural systems have been proved to be a cost-efficient alternative to cast-in-place reinforced concrete and structural steel systems. Advantages of these structural systems are high speed of construction, improved quality control, reduced total construction cost, versatility, flexibility in the architectural form of the members, and efficient and sustainable material use. Despite many advantages of precast concrete, it is not widely used in the United States, especially in areas of high seismic risk due to lack of knowledge about their performance. Several precast parking structures showed poor performance in the 1994 Northridge earthquake due to incorrect detailing of the connections. This study aims to investigate the behavior and develop detailing of hybrid beam-column connections to be used in precast moment resisting frames. Three-dimensional (3D) nonlinear finite element models were built to compare and validate the behavior of precast hybrid beam-column connections subjected to cyclic loading against experimental work. The models include detailed analysis and investigation of the concrete and steel behavior up to failure. Good comparison between the FE results and previously tested members has been achieved which leads to studying and investigating multiple parameters that affect the performance of such connections: reinforcement amount of beam elements, geometry of steel connection components, amount of bolt pretension, and method of anchoring the connection components in beam elements. Prying action in steel angles, a function of strength and stiffness of the connection elements under tension, was also investigated as a failure mode of such connections.

Strut-and-tie models are principally the discretized stress fields, which simplify the dimensioning and detailing of reinforced concrete members. The computational generation of stress fields currently relies on finite element analysis or optimization methods. This research addresses the limitations of optimization algorithms in producing reasonable strut-and-tie configurations. The computational procedure of this paper utilizes layout optimization and graphic statics cooperatively to create strut-and-tie models and stress fields for two-dimensional cases. The presented examples demonstrate the capabilities of the mentioned methods to produce some desired results for two-dimensional scenarios and suggest a similar approach to solve the strut-and-tie problem for three-dimensional cases.

Adequate bonding between rebar and concrete is critical to ensuring the reliable performance of RC structures. It is found empirically that bond behavior is affected by many factors, including concrete cover, transverse reinforcement, rebar geometry, concrete properties, etc. While many past studies have focused on the prediction of bond strength, how those factors influence the bond failure mode is not well investigated. The goal of this research is to develop a bond failure mode prediction model considering corrosion. The model development is based on bond testing results of 44 beam-end specimens with various rebar size, corrosion levels, covers, and stirrup confinement. This study adopts logistic and lasso logistic regression, where the failure mode is the categorical dependent variable and the aforementioned factors that could influence the bond behavior are the independent variables. The developed model can be can be further used for corroded RC structure performance evaluation.

The damage reported from structural and non-structural elements during severe windstorms promoted the extension of the performance-based design (PBD) philosophy to wind-excited tall buildings. A critical part of PBD is the assessing the risk of the facility to extreme wind events. Risk assessment allows the estimation of the probability of failure of the structure considering the uncertainties arising from the external hazard and the structural properties. This paper presents a framework for the risk-based assessment of wind-excited tall buildings using surrogate models. In the proposed framework, the surrogate models are leveraged to reduce the computational burden of time-consuming wind time history analyses. The risk of the building is quantified using the convolution of fragility functions and hazard curves at the site of the building. The surrogate model is constructed using a data-driven approach, where the training data set is derived from a high-fidelity computational model. Then, the surrogate function is used as a representation of the original computational model for risk assessment and future predictions. The proposed procedure is applied to a 39-story building. The building is equipped with motion control devices for wind-induced vibrations mitigation. The wind load is simulated in the time domain as a multivariate stochastic process and numerically applied to the structure. To create the training dataset, the structural response of the building in terms of peak acceleration and inter-story drift is estimated under different wind time histories. Two cases are considered. In the first case, the mean hourly wind speed and the terrain roughness are considered as random variables, while in the second instance the capacity of the damping devices is considered as uncertain. In both cases, the surrogate model parameters are optimized using the maximum likelihood estimation method. Results show that the proposed approach can be used for improving structural resilience under extreme wind events, where the use of surrogate model represents a viable data-driven solution for uncertainty-based risk evaluation.

Assessment of the seismic resilience of communities requires modeling the interactions that take place between the multiple systems of society, including engineering, economic, social, financial, environmental, political, and others. The complex interdependencies that arise between these systems is challenging to model because of the multi-disciplinary nature of the problem and range of temporal and spatial scales involved. With this motivation, a fully scalable and adaptable framework is developed for modeling the seismic resilience of communities. The framework includes different simulators, each of which represents various aspects of the problem, such as city layout, regional seismic ground motion, structural response, structural and non-structural damage, and loss assessment. Each simulator is considered as a black box that takes inputs from other simulators and provide outputs in a specific format to be used by other simulators. The proposed framework is demonstrated through a case study that is focused on modeling the resilience of an archetype community facing a seismic hazard.

Cold-formed steel (CFS) construction provides efficient, affordable, and resilient building systems that meet both domestic and international demands. The most significant advantages of cold-formed construction can be listed as the high strength-to-weight ratio (increased structural efficiency and economy in production, transportation, and handling by reducing labor costs and worker fatigue); weather and rot-resistant galvanized members; and rapid construction due to repetitive framing and modular-style walls. These listed qualities make CFS construction especially important for earthquake-prone regions where light, durable, and resilient structures are required. The CFS research has evolved significantly during the last two decades with the introduction of detailed design and construction guidelines. However, there are still many research questions regarding as-is geometrical integrity and its effect on member behavior. Currently, in order to predict the physical response of CFS members, the geometrical properties of the input sections are used. Since the member thickness to dimension ratio is significantly low, any existing geometrical imperfection may result in significant changes in member behavior. In order to investigate this topic further, a novel strategy, which aims to capture geometric imperfections on CFS members by using 3D images, is developed. These 3D images are generated from high-resolution images captured by a standard camera. Member skeleton tracking methods are used on an investigated CFS member for locating and quantifying the geometrical imperfections. The extracted geometric imperfection information is also compared with micrometer measurements in order to assess the accuracy of the developed strategy.

This project presents novel research in structural design and analysis of an ultra-transparent pedestrian bridge made exclusively of glass sheets in a double layer, funicular, compression-only configuration. The funicular form of the bridge maximizes its structural performance and minimizes the use of materials and resources. The structural form of the project has been developed using 3D graphic statics (3DGS) that is a geometry-based structural design method allowing the extensive exploration of funicular structural solutions in three dimensions. Using the 3DGS method results in structural forms that are polyhedral geometries with planar faces. Therefore, not only does 3DGS find the efficient structural forms, but its planarity constraint facilitates the construction using flat sheet materials. The current structure of the bridge consists of three-dimensional polyhedral cells as hollow glass blocks with planar glass faces held together in compression by using transparent silicon-based substance. The total span of the bridge is 10 m (32.81 ft) with a one-meter deck for pedestrian traffic. The asymmetric geometry of the bridge will significantly improve the behavior of the bridge under asymmetric and lateral loading conditions.

The main challenge with mass concrete structures lies in temperature rise and temperature differentials resulting from the heat of hydration of cementitious materials. Therefore, controlling the heat of hydration in mass concrete structures is important in order to minimize and potentially prevent cracks from forming. In this study, a novel material and/or combination of materials were utilized to study the effect on the heat of hydration. An isothermal calorimeter is used to measure the heat of hydration in concrete mixtures including barium oxide (BAO), which is a phase changing material. Different percentages of other supplementary cementitious materials were utilized based on the amount of total cementitious materials in the mixtures. The results were also compared with the heat of hydration of mixtures containing conventional mass concrete mixtures containing cement supplementary materials such as slag and fly ash. It is concluded that BAO significantly retarded the rate of hydration and slightly reduced the magnitude of the heat of hydration peak in concrete mixtures.