Journal of Structural Engineering

This paper presents a concise state-of-the-art survey on the research work pertaining to the seismic response of reinforced masonry shear walls (RMSW) with a focus on the published research work as of the 1980s on mainly RMSW built using concrete blocks. The paper is organized into two main focus areas: RMSW components (i.e., individual walls) and RMSW systems (i.e., complete buildings). To facilitate readability, the components literature survey is further categorized into five sections. These sections highlight the experimental and, to some extent, the numerical and analytical studies related to the seismic response of RMSW that are either: (1) fully grouted and squat; (2) fully grouted and slender; (3) fully grouted and end-confined; (4) fully/partially grouted and coupled or with openings; and (5) partially grouted. Each of these sections is presented from three perspectives that cover the historical overview, the current state of the art, and future research needs. Similar to the RMSW components focus area, the RMSW systems literature survey is also presented from three perspectives that cover the historical overview, the current state of the art, and future research needs. The paper concludes by briefly summarizing future challenges facing reinforced masonry construction under seismic loads and possible solutions through collaborative and individual research efforts.

Existing steel concentrically braced frame (CBF) buildings subjected to seismic hazards can exhibit an undesirable soft-story response, in which drift and damage are concentrated in a single story, whereas other stories remain relatively undamaged. This paper investigates the fundamental behavior and proposes a rehabilitative design procedure that uses a stiff rocking core (SRC) to redistribute lateral demands, thereby preventing soft-story response. The technique is relatively nonintrusive compared to traditional rehabilitative measures and can satisfy a maximum specified story drift for a given hazard level. Representative low-rise and midrise prototype CBFs are used to illustrate the fundamental mechanical and dynamic behavior of the SRC in support of the proposed rehabilitation design procedure. Results from nonlinear transient seismic analysis of both existing and SRC-rehabilitated CBFs are used to evaluate the SRC’s ability to improve the seismic performance of existing CBF structures. These results indicate that the SRC can be designed to prevent soft-story formation and, at the same time, achieve a target maximum interstory drift for a given seismic hazard.

Most deployable structures, such as operable roofs and masts, move over one degree of freedom. This paper describes a structure that involves loosely coupled movement over several degrees of freedom. Analysis models of these structures are typically inaccurate. A source of inaccuracy is joint friction. Static and kinetic friction are studied experimentally and analytically. Simulations have been modified to account for these effects, and two methods are used to quantify friction effects. Friction has a significant effect on the movement of the tensegrity structure. Of two candidate parameters, cable tension and interior cable angle, cable angle is the factor that best characterizes friction effects. Values of static and kinetic friction coefficients are not significantly different in this context, and this leads to a reduction in the complexity of the friction model for simulation. Including friction effects in analysis decreases the difference between simulations and tests. Lastly, strut elements of the tensegrity structure are most critically affected by friction.

The open-space damping system has been developed to preserve open space within the frame of its installation. An earlier paper by the authors described its function, presented a theory to describe its behavior, and presented computational models to verify the theory. This paper describes an experimental study of a large-scale model with the open-space damping system that is used to acquire data for validating the developed analytical and computational models. Testing consisted of (1) a single portal frame tested under imposed lateral motion, and (2) a single story 146 kN model tested on an earthquake simulator under seismic excitation. Two different configurations of the open-space system (plus a third variant of one of the two) in three different structural system configurations were tested. The tests demonstrate the increase in damping provided by the damping system. Comparisons of experimental results (in terms of structural drift, floor accelerations, and force-displacement loops) to results obtained by computational tools demonstrate the validity of the computational model.

The use of a stiff rocking core (SRC) has been proposed as a seismic rehabilitation technique to mitigate soft-story response in low-rise to midrise steel concentrically braced frame (CBF) structures. This technique uses a stiff, elastic “spine” to provide corrective lateral forces at the onset of soft-story response but otherwise remains passive for the first mode vibration response. Yielding link element can also be incorporated in the SRC-to-structure connection to dissipate energy and reduce overall building drift. An experimental testing program was performed to investigate the fundamental behaviors of the SRC rehabilitation technique applied to two approximately 1/3-scale prototype CBFs representative of modern and older design practices. Hybrid testing methods were used to simulate building dynamics, the influence of gravity framing, and response of upper stories for a midrise prototype building. Each prototype frame was subjected to two seismic ground motions to evaluate cumulative damage followed by quasi-static cyclic testing to failure. The results from these tests indicate that the SRC is effective at mitigating soft-story response by vertically redistributing lateral demands throughout the structure.

The development of system-level seismic fragility curves, which describe the probability of building systems reaching different damage states under a given ground motion intensity level, is an essential step in preearthquake and postearthquake risk assessment and resilience quantification. Nonetheless, current methodologies for generating fragility curves do not provide clear directions regarding how to integrate the fragility of different building components within the overall building seismic risk assessment. However, several recent studies demonstrate that neglecting some of these components’ contributions may lead to an erroneous seismic risk prediction of the overall building system. Recent research has also emphasized the need to develop alternative techniques to evaluate the system-level fragility to be adopted in the next generation of seismic risk assessment and resilience quantification standards. To address these issues, this study presents a new methodology that adopts two approaches, based on either component-level seismic losses or component strengths, to evaluate the overall system-level fragility. To demonstrate its practical application, the methodology is used to generate fragility curves for a reinforced masonry shear wall building with boundary elements. In this respect, OpenSees is used to develop a three-dimensional model of the building and subsequently conduct incremental dynamic analyses (IDA) by using a suite of 44 ground motion records. On the basis of the IDA results, component-level damage states are identified and used to generate component-level and, subsequently, system-level fragility curves. The analysis results show that the two proposed approaches yield consistent results, for the studied building configuration, that fall between a lower- and an upper-bound fragility estimate of the individual building components.

This study applies a plastic approach to the analysis of shear at a joint or interface in reinforced concrete. Push-off tests have been used historically to investigate combinations of shear and compression across an interface in reinforced concrete. Such tests can also be modified to model combinations of shear and tension, as is often found at critical interfaces such as joints in reinforced concrete structures. New experimental results are presented for modified push-off tests subject to a range of combinations of shear and tension. These results, along with a number of historical results reported in the literature are analyzed using the upper-bound theory of plasticity for interface shear. It is shown that the behavior predicted by the upper-bound theory is consistent with the new experimental results for an initially uncracked concrete interface subject to combinations of shear and tension. Effectiveness factors for the plastic analysis indicated by the experimental results are proposed.

Unanchored equipment and contents (EC) in buildings are of primary concern during an earthquake because not only can they contribute to substantial nonstructural losses but also pose a serious safety risk to building occupants. Base isolation is widely considered to be an effective technique for reducing seismic demands on nonstructural components, but recent research has noted situations, under broadband ground motions, where isolating a building can in fact amplify the response of unanchored EC that are prone to sliding. This study investigates the sliding response of unanchored EC in base-isolated buildings subjected to analytical pulse excitation representing pulselike ground motions. Describing the excitation by analytical pulses enables the application of dimensional analysis on the problem to provide insight into how different parameters of the nonlinear problem affect the response. The EC are idealized as freestanding rigid bodies, and the contact surface between the EC and floor is described by a Stribeck friction model taking into account the transition from static to kinetic friction. The isolation system is treated as either viscoelastic or bilinear. The study shows that the peak sliding response of rigid objects exhibits complete similarity in the ratio of kinetic-to-static friction coefficient. Therefore, a simple Coulomb model with a single friction coefficient value is adequate for estimating the peak sliding displacement. Moreover, it is observed that as the isolation damping increases, the sliding response exhibits complete similarity in the ratio of isolation-to-pulse period. The study concludes that certain combinations of the isolation design parameters can result in amplification in the peak sliding response of contents, compared to the fixed-base building.

Recent studies show that characteristics of hurricane surface winds are different from those of nonhurricane surface winds. The characteristics relevant to analyzing high-rise buildings include mean wind speed profile, turbulence intensity, and turbulence spectrum. The objective of this study is to quantify how these differences influence along-wind response of high-rise buildings in an open terrain. After summarizing recent findings in hurricane boundary layer winds, the characteristics of high-rise buildings in terms of natural frequency and dimension aspect ratio were discussed and the role of aerodynamic admittance in unsteady analysis of high-rise buildings were investigated. To illustrate the discussion, three different sample high-rise buildings with various characteristics were chosen for unsteady analysis of the along-wind effects of hurricanes. The results showed that for very-high-rise buildings, hurricane winds caused higher along-wind forces and responses compared with regular boundary layer high winds. This difference between hurricane winds and regular boundary layer winds decreased for lower heights and higher natural frequencies. Results for regular boundary layer high winds were well matched with high-frequency force balance (HFFB) measurements; however, for hurricane winds, root-mean-square base moments were higher than those from HFFB measurements.

The research presented in this paper addresses the influence of nonstructural masonry infill on the resistance of multistory buildings to progressive collapse under sudden column loss scenarios. In particular, the structural response of infilled frames in peripheral bays is investigated within the scope of a design-oriented robustness assessment framework previously developed at Imperial College London. This allows due consideration of structural redundancy, ductility, strength, dynamic effects, and energy absorption capabilities in a unified manner. The realistic contribution of masonry panels toward collapse arrest is examined considering the results from full-scale laboratory tests performed on different two-bay frames with brick-masonry infill subjected to incremental pushdown deformation, capturing the dominant deformation mode found following removal of an edge column. In these physical tests, it is observed that the failure mechanisms and damage patterns displayed by the infill panels under pushdown deformation are similar to those activated by lateral pushover loading. Clear evidence of diagonal cracking and shear sliding, eventually culminating in crushing of the compressed corners, is noted. Different infill configurations are tested, including central openings and an initial gap between masonry and frame elements. Overall, a global stable response is observed even in the presence of severe damage in the masonry panels, delivering a monotonic supply of energy absorption with increasing downward displacement. The outcome from this experimental research provides mechanically sound and quantifiable evidence that nonstructural masonry infill panels in peripheral frames offer a reliable and efficient source of enhanced robustness under column loss events. Because of the widespread application of masonry infill panels, this is believed to be particularly relevant within the context of retrofitting operations for robustness enhancement of existing structures, as a result of the growing demand for upgraded resilience of urban infrastructure. Similarly, due account for masonry infill subject to proper quality control during the construction process is recommended for rational robustness design of new buildings.

A well-instrumented drop-weight test program was developed to investigate shear failure modes of large-scale RC beams under impact loading. Test variables included beam span, transverse reinforcement ratio, impact mass, and impact velocity. The impact and reaction forces, and midspan deflection and accelerations at discrete locations along the beam were measured, and crack propagation was recorded using a high-speed video camera. Nonlinear finite element simulations also were carried out to study the feasibility of modern commercial software to reproduce observed behavior. Findings from the study indicate that as the impact velocity increases, specimens tend to fail in shear with diagonal cracks forming a shear plug near the loading point. These major diagonal cracks develop within a very short duration after impact when stress wave propagation has a significant influence on the impact responses, causing them to deviate from well-known behavior under static loading conditions. Providing additional transverse reinforcement was found to inhibit the development of shear cracks and the effect of stress wave propagation on impact response was more pronounced with increasing beam span.

Boundary conditions of precast concrete frames play a crucial role in their progressive collapse resistance under middle column removal scenarios. Interior and exterior frames behave differently as a result of different horizontal restraints on side columns. This paper presents an experimental study on four precast concrete frames with either 90° bend or lap-splice of the bottom reinforcement in the beam-column joint. The resistance of interior and exterior frames were determined quantitatively. Reinforcement detailing in the beam-column joint dominated structural resistance and deformation capacity of interior frames. Side columns of interior frames remained intact under compressive arch action (CAA) and catenary action, in spite of significant horizontal deflections and severe cracking because of initial horizontal compression at the CAA stage and subsequent tension at the catenary action stage. However, one exterior frame exhibited flexural failure of the side column when subject to catenary action, evidenced by concrete crushing in the compression zone. In side beam-column joints, diagonal shear cracks were observed at the CAA stage, and shear links were mobilized to sustain the shear force. Finally, relevant conclusions on the progressive collapse design of precast concrete frames are drawn from the experimental findings.

A nonlocal formulation with the potential to mitigate mesh dependence in fiber models for steel elements is presented. The formulation addresses two common modes of localization in prismatic steel bars: tension necking and compression buckling. These modes are induced by geometric nonlinearity, unlike those addressed by previous nonlocal formulations that focus on localization induced by material softening. Continuum finite element (FE) simulations are conducted to provide benchmark data for development as well as validation of the nonlocal formulation. The nonlocal formulation is implemented through a one-dimensional (1D) line-element-based structural model and has the following features: (1) a uniaxial stress-strain relationship with softening; (2) a length scale representing the necking or buckling process; (3) a volume-averaged nonlocal strain measure that incorporates this length scale; and (4) an imperfection pattern. For both necking and buckling, the nonlocal formulation successfully mitigates mesh dependence shown by the local models, implying that it can reproduce softening load deformation response accurately regardless of mesh discretization. Additionally, comparison to FE benchmark data indicates that the nonlocal formulation is able to characterize the strains inside the localized zone. This latter observation has important implications for simulation of fracture or fatigue that originates in zones of localized strains, such as during cyclic buckling of rebar or local buckling-induced fracture in rolled shapes. Limitations of the study are outlined, identifying challenges for incorporation into fiber models for beam-column elements.

The shear strength ($V$) of reinforced concrete (RC) beams consists of two parts: shear resistance of concrete ($V_c$) and contribution of the transverse reinforcement ($V_s$). Previous experimental results can only give the total shear strength $V$ of a beam. Until now, no existing experimental means could measure the two aforementioned contributions separately with reasonable accuracy during the test of RC beams. This paper reports an experimental method that is able to quantify the two parts in conventional shear tests of RC beams. This was achieved by measuring the strains along the full length of each stirrup in the shear span without disturbing the bond. Thus, the variation in $V_c$ and $V_s$ can be recorded during a beam test. Preliminary tests using this method on particular beams show that not all the shear reinforcement intersecting a critical diagonal crack yields at the onset of shear strength. Both $V_c$ and $V_s$ are not at their maximum values when the shear strength is reached in a beam. The value of $V_c$ is not constant under increasing deformation: it first increases and slightly drops after it reaches a peak, followed by a relatively stable plateau until final shear failure. The variation in $V_c$ with respect to member deformation does not match the predictions of existing models.

Prestressed concrete (PC) hollowcore slabs when exposed to fire are susceptible to failure under shear limit state. However, current approaches do not consider shear limit state in evaluating failure of hollowcore slabs under fire conditions. This paper presents an approach for modeling the response of PC hollowcore slabs by considering the shear limit state. A three-dimensional finite-element model is developed for evaluating failure of fire-exposed PC hollowcore slabs under various limiting states, including through shear. This nonlinear finite-element model uses a transient thermostructural analysis to trace the response of typical hollowcore slabs under fire conditions. The model accounts for temperature-induced degradation of properties of concrete and prestressing strands, cracking in concrete, material and geometrical nonlinearities, realistic fire, load and restraint conditions, and different failure limit states. The validity of the model is established by comparing temperature, deflection, fire resistance, and failure mode from the numerical model with data obtained from fire tests on different hollowcore slabs. In addition, a case study is carried out to illustrate the significance of shear failure mode in hollowcore slabs under fire conditions. The results from the case study show that slab depth and loading pattern have significant influence on the resulting failure mode, and under certain scenarios, failure of hollowcore slabs can occur through shear limit state before attaining flexural failure.

Rocking columns reinforced with unbonded prestressing offer advantages for bridges constructed in seismic regions because they can recenter the structure after an earthquake. Under lateral load, the columns rock on the foundation and cap beam, and rotate as rigid bodies rather than deforming. This paper describes cyclic load tests of two subassemblies representing parts of a bridge bent constructed using precast pretensioned rocking columns, spread footings, and a precast cap beam. The subassemblies, representing two halves of a single column, were subjected to cyclic lateral displacements of increasing amplitude under a constant vertical load. The proposed column design has several advantages over conventional cast-in-place construction. The use of precast columns and cap beams reduces on-site construction time. The use of unbonded prestressing minimizes residual displacements after an earthquake. The strands are deliberately debonded through the clear height of the column and bonded to the column concrete at the top and bottom, where the column is embedded in the cap beam and footing, respectively. The columns are confined by steel tubes and annular end plates at their interfaces with the footings and cap beams to minimize concrete damage when the columns rock. In the tests, the columns returned to their initial location with essentially no concrete damage after being displaced to peak drift ratios exceeding 10%. At the end of the tests, the columns’ lateral strengths still exceeded 80% of their peak values. The tests also provided the opportunity to evaluate practical procedures for proportioning key details of the system.

Low-rise metal buildings constitute a large portion of the nonresidential construction in the United States. These buildings are, in most cases, characterized by a pinned column-to-foundation connection. Although previous research has been conducted on other components of metal buildings (e.g., knee joints, tapered rafters), there is a lack of available data on the performance, particularly in terms of elastic stiffness, deformation capacity and energy absorption characteristics, of the pinned base-plate connections. The objective of this research is to evaluate the performance of the commonly used column base-plate pin connections in low-rise metal building systems. An experimental program is presented in which 11 column stubs were tested on concrete foundations and a systematic investigation was performed to study the influence of various parameters, including base-plate dimensions, number of anchor rods, anchor rod diameter and gage distance, on the connection behavior. The tests were performed on full-scale specimens subjected to horizontal cyclic displacements with an increasing amplitude and a constant axial load. All of the tested specimens showed high deformation capacity, and moderate strength and energy absorption. This paper presents the observed hysteretic behavior, elastic stiffness, moment and deformation capacity, and damage patterns of the tested specimens.

Despite the frequent use of C-shaped reinforced concrete (RC) cores as the primary force-resisting system in multistory buildings, there are still challenges in estimating their inelastic seismic response, especially when they are used as a coupled wall system. Recent studies showed the inadequacy of old code provisions in predicting the seismic shear demands of these systems. This means that many existing RC cores are structurally deficient and need to be retrofitted. One alternative is to retrofit RC shear walls using FRP composite materials to enhance the capacity and ductility of the system. The current paper focuses on two aspects of coupled C-shaped RC core systems: (1) seismic collapse of the system for different torsional sensitivities, and (2) effect of FRP retrofitting on the seismic response of the structure. Modifications are proposed to the wide column model recently proposed by other researchers to accurately capture the inelastic torsional behavior of RC cores, including different modes of failure. Moreover, a simplified spring model is proposed to consider the effect of fiber reinforced polymer (FRP) retrofitting with vertical strips along with X-bracing. The proposed modeling approach is validated against available experimental data. Nonlinear incremental dynamic analysis (IDA) of a typical 12-story RC building structure located in Eastern North America was performed using OpenSEES, following the FEMA P695 methodology. It was shown that, although torsional sensitivity has no significant effect on the interstory drift ratios of the building, it can significantly decrease the collapse margin ratio (CMR). Combined shear/flexural failure was found to be the most common failure mode. Observed results also confirmed that FRP strengthening can be used as an efficient method for enhancing the collapse resistance of RC core wall systems. By using a proper strengthening scheme with FRP material, a more than 60% increase in the CMR can be achieved for the structural system.

A new adaptive self-centering device for structural protection has been developed using the mechanism of traditional bicycle, which uses a combination friction-ratchet-pawl-lever mechanism. This device can be installed within a chevron bracing setup in a portal frame or can be used as an isolator. It manifests adaptive force-deformation behavior which entails lower postelastic stiffness and dissipation for smaller excitations and higher postelastic stiffness and dissipation for larger excitations. It also allows for adjustable slip load which is independent of the structure weight. The main components of the device are (1) two friction wheels, (2) two ratchet wheels, (3) two pawls, (4) a central shaft, (5) two recentering springs, (6) three horizontal sliders, and (7) a set of levers. The friction wheels and the ratchet wheels rotate about the central shaft, which is static. Each pawl is pinned to one friction wheel and presses the rim of one ratchet wheel through a torsion spring. A counterweight force is applied radially to the friction wheel. External lateral force that originates from structural vibrations is applied tangentially to the ratchet wheel through the horizontal sliders and levers. These levers are responsible for the adaptive nature of the device. The adaptive force-deformation hysteretic behavior of the device for quasi-static displacement input and for various values of counterweight is generated experimentally. These responses are also captured analytically by using basic mechanics. Sensitivity analyses are performed to evaluate the desired design parameters of the device. Preliminary nonlinear dynamic analyses conducted with selected strong-pulse cycloidal ground motions suggest that the proposed device will protect the parent structure better than the existing self-centering devices and state-of-the-art isolators such as the triple friction pendulum.

This paper proposes a new efficient model for the prediction of low-amplitude ground-borne vibrations in buildings. The model takes into account the three-dimensional nature of the building structure by analytical and semianalytical means, making it ideal for performing parametric studies or large-scale vibrations predictions. Its formulation assumes that the principal component in floor vibrations is the vertical one and assumes that the vibrations are transmitted to the various floors through the building columns. The correctness of the model is tested by comparing, in two 3-story building examples, its results with those obtained using a numerical model. Results regarding the isolation efficiency of implementing a thicker lower floor or columns with a larger cross section are also presented. The building-soil coupling is formulated considering piled foundations in a stratified soil. To ensure the computational efficiency of the calculations, the piles’ response to an incident wavefield is modeled considering the Novak pile model for a layered half-space. Finally, a study of the importance of the soil mechanical parameters in the considered problem is conducted using the building-soil coupled model.

This paper presents a simple and reliable homogenization approach coupled with rigid elements and homogenized interfaces for the analysis of out-of-plane loaded masonry panels. The homogenization approach proposed is a coarse finite element discretization wherein bricks are meshed with a few elastic constant stress triangular elements and joints reduced to interfaces with elastoplastic softening behavior with friction, tension cutoff, and a cap in compression. Flexural behavior is deduced from membrane homogenized stress-strain relationships through thickness integration (Kirchhoff–Love plate hypothesis). The procedure is robust and allows obtaining homogenized bending moment/torque curvature relationships (also in presence of membrane pre-compression) to be used at a structural level within a rigid body and spring mass model (RBSM) implemented in a commercial code. The model relies on rigid quadrilateral elements interconnected by homogenized bending/torque nonlinear springs. The possibility of extending the procedure to a finite element package, with standard built-in solution procedures, allows for a robust reproduction of masonry out-of-plane behavior beyond the peak load, in the presence of global softening. The procedure is tested on a set of windowed and full masonry panels in two-way bending. Excellent agreement is found with both experimental data and previously presented numerical approaches.

Recently, multihazards engineering has paid more attention to analyzing the behavior of a system exposed to different types of hazards and to estimate the loss data from cascading events attributed to the primary hazard. This paper investigates the principle of multihazards and develops a new methodology to assess the total damage of structural elements caused by cascading hazards. For each hazard, a physical model is used to assess the conditional probability of exceeding a certain intensity level due to the occurrence of the previous hazard. The method is applied to a hospital located in California subjected to three cascading hazards (earthquake, blast, and fire). Nonlinear time-history analyses are performed using seven ground motions scaled to five earthquake levels and the seismic response of the structure is evaluated. The seismic input produces damage to the hospital’s power supply (liquid propane gas reservoir tank), which may cause a blast. The probability of explosion is estimated by taking into account the probabilities of fuel leakage, fuel concentration, and ignition. A set of nine blast-intensity levels is considered in the analyses, corresponding to different quantities of fuel content inside the tank. Afterward, a fire hazard is generated following the explosion, the intensity level of which is evaluated using compartmental heat flux. The fire effects are modeled assuming an increment of temperature in the steel frames. The proposed multihazard approach can be used for both improving the structural safety and reducing the building lifecycle costs to enhance the resilience of the hospital. Results show that this methodology can be used to provide risk mitigation measures within a more general resilience framework.

Fire poses a great threat to steel structures. An accurate estimation of the temperatures in structural member cross sections is the first and most crucial step to calculate fire-induced forces and moments and ultimately to evaluate the fire performance of a structural system. This study focuses on the thermal behavior of perimeter I-section columns in steel buildings subjected to the standard fire curve. Because I-sections have a concave enclosure or cavity, the surfaces in the enclosure exchange heat by radiation, which significantly changes the thermal gradient in the section. An efficient algorithm is developed to calculate the radiation heat flux generated by surface heat exchange in I-section enclosures. The results show that the surface heat exchange in the enclosure reduces the thermal gradient as much as 40% for shorter and wider sections. The fire test results confirm the numerical findings. Using a simplified equation of a partially restrained column, it is shown that the thermally induced moment reaches as much 60% of the column plastic moment capacity, which indicates a significant reduction in the load-bearing capacity of the building structure.

The effect of axial force on the flexural strength of steel members, not connections, has been extensively researched for nonseismic loading conditions. To address the latter for seismic applications, four nominally identical beam-column subassemblies with a welded unreinforced flange-welded web (WUF-W) moment connection were cyclically tested. The specimen design included built-up I-shape beams ($d_b=\mathrm{1,118}\mathrm{mm}$) and built-up I-shape columns ($d_c=\mathrm{1,219}\mathrm{mm}$). Because the member sizes and weights significantly exceeded those permitted by current standards for use as a prequalified WUF-W connection, all except one specimen had flared beam flanges with the goal of protecting the beam flange complete-joint-penetration CJP groove welds. A constant axial tension force in the beam (16% of nominal beam yield strength) was applied to three specimens, whereas one flared specimen did not have axial tension. When tension was present, testing showed that beam local buckling drastically diminished. A higher flexural strength was developed in the plastic hinge, indicating that the $C_{pr}$ value in current standards for capacity design is nonconservative when tension is present. Fracture in the beam web instead of flange CJP welds dominated the failure mode because of a change in the load transfer mechanism. More stringent beam web welding requirements than those specified in current standards were shown to improve connection performance.

Annualized hurricane-related losses in the United States are in the billions of dollars. The majority of the coastal population lives in buildings prone to hurricanes, which could result in wind damage (due to high wind and/or wind-driven rain infiltration) and water damage (due to storm surge and waves or freshwater flooding), which are typically insured by separate entities. In the event that a structure is subjected to damage from both wind and water hazards, the proper allocation of damage for insurance purposes is challenging because wind and water vulnerability are often assessed with separate models. The challenge is how to combine the results of these different models and properly assign damage causation. This paper proposes a methodology for the assessment of multihazard vulnerability for implementation in the Florida Public Hurricane Loss Model, in which the damage from each hazard (wind and rain, storm surge, and freshwater inundation) is calculated separately. An engineering approach in conjunction with hazard information (intensity, timing) and statistical methods is utilized to allocate damage.

An improved numerical model that can simulate the nonlinear behavior of RC beams subjected to blast loadings is introduced in this paper. The model is based on the moment-curvature relationship of a RC section, and a dynamic increase factor (DIF) defined with the curvature rate is newly designed to be used in the moment-curvature relationship. The plastic hinge length is considered in the finite-element (FE) idealization of RC beams to accurately reflect the effects of the plastic deformation concentrated at the midspan or beam-column joint after yielding of the main reinforcement. A modification of the moment-curvature relationship is also proposed to take into account the fixed-end rotation accompanied by large bond-slip at the yielding stage of the main reinforcement. The advantages of the proposed model, compared with the layered-section approach, are reduced calculation time and memory space in application to large-frame structures with many degrees of freedom. Finally, correlation studies between analytical results and experimental studies are conducted to establish the validity of the proposed model, and the effect of the finite-element mesh size is also discussed in connection with the importance of considering the fixed-end rotation. The results are also compared with those obtained from the single-degree-of-freedom (SDOF) model to demonstrate the better prediction capability of the proposed method.

The current study proposes a simple and mechanically sound analytical approach for crack analysis of reinforced concrete (RC) flexural members at the stage of stabilized cracking. The philosophy behind the proposed methodology is to establish mean spacing between the primary cracks through the compatibility of the stress transfer and mean strain approaches. The governing parameters of crack spacing are obtained by equating mean strains of the tension reinforcement defined by these approaches. The model assumes that a single RC block of a length of mean crack spacing represents the averaged deformation behavior of the cracked member. Based on the experimental evidence, reinforcement strain within the block is characterized by a strain profile consisting of straight lines representing zones with different bond characteristics. It was shown that crack spacing is mostly governed by four geometrical parameters given in the order of significance: section height, reinforcement ratio, bar diameter, and cover. A limited comparative analysis has demonstrated that the predictions of mean crack spacing by the proposed model agree well with the tests. Considerations are given to extend the proposed methodology to the analysis of maximum crack width.

Small-amplitude cyclic vertical motions of timber floors perceived as unacceptable by humans are commonly the result of walking impact forces. Contemporary vibration serviceability guidelines mainly require prediction of static displacement and modal frequencies of floors. This study used an advanced finite-element (FE) analysis approach to model glulam beam-and-deck floor systems. This permits prediction of static displacement and modal response characteristics that closely match values determined by testing full-scale floor. The verified modeling method is used to show how variations in floor details such as span and floor width affect the vibration behaviors of these floors. This shows that changing the floor width has little effect on the fundamental frequency and midspan deflection of a floor, but higher-order modal frequencies are strongly affected. Although fundamental frequency of floors is not highly sensitive to the flexural rigidities of decking layers, higher-order modes are strongly affected. The broad conclusion is that reliable prediction of parameters engineers used to predict vibration serviceability of such floors depends on the use of appropriate models. Appropriate models are ones that incorporate deep system effects on motions stemming from the layered nature of beam-and-deck element floors and depths of glulam elements used as the beams.

Reducing the potential impacts from a future disaster can be accomplished through decreasing the hazard exposure and reducing the community’s vulnerability. Moreover, communities have both physical and social vulnerabilities that deserve attention; however, most engineering studies focus on assessing and mitigating the physical infrastructure without fully considering the social infrastructure. This paper offers a more holistic examination of vulnerability. Specifically, a two-stage analytical approach is presented that treats both an earthquake and a community’s socioeconomic and demographic makeup as hazards. The first stage addresses the physical vulnerability of a community through retrofitting the residential building stock using an inventory of woodframe building archetypes. The second stage incorporates the social characteristics of a community through modeling six social vulnerability variables. A social disaster factor (SDF) is introduced to offer a quantifiable approach for understanding the intersections between physical and social vulnerabilities. Case studies are presented for three communities: a middle-class ZIP code, the poorest ZIP code, and the wealthiest ZIP code, all in Los Angeles County, California. The SDF is computed and compared for the case studies during both stages of the analysis. The analyses demonstrate that when only physical vulnerabilities are modeled, one might incorrectly conclude that the impacts of the event are virtually eliminated. However, when social vulnerabilities are modeled as a hazard alongside the physical vulnerabilities, the projected impacts of the disaster are severe, especially for the most vulnerable populations, in terms of injuries, fatalities, posttraumatic stress disorder diagnoses, and number of dislocated households. In the combined model, these impacts run along racial and economic fault lines, with the most marginalized communities experiencing the most extreme projected losses. These results may have implications for both theory and practice.

Experiments on deformed reinforcing bar anchorages developed in strain-resilient cementitious composites (SRCCs) with high tensile deformation capacity illustrate that the bar-matrix assembly may respond in a ductile manner marked by pullout failure with no cover splitting—even in the absence of external confinement. This ductile bond-slip response is owing to the extremely high tensile fracture energy of the matrix, which is attributed to the reinforcing action of the dispersed microfibers in the cementitious matrix. This enhances the associated bond-slip law with higher strength and a slowly descending branch, very similar in form to the response curve of confined anchorages that demonstrate ductile, resilient response. To understand and model the structural response of an elastic bar anchorage in a SRCC matrix, the analytical solution of the field equations that govern the bond problem are established with reference to the entire range of the bond-slip law up to large levels of slip, including the postpeak descending branch, which quantifies the fracture energy of the matrix. The accuracy of the mathematical solution is verified through correlation with laboratory evidence, benchmark finite-element analysis examples, and numerical solutions of the discretized problem. The mathematical solution is used in order to conduct a parametric investigation that accounts both for the bond toughness and the anchorage geometry, to illustrate their significance as prerequisite for development of high-strength reinforcement.

This paper describes the experimental performance of D-region reinforced concrete bent specimens affected by varying levels of alkali-silica reaction (ASR) from none to mid-to-late stages, as determined from petrography analysis and from the presence and extent of concrete expansion and cracking. It also describes the analytical methodology employed. It is shown that specimens showing varying degrees of ASR compared with the control specimen without ASR had slightly greater stiffness, strength, and ductility, with no evident detrimental effects on structural response. The apparent improved behavior can be explained as a result of the activation of the specimen’s reinforcing steel due to concrete expansion primarily from ASR, which effectively prestresses and confines the core concrete. Analytically, conventional code-based methods, including sectional analysis and strut-and-tie modeling (STM), underestimate the strength capacity of the specimens when tested to failure.

Unlike the use of bonded reinforcement to anchor a masonry wall to its foundation, the use of unbonded posttensioning may result in a controlled rocking response of the wall. Considering that conventional analysis techniques routinely employed for monolithic structures are inadequate to describe a controlled rocking response, this paper introduces analysis methods that are able to predict the monotonic force-displacement responses of masonry walls with unbonded posttensioning. These methods include (1) an iterative procedure that employs sectional analysis and accounts for the confinement effects attributable to lateral friction at the wall-to-foundation interface and (2) a simplified procedure that is based on equivalent stress block analysis. The two methods are compared against experimental data from three past research studies, and high-fidelity finite-element models are used to verify predictions of the wall responses, including the neutral axis depth (NAD) at the wall-to-foundation interface. Comparisons show the proposed analysis methods to adequately capture the experimental force-displacement responses and produce NAD variations that agree well with the finite-element models.

Glass beams having T or I cross sections can be obtained as glass panels or laminated glass (LG) panels assembled with polymer adhesives of different types, such as semirigid (silicones, modified silicones, and polyurethanes) and rigid (epoxy resins, acrylic). Beams can be used mainly as members of transparent roof or floor structures, and as stiffening fins for large-area glass facades. The glued joints between panels constituting the web and flanges of a cross section, created using semirigid polymer adhesive, are the key element of the composite structures, assigning a load-carrying capacity. This paper focuses on the choice of the type of adhesive and of the shape and dimensions of the transverse cross section of glass beams for structural applications. An analytical model is presented for a preliminary design of composite glass beams. The model, able to predict the load-deflection response of the beam, includes limit states due to tensile strength of the glass and glue shear failure. Experimental data given in the literature are utilized to show the effectiveness of the analytical model to reproduce experimental results.

This paper presents a three-dimensional (3D) finite-element model (FEM) of part of a contemporary timber-framed house for assessing the load sharing and contribution of lining elements to load sharing. Assembled with intercomponent connections (i.e., batten-to-cladding connections, batten-to-truss connections, and roof-to-wall connections), the model consists of structural frame elements (e.g., trusses, battens, metal roof cladding, top plates, bottom plates, and wall studs) and lining elements (e.g., ceiling, wall lining, and ceiling cornice). The model analyses agree favorably with results from full-scale structural tests. The FEM shows that adding lining elements decreases the vertical reaction of the roof-to-wall connection by approximately 25%. This validated model provides confidence for assessing the structural response of a range of typical house geometries and materials including the effects of construction defects to wind loads.

In order to assess the robustness of a building structure to progressive collapse, the removal of a structural key component is utilized. For a steel moment-resisting frame under a column-removal scenario, the two most prominent collapse mechanisms are the yielding type (beam plastification) and the stability (column buckling) collapse mode. This paper presents an analytical method that can predict the progressive collapse mechanism of a 2D steel moment-resisting frame under any column-removal scenario and estimate the collapse load and location of the buckled column in case of loss of stability. The method uses only two linear elastic analyses and therefore avoids the computational cost that a complete progressive collapse analysis would require. The presented solution leads to the development of new Euler-type progressive collapse curves, which, similarly to the Euler curve for a single member under compression, refer to a steel frame and describe its response under any column removal. The new analytical method is applied through an extensive parametric study and the results are validated using advanced finite element simulation techniques, showing almost absolute consistency between the analytical method and the FEM results.

Progressive collapse incidents of truss structures are often reported; however, studies on the collapse resistance of truss structures are comparatively few. In order to investigate the collapse-resisting mechanisms of truss structures, this paper presents a comprehensive and detailed study on the collapse-resisting performance of planar trusses subjected to local damage at various locations, using both finite-element (FE) and analytical approaches. An improved FE analysis procedure is proposed to improve the computational efficiency. The main conclusions include the following: (1) in the case of a sudden loss of a top chord member or a diagonal member, catenary action will be the primary mechanism to provide the bridging-over capacity of the remaining structure, and severer damage can result when the removed member locates in the midspan; and (2) if a bottom chord member is suddenly lost, arch action will be the main mechanism to provide the bridging-over capacity of the remaining structure, and severer damage can result when the removed member locates next to the support or in the midspan.

Concrete-filled sandwich steel panel (CFSSP) walls are composed of two steel skin plates interconnected by tie bars, with the space between the skin plates filled with concrete. These walls are attractive for use in seismic regions, but limited knowledge exists on their in-plane cycling inelastic flexural behavior. This paper reports results from an experimental study investigating this behavior by testing four cantilever CFSSP walls with and without circular boundary elements, having length-to-width ratios of 2.46 and 2.76, respectively. All of the tested walls were able to exceed their theoretical plastic moment capacity, calculated assuming a full plastic stress distribution of the cross section. The tested specimens exhibited stable ductile behavior up to 3% drift (and beyond in some conditions). Local buckling of the steel skin led to minor degradation in flexural strength. Fracture of the skin plates eventually developed as the ultimate failure mode. The effect of using different tie bars spacing to steel plate thickness ratios, and different techniques for welding the tie bars to the skin plates, are also addressed.

This paper quantifies the collapse risk and earthquake-induced economic losses of steel-frame buildings with special concentrically braced frames designed in urban California. A probabilistic building-specific loss estimation methodology that can explicitly account for the main sources of variability related to seismic hazards and structural response is used for this purpose. It is shown that, depending on the choice of the loss metric, at seismic events with low probability of occurrence (i.e., 2% probability of occurrence in 50 years), losses because of demolition and structural collapse in steel-frame buildings with special concentrically braced frames designed in highly seismic zones may be significantly overestimated when ignoring the contribution of the composite floor and gravity framing system to the analytical model building representation. For frequent and moderately frequent seismic events (i.e., 50 and 10% probability of exceedance over 50 years of building life expectancy), acceleration-sensitive nonstructural component repairs govern building losses regardless of the analytical model representation used. For the same seismic events, an appreciable contributor to total losses in steel-frame buildings with special concentrically braced frames is structural repairs because of steel brace flexural buckling. It is suggested that dual-parameter rather than drift-based steel brace fragility curves should be used in loss computations conditioned on a single seismic intensity. Otherwise, the expected annual losses should be used as a metric for building-specific loss assessment of steel-frame buildings with special concentrically braced frames.

Lack of sufficient earthquake records for a given site and hazard level is a frequent challenge in seismic response assessment. This paper considers the response of several simple nonlinear systems to “amplitude-scaled” ground motions suites to determine bias in the response obtained compared with unscaled records. The dependence of this bias ratio on properties of the nonlinear system (e.g., elastic period and yield strength) and the parameter used to scale the ground motions [e.g., peak ground acceleration (PGA), peak ground velocity (PGV), and elastic spectral displacement] are investigated. Results showed that the amount of the bias is considerable and dependent on the properties of the nonlinear system, scaling parameter, and amplitude, and the bias can significantly affect the results of performance-based analyses. The origin of the bias was investigated and, consequently, a new metric is proposed to predict the bias induced by ground motion scaling without nonlinear analysis. Results demonstrated that using the predictor as a scaling parameter can significantly reduce the bias for various nonlinear single- and multi-degree-of-freedom structures.

Masonry-infilled (MI) panels, which serve as partitions in buildings, are normally considered as architectural elements. Their weights are considered in progressive collapse analysis, but the resistance of the walls is normally ignored in design guidelines. Simple structural analysis predicts that the infill walls, which are commonly equivalent to compressive struts, increase not only the lateral load resistance but also the vertical load resistance of the reinforced concrete (RC) frames. Because extra vertical resistance might reduce the risk of failure, it is necessary to quantify the effects of MI walls on the load resisting capacity of RC frames to mitigate progressive collapse. However, few studies, especially experimental studies, have been carried out on this topic. Thus, six multistory by multibay RC subframes were designed and tested, subjected to push-down loading regimes. The six subframes were categorized into two groups: (1) bare frames without MI walls and (2) infilled frames with MI walls. The failure modes, load-displacement curves, deformation shapes, and strains of the specimens are measured and compared. The effects of the MI wall on the load resisting capacity, initial stiffness, and load resisting mechanisms of RC frames to resist progressive collapse were also evaluated and discussed. The experimental and analytical results indicated that ignoring the effects of MI walls in progressive collapse design may result in substantial inaccuracy in predicting the stiffness, strength, and failure modes of infilled frames to resist progressive collapse. Infill walls with low height/span ratio may fail in splitting of the equivalent compressive struts prior to crushing.

This paper presents a nonlinear inelastic solution for the length of the critical plastic region in the case of nonlinear moment profiles along RC bridge columns. A new analytical expression for the length of the plastic region capturing the combined effects that column slenderness, second-order $P\text{-}\delta$ moments, and the reduced postyield flexural stiffness have on the spread of plasticity over the column length is proposed. Variable flexural stiffness along the column height was also considered. Experimental results from three slender RC bridge columns with aspect ratios (shear span to diameter) greater than 10 were used to verify the analytical solution. Moreover, the results from the proposed solution were compared against previous models and it was found that the presented nonlinear inelastic solution offers better performance over linear and nonlinear elastic solutions for predicting the length of the plastic region and how it is affected by geometric nonlinearities and $P\text{-}\delta$ moments.

This paper adapts and validates a three-dimensional finite element (3D-FE) model of reinforced concrete (RC) plates subjected to repeated low-velocity impact loads that were formerly tested by the authors. A brief description of the experimental tests that are required to facilitate the finite element (FE) modeling is provided. Numerical simulations have been performed using an explicit FE commercial code. A concrete damage plasticity (CDP) model is adapted to consider nonlinearity, stiffness degradation, and strain rate effects of concrete. The classical metal plasticity model is used to define the full response of the steel reinforcement. CDP parameters are calibrated based on the test results of a control specimen. Thereafter, the predictive capability of the calibrated model has been demonstrated by simulating different plates with varied steel reinforcement ratios and arrangements. The numerical results showed that computed responses are sensitive to CDP parameters related to the plastic expansion, and damage parameters. Additionally, strain rate effect inclusion is critical to properly predict the punching shear failure pattern. Results confirmed also the ability of the calibrated model to predict the response of RC structures under low-velocity loading conditions.

Progressive collapse accidents of single-layer latticed domes seriously threaten public safety and social security. Structural integrity and progressive collapse–resisting capacity are gradually becoming essential requirements in structural design. The Kiewitt Lamella and geodesic single-layer latticed domes are typical of domes used in large-scale public facilities. In this paper, an experimental study and a numerical simulation were carried out to understand the mechanism of internal force redistribution in the progressive collapse of domes. Three effective methods to evaluate progressive collapse resistance and critical displacement were determined and verified. The results indicate that both the Kiewitt Lamella dome and the geodesic dome exhibit undergo snap-through collapse. The collapse of the Kiewitt Lamella dome was induced by unexpected local instability around the initial failure members, whereas that of the geodesic dome was the result of a rapid change in nodal displacement and a sharp decline in structural stiffness.

Historic masonry monuments experience aging and accumulated damage, which consequently degrade both their stiffness and strength. Stiffness degradation can be quantified through nondestructive testing and has been widely used to determine the onset of structural damage by monitoring the changes in monuments’ dynamic behavior. For justifying and configuring repair and rehabilitation activities, strength degradation (i.e., loss in load-carrying capacity) provides a more relevant indicator than does stiffness degradation. However, strength degradation is also significantly less feasible to assess because it requires the use of destructive testing. In this paper, the authors estimate strength degradation by establishing an empirical relationship between loss in structural redundancy due to damage and the corresponding loss in load-carrying capacity. Here, structural redundancy is represented as the ability of the structure to accommodate the applied load through alternative load paths. Loss in structural redundancy is approximated as the disturbance in the load path due to the development and progression of cracks. The proposed redundancy measure is demonstrated on a historic masonry coastal fortification considering differential settlement of supports.

Tornado-induced wind load modeling has advanced significantly in recent years, but comparison of the experimental or numerical models to observed tornado damage is limited. This paper describes the development of empirically derived tornado fragility functions for residential structures following the 22 May 2011 Joplin, Missouri tornado. The fragility functions were created by combining a residential structure damage assessment of the Joplin tornado using the enhanced Fujita (EF) scale and a tornado wind field model conditioned to tree-fall patterns. The damage states for the fragility functions used the degrees of damage (DOD) for one- and two-story residential structures from the EF scale. The empirical tornado fragility functions were compared to analytically derived fragility functions for straightline winds from the FEMA Hazus hurricane model to provide a first attempt at ascertaining how different or similar failure wind speeds are for residential structures under tornado-induced and straightline wind loads. Median failure wind speeds from the empirical tornado fragility functions increased monotonically with DOD, from $33.4\mathrm{m}/\mathrm{s}$ for DOD1 to $85.6\mathrm{m}/\mathrm{s}$ for DOD9. Median failure wind speeds of the empirical tornado fragility functions and Hazus hurricane straightline wind fragility functions differed by 5% or less when suburban terrain was assumed throughout the damage path, and 25% or less when open terrain was assumed. The results suggest that tornado load amplification factors are at worst no more than 55% for residential structures, and may be lower than 10%.

The design philosophy of strong-column-weak-beam (SCWB) in which plastic deformation is predominantly allowed to occur in beams while columns remain essentially elastic is commonly adopted in seismic design codes for moment-resisting frames. Practical design of SCWB frames is employed by using the beam-to-column-joint ratio, which is mainly done to prevent formation of plastic hinges in columns without consideration of the global inelastic behavior of the SCWB frame. This paper investigates the inelastic behavior of SCWB frames with different distributions of beam and column plastic strengths at different ductility demand levels. Midrise 9-story steel frames were designed as SCWB frames with the same lateral strength but with different column strength and stiffness relative to those of the beams. Nonlinear static and dynamic analysis results indicate that the relative plastic flexural capacities of the beams and column bases have a significant effect on the structural deformation and seismic response of SCWB frames. The structural response and beam-to-column-joint demand strongly depend on the column strength and stiffness. The results indicate that a global parameter may be used in addition to the beam-to-column-joint ratio to control the inelastic response behavior of strong-column-weak-beam frames.

This paper documents the findings from a dynamic collapse experiment carried out on a single-story two-by-two bay reinforced concrete flat-plate substructure. The test specimen had a 0.4 scale, represented older flat-plate buildings designed without structural integrity reinforcement in slabs, and was subjected to an instantaneous removal of an exterior supporting column. Tests were conducted three times with different levels of gravity load until a progressive collapse occurred. The specimen survived a gravity load corresponding to 42% of the normal loading capacity defined by the direct design methods but collapsed at a load of 49% of the design loading capacity. The collapse of the specimen was initiated by the punching failure at an interior slab-column connection carrying the most redistributed load after the exterior column removal. The tests confirmed the existence of slab compressive membrane action and examined the strain rates of material under dynamic response. The tests also indicated that a slab-column connection without continuous slab bottom reinforcement through the column has limited post-punching resistance. The experiment indicated that an older flat-plate building is vulnerable to a progressive collapse when it is subjected to a sudden exterior column removal. Numerical simulations of the experiments using a macromodel were conducted and its effectiveness was confirmed.

Despite their importance in building design, ground snow load requirements remain largely undefined for the western United States. This paper proposes an adaptation of the Parameter-Elevation Relationships on Independent Slopes Model (PRISM) for predicting ground snow loads, using Utah as the area of interest to test the efficacy of the algorithm. It can be concluded that data filtering is exceptionally important to effective extreme-value estimations. In addition, using the log transform of the resulting 50-year ground snow load estimates as the response variable satisfies the basic linearity assumptions required for any linear regression–based estimator. A comparison of PRISM predictions with the current ground snow load requirements defined for Utah shows that PRISM yields lower absolute errors and less bias than the current methods used in the state. These predictions also eliminate existing discrepancies in ground snow load requirements along county boundaries within Utah and provide the framework for the elimination of ground snow load requirement discrepancies along state boundaries throughout the western United States.

In this paper, the classical linear tuned mass damper (TMD) is coupled with an inerter, a two-terminal device resisting the relative acceleration of its terminals, in various tuned mass-damper-inerter (TMDI) topologies to suppress excessive wind-induced oscillations in tall buildings causing occupant discomfort. A parametric numerical study is undertaken involving a top-floor-TMD-equipped planar frame accurately capturing the in-plane dynamic behavior of a 74-story benchmark building exposed to a quasi-stationary spatially correlated wind-force field accounting for vortex shedding effects in the across-wind direction. It is found that the TMDI reduces peak top-floor acceleration more effectively than the TMD by considering smaller attached-mass values, and TMDI topologies in which the inerter spans more stories in linking the attached mass to the host structure. Moreover, the inclusion of the inerter dramatically reduces the TMD stroke, and it has been verified that the magnitude of the developing inerter forces can be readily accommodated by the host structure. Pertinent illustrative examples are included showcasing that the TMDI meets code-prescribed serviceability design requirements for new tall buildings using significantly smaller attached mass compared with the TMD, and that inerter devices can be used to upgrade the performance of existing TMD-equipped tall buildings without changing the attached mass.

Elastic buckling and second-order analyses are conducted to establish a more rigorous design procedure for single-level guyed towers, in which the interrelationship between the strength and rigidity requirements of the guys are considered to provide adequate lateral bracing. First, the guyed tower is simplified to a laterally braced column using an equivalent spring model for the guy action. Then, elastic buckling analysis is conducted to investigate the buckling axial force and the bracing rigidity requirement of an ideal laterally braced column. Using the exact stability stiffness matrix, the eigenproblem is formulated and solved. The influences of base fixity factor and lateral bracing rigidity on the buckling axial force are discussed. Second-order analysis is conducted to examine the inverse relationship between the strength and rigidity requirements in the lateral bracing design of a real column with initial imperfections and lateral loads. The differential equation of equilibrium for the laterally braced column considering geometric nonlinearity is established and solved. The lateral bracing strength limit is determined for guyed towers and the bracing rigidity requirement is formulated based on this strength limit. Finally, the design procedure and a design example are presented in three parts: tower stability design, guy rigidity design, and tower detailing and strength examination. Design implications for multilevel guyed towers are further noted.

Steel arches are applied in many engineering structures because of their excellent capacity to resist various transverse loadings. Modified (or normalized) slenderness plays an important role in the strength design of steel arches. The elastic lateral-torsional buckling load of steel arches is essential in calculating the modified slenderness for the out-of-plane strength design. This paper is concerned with analytical investigations of the elastic lateral-torsional buckling of steel pin-ended arches having in-plane rotationally restrained ends under an arbitrary radial concentrated load, which has not been reported in the literature. Nonuniform unsymmetrical distributed internal actions are produced by the arbitrary load and are significantly influenced by the load position. The arch suddenly reaches its ultimate resistance in a lateral-torsional buckling mode when the internal actions reach certain values. This paper conducts a theoretical investigation into the elastic lateral-torsional buckling of steel arches and derives the analytical solution for the buckling load based on accurate internal forces obtained by an exact prebuckling analysis. The fourth-order differential equations in terms of axial and radial displacements, which are successfully used for the prebuckling analysis of steel arches under symmetric loads, are found to be difficult to solve for steel arches under an arbitrary concentrated load. A proper method is explored and found useful for accurately determining the prebuckling internal forces. The analytical solutions for the elastic lateral-torsional buckling load based on the accurate prebuckling internal forces are compared with the independent finite-element results, and the comparisons show very good agreements between them. The effects of the load position on the lateral-torsional buckling loads of arches are investigated. It is found that the buckling loads are significantly influenced by changes in load position. The lateral-torsional buckling load increases as the load position moves away from the crown of the arch. The influence of the load position on the lateral-torsional buckling load of steel arches with a rectangular section is slightly significant than that of steel arches with an I-section. The elastic lateral-torsional buckling load obtained in this paper provides a sound basis for out-of-plane strength studies of steel arches in the future.

Recent experimental and computational studies have shown that the inelastic behavior of deep steel columns, where the cross-section depth is substantially greater than the flange width, is not yet well understood. To address this shortcoming, detailed finite element models that are validated using available experimental data, are used to study the response of deep steel columns subjected to combined axial and lateral loading. Two loading protocols are considered: (1) members that undergo monotonic lateral loading under a constant compressive force until failure (load then drift, i.e., LTD protocol); and (2) members that are subjected to various initial axial loads, displaced to a specified drift and then further loaded until failure (drift then load, i.e., DTL protocol). The loading protocols are designed to determine the effect that initial axial load, axial shortening, and local buckling effects play in predicting the failure mode and axial resistance of the member. Regression analysis is performed on the results to determine which parameters are most significant. The simulation studies show that global out-of-plane slenderness is a key parameter influencing behavior and that the effective buckling length of deep steel columns could be substantially greater than its initial value, a finding that has implications for seismic design.

Wind-induced vibrations of the Hardanger Bridge deck were studied with reference to turbulence characteristics at the bridge site to evaluate the performance of the state-of-the-art methods for buffeting response analysis. Long-term monitoring data from an extensive monitoring system were used to obtain the bridge vibrations and wind characteristics. The acceleration response of the bridge was calculated in the frequency domain using multimode buffeting theory. Design regulations were used directly and also modified using measurement data to deduce the wind turbulence spectra. The aerodynamic properties of the bridge section obtained from previous wind tunnel tests were used in the analyses. The predicted root mean square acceleration response was compared to the measured response. The analysis using the design methodology gave underestimations of the measured responses. The use of average values of wind statistics obtained from the monitoring data only slightly improved the results. When the variability of the wind field was reflected into the design method by using the probability distributions of the wind field parameters, more satisfactory design curves were obtained.

In this paper, the results of an experimental investigation on the characterization of a compliant liquid column damper (CLCD) are presented to validate its tuning criterion and to establish the damping mechanism of the system. The experimentally obtained frequencies are found to be very close to those obtained from a coupled eigenvalue analysis of the CLCD model. The orifice head-loss coefficient is evaluated and thereby the CLCD damping is estimated. It is established that effective damping is provided by the oscillating liquid column through the orifice(s) even at the nonresonant liquid frequency. A SDOF structure-CLCD system is also excited experimentally. The experimentally evaluated structural response mitigation achieved by the CLCD is satisfactory and quite close to the results obtained by a simulation study.

The relatively high story shears observed in inelastic dynamic analysis of shear wall buildings are attributed to higher mode effects. At the same time, soil-structure interaction can alter the frequency content of incident ground motions. This study examines the effect of base-slab averaging on peak story shears for an eight-story reinforced concrete shear wall building. Base slab averaging was found to reduce peak story shears. The reduction in peak story shears was found to be a function of the characteristic period of the ground motion; the largest percentage reductions are found for ground motions having the smallest characteristic periods.