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This paper discusses the results of 1∶25 scale shake table tests evaluating the seismic response of multiblock tower structures (MTSs) conceived as energy storage systems. The tests described here are a part of a comprehensive research campaign involving smaller physical models, computational model validation, and the theoretical background required to compare results across scales. The 6.46-m-high MTSs consisted of over 7,000 concrete blocks stacked vertically without any bonding agent, interacting only by friction and rocking. Three MTSs were tested under two different ground motions. Dynamic digital image correlation (DIC) and low-cost micro electrical mechanical system (MEMS) accelerometers were used for dynamic response measurements. Towers 1 and 3, subjected to repeated strong-intensity earthquake ground motions, collapsed during the third repetition due to the accumulation of residual displacements. Tower 2 was subjected to a single near-fault ground motion representing an extreme event and collapsed during the test. Different collapse mechanisms were identified in the test program. Data collected from individual blocks showed in-plane and out-of-phase block rotation and sliding, which contributed to the system's energy dissipation during the tests. [ABSTRACT FROM AUTHOR]

Predicting the moment-rotation response parameters of semirigid steel connections can be challenging given the many components contributing to the connection's elastic and plastic deformations. This is the case for the popular flush endplate beam-to-column connections (FEPCs). The literature has highlighted the limitations of current analytical, mechanical, and traditional empirical models in providing accurate predictions of the FEPCs' moment-rotation response. Considering this limitation, machine-learning methods have gained wide attention recently in structural engineering applications to address problems associated with complex structural deformation and damage phenomena. To that end, the superior nonlinearity of artificial neural networks (ANN) is employed herein to predict the response characteristics of FEPCs. A large data set of about 200 specimens, collected from past experimental programs, is utilized to train the ANN for predicting the bilinear response of FEPCs including strain hardening. The paper describes the deduction of the response parameters from test data using data fitting, the determination of significant geometric, material, and layout features, the ANN architecture and algorithms, and the accuracy metrics of the new model. The Shapley algorithm is used to explain the inner workings of the model. A computer tool as well as a descriptive guide to the mathematical construction of the ANN are provided to aid with model implementation in practice. [ABSTRACT FROM AUTHOR]

This paper presents an extensive numerical study on the seismic performance of steel eccentrically braced frames (EBFs) designed according to the ASCE 7-16 standard. A series of EBF building structures ranging from 2 to 12 stories located in downtown Los Angeles are designed with different yielding links, including conventional and replaceable links. The performance of the structures is investigated through nonlinear time-history analyses (NLTHAs) under a suite of 40 ground motions, selected and scaled to match the target uniform hazard spectrum. The peak deformations are first examined to assess the performance of the buildings as well as the design procedure. Residual deformations are also evaluated and critically compared with acceptable limits, to provide insight into the downtime and recovery time of EBFs after major earthquakes. Previous studies have demonstrated that the response of stable yielding systems to major earthquakes is often accompanied by significant residual deformations, and that residual drifts exceeding 0.5% can cause hindrance to the buildings occupants. In EBFs, in addition to residual drifts, residual link rotations are also relevant and expected to be more severe due to the localization of inelastic deformations in the yielding link. For replaceable modular yielding links, significant residual link rotations after major earthquakes will hinder repairs and the link replacement process, which is one of the important design objectives. The performance of EBFs is also compared with what was observed in previous studies for buckling restrained braced frames and special moment resisting frames. In the end, the results from the extensive NLTHAs are used to establish a relationship between peak drifts and peak link rotations in EBFs. [ABSTRACT FROM AUTHOR]

Mitigating tornado damage remains a critical challenge for communities throughout much of the United States. Enhanced construction techniques typically used in hurricane-prone regions are often recommended as at least part of the solution, but the effectiveness of these techniques lacks empirical evaluation. This study investigates the performance of modern wood-frame residential structures in Arabi, LA, constructed to hurricane-resistant standards, that were impacted by a strong tornado on March 22, 2022. Field teams deployed beginning March 25, 2022, just three days after the tornado touched down, capturing perishable data on the building performance using vehicle-mounted surface-level panoramic cameras, forensic engineering investigations, and unmanned aerial systems. This paper describes the field deployments and identifies common failure mechanisms observed by the field teams. Analytical fragility functions are developed based on the load path observations and compared to empirical fragility functions generated from linking the building performance observations with wind speed estimates at each building derived from a parametric wind field model conditioned to tree-fall patterns. The study finds that despite the frequent use of hurricane-resistant hardware, such as hurricane straps and anchor bolts, key weak links elsewhere in the load path compromised the resistance and led to premature failures. The agreement between the empirically- and analytically-derived fragility functions was lacking, demonstrating the challenges that remain in understanding near-surface tornado wind loading and structural response. Nonetheless, the study provides a consensus framework for future tornado assessments that can help improve our understanding of tornado loading through the utilization of reconnaissance data. Further, the study findings on deficiencies in the load paths of homes in hurricane-prone regions have practical value to risk assessments and future construction practices. [ABSTRACT FROM AUTHOR]

Shape memory alloys (SMAs) show great potential in self-centering structures because of their appealing superelastic feature and good energy dissipation capability. The mechanical properties of SMA bars have been extensively studied over the past decades. However, the characteristics of smooth surface and poor machinability of the SMA bars, especially the widely used nickel–titanium SMAs, bring challenges to the anchorage systems in practical applications. This existing limitation is especially prominent for SMA bars designed to be used at the critical deformation locations of structural members or in seismic devices experiencing extreme working conditions. For this reason, this paper develops a novel hybrid threaded-swaged anchorage system to overcome the limitations of the current SMA mechanical splices. The uniaxial behavior of the threaded-swaged anchorage systems under different loading conditions was investigated experimentally with emphasis on the seismic application-oriented responses. Furthermore, the influence of eccentricity on the anchorage system was also considered to evaluate the SMA bars with large end rotation induced by the rocking behavior of the self-centering structures during earthquake shaking. Test results reveal that the performance of the proposed anchorage system is satisfactory with stable behavior under different loading conditions, which can provide a promising anchorage solution for SMA bars used in seismic resilient design. Moreover, a practical design method for this anchorage system is proposed for implementation in seismic applications. [ABSTRACT FROM AUTHOR]

Elastomeric isolation bearings exhibit complex coupled horizontal-vertical behavior. Most existing macroscopic models simulate the quasistatic test results well but have deficiencies in simulating the dynamic behavior of bearings. In this paper, the experimental observations of previous dynamic bearing tests were investigated. The simulation capacity of existing macroscopic models was checked by comparison with the test data. The results show that the calculated axial load and hysteresis loops exhibit undesired oscillations under dynamic excitation. The intrinsic deficiency of existing models in simulating the dynamic response of a bearing was identified as the coupling or off-diagonal terms in the tangent stiffness matrix and the variation of vertical stiffness of the model. Motivated from this key observation, a new macroscopic model was developed to account for the dynamic behavior of bearings, followed by the suggestion of its numerical implementation. Through the introduction of a new axial load expression, the tangent stiffness matrix of the new model was semidecoupled, and the vertical stiffness of the new model remains unchanged, which reduced the interaction between the horizontal and vertical behavior. The simulation capacity of the new model was then validated by comparison with previous test data. The results show that the new model effectively captures the axial load variation and hysteresis loop of the bearings under dynamic excitations. Moreover, it was found that the consideration of the bearing height improved the simulation accuracy, and the size effect of the bearing is critical for isolated structures with large bearing-to-superstructure-height ratio, such as low- to medium-span bridges. [ABSTRACT FROM AUTHOR]

This paper investigates experimentally and numerically the buckling behavior of three-layered cross-laminated timber (CLT) panels under in-plane axial compression. The main aim is to assess the panels' ultimate limit load and their typical failure mechanisms. A total of 14 specimens were tested. Seven of them were homogeneous (HO series), entirely made of beech, whereas the others were hybrid (HB series), made of beech (outer layers) and Corsican pine (inner layer). The tests gave evidence of a rather stable column buckling capacity for CLT panels, with evidence of major failure mode due to bending. In some cases, rolling shear and delamination were highlighted as additional failure mechanisms. Finally, further assessment of experimental evidence is provided by extended analytical calculations (based on existing formulations, including the Eurocode 5 approach) and even finite-element (FE) numerical analyses for the examined three-layer CLT compositions. Comparative results are discussed in terms of structural performance, capacity, and weakness of analytical models for CLT solutions. [ABSTRACT FROM AUTHOR]

This correction notice addresses errors in the article "Collapse Resistance of Reinforced Concrete Frame Beams under Sustained Loads" by Ghazaleh M. Laleh, Ying Tian, and Sarah L. Orton. The errors occurred when converting imperial units to metric units in the "Bending Moment" section of the paper. The correction involves dividing the numbers on the horizontal axes of Figures 16 and 17, as well as the vertical axis of Figure 18, by 12. Additionally, two values in the last paragraph of this section need to be changed. The corrected figures are provided in the erratum. The purpose of this correction is to ensure the accuracy of the published version. [Extracted from the article]

The dynamic characteristics of large-scale civil structures are generally evaluated by performing operational modal analysis based on ambient vibration records measured by contact sensors, e.g., accelerometers. However, owing to accessibility restrictions, it is sometimes inconvenient to conduct dynamic response measurements by contact sensors. Therefore, there is a need to adopt noncontact measurement technologies for monitoring the dynamic performance of civil structures. On the other hand, only response records are available for operational modal analysis on account of the unknown nature of ambient excitations, which may lead to uncertainties in modal estimates, particularly damping estimates. In this regard, this paper adopts a combined method consisting of modal decoupling, natural excitation technology, and an eigensystem realization algorithm to perform high-accuracy modal identification with uncertainty quantification. Through numerical simulation study of a frame structure, the accuracy and effectiveness of the combined method for identifying structural modal parameters are verified. Then, taking advantage of noncontact simultaneous multipoint measurements by an interferometric radar system and the combined modal estimation scheme, the noncontact operational modal analysis strategy is utilized to evaluate structural dynamic characteristics of a supertall building after experiencing a sudden vibration event that attracted considerable concern from the public. The purpose of this study is to provide a practical and reliable means of conducting modal estimation with uncertainty quantification from a single measurement and suggest a noncontact modal analysis strategy for structures with difficulty installing contact sensors. [ABSTRACT FROM AUTHOR]

Steel fibers in ultra-high performance concrete (UHPC) have been demonstrated to improve resistance to crack growth, decrease deflection, and increase fatigue life under cyclic loads. Using steel fibers as shear reinforcements, this paper investigates its effect on the postcracking shear fatigue behavior of nonstirrup UHPC beams. The study involved five UHPC beams comprising two static and three fatigue specimens to test the effects of the upper fatigue load, steel-fiber ratio, and stirrup ratio on the shear fatigue response. The test results showed that increasing the initial crack width in the nonstirrup UHPC beam from 0.05 to 0.2 mm (the equivalent of doubling the upper fatigue load) decreased the fatigue life from over two million to 24,875 cycles. The use of steel fibers in place of stirrups increased the residual-to-static strength and residual-to-initial stiffness ratios by 5% and 16%, respectively, after two million cycles. Compared with the specimen with stirrups, the steel-fiber-reinforced specimen had a lower midspan fatigue deflection-to-ultimate static deflection ratio owing to the relieved fatigue strain localization and increased tensile steel reinforcement-UHPC bond fatigue strength. The current codes predict the shear fatigue strength conservatively. A calculation model for accurately predicting fatigue deflection was proposed and compared with the existing test results. A future study on the wider parametric analysis and large-scale beam tests on the fatigue performance of these beams should be conducted. [ABSTRACT FROM AUTHOR]

Displacement-based design (DBD) methods were originally developed in the 1990s for concrete structures and later modified for light-frame wood buildings and mass timber buildings. DBD methods use displacement as the design criterion to minimize economic losses, control component damage, and enable rapid return to functionality for increased resilience. This paper introduces a performance-based design check procedure that uses the direct displacement-based design (DDD) method and numerical pushover analysis for the design of cross-laminated timber and light-frame shear (CLT-LiFS) buildings. Prestressing CLT panels with embedded posttensioning high-strength steel cables or external high-strength steel rods enable them to provide robust lateral load resistance and self-centering capacity. LiFS walls offer additional lateral load resistance and energy dissipation through the slip of nail connections. A six-story CLT-LiFS building was used as a design example meeting three performance levels (damage limitation, life safety, 15 and collapse prevention) based on ASCE/SEI 41-17 criteria. Each performance level corresponds to a set of three criteria: interstory drift limits, cable stress limits, and CLT compressive strain limits at the rocking interface. The design was checked using a series of nonlinear time history (NLTH) analyses with a suite of ground motion records. The results from the design check procedure and the statistical distributions of performance criteria from NLTH analysis confirmed that the six-story CLT-LiFS building met performance expectations. Additionally, a collapse fragility curve was developed to provide a comprehensive understanding of the building's behavior. [ABSTRACT FROM AUTHOR]

The first step in current methodologies for the (probabilistic) performance-based fire safety design and assessment of structures is characterizing fire hazard scenario(s). Next, structural response analysis is performed to estimate hazard consequences in terms of damage or loss metrics of interest. These metrics are eventually appraised to verify whether various performance objectives are achieved and design iterations are needed. Nevertheless, such approaches rely on preliminary assumptions on the structural configuration and features characterizing scenarios used as thermal inputs. Consequently, they do not fully exploit the fire–structure coupling effect, where fire affects a structure, and the characteristics of the structure also affect the combustion process and fire dynamics. Indeed, the structural design choices define the fire scenarios that could potentially affect the structural and nonstructural performance. This paper introduces a consequence-oriented fire intensity optimization (CFO) approach to the fire safety design of structures to address such limitations. The proposed approach considers fire scenarios as additional design variables and delivers them as procedure outputs, optimizing the balance between increasing structural capacity and decreasing fire intensity. Furthermore, it evaluates the effect of input uncertainties through Monte Carlo sampling. A single-span bridge subject to a car fire is used to showcase the proposed approach. For this case study, it is shown that fire scenario characteristics (fuel bed and traffic load positions, heat release rate history) maximizing consequences are strongly correlated to the structural features and cannot be set a priori. Finally, design decisions exploiting the described coupling effect to achieve various performance objectives are discussed. Overall, the proposed approach highlights the benefits of enhancing the fire and heat transfer model's capability to capture the fire–structure coupling effect for achieving more optimized design solutions. [ABSTRACT FROM AUTHOR]

This paper presents a design approach, the direct stiffness–strength method (DSSM), for the strength prediction of sheathed cold-formed steel (CFS) structural members. The DSSM considers each sheathing–fastener connection as a bracing point and incorporates its stiffness and strength in the CFS wall panel design. The DSSM is formulated and validated based on large experimental test results. The motivation for this work is to address research gaps in the latest American Iron and Steel Institute (AISI) standards for the sheathing braced design of CFS structural members. A total of 41 individual sheathing–fastener connection tests were carried out, including parameters such as four different sheathing board types (to account for the performance of different sheathing) and seven different dimensions of the CFS Z-sections (to account for the slenderness). A new set of expressions was formulated to predict the stiffness and strength of the individual sheathing–fastener connections (bracing points) based on the observations from tests. A design-oriented assessment (comparing the design results with full-scale wall panel test results) indicated that the expressions formulated for DSSM are appropriate for the use of sheathed CFS Z-section member design. Further, this study used a design example to demonstrate the appropriateness of the DSSM approach. Since the introduction of the sheathing braced design concept in conjunction with the direct strength method (DSM) established by the American Iron and Steel Institute in RP13-1, this approach has gained traction among researchers to further enhance it for the various failure modes of the CFS structural members. However, there is an inconsistency in the sheathing bracing design concepts of the AISI design standards. The proposed DSSM is a simple one; it considers each sheathing fastener connection as a bracing point and incorporates its stiffness and strength in the CFS wall panel design. This proposed DSSM can be completed in two steps by checking the bracing ability of the provided sheathing. The DSSM method can be used with any design specification for determining the moment capacity of the CFS member with the contribution of the sheathing board. The design steps involved in DSSM are demonstrated with flowcharts and a design example. The DSSM proved that use of sheathing boards can eliminate the additional steel bracings at the intermediate length and breadth of the CFS wall panels, but steel bracings are required at the building corners for stability. This design method can realize up to a 15% reduction in steel consumption in the CFS building construction. [ABSTRACT FROM AUTHOR]

This paper presents an experimental study of the seismic behavior of steel gravity frames with concrete on metal deck floor systems using multibay test specimens subjected to cyclic lateral loads. Fully bolted double-angle connections were used for the primary gravity connections under investigation. Key design variables and construction details under investigation include metal deck orientation, positioning of metal deck seams, and increased deck reinforcing ratios around the columns. Test specimens were simultaneously subjected to gravity loads and quasi-static displacement-controlled cyclic lateral loads. Results show that composite gravity connections exhibit substantial flexural stiffness, strength, and ductility, with some differences in response depending on connection design variables and construction details. Results from the system-level experiments using multibay test specimens demonstrate significant differences compared to previous subassembly tests, which indicates that the moment-resisting capacity of connections may potentially be underestimated in subassembly level tests. [ABSTRACT FROM AUTHOR]

A variety of self-centering devices and structural systems have been proposed and investigated in recent years to eliminate or reduce postearthquake repair, but so far their applications are still very limited. This paper reports the seismic resilience enhancement of an irregular space structure by using friction-damped self-centering tension braces (FSTBs). First, the configuration, performance, and numerical model of FSTBs are introduced, and then a seismic design procedure for enhancing the seismic capacity of a torsional irregular structure is proposed. Taking the terminal building at the Harare Airport, a lifeline project in Zimbabwe, for example, unidirectional and three-dimensional nonlinear dynamic analyses were conducted on the building designed with and without FSTBs. The result shows that FSTBs can significantly reduce both story drifts and residual story drifts of the bottom reinforced concrete frame and displacements of the steel roof. To this end, the field assembly of FSTBs is briefly reported. The presented study provides references to the use of self-centering devices in seismic resilience upgrades of important engineering projects. [ABSTRACT FROM AUTHOR]

The composite pier, which consists of ultra-high-performance concrete (UHPC) and normal strength concrete (NSC), is a promising option for practical engineering due to its remarkable mechanical performance. However, the cyclic behavior and seismic design mechanism of the composite pier have not been thoroughly investigated. This paper aims to study the cyclic performance of the composite pier by conducting cyclic tests on 10 specimens. The thickness of the UHPC tube, strength of reinforcement, spacing of stirrups, and other parameters are considered. The crack distribution, hysteretic response, and failure modes are observed and analyzed. Results show that the composite pier exhibits good crack-control ability, large bearing capacity, and effective energy dissipation. The expansion of the inner NSC may exacerbate the buckling of the UHPC tube, thus leading to more severe seismic damage. To further investigate the composite pier, a numerical model is established to analyze the optimal thickness of the UHPC tube. The ultimate state of the composite section is taken into consideration, and the upper and lower limits of the height of the compression zone are proposed. Based on the parametric analysis, a recommended range of the UHPC tube thickness is derived. [ABSTRACT FROM AUTHOR]

In this paper, the problem of wind-induced vibration in tall buildings is addressed by utilizing a new type of damper, the tuned mass damper fluid inerter (TMDFI). The TMDFI incorporates an inerter in the classical tuned mass damper (TMD), which is physically realized using fluid in a helical channel. The device arrangement is optimized using a proposed nonlinear procedure and it is demonstrated through numerical simulations that the application of the TMDFI achieves excellent vibration control performance. Specifically, it has been found that the TMDFI requires lower mass and stroke requirements than traditional passive dampers while achieving comparable or better vibration reductions. It has been shown numerically that the damper demonstrates excellent vibration control capabilities by reducing the RMS displacement of the building by ≈50% and the RMS acceleration by 35%–80%. The results presented here show that the TMDFI is a damper capable of mitigating wind-induced vibrations in tall buildings with relatively simple design requirements. This new damper has the potential to significantly improve the safety, comfort, and durability of tall buildings subjected to wind loads. [ABSTRACT FROM AUTHOR]

Steel multitiered concentrically braced frames (MT-CBFs) not specifically detailed for seismic resistance with a response modification factor of R=3 are permitted in moderate seismic regions. Past research studies, however, have raised concerns regarding the seismic performance of MT-CBFs and CBFs designed using R=3 provisions, namely the stability of columns in MT-CBFs and connection limit states in R=3 CBFs. This paper examines the seismic response of R=3 MT-CBFs and proposes a design method to improve their seismic performance. A set of 16 prototype R=3 MT-CBFs, ranging from 8 to 20 m tall with two to five tiers and located in a moderate seismic area, was selected and designed in accordance with 2016 US design guidelines. Nonlinear response-history analyses were then performed to examine the seismic response of these frames using fiber-based numerical models. R=3 MT-CBFs designed to 2016 design guidelines are shown to experience premature fracture in brace-to-beam/column connections in a single tier, which imposes high in-plane bending demands on columns and in some cases, leads to column instability or a tier-sway mechanism. New seismic design recommendations, including requirements for intermediate struts, columns, and tier drift, are proposed. The design method aims to prevent column instability or a tier-sway mechanism and protect brace connections from excessive deformation. [ABSTRACT FROM AUTHOR]

This paper proposes a probabilistic metamodeling framework for predicting the joint probability distribution of the interstory drift ratio (IDR) profile of multistory buildings. IDR is an engineering demand parameter that correlates well with structural and nonstructural damages. However, the use of IDR for regional loss estimation has not been practiced due to the high computational cost of such estimations. The metamodel proposed herein efficiently estimates the IDR profile while accounting for the cross-correlations. This facilitates the use of component-level damage and consequence models for regional loss estimations and significantly refines the resulting risk estimates compared with the current state of practice in regional risk analysis, which relies on a single-degree-of-freedom representation of a building. The proposed framework employs multivariate Bayesian regression calibrated using a large data set produced using detailed nonlinear time-history analyses. To showcase the methodology, metamodels are developed for predicting the IDR profile of special steel moment frame buildings of various heights ranging from three to 12 stories. The resulting models are validated against the output of detailed multidegree-of-freedom models at different levels of ground motion intensity. Finally, the proposed metamodel is employed for estimating the seismic loss of a nine-story building, and the results are compared with the loss using two extremes of modeling in terms of refinement and computational effort: the FEMA P-58 approach and the Hazus approach. The results confirm that the proposed metamodel significantly refines the loss estimates compared with those of Hazus with a computational effort that is four orders of magnitude smaller than that required by the FEMA P-58 approach. [ABSTRACT FROM AUTHOR]

This paper presents an experimental study on the multidirectional cyclic lateral-load response of post-tensioned self-centering (SC) cross-laminated timber (CLT) shear walls. SC-CLT shear wall damage states are introduced and qualitatively defined in terms of the repairs needed to restore the lateral-load response of the SC-CLT wall. A comparison between SC-CLT wall damage states under unidirectional (in-plane) and multidirectional (in-plane and out-of-plane) lateral loading is presented. The experimental results show that the initiation of SC-CLT wall damage occurs at smaller story drifts under multidirectional loading compared to unidirectional loading. Engineering demand parameters (EDPs) are used to quantify the SC-CLT wall damage states. Uncertainty in the EDP value when a damage state occurs is considered and quantified. Using the experimental results, component (i.e., a CLT wall panel corner) and system (i.e., an entire SC-CLT wall) fragility functions are developed and presented. [ABSTRACT FROM AUTHOR]

When designing steel members with nonsymmetric cross sections, it is essential to consider twisting effects when performing stability checks via second-order analysis according to the ANSI/AISC 360-22. Existing line-element formulations for nonsymmetric sections are mostly derived based on thin-walled assumptions, leading to an overestimation of member strength due to the inaccurate prediction of member behavior, especially when the cross sections have moderate wall thickness. This paper proposes an efficient line-element method for second-order analysis of steel members with nonsymmetric thick-walled sections considering the warping degree of freedom (DOF) and the twisting effects along with the transverse shear deformations. Additionally, a two-dimensional (2D) finite-element cross section analysis method employing the constant strain triangle (CST) element is developed to calculate the section properties for arbitrary cross sections, including the Wagner and the shear coefficients. The proposed method is implemented in the educational structural analysis software MASTAN2 and verified through two sets of examples. [ABSTRACT FROM AUTHOR]

In the presence of softening section constitutive relations, classical beam theories predict erroneous strain singularities, and the corresponding force/flexibility-based (FB) beam-column element formulations result in strain localization and loss of response objectivity, i.e., divergence, rather than convergence, with progressive mesh refinements. To address this challenge, various FB element formulations have been proposed in the literature. One of these formulations is the so-called "gradient inelastic" (GI) FB formulation, which is a two-node element formulation that eliminates the strain localization and achieves response objectivity through strain gradient nonlocality relations. Although a single two-node GI element can effectively simulate an entire beam or column, simulating such a member via multiple two-node GI elements in series (e.g., to apply intermediate point loads, to more accurately capture geometric nonlinearities, or to represent cross-section variation) would not lead to accurate response predictions. This is because, in a model with multiple two-node GI elements in series, the nonlocality relations are not enforced at the intermediate/connection nodes between adjacent elements. Instead, end member boundary conditions (BCs) are enforced at those connection nodes because the two-node GI formulation has been designed to simulate an entire member. To tackle this shortcoming, this paper proposes an innovative multinode GI FB element formulation. To enforce the nonlocality relations at the connection nodes, two different sets of mathematically admissible section strain compatibility conditions (CCs) are adopted. The multinode formulations using both sets of CCs are evaluated through several simulation examples, including beams and columns subjected to various loads. The evaluations demonstrate the ability of both element formulations to produce objective softening responses, while one set of CCs is found to more closely predict the responses of previously tested RC beams under midspan loading. [ABSTRACT FROM AUTHOR]

While the use of cross-laminated timber (CLT) panels for building construction has increased over the last several decades, current standards and existing literature provide limited information regarding the design of CLT diaphragms or the prediction of their deflections when subjected to wind and strong earthquake motions. This paper presents the design and assessment of a CLT diaphragm that was part of a full-scale two-story structure subjected to shake-table testing. An analytical model is proposed for diaphragm deflection accounting for in-plane shear and bending stiffness, as well as the stiffness of various connections. Moreover, a refined numerical modeling strategy is proposed in order to consider phenomena such as panel-to-panel gap closure. Results indicate that the analytical model yields conservative results both in terms of deflections and forces when compared to the numerical model that simulates similar sources of strength and stiffness. The analytical model is suitable for the design of symmetric diaphragms with regular shapes, whereas the numerical model can also be used to model asymmetric diaphragms with irregular shapes. [ABSTRACT FROM AUTHOR]

Balloon-type mass timber shear walls are one of the most efficient structural systems to resist lateral loads induced by earthquakes or high winds. They are a viable solution for high-rise buildings because they have several key advantages, such as reducing connections and avoiding accumulating compression perpendicular to grain in the floors. This system, however, is not included in current Canadian building code and has no design guidelines in the Canadian timber standard, so it is out of reach of most designers. A multiyear research project has been initiated to quantify the system performance and develop the necessary technical information to codify balloon-type mass timber shear walls. In this paper, the limits for the building height of balloon mass timber shear walls were investigated theoretically. A mechanics-based analytical model was developed to analyze the building height limits governed mainly by the mass timber panels. The influence of loading types (seismic versus wind loads), lateral load levels, panel deformation contribution, seismic force modification factors, and vertical joints between panels on the building heights was investigated using the developed model. The results of this study will give a valuable insight into the seismic performance of balloon type cross-laminated timber (CLT) shear walls. [ABSTRACT FROM AUTHOR]

This paper presents experimental investigations on the lateral performance of cross-laminated timber (CLT) shear walls with customized self-tapping screw (STS) connections. The panel-to-base (hold-downs and shear brackets) and panel-to-panel (spline) connections were tested under quasi-static monotonic and reversed cyclic loading to derive design values of STS, which were shown to be 2.8–3.6 times higher than those calculated using the current Canadian timber design standard. Then, a total of 26 CLT shear walls, including single-, double- and triple-panel configurations, were tested, again under quasi-static monotonic and reversed cyclic loading. The shear walls consisted of five-ply, 139-mm-thick and 3-m-high CLT panels with aspect ratio of either 2∶1 or 3∶1 , and different numbers of STS in the connections. The shear wall strength and corresponding displacements increased with the number of screws in hold-downs and spline joints; further, it increased with number of connected panels and decreased as a function of aspect ratio. The data can be used for developing and calibrating numerical models to investigate the lateral responses of CLT shear walls with different configurations. [ABSTRACT FROM AUTHOR]

Protecting critical equipment in seismically excited buildings is essential to ensure functionality after an earthquake. Individual equipment or equipment sets can be seismically isolated from the building motion. Special isolators can be employed to mitigate the most severe accelerations that occur in the horizontal direction of a building. This paper presents the results of an investigation of the performance of an uncoupled bidirectional isolation system for horizontal isolation using a novel adaptive restoring force (ARF) device. The device changes the structural response transmitted to floor-mounted equipment by filtering the most intense portions of input floor acceleration histories to minimize the acceleration of the equipment and the stress demands imposed by the supporting structures. The ARF device utilizes restoring and damping elements to generate restoring forces that vary nonlinearly with displacement, resulting in a force–displacement curve with varying slopes and loading and unloading paths. The force–displacement relationship of the ARF device is characterized by high stiffness at small and large displacements, and low stiffness in between. A small-scale prototype was constructed to validate the ARF concept, and its force–displacement properties were observed for cyclic loading. A numerical model was developed that accurately predicted the relationship between the device force and displacement. The system's performance was evaluated through numerical analysis of equipment installed on different levels of multistory buildings subjected to measured floor accelerations. The results showed that the horizontal isolation system effectively limited the transmission of the floor accelerations to the equipment. Furthermore, the results showed that the isolation system transformed the seismic acceleration profile from a high-amplitude and -frequency signal to one with a low quasi-constant amplitude and low frequency, acting as a low-pass filter under the most intense time window of the floor acceleration. Protecting critical equipment can be a significant concern for those who manage or work in facilities vulnerable to earthquakes. This study presents a new technology for horizontal seismic isolation of equipment, the adaptive restoring force device, that effectively minimizes the damaging effects of earthquakes on floor-mounted equipment in multistory buildings. The ARF device protects equipment by filtering out the most intense and destructive vibrations accompanying earthquakes, thus reducing accelerations on the equipment and its supporting structures. It transforms high-amplitude and -frequency vibrations to lower, more-constant levels. Unique to the ARF device is its adaptability to work effectively on any floor of a building, even on rooftops, while allowing considerable relative movement between the equipment and the floor. The results of this study are promising—equipment experienced reduced and nearly constant low-frequency accelerations during simulated seismic events. Although further research is required to address more complex problems, such as building torsion and vertical seismic effects, preliminary findings suggest that the ARF device offers a practical solution for preserving vital floor-mounted equipment in multistory buildings in earthquake-prone regions. This device can prove invaluable as a tangible solution for businesses, industries, and hospitals dependent on critical equipment. [ABSTRACT FROM AUTHOR]

The present paper deals with the optimal design of nonprismatic beams, i.e., beams with variable cross section. To set the optimization problem, Euler-Bernoulli unshearable beam theory is considered and the elastica equation expressing the transverse displacement as a function of the applied loads is reformulated into a system of four differential equations involving kinematic components and internal forces. The optimal solution (in terms of volume) must satisfy two constraints: the maximum Von Mises equivalent stress must not exceed an (ideal) strength, and the maximum vertical displacement is limited to a fraction of beam length. To evaluate the maximum equivalent stress in the beam, normal and shear stresses have been considered. The former was evaluated through the Navier formula, and the latter through a formula derived from Jourawsky and holding for straight and untwisted beams with bisymmetric variable cross sections. The optimal solutions as function of material unit weight, maximum strength, and applied load are presented and discussed. It is shown that the binding constraint is usually represented by the maximum stress in the beam, and that applied load and strength affect the solution more than material unit weight. To maintain the generality of the solution, the nondimensionalization according to Buckingham Π -theorem is implemented and a design abacus is proposed. [ABSTRACT FROM AUTHOR]

Since the Ronan Point collapse in the UK in 1968, the progressive collapse analysis of residential buildings has gradually drawn the attention of civil engineers and the scientific community. Recent advances in computer science and the development of new numerical methodologies allow us to perform high-fidelity collapse simulations. This paper assesses different scenarios that could have hypothetically caused the collapse of the Champlain Tower South Condo in Surfside, Florida, in 2021, one of the most catastrophic progressive collapse events that has ever occurred. The collapse analysis was performed using the latest developments in the Applied Element Method (AEM). A high-fidelity numerical model of the building was developed according to the actual structural drawings. Several different collapse hypotheses were examined, considering both column failures and degradation scenarios. The analyses showed that the failure of deep beams at the pool deck level, directly connected to the perimeter columns of the building, could have led to the columns' failure and subsequent collapse of the eastern wing of the building. The simulated scenario highlights the different stages of the collapse sequence and appears to be consistent with what can be observed in the footage of the actual collapse. To improve the performance of the structure against progressive collapse, two modifications to the original design of the building were introduced. From the analyses, it was found that disconnecting the pool deck beam from the perimeter columns could have been effective in preventing the local collapse of the pool deck slab from propagating to the rest of the building. Moreover, these analyses indicate that enhancing the torsional strength and stiffness of the core could have prevented the collapse of the eastern part of the building, given the assumptions and initiation scenarios considered. Building catastrophic collapses can cause significant lives and economic losses. Poor design and maintenance, in combination with aging, will more likely increase, in the next years, the number of buildings potentially vulnerable to the risk of collapse, due to either seismic, accidental, or degradation actions. This research focuses on the analysis of the Champlain Tower South condo collapse, which occurred in Surfside, Florida, in 2021. Different hypothetical collapse scenarios were simulated, comparing the analysis results with the actual evidence of the collapse. The analyses have shown that the degradation of the pool deck slab, due to corrosion, may have contributed to the collapse of the building. Finally, two different minor revisions of the original design of the building were analyzed to reduce the risk of failure and understand how the collapse of similar residential buildings could be prevented. [ABSTRACT FROM AUTHOR]

In this paper, the optimum outrigger locations of the outrigger-braced structure are studied by considering the influence of the core-wall width and structural asymmetry. The axial forces in the columns are taken as unknowns, and the compatibility equations of the columns' axial deformation are formulated in terms of the axial forces. Then, the equations governing the optimum locations of the outriggers are formulated to minimize the top drift of the core wall. After that, the parametric analysis on the optimum locations of outriggers, drift-reduction efficiency, and moment-reduction efficiency in the base of the core wall are conducted numerically. The influences of different structural parameters on the optimum locations of outriggers, drift-reduction efficiency, and moment-reduction efficiency in the base of the core wall are all discussed. The change of optimum outrigger locations with the increase of ω is obviously when r=2 or η=0. For the structure with a larger core-wall width, a smaller number of outriggers can be adopted regarding the drift or moment-reduction efficiency. For instance, the drift or moment-reduction efficiency of the structure with one outrigger when η=0.5 is close to the drift or moment-reduction efficiency of the structure with two outriggers when η=0.25. Some results are presented for reference in the preliminary structural design of asymmetrical outrigger-braced structures with limited core width. [ABSTRACT FROM AUTHOR]

Corrosion-induced concrete cracking significantly weakens the integrity, serviceability and durability of reinforced concrete (RC) structures. Existing reliability analysis of corrosion-induced concrete cracking often considers the corrosion of reinforcement as a uniform process, in favor of implementing the analytical formulation of corrosion rust progression. However, corrosion distribution in RC structures is seldom uniform around the steel reinforcement, hence the corrosion-induced pressure. Thus, considering the nonuniform corrosion process in the reliability analysis becomes important. This paper develops a time-dependent reliability methodology, combining mesoscale heterogeneous fracture modeling and a state-of-the-art machine learning algorithm, to assess the serviceability of the RC structures subjected to nonuniform development of corrosion. The effects of critical crack width, corrosion nonuniformity, chloride content, temperature, and relative humidity on the failure probability are investigated. The worked example demonstrates the importance of considering the nonuniformity of the corrosion product distribution, which provides reliable evaluation of the remaining safe life of RC structures compared with the use of a uniform corrosion model. The developed unified assessing methodology for corrosion of RC structures can serve as a useful tool for engineers, designers, and asset managers for their decision making with regard to repair and maintenance of corrosion-affected RC structures. [ABSTRACT FROM AUTHOR]

This paper investigates the progressive collapse behavior of composite beam-column connection subassembly under column removal scenarios. An analytical model is proposed based on the rigid-plastic assumptions, in which the plastic hinges and inelastic rotations are assumed to develop concentratedly at only the connection interfaces, whereas the remaining parts are rigid except for the axial shortening/lengthening deformation when subjected to compressive/tensile forces. The component-based joint model proposed by Eurocodes is utilized to approximate the axial and plastic moment resistances of composite beam-column connections. The method to determine the force-displacement relationship of each connection component is presented in detail, particularly for the concrete slab and profiled steel decking where the actual nonuniform stress distributions along the slab thickness and width are carefully considered. By comparing with the published test results of composite joints under respective hogging and sagging moment, the proposed rigid-plastic model is capable of predicting the progressive collapse behavior of composite beam-column connection subassembly with reasonable accuracy. Based on the verified model, a parametric study is conducted with focus on the effect of lateral restraint stiffness on the collapse-resisting capacity of composite beam-column connection subassembly under column removal scenarios. [ABSTRACT FROM AUTHOR]

This document is a correction notice for the article titled "Behavior and Design of Steel-Concrete Composite Columns Subjected to Combined Axial Compression and Biaxial Moment" by Amirfarzad Behnam and Mark D. Denavit. The correction states that Equation (9b) in the published paper is incorrect and provides the correct equation. The authors apologize for the error and note that the correction has been made only in this erratum to preserve the published version of record. [Extracted from the article]

Derivatives of nonlinear dynamic response are calculated in an exact and efficient manner with respect to material, geometry, mass, and damping parameters. Developments are presented for the Rayleigh and modal damping options that use the updated tangent stiffness. The calculation of exact response sensitivities for those options requires the calculation of derivatives of eigenvalues and eigenvectors; it is also shown that the third-order tensor formed by the derivative of the stiffness matrix with respect to the displacement vector is needed. That tensor, which amends the coefficient matrix of the system of equations that governs the response sensitivities, is nonzero for materials with continuously varying stiffness. The Bouc–Wen material model exhibits that feature and is selected to demonstrate the developments. Correct differentiation and assembly at the material, section, and element levels are highlighted. The results, verified by finite difference, suggest that the sensitivity of the response is influenced by the choice of damping model, strongly for some parameters, particularly when higher modes contribute to the nonlinear structural behavior. [ABSTRACT FROM AUTHOR]

Significant research has been conducted in the field of high-strength RC. This body of work encompasses a wide range of topics from material behavior to seismic performance, which has been instrumental in shaping design codes for high-strength RC structures. However, a notable gap remains in understanding the postfire seismic behavior of high-strength RC members. This study addressed this gap by conducting experimental tests to explore the seismic behavior of high-strength RC columns after fire exposure. The experimental program subjected column specimens to both fire exposure and cyclic loading tests, with key variables including varying concrete strengths and a standard 2-h fire exposure. This study extensively analyzed the impact of fire exposure on seismic performance, focusing on temperature gradients, damage patterns, load-displacement hysteresis responses, displacement composition, and plastic region length. The results indicated that fire exposure caused more significant structural degradation in high-strength concrete (HSC) columns compared with normal-strength concrete (NSC) columns. Specifically, fire exposure moderately reduced the peak strength of NSC and HSC columns by 8% and 12%, respectively, and significantly decreased their initial stiffness by 48% and 55%, respectively. Despite considerable spalling in the cover concrete of the HSC column, the core concrete and longitudinal reinforcement remained largely intact, effectively sustaining the postpeak behavior under cyclic loading. Complementing the experimental work, the study also proposed suitable computational models to simulate the postfire seismic responses of NSC and HSC columns. These models aim to enhance the predictive understanding of structural behavior in postfire scenarios, contributing valuable insights for the design and assessment of fire-affected RC structures. [ABSTRACT FROM AUTHOR]

This study proposed novel designs for achieving self-centering (SC) behavior using superelastic shape memory alloy (SMA) buckling-restrained plates (BRPs). Compared with previous studies relying on small-diameter SMA bars, this study employed large-dimensional SMA plates that could provide sufficient strength for real construction projects. The design concept and configurations of SMA-BRPs were first introduced. Corresponding tests were then conducted. Three specimens were tested, including one that was unsatisfactory and two that were acceptable. Based on the initial examination of the behavior and failure mode of the unsatisfactory trial specimen, the corresponding modifications were made to achieve the improved performance of two acceptable specimens. Subsequently, the hysteresis and SC behaviors, energy dissipation capacity, and yielding strength degradation of the two acceptable specimens were investigated. Both specimens exhibited high-quality flag-shaped behaviors in their tension–compression cycles, with their strengths reaching around 200 kN under tension and more than 310 kN under compression, representing one of the largest strength values shown by a single SMA element in the literature. Asymmetric behavior was observed under tensile and compressive loadings, primarily due to the asymmetric behavior of the SMA base material, high-mode inelastic buckling under compression and friction between the SMA core plate and buckling-restraining device. After the tests, finite element models were developed to obtain an in-depth understanding of the detailed behavior of SMA-BRPs. The studies showed that SMA-BRPs successfully achieved the SC buckling-restraining design target. The design incorporating end restrainers was preferred due to its flexibility, which reduces application restraints. [ABSTRACT FROM AUTHOR]

This study builds on existing researches to further investigates cyclic responses of the steel tube-confined reinforced concrete (RC) columns, with a primary focus on those subjected to high-axial load. A total of eleven column specimens were tested under lateral displacement reversal and axial load of either 0.3Ag fcm,c or 0.5Ag fcm,c , where Ag and fcm,c refers to concrete cross section area and tested concrete strength of the column, respectively. Three specimens represented the conventional reinforced concrete (RC) columns while the rest were the steel tube-confined circular RC columns. The key test parameters included (1) amount of longitudinal reinforcement, (2) axial load level, (3) continuity of the confining steel tube, and (4) clear cover of the longitudinal reinforcement. Test results showed that all the steel tube-confined RC specimens sustained the target axial load and maximum lateral strength up to around 10% drift ratio. A simple strength model was proposed to reasonably estimate the maximum strength of the steel tube-confined RC columns. The flexural rigidity ratio, (EI)test/Ecm,cIg , for RC specimens and specimens confined by continuous steel tube ranged between 0.6 and 0.8, approximately. Specimens confined by the cutoff steel tube showed lower (EI)test/Ecm,cIg ratio between approximately 0.3 and 0.6. [ABSTRACT FROM AUTHOR]

A resilient dual frame-wall lateral force-resisting system, designed to mitigate frame-expansion challenges in self-centering structures, has been introduced. One notable obstacle encountered when applying direct displacement-based design (DDBD) to this dual frame-wall system is the ductility-damping relationship that can be used for estimating nonlinear structural responses. To address this issue, more than 3.5 million damping data points were generated through nonlinear time-history (NLTH) analyses by creating the linearized substitute system. These analyses span a broad range of parameters, including the fundamental period of the original system, ductility, normalized subsystem stiffness ratio, and post-yielding stiffness ratio of the subsystems. The results reveal that the equivalent viscous damping ratio (EVDR) exhibits significant period dependency for a wide range of periods. Both ductility and the subsystem stiffness ratio, which govern the hysteresis response area, exert a substantial influence on EVDR, except for the post-yielding stiffness ratio. Consequently, an EVDR model that takes into account the effective period, ductility, and normalized subsystem stiffness ratio was formulated and was validated using an additional data set of over 0.2 million data points. Ductility-period design displacement spectra were also proposed to illustrate the implementation of the proposed EVDR model and provide an easy way to understand the equivalent procedure. [ABSTRACT FROM AUTHOR]

A new type of buckling-restrained brace (BRB), called induction-hardened buckling-restrained brace (IHBRB), is proposed in this study. The IHBRB uses a round bar as the core steel and a hollow round section as the restrainer. The core steel undergoes partial induction hardening, which makes its strength lower in the middle but higher at the two ends. This strength difference along the length is expected to trigger energy dissipation in the middle but keep the ends undamaged. The restrainer has an inner diameter similar to that of the core steel, which minimizes the gap between them and avoids time-wasting grouting. This study introduces experimental and analytical research on four types of IHBRB. Tensile coupon tests revealed that the core steel of the IHBRB-600 series satisfied the target yield strength of 600 MPa in the middle and 1,200 MPa at both ends. The core steel of the IHBRB-800 series also satisfied the target yield strength of 800 MPa in the middle and 1,200 MPa at both ends. The ascending cyclic loading test showed that the IHBRB exerted a load capacity of over 1,000 kN as designed and exhibited tensile-compressive symmetric hysteresis behavior. IHBRB-600L, the specimen that failed by tensile fracture, showed that the high-strength brace end succeeded in remaining elastic as planned, while the low-strength brace middle showed a higher-order mode buckling. However, unexpected overall buckling at the joint occurred on other specimens. The low cycle fatigue specimens showed large cumulative inelastic deformation ratios of more than 200. A three-dimensional finite-element model of IHBRB-800L built by ABAQUS/Explicit (Dassault Systèmes Simulia Corp., Paris) captured the experimental results well. A parametric study revealed that the longer restrainer fixed at one side of the core steel end was one of the solutions to guarantee the great seismic performance of the IHBRB. [ABSTRACT FROM AUTHOR]

Saddle-shaped roofs are one typical kind of large span roofs, but there are few studies on the equivalent static wind load (ESWL) of saddle-shaped roofs, which is important for structural design. This study conducts wind pressure measurements of saddle-shaped roofs with three typical rise-span ratios (f/S=1/6 , 1/8 , 1/12) by wind tunnel tests. Subsequently, the influences of wind and structural parameters on dynamic responses and ESWLs are investigated for 81 single-layer saddle-shaped shells with different structural stiffness, including rise-span ratio, span length, roof mass, and incoming mean wind velocity. The results show that the most unfavorable wind directions of the peak structural responses for single-layer saddle-shaped shells are 60° and 90°, as well as the axisymmetric wind directions corresponding to these two wind directions, i.e., 120°, 240°, 270°, 300°. Finally, a simple fundamental vector is proposed to express the multitarget ESWLs for single-layer saddle-shaped shells to reproduce multiple peak responses at the most unfavorable wind directions. Through parametric analysis, mean pressure coefficients of roof zones are proposed. Within the investigated parameter ranges, the fluctuating ESWL coefficients are expressed as the functions of the reduced structural frequency at the most unfavorable wind directions, which is very convenient for structural engineers to determine the wind loads on main force resisting structural systems. [ABSTRACT FROM AUTHOR]

To address the challenges in predicting the aeroelastic phenomenon and the resulting wind-induced forces on slender bridges, a real-time aeroelastic hybrid simulation (RTAHS) system was developed. The RTAHS system directly measures the aerodynamic and aeroelastic forces through load cells. It controls the next step's position of the deck section model with linear motors by solving the governing equations of motion in real time. Given the complex shape of a bridge deck section geometry, load cells are chosen for force measurement instead of as pressure sensors. In the previous RTAHS system proposed by the authors, the inertial forces of a rectangular section model were eliminated from the measured forces under the assumption of the model's rigid-body motion. However, when conducting RTAHS experiments with a realistic bridge deck section model, increasing the mass ratio between the mass of the model and the target mass input to the hybrid system results in unstable vibrations. This instability is primarily attributed to forces generated by the model's flexibility. This study developed an improved RTAHS system, which took into account the inertial forces arising from the nonrigid motion of the flexible bridge deck section model. An accelerometer was additionally installed at the midpoint of the model, and the inertial forces caused by the nonrigid behavior were compensated using a calibration factor derived from impact hammer tests. This approach was validated by comparing the spring-supported experiments conducted on a realistic bridge deck section model. [ABSTRACT FROM AUTHOR]

Shape-memory alloy (SMA) knee-braced frames (KBFs) are a type of seismically resilient frame buildings. Knee braces (KBs) in this system are the SMA buckling-restrained braces, which provide both self-centering and energy-dissipating capacity. SMAs are known for their noticeable thermal-mechanical property, but there remains a lack of understanding regarding the temperature effect on the seismic responses of SMA KBFs. Hence, this study aims to address this issue at both component and system levels. Cyclic loading tests were conducted on reduced-scale SMA KB specimens under five distinct ambient temperatures ranging from −20°C to 20°C. The experimental data were then used to quantify the relationship between the hysteretic parameters of interest and the ambient temperature. At the system level, a multistory steel frame located in Tangshan City, China, was selected as the example structure. The probability density function was built to describe the temperature variation of the selected region, and the parameters of the function were determined using the maximum likelihood estimation method. The probabilistic analytical framework that considered the temperature effect was described. Then, this work conducted seismic design at the reference temperature (20°C). In what followed, within varying temperature conditions, nonlinear time-history analysis and multistripe analysis were conducted. The seismic response indexes under discrete temperature levels were compared. Finally, the temperature effect was understood by generating the joint fragility curves under various levels of temperature and seismic intensity. The findings indicated that the temperature effect on SMA KBs was noticeable. However, the temperature effect on SMA KBFs was minor, even though the extent of temperature variation was up to 60°C. [ABSTRACT FROM AUTHOR]

Many design regulations around the globe rely on member deflection as a governing criterion for resistance assessment in fire. The deflection evaluation in fire is generally achieved by conducting expensive experiments or computationally expensive finite-element analyses. This often restricts practicing engineers from using robust performance-based design philosophy for typical structures. Instead, they rely on objective design guidelines, often resulting in inefficient sizes of reinforced concrete (RC) members. Therefore, semiempirical relations are derived in the current study to determine the maximum deflection of the RC beam and RC column in a fire. Three separate end conditions are considered within the beam category: fixed-fixed beam, propped cantilever beam, and simply supported beam. Plausible variables are first identified that could affect the overall deflection of the member, and their proportionality is subsequently determined by performing one-on-one regression analysis. Furthermore, these relations are developed in terms of the most suitable fire intensity measures derived from the literature, which makes them applicable irrespective of the type of fire framework. The credibility of the deflection equations is validated through visual analysis followed by the three popular error indicator parameters, namely, Pearson's correlation coefficient, relative root-mean squared error (RRMSE), and performance index. Results indicated that all deflection equations accurately predict the RC member behavior under fire. [ABSTRACT FROM AUTHOR]

Steel tube–reinforced concrete (STRC) columns are composite members consisting of an inner concrete-filled steel tube (ICFST) component and an outer reinforced concrete (ORC) component. These columns are commonly used in the bottom columns of high-rise buildings and bridge piers to withstand significant axial loads. However, the stress state of the components in a STRC composite column differs from that of a single confinement component. As a result, the existing lateral strain model and concrete constitutive model cannot be directly applied to describe the stress–strain development of each component. To address this issue, this study combines the existing confined concrete models with the stress balance condition and strain development characteristics of the cross section of a STRC composite column. Theoretical models are proposed to simulate the development of lateral strain and confining stress in both the ICFST component and ORC component. Additionally, the biaxial stress state of the steel tube is considered based on the generalized Hooke law and Prandtl-Reuss theory in the theoretical model. Consequently, an incremental iterative calculation model for the whole axial load–strain curve is proposed. The effectiveness of the proposed models is verified by comparing the calculation results with the experimental results. [ABSTRACT FROM AUTHOR]

A full-scale, two-tiered steel buckling-restrained braced frame (BRBF) was tested to evaluate experimentally the seismic behavior of steel multitiered BRBFs, namely, column stability response, column seismic demands, and tier deformations under a loading protocol representing earthquake ground motions. The test specimen consisted of diagonal braces oriented in opposing directions in the two adjacent tiers to create the most critical multitier response. The test frame was designed in accordance with the 2010 AISC Seismic Provisions as a lateral load-resisting system of a single-story building. The frame was subjected to a three-phase loading protocol consisting of lateral displacement time histories corresponding to a far-field ground motion record and a near-field ground motion record applied sequentially achieving total frame drifts in excess of 3.5%, followed by a final monotonic lateral displacement corresponding to 4.5% story drift. The test frame exhibited a stable response despite a non-uniform distribution of frame inelastic deformation between the tiers, which induced significant in-plane bending moments in the columns. Flexural bending, combined with a large axial compression force, led to partial yielding in the columns. Large deformation demands were also observed in the BRB yielding in tension and attracting the majority of frame lateral deformation. On the basis of test results, a displacement-based analysis approach was proposed to relate column in-plane bending and flexural stiffness to relative inelastic tier deformations. [ABSTRACT FROM AUTHOR]

Eight half-scale confined masonry (CM) walls with and without confinement around the openings were tested under cyclic in-plane loads. Initially, four CM walls, one solid and three having different openings without confinement, were tested. Thereafter, wall specimens with confining elements around the openings were tested under similar loading cycles. The experimental study indicated that the presence of tie elements around the openings significantly enhanced the performance parameters of the CM walls in terms of their in-plane capacity, energy dissipation, stiffness, strength degradation, distortion of openings, and displacement profiles. The accuracy of the available equations in predicting the strength reduction due to openings was also evaluated. It was observed that no equation considers the confining effect of tie elements around the openings. Thus, based on the available experimental data set, a novel method is recommended for estimating the contribution of confining elements around the openings in CM walls. [ABSTRACT FROM AUTHOR]

This work was conducted first to devise an explicit equation for the ultimate strength of reinforced concrete dapped-end beams failing in diagonal tension caused by re-entrant corner cracks and second to gain insight into its mechanical behavior. To these ends, we introduce force equilibrium equations that explicitly account for the relevant internal force-resisting components: hanger reinforcement; dowel action of longitudinal reinforcement; concrete compression zone; aggregate interlock; and other reinforcement-related terms. These equations are solved within the framework of a constrained optimization problem. The solution process enables us to quantify the ultimate strength and the contributions of all force transfer actions. Strength prediction validity was confirmed through comparisons with experimentally obtained strength data from 50 specimens collected from the available literature. Our findings indicate the prediction accuracy as superior to that of a strut-and-tie model and design provisions of the Precast/Prestressed Concrete Institute. For practical purposes, a minimalist version of the equilibrium equation is derived to estimate the ultimate strength of diagonal tension failure based on rational simplifications of the force transfer mechanisms. [ABSTRACT FROM AUTHOR]

This study quantifies the effects of long-duration earthquakes on the behavior of reinforced concrete (RC) buildings subjected to successive earthquake-tsunamis through the development of fragility surfaces. The suite is comprised of both ductile and nonductile systems, representing a portfolio of RC structures that could be found in a (coastal) community. Previous research has shown that long-duration earthquakes can significantly influence the structural responses and even the collapse behavior of building systems. Earthquakes with large moment magnitudes that produce tsunamis are often long duration events, yet ground motion duration has not been fully considered when generating tsunami fragility curves or successive earthquake-tsunami fragility surfaces. This study incorporates earthquake loading through a nonlinear time history analysis (NLTHA) and subsequent tsunami loading with a nonlinear static procedure. Detailed probabilistic structural models are subjected to both long-duration and regular-duration earthquakes through the NLTHA phase of the successive simulation to explore the possible impact of long-duration earthquakes on earthquake-tsunami fragility surfaces used to represent the behavior of these RC buildings. Results show that failure probabilities from the fragility surfaces are increased by up to 40% in some cases, with low- to mid-rise RC structures (ductile and nonductile; up to 8 stories) being adversely affected by long-duration earthquakes. Furthermore, this study reports the governing parameters of scalar and vector-valued fragility functions in the proposed RC portfolio exposed to long-duration earthquakes and tsunami hazards. These fragility surfaces can be useful in developing community-level models in risk-based or resilience-based decision-support for disaster mitigation. [ABSTRACT FROM AUTHOR]

The design of connections of gusset plates, beams, and columns of concentrically braced frame systems is typically based on the forces generated by brace actions without considering the frame actions. This may result in underestimating the design force demand on gusset plates, potentially leading to the failure of interface weld connections at higher lateral drift levels. The present study aims to estimate the force demands at the connection interfaces, typically about a 2% story-drift ratio (SDR), corresponding to the design-level ground motions for braced frame systems. The study considers both the forces of frame and brace action on the corner gusset plate in the design process. It also aims to develop suitable design recommendations to prevent premature weld failures at higher lateral drift. High-fidelity finite-element models of in-plane buckling (IPB) braced frame systems are developed and analyzed under various loading modes. A current standard design method to determine the interface weld size was found to be inadequate to prevent premature failures at the higher drift levels. This is primarily due to the accumulation of the plastic strain at the tip of the gusset at higher drift. The out-of-plane bending of the gusset plate due to geometric imperfection was also found to contribute toward the development of high plastic strain at the tips of gusset plates. Three different connection configurations are considered and analyzed under critical cyclic loading conditions. Finally, design recommendations are presented to avoid stress concentration and premature fracture of gusset plate connections of the IPB braced frame systems. [ABSTRACT FROM AUTHOR]

Self-centering columns (SC), while attracting interest for their high recoverability, do not dissipate seismic energy as efficiently as conventional reinforced concrete or steel columns, potentially leading to a more significant seismic response. This study proposes a concept aimed at enhancing both energy dissipation during earthquakes and postearthquake restoration performance. This is achieved by exhibiting an SC capacity only during restoration. The proposed aseismic column consists of a central component, the SC core constructed from steel tubes filled with high-strength mortar, and energy-dissipation (ED) components made from steel plates. This SC core generates a moderate SC force sufficient to counteract the P-Δ effect. Given the minimal SC force from the SC core, the plasticization effect of the ED components becomes more conspicuous during large earthquakes, resulting in the emergence of a spindle-shaped lateral load capacity, leading to residual displacement in the columns. During restoration after earthquakes, the SC force emerges when the ED components are removed. The residual displacements of the columns can be gradually reduced during this process. Cyclic loading tests are conducted on the proposed column prototype followed by removal tests of the ED components with vertical axial forces acting on the column with residual displacement. In the cyclic loading tests, we confirmed the superior ED performance of the proposed column prototype, although residual displacement occurred in the column. In the ED component removal tests, a substantial reduction in the residual displacement of the column was observed when the ED components were removed. Specifically, the residual displacements were reduced by up to 96.2%, to a value of only 0.13% of the column height. In conclusion, the proposed concept can achieve superior energy absorption during earthquakes and high restoration performance afterward. [ABSTRACT FROM AUTHOR]

The performance of concrete-filled steel tubular (CFST) column joints with a group of extended hollo-bolts has been experimentally investigated under the influence of shear loading. The primary focus was to understand the performance of extended hollo-bolts in enhancing the transfer of shear load to the concrete core of the column by bolt bearing. The joint assembly was fabricated with a rigid end-plate, thereby overcoming the influence of endplates in the joint global behavior. A series of full-scale group hollo-bolted CFST column joint tests was carried out, where eight specimens were fabricated with a group of two hollo-bolts, arranged in one row and two rows in the assembly; another five specimens were fabricated with a group of four hollo-bolts, arranged in two rows. Apart from bolt arrangement, the other parameters studied included the use of standard and extended hollo-bolts, the embedment length of the hollo-bolt, and the bolt pitch distance. From the investigation, it is observed that all the joints failed in pure shear signifying utilization of the full capacity of the hollo-bolt, and no prominent bearing failure of concrete was observed. Enhanced composite behavior was achieved using the extended hollo-bolts as the shear load was transferred to the concrete core effectively. A group of two extended hollo-bolts in a single row transmits equal forces to the concrete core, whereas, when two or four extended hollo-bolts are in two rows, the upper row transmits more forces as compared to the bolts in the lower row. Lastly, with pitch distance of 2.5 times bolt hole diameter and beyond, the total strength of the joint is equal to the sum of strength of individual bolts, which confirms that the group action did not deteriorate the joint capacity. Subsequently, an analytical model for the global force-displacement behavior and joint shear strength is proposed by calibrating the test data obtained through this study. [ABSTRACT FROM AUTHOR]