Journal of Structural Engineering

Performance-based design optimization (PBDO) aims to design safe, resilient, and cost-effective structures. Methods used for PBDO have evolved by integrating numerical modeling, performance-based design principles, and optimization algorithms. The PBDO framework enables the design of structures with optimal performance and cost. This paper provides researchers with a comprehensive review of the rapidly growing field of PBDO. The evolution of PBDO methods is discussed with the goal of identifying the challenges that must be addressed in future studies. Knowledge gaps are brought to the forefront to emphasize the need for further investigation that expands on the application of PBDO in structural design. Various deterministic and probabilistic formulations for PBDO of structural systems under seismic and wind loading are reviewed. The formulations encompass one or more objective functions, including the upfront, life-cycle, and repair costs. Furthermore, the paper reviews retrofit design studies that have used PBDO methods. The high computational demand in performing PBDO is identified as the major challenge. Possible approaches to alleviate this and other challenges are discussed.

Three-dimensional (3D) concrete printing is increasingly becoming popular because it provides a powerful platform for the fabrication of structural components in freeform architectural shapes. Although manufacturing technology and material property improvement are advancing rapidly, the development of methods to predict the structural capacity of printed elements is lagging. This paper presents an experimental and numerical investigation to predict the axial load capacity of a printed concrete wall module. The module geometry contains two parallel thin wall sections connected by an internal sine wave. The thin wall section reduces the concrete consumption, and the internal sine wave provides lateral stability during printing and in the hardened state. It is a popular pattern printed by many researchers and in some real constructions. Two wall module specimens with the prescribed geometry were 3D-printed and tested under compression. The maximum loads of 2,890 and 2,924 kN were obtained for the first and second wall specimens, respectively. Additionally, samples were taken from different locations of a printed prototype to identify printed material characteristics. These experimental characteristics were then introduced to a finite-element numerical model for predicting the structural performance of the printed wall module under compression load. The results showed that the experimental maximum load and stiffness have 1% and 5% differences with numerical outputs, respectively. Based on such a validated model, the failure modes are discussed, and an analytical method is proposed for predicting the axial capacity for the prescribed geometry.

This study proposed a novel type of self-centering (SC) timber beam–column connection utilizing shape memory alloy (SMA) bars and investigated its cyclic behavior through experimental and numerical studies. In this SC connection, anchor bars consisting of SMA bars, steel bars, and couplers were utilized to connect the beam and column and achieve SC and energy dissipation capabilities. The configuration of the SC timber beam–column connection and material properties of the SMA bars were first introduced. The cyclic behavior of the SC timber beam–column connection was systematically investigated through experimental and numerical studies. A series of cyclic loading tests were conducted on the SC timber beam–column connection to evaluate its stiffness, SC, and energy dissipation capabilities, and the effect of multiearthquake loading. A detailed finite element model of the timber connection was also built and validated using the experimental results. Results indicated that the timber connection could exhibit a desirable flag-shaped hysteretic behavior, indicating favorable SC and moderate energy dissipation capabilities. The connection remained functional without any repair work after experiencing two consecutive cyclic loads up to 4% drift ratios, demonstrating its potential to withstand multiple seismic events.

Self-centering (SC) techniques have attracted widespread interest for the improvement of the seismic resilience of building structures. One typical representative is the self-centering energy dissipation (SCED)–braced frame structure, which is characterized by the ease of substitution with other conventional braced structures. Previous studies on the seismic performance of SCED-braced moment-resisting frame (MRF) structures were based on the expectation of full SC capacity. However, full SC performance is generally limited by the available deformation stroke of the SC mechanism in the SCED brace. Consequently, two partial SC design concepts, (1) reducing the structural SC ratio to ensure sufficient brace deformation capacity and (2) activating a sliding mechanism after the brace exhausts the available deformation stroke, are proposed to solve the noted design problems. To comprehensively understand the seismic performance of such partial SC structures, the SCED-braced MRF is represented by a dual-system single-degree-of-freedom (SDOF) model to consider the respective contributions of the frame and brace portions. An extensive parametric study, in which five levels of structural design parameters were considered, was performed to evaluate the seismic performance of SCED-braced MRFs designed with different partial SC concepts based on the dual-system SDOF model. Several useful suggestions for the design of SCED-braced MRFs with partial SC capacity were gleaned. The analysis results indicate that the SCED-braced MRF with a low SC ratio of 0.4 still has a satisfactory control effect on both the maximum displacement response and residual displacement. Moreover, the sliding mechanism is favorable for the structure in the medium to long range of the structural vibration period to control the amplified residual deformation within a limited range.

Cross-laminated timber (CLT) buildings are constructed by connecting CLT panels with dowel-type fasteners and mechanical anchors, which govern the lateral behavior of these structures. Although these connections are mostly distributed along the perimeter of the CLT panels, creating highly redundant structures, previous research on the lateral behavior of CLT structures has mainly focused on the behavior of the connections placed at the base of the CLT shear walls, such as hold downs and angle brackets, while limited attention has been paid to the connections between perpendicular walls and their effect on the lateral response of CLT shear walls. This paper presents a comprehensive experimental study aimed at investigating the effects of the interaction between perpendicular walls on the lateral response of CLT shear walls. CLT shear walls with three different aspect ratios were analyzed by means of monotonic and cyclic tests, both in single wall configuration and connected to perpendicular walls. The experimental findings demonstrate that the structural interaction due to the perpendicular walls significantly affects the lateral response of a CLT shear wall, resulting in increased lateral stiffness, lateral capacity, and deformation capacity. In addition, the study presents two analytical models for the prediction of the lateral stiffness and the lateral capacity of CLT shear walls connected to perpendicular walls. The analytical models were validated based on the experimental results, showing reasonable agreement.

This study presents a robot-assisted solution for the automated identification of bridge frequencies and high-spatial-resolution mode shapes using a minimal number of sensors. The proposed approach employs programmable wheeled robots, whose movement can be remotely controlled, as the mobile platform carrying accelerometers. The output-only frequency domain decomposition (FDD) algorithm is adopted for use with the proposed stop-and-go mobile sensing scheme, resulting in the identification of frequencies and high-resolution mode shapes. The solution was verified via two numerical case studies and was validated on a full-scale test of a footbridge. The results reveal that the frequencies and high-resolution shapes of the excited structural modes are identified successfully using only two accelerometers, confirming the satisfactory practicality and efficiency of the proposed solution.

It is the purpose of this study to evaluate, through combined experimental and numerical research, the performance of ultra-high-performance concrete (UHPC) jackets as a means of seismic retrofitting of columns with brittle detailing under cyclic loading. A series of conventionally designed RC column elements were constructed based on detailing methodologies of pre-1980s standards. After imparting preliminary damage to the columns, simulating the aftereffects of seismic excitation, the plastic hinge zone was repaired using cover replacement by a commercial-grade tension-hardening UHPC jacket and tested under cyclic displacement reversals to obtain quantified evidence regarding the performance of this retrofit methodology. Significant improvements in strength and ductility were observed in both the UHPC-repaired and -strengthened specimens, while failure modes associated with the limitations of lap-spliced connections at the column–footing interface were eliminated. Parallel finite-element analysis (FEA) simulations were used to evaluate the broader distributions of the longitudinal strains in the flexural reinforcement, illustrating the contribution of the UHPC jackets in prolonging the seismic response of retrofitted members.

Currently, the investigation on the collapse performances of steel frames with various structural scales has not formed a system resultant force, which leads to the current “overall qualitative and local quantitative” modes of structural system anticollapse resistance design. This paper numerically and analytically investigated the load-bearing capacities of the frame assemblies with various structural scales extracted from an overall steel frame structure subjected to the removal of an internal column. First, the accuracy of the numerical simulation methods was verified by comparing with the experimental results of the representative experimental collapse tests with various structural scales. Afterwards, numerical simulation analysis was conducted to investigate the variations in load-resisting capacities, axial forces generated in beams, and bending moments at beam ends in frame assemblies with different structural scales. The finding revealed that the boundary constraint is the one of the most critical parameters influencing the development of various load-bearing mechanisms, which is critical to identifying the internal links among the load-resisting capacities of assemblies with varying different scales. Finally, theoretical analysis methods for achieving the correlation transformation of the collapse capacities of steel frames with different structural scales were proposed, using member resistance based on the evolution laws of internal force among each story beam. The load-displacement curves generated by the display expression and its corresponding numerical models demonstrate a high level of accuracy, which demonstrates that the analytical methods can be employed for structural resistance evaluation before the anticollapse design.

The accurate representation of real floor behavior is crucial for assessing human-induced vibration serviceability. Many researchers focus on developing computational models and field testing to reflect actual serviceability conditions. Although traditional boundary conditions are commonly used, limited attention has been given to optimizing these conditions. To begin with, this paper introduced semirigid boundary conditions into a finite-element model of the floor and optimized physical parameters and boundary constraint stiffness using the simulated annealing-particle swarm optimization (SA-PSO) method, resulting in a more realistic computational model. Subsequently, a random crowd load model was established by combining the social force model (SFM) and the pedestrian load model, and a random crowd-floor mutual coupling calculation model was established based on the improved pedestrian biomechanical model. In addition, the mode shape functions of the floor with semirigid boundary conditions were obtained by extracting the optimized mode shape vector of the floor and using cubic spline interpolation. The dynamic response of the floor was computed using the modal analysis method, and the accuracy of the suggested method and model was verified by experiment. Furthermore, the effect on the vibration serviceability of the floor was analyzed under crowd walks randomly on the floor with different boundary conditions both before and after optimization. This study revealed: (1) achieving a computational model consistent with real floors requires optimization of relevant parameters and boundary conditions, reducing the error in floor frequency from 39.48% to 5.44% compared to measured results. (2) The human-induced vibration serviceability for existing floors may be misjudged by using traditional boundary conditions. The mean value of peak acceleration of floor with semirigid boundary conditions increased by 35.92%, with a 42% increase in the probability of serviceability problems compared to the SSCC boundary. (3) High-frequency floors also experience human-induced vibration serviceability issues. For a floor with a fundamental frequency of 10.3540 Hz, simulation and experimental results during five-person random walks indicate that peak acceleration at the middle position of the floor exceeds serviceability limits.

This study presents a novel approach to enhancing the progressive collapse resistance of a fully welded joint (FWJ) by introducing sliding inner cores within the joint, which is referred to as the FWJ with sliding inner cores (FWJS). Two specimens were prepared and designed with additional consideration of composite action of the slab. Quasi-static tests and refined numerical simulations were conducted to analyze the damage mode, deformation behavior, strain distribution patterns, internal forces, and resistance development in both specimens. The test results revealed that the first fracture occurred in the tensile beam flanges for both FWJ and FWJS specimens, whereas the FWJS specimen exhibited delayed crack of the tensile beam flange compared to the FWJ specimen. The FWJS specimen demonstrated better utilization of the catenary mechanism during the flexural–catenary combined stage. Additionally, in the elastic, elastic–plastic, plastic, and flexural–catenary combined stages, the addition of the sliding inner cores in the FWJS specimen significantly enhanced its resistance by 15.6%, 22.3%, 23.4%, and 70.2%, respectively. It is also revealed that the response of the sliding inner core consisted of bending, transition, and full tension stages, which was shown to effectively replace the fractured beam flange in redistributing the internal forces. Based on the analysis of the working mechanism and numerical parametric analysis, optimal values for the 10 design parameters of the FWJS are suggested, and a comprehensive design procedure for the FWJS is proposed.

In this study, the authors conducted five low-cycle reciprocating loading tests on hexagonal ultrahigh-performance concrete (UHPC)-filled steel tubular (UHPCFST) and UHPC-filled double-skin steel tubular (UHPCFDST) columns. The main parameters investigated in this research program are the hollow ratio, axial load ratio, and column type. Based on the experimental results, the failure modes, lateral load-story drift ratio curves, lateral load-strain curves, ultimate lateral load and corresponding base moment, and ultimate story drift ratios are obtained and discussed. The results show that hexagonal UHPCFST and UHPCFDST satisfy the requirements of ductility in GB 50936-2014. Moreover, the authors developed a fiber beam model (FBM) to predict the hysteretic behavior and strength under combined compression and bending. Subsequently, a parametric study was conducted, based on the validated FBM, to investigate the effect of material strength, outer steel tube thickness, and hollow ratio on the strength of hexagonal columns under combined loadings. Comparisons of the predictions from T/CESS 7, AISC 360, and EC4 and numerical results suggest the necessity of a design method with higher accuracy. Finally, the authors proposed a calculation formula for hexagonal UHPCFST and UHPCFDST columns, which effectively predicts the strength of these two types of columns under combined compression and bending.

Interaction between masonry infill walls (MIWs) and a main structural system can impact the overall structural performance. However, there is no test to investigate the impact of MIWs on self-centering prestressed concrete (SCPC) frames, nor has there been a probabilistic performance evaluation considering the coupling effects of peak interstory drift ratio (PIDR) and residual interstory drift ratio (RIDR). This study compares the seismic performance of SCPC frames with and without MIWs through quasi-static tests and seismic risk assessment under mainshock–aftershock (MSAS) sequences. To begin, quasi-static tests on one-story SCPC frames with and without MIWs are performed to assess their seismic performance. A numerical simulation method for the SCPC frame with MIWs is then proposed and validated. Following that, the seismic performance of four multistory SCPC frames with and without MIWs is investigated under MSAS sequences at the maximum considered earthquake level. Finally, the seismic vulnerability assessment, considering the coupling effect of PIDR and RIDR under MSAS sequences, is conducted. The results indicate that cracks on the MIW present diagonal stepped cracks, and the MIW does not cause damage to the SCPC frame. When the MIW is damaged, the RIDR of the SCPC-MIW frame increases significantly; when the crack development is stable, the RIDR increases slowly as the interstory drift increases but remains at a very low level. Besides, when the MIW is damaged, an obvious deformation concentration effect occurs on the SCPC-MIW frame. The SCPC-MIW frame has a lower probability of exceeding the immediate occupancy level $P(\mathrm{IO})$ than the SCPC frame, but it has a higher probability of exceeding the repairable level $P(\mathrm{RE})$ when the seismic intensity is relatively small. Overall, the $P(\mathrm{IO})$ and $P(\mathrm{RE})$ of the SCPC and SCPC-MIW frames are higher under MSAS sequences than under MS-only sequences, except for the SCPC25 frame.

This study aims to develop optimized interaction equations for more efficient design of cold-formed steel (CFS) lipped channel beam-columns under combined compressive load and biaxial bending, aligned with the direct strength method (DSM). A comprehensive data set was first generated using detailed experimentally validated finite element (FE) models of over 500 CFS sections subjected to combined compression and uniaxial and biaxial bending moments while the effects of initial geometric imperfections and material nonlinearity were included. The compiled data set consisted of a range of key design variables, including cross-sectional geometry and element length, as well as combinations of compression and bending moments caused by various eccentricity levels in terms of direction and value. The results were subsequently utilized to evaluate the efficiency of the simplified interaction formula prescribed by the Australian/New Zealand Standard (AS/NZS-4600) and American Iron and Steel Institute (AISI-S100), as well as the extended DSM, in predicting the capacity of CFS lipped channel beam-column elements. It was demonstrated that, on average, using existing interaction equations may lead to a 32% error in the capacity predictions of CFS beam-column members. Following a reliability analysis, a new interaction expression was developed with optimized parameters using DSM nominal pure strength values. For the first time, different exponent parameters were proposed for minor- and major-axes bending, which resulted in a considerable improvement in the accuracy of the beam-column strength predictions compared to the existing methods.

While numerous experimental tests have been conducted on single-story cross-laminated timber (CLT) shear walls, research addressing the drift performance of multistory CLT structures remains limited. This paper presents an experimental parameter study of the lateral performance of two-story platform-type CLT shear wall structures utilizing self-tapping screw connections. The test program consisted of six reversed cyclic tests investigating the impact of: (1) additional floor mass; (2) different angle bracket connections between floors; (3) different tension strap connections between floors; and (4) acoustic insulation layers on both sides of the first-level floor. The results showed that additional dead load increased the lateral resistance and that designing angle brackets to remain elastic limited the sliding contribution to total lateral deformations to less than 10%. The results also showed that the acoustic layer had minimal effect on the performance of the shear walls under the tested conditions. The tension straps significantly influenced the rocking performance, underscoring their importance to achieve similar story drifts in multistory CLT shear wall structures. Finally, while preceding single-story shear wall tests allowed designing the structures, hold-down uplifts on single-story tests were shown not to be representative for tension strap uplifts in multistory tests.

This study quantitatively evaluated the level of conservatism or accuracy of four typical directions used to assess the maximum structural response over all nonredundant seismic input angles: fault-normal and fault-parallel (FN and FP), the direct maximum direction (MD), the maximum peak ground velocity (PGV) direction, and the principal axes directions. Two eight-story models of symmetric and asymmetric buildings were developed, and two ensembles of ground motion records were selected considering three varying ground motion intensities. Bidirectional nonlinear response-history analyses (RHAs) were performed by rotating each pair of ground motion horizontal components to 26 orientations, from 0° to 170° in increments of 10° as well as four critical and their orthogonal directions. The effect of rotating the ground motions on several engineering demand parameters (EDPs) was investigated and the seismic demands in four critical directions were compared and evaluated deterministically and probabilistically. The four critical directions were re-evaluated by considering the largest response between two orthogonal pairs. The results show that the response in the maximum PGV direction is very close or equal to the maximum value over all orientations, especially for high levels of ground motion intensities, and thus is recommended for ground motion selection in performance-based seismic design and assessment. In addition, the influence of rotation angle is effectively reduced when using the larger seismic response value of the two orthogonal pairs while maintaining the same number of RHAs.

Past research efforts have developed several self-centering beam-to-column connections for minimizing structural damage in steel moment frames after severe earthquakes. However, less focus has been on low-damage column base connections. Severe damage at the base of columns in conventional steel structures with moment frames is likely during an intense earthquake, rendering the building nonresilient. This paper evaluates the application of a recently developed viscoplastic damper in low-damage column base connections. The proposed viscoplastic damper is a rubber-steel core damper (RSCD), which consists of a high-damping rubber layer and several ductile steel bolts. The proposed column base connections prevent damage and inelastic deformations in the steel column and its base plate by allowing a rocking mechanism at the base of the column and limiting damage to easily replaceable steel bolts in the dampers. The paper discusses the design and behavior of the column base connections equipped with RSCDs. Continuum finite element models of RSCD dampers were developed and validated using experimental results. The rocking response was validated using experimental results for rocking columns with a silt damper. A total of 21 finite element models of rocking columns with RSCD were used to numerically examine the column response to combined axial loading and cyclic lateral loading. The influence of different parameters on the cyclic response of the proposed column base connections was also evaluated. These parameters are steel bolt diameter-to-length ratio ($d/h$), rubber thickness, column axial compressive load, number of bolts, and steel material type. The results confirmed the effectiveness of the proposed column base connection for minimizing damage to the steel column and its base plate. An optimal $d/h$ ratio of 0.4 was found for the design of RSCDs. In addition, analytical formulas are presented to evaluate the yield and ultimate strength of the proposed column base connection, and the comparison with FEM results indicates that the presented mechanism has sufficient accuracy.

Built-up back-to-back cold-formed steel (CFS) channel members (BBC members) are utilized as CFS compression members with enhanced load-bearing capacity in building structures. In this study, finite-element (FE) models of BBC compression members with pinned warping-fixed and pinned warping-free ends were established and verified using test results available in the literature. Using the developed FE models, detailed parametric studies were conducted to assess the behavior and capacity of slender BBC compression members with pinned warping-free ends, varying cross sections, and screw arrangements. The results were first compared with those of their individual (channel) members and BBC members with pinned warping-fixed ends. They were then used to evaluate the direct strength method (DSM) design rules in the CFS design standards used in North America and Australia/New Zealand. Finally, new reliable design rules based on the DSM equations and some analytical equations in the literature were proposed for the BBC compression members with pinned warping-free ends, together with suitable recommendations. This paper includes the main details of this study with a summary of its important findings and proposals.

Previous studies have demonstrated that elevated temperatures exert a significant influence on the structural performance of reinforced concrete (RC) members. However, the residual shear performance of the RC beam under the combined effects of stirrup corrosion and fire has not been thoroughly explored. Therefore, this paper aims to investigate this aspect by prefabricating eight RC beams and employing experimental, numerical, and theoretical methods. The influence of varying stirrup corrosion degrees and fire exposure time on the residual shear capacity of these beams was examined. It was observed that corrosion-induced cracks had an impact on the distribution of the temperature field within the RC beams. Furthermore, the exposure to the corrosion–fire combination significantly affected the shear capacity of the RC beams. Notably, stirrup corrosion may lead to a more brittle failure after a fire. To assess the impact of corrosion degree and fire exposure time on the temperature field and residual shear properties of RC beams, a simplified finite element (FE) model considering the effect of concrete spalling was developed. The accuracy of this model was validated through a comparison with experimental results. Finally, three theoretical methods for predicting the residual shear capacity of postfire RC beams with corroded stirrups were proposed, based on Chinese, American, and European codes. A comparison between the calculated and test results revealed a good agreement. These methods can provide conservative predictions for practical engineering applications.

In this study, we utilize two metaheuristic algorithms, particle swarm optimization, and biogeography-based optimization, to select and scale ground motion (GM) records for use in the time history analysis of structures. This method ensures that there is no alteration to the phase or shape of the response spectra of the records. The proposed methodology demonstrates an ability to search through hundreds of earthquake records and propose a combination of 11 record pairs and scaling factors, resulting in a mean spectrum that aligns with the target spectrum. We applied the proposed research to two sites in separate geographical regions in the United States: Memphis and San Francisco, and we followed the ASCE 7-22 procedure. Selected ground motions underwent scaling adjustments represented by scalar values in a user-defined range. Furthermore, we present error metrics, comparing the target spectrum with the mean spectrum derived from the selected records. To showcase the effectiveness of our approach, we conducted a comparative analysis against results obtained from PEER-NGA methodology. The outcomes show that the methodology can be viewed as an effective and reliable approach for obtaining appropriate GM records for the time history analysis of structures.

High-rise buildings are sensitive to multihazard loads from both short and long-term perspectives. Adding tuned mass dampers (TMDs) is a well-established method to improve the performance of tall buildings, but the cost-benefit of adding TMDs is still a research question to be tackled. To answer this question, a methodology for optimal simultaneous design of reinforced concrete components and TMDs in high-rise buildings is developed for the first time. A cost-benefit focused optimization problem is defined, adopting a monetary cost function that includes direct and indirect costs and the multihazard long-term repair costs. Design variables related to the primary structure and the dampers are selected, as well as a set of constraints. The shear wall rigidities and capacities are included by generating a database of moment-curvature relations, followed by a curve-fitting procedure. An efficient gradient-based algorithm is developed to solve these challenging problems. Using this algorithm, 35 problems are solved, considering three building heights and three metropolitan areas in Israel, with their specific hazard and cost inputs. The results show that for 40-story buildings, adding TMDs is not profitable. For 50-story buildings, this is profitable for Jerusalem, marginally profitable for Tel-Aviv and not practical for Haifa. For 60-story buildings, adding TMDs is profitable for all the locations, with the greatest benefit being detected for Jerusalem, and then for Tel-Aviv in second place. The results are explained by the different building heights, wind load magnitudes and surface selling prices. The framework is shown to be flexible and appropriate for a preliminary TMD profitability assessment.

Experimental tests of cross-laminated timber (CLT)-concrete composite floor panels were conducted. The tests consisted of linear-elastic tests of square CLT-concrete composite panels with a novel shear connector to determine elastic orthotropic plate properties. After the linear-elastic tests, the panels were subjected to a patch load at the center of the panel and tested to failure. To investigate load transfer across longitudinal joints between adjacent panels, nonuniform bending tests were conducted. Results from the experimentally measured orthotropic plate properties showed that the shear connector increased the bending stiffness in the weak direction of the panel compared to prior test results using conventional shear connectors. The tests to failure exhibited larger differences in behavior between the strong and weak orientations of the specimens, with both showing substantial inelastic behavior prior to failure. Numerical finite element models of the patch-load test showed good agreement with experimental results. Analytical formulas using the obtained orthotropic plate properties did not agree with experimental results for the patch-load at linear scales, suggesting the simplified method is currently not suited for CLT-concrete two-way bending. Load-transfer tests found that the reinforced concrete topping is capable of transferring load across the longitudinal joint of two parallel panels to enable two-way bending of composite timber–concrete floors and that the addition of a plywood spline with closely spaced screws enables a higher degree of force transfer.

Self-centering braces are an attractive new type of brace able to reduce structural residual deformations after earthquakes, with no requirement of major modifications to structural joints. One primary challenge in widespread implementations of self-centering braces is their high demands of prestressing forces, in order to counteract the anti-recentering resistance induced by their energy-dissipation system. This paper introduces a novel self-centering (SC) brace, denoted as a viscoelastic low-prestressing self-centering (VE-LPSC) brace, that needs only a low level of prestressing force to achieve self-centering. The proposed brace incorporates a novel frequency-independent viscoelastic damper (VED) as its energy-dissipation system. The new VED behaves similarly to displacement-based dampers that provide stable stiffness and damping across various frequencies. Meanwhile, as loading ends, the VED does not generate residual anti-recentering forces, unlike conventional velocity-based dampers. Performance tests on the VEDs were first conducted using three specimens to examine the material’s deformation capacity, frequency-independent characteristic, fatigue-resistance capacity, and recovery capacity. Then, six full-scale brace prototype specimens were manufactured and tested, considering three levels of prestressing forces (15, 50, and 100 kN). Test results revealed that the brace achieved complete self-centering and consistent stiffness and strength under various frequencies, even with a prestressing force of 15 kN. With conventional steel strand and Belleville springs as its prestressed elements, the new brace was able to elongate 2.27% (corresponding to a story drift of 4.54%) while maintaining its recentering capacity. The VE-LPSC brace may experience some strength degradation after loading lower to 90%, but its capacity can recover to 98% of the original strength after 2 weeks.

This paper primarily presents an investigation into rectangular hollow section (RHS) cross- (or X-) connections with the branches fully laterally offset and loaded in axial tension. A set of 10 full-scale experimental specimens, carefully fabricated with noncritical welds, are tested in the laboratory, and the results are used to validate nonlinear finite-element models. To enhance the range of available data, the calibrated models are varied in an expanded parametric numerical study. A chord failure limit-state model based on a yield-line mechanism, which was identified in prior research on branch compression loading, is verified herein for branch tension loading. Furthermore, the limit state of branch failure is investigated by means of the combined experimental and numerical database produced. Design recommendations for laterally offset cross-connections loaded under branch tension, based on chord and branch failure modes, are presented. The application of current design recommendations for traditional cross-connections (with centered branches) to connections with full-width branches and laterally offset branches is also evaluated.

This study investigated the seismic performance and self-centering behavior of a three-story steel frame equipped with self-centering brace (SCBs) using pseudodynamic tests aided by OpenSees version 2.5.7 and OpenFresco version 2.7.0. The three-story self-centering braced frame (SCBF) was simplified to a three-story shear building model, and a generic experimental element with three nodes with horizontal degrees of freedom was used to establish a two-dimensional (2D) numerical model. The input ground motions were scaled to a service level earthquake (SLE), design basis earthquake (DBE), maximum considered earthquake (MCE), and a very rare earthquake (VRE) with 63%, 10%, 2%, and 0.5% probability of exceedance in 50 years, respectively. The test results demonstrated the excellent seismic performance and self-centering behavior of the SCBF. The maximum story drift ratio and maximum residual story drift ratio of the SCBF under a VRE were 1.91% and 0.119%, respectively, below the thresholds of 2.0% and 0.5%. The SCBs provided more than 90% of the initial lateral stiffness of the SCBF and dissipated approximately 55% of the seismic input energy. The seismic performance of the SCBF satisfied the no-damage criterion under an SLE and DBE. Although the columns in Story 1 yielded under an MCE and VRE, no visible residual deformation of the column flanges was detected in Story 1 after the tests. In addition, the maximum residual drift ratio of Story 1 was only 0.066%. Therefore, the columns in Story 1 only required simple and quick reinforcements before being usable. Unexpected factors, such as the fit-up tolerances around the pins, out-of-sync activation of the SCBs in the same story, residual deformation of the SCBs, and the out-of-sync activation of the two groups of disc springs in the same SCB, did not affect the seismic performance and self-centering capacity of the SCBF.

Existing studies have shown that the interface friction force positively affects and improves the shear behavior at the stud-connected steel–ultrahigh performance concrete (UHPC) interface. However, the effects of the interface friction force have not been well understood and quantified yet. The present study proposes a novel model to quantify the interface friction force and count it in the shear strength prediction for stud-connected steel–UHPC interfaces based on the compression-dispersion model and elastic foundation beam theory. The proposed formula is simple but with clear physical meaning, which has been verified with high accuracy. The proposed model can also be used to identify the yielding state of concrete in front of the stud and predict the interface friction during the whole static loading process, which improves the accuracy of shear strength prediction for steel–UHPC interfaces and reveals the influence of different parameters. For the steel–UHPC interface with UHPC strength greater than 120 MPa, the UHPC in front of stud is hard to yield and the percentage of friction force remains almost constant at 10%–14% during the whole static loading process. The positive effects of friction force on the shear strength of the steel–concrete interface is negligible for the cases with concrete strength less than 60 MPa.

This brief technical note compares the adjusted collapsed margin ratios for concrete-filled coupled composite plate steel walls, as obtained from the FEMA P695 methodology, separately considering only subduction zone earthquakes and only shallow earthquakes. For shallow earthquakes, collapse margin ratios were similar to those obtained in prior studies, but they were substantially smaller for the set of subduction earthquakes. While both sets of collapse margin ratios were considered to provide satisfactory seismic performance, this study provides insights into the impact of considering subduction earthquakes in FEMA P695 studies and, by inference, on expected collapse margin ratio for subduction earthquakes.