Journal of Structural Engineering

This paper presents a unique study on the dynamic identification of the tallest glue-laminated timber frame building in the world using forced vibration tests (FVTs) and long-term ambient vibration tests (AVTs). Because the amount of sway in service under wind has become the governing design criterion for tall timber buildings, this paper aims to provide useful information and evaluate available tools and methods for modal identification in tall glulam timber frame buildings. First, combined operational modal analysis schemes based on the variational mode decomposition with the stochastic subspace identification and the random decrement technique were adopted to identify the modal properties from nonstationary ambient data. Then, unique full-scale forced vibration tests were conducted using two different methods to excite the building: measured electrodynamic shakers excitation and unmeasured rhythmic human-induced excitation. Finally, a finite-element (FE) model of the tall glulam frame building was developed and frequency response function (FRF)–based model updating was conducted showing that the FE model was able to predict the modal behavior of the test building. The results show that natural frequencies identified from output-only techniques are in good agreement with the FVT results. Damping ratios obtained from both AVTs and FVTs exhibited amplitude-dependent behavior with a larger variation observed in the FVT results due to larger range of response amplitudes. These results have significant consequences for the design of tall timber buildings under serviceability-level loading, where damping plays an important role. The resulting damping ranges presented in this paper can serve as a useful guideline for practicing engineers in developing their prediction models of tall timber buildings under serviceability-level loading.

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.

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 ($\mathrm{f}/\mathrm{S}=1/6$, $1/8$, $1/12$) 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.

Aside from aesthetic appearance, recycling, ease of disassembly, decent resistance against corrosion, and no intense moisture condensing and thermal bridge, compared with steel fasteners, wooden fasteners also have the compatibility of stiffness with the assembled timber members, which reduces the risk of splitting of the assembled timber members. Due to higher mechanical properties, densified wood (DW) has become an alternative to natural wood as wooden fasteners. At present, investigations have mostly focused on timber-to-timber joints with single DW dowel, while multidowel timber joints are common in practice. In this study, the timber-to-timber joints with laterally loaded single and multiple DW dowels were tested under the loading parallel to the grain in order to explore the effects of the number of DW dowels, moisture content, and joint geometry, i.e., spacings and edge and end distances for DW dowels on mechanical behaviors of timber joints. The tests on the timber-to-timber joints with steel dowels were also performed to compare with those with DW dowels. The load-carrying capacities provided by individual DW dowels showed no reductions with the increases in the number of DW dowels and moisture content and the decrease in joint geometry. The experimental results suggest that the load-carrying capacity of multiple DW dowel joints can be estimated by using the load-carrying capacity of single DW dowel joints multiplied by the number of DW dowels in the range of joint geometries and numbers of DW dowels adopted in this study. The smaller spacings and edge and end distances for DW dowels adopted in this study than the minimum joint geometry requirements in Eurocode 5 are feasible.

Abstract

This paper investigates the fire resistance of extended end-late beam-column middle (EEBM) joints, taking into account the gradient temperature effect under postearthquake fire (PEF). First, finite element (FE) models of the EEBM joints were established based on mechanical models under different conditions, the accuracy of the models is validated by existing experiments. Next, the gradient temperature distribution, residual deformation and stress in the EEBM connections were analyzed. Finally, 125 FE models were established to conduct parameter analysis including the column flange width-thickness ratio ($\alpha$), column web height-thickness ratio ($\eta$), beam flange-to-end plate thickness ratio ($\gamma$), beam flange width-thickness ratio ($\delta$), beam web height-thickness ratio ($\beta$) and damage variables ($\tilde{D}$). The generalized failure point to determine the generalized ultimate displacement and a calculation method for the flexural capacity at high temperatures are proposed against the EEBM connections. The results demonstrate that the $\alpha$, $\eta$, and $\gamma$ have a significant impact on the failure modes of the EEBM connections. The generalized ultimate displacement of the EEBM connections is approximately 1/40 of the beam span. The $\alpha$, $\gamma$, and $\tilde{D}$ dramatically affect the fire resistance of the EEBM connections. The weakening of the flexural capacity due to damage is greater than that due to high temperatures. The findings can provide basic data, theoretical reference, and technical support for the design and research of EEBM connections under PEF.

Practical Applications

EEBM connections are widely used in multi-story steel frame and portal frame, etc. Postearthquake fire is common, which will cause significant casualties and economic losses. On account of the residual stress and deformation caused by earthquake in EEBM connections, it is impossible to accurately evaluate the reliability and safety of EEBM connections under postearthquake fire using the failure mechanism of EEBM connections under fire. Therefore, the findings of this study can provide valuable reference for design, reinforcement and repair of EEBM connections.

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.

The research on cold-formed steel (CFS) built-up columns, which has grown over the past decade, has been instrumental in developing new CFS built-up columns with transversely spaced chords, demonstrating better axial performance than conventional I-type built-up columns. However, previous research findings on CFS laced columns have been limited, with no data available on stub columns. This paper presents the first test program for cold-formed steel laced stub columns using plain channels. The program involved fabricating 12 specimens with a single lacing configuration, connecting lacing elements and end plates to the chords using self-drilling screws, and evaluating the impact of critical parameters on column performance under concentric axial loading. Important variables such as lacing slenderness, end plate length, and transverse chord spacing were examined, with the built-up section’s aspect ratio varying from 0.75 to 1.25. The failure modes, peak strengths, and load-displacement curves of the stub column specimens were used to evaluate their performance. In addition, the study compared strength predictions from the current American Iron and Steel Institute (AISI S100-16) and Eurocode (EN1993-1-3) standards against the test strengths. Unlike slender column axial strength, these current standards predicted the axial strengths of the stub columns better, with an overprediction of less than 5%. It was verified that lacing slenderness and end plate length variation does not change the failure mode in CFS laced stub columns. Further, earlier recommendations on end plate length for CFS laced columns cannot be extended to CFS laced stub columns.

This paper presents a numerical parametric study to examine the structural response of drilled shaft footings (pile caps) presenting different design characteristics, which have not been studied in depth in previous experimental studies. The numerical analyses were conducted with nonlinear finite element models representing typical designs and details of actual footings. The modeling scheme was validated using experimental data from large-scale drilled shaft footings. Key parameters of the numerical study included footing geometric properties, concrete strength, and reinforcement ratios. The results of the parametric studies were examined to identify key behavioral and design aspects to be considered when using 3D strut-and-tie models for the design of drilled shaft footings. The analysis results show that influences associated with footing and column aspect ratios were essentially negligible. However, it was estimated that an increase of the angle of inclination between the compression strut and the vertical axis led to significant reductions in footing stiffness and load capacity. The effect of shaft diameter was also examined in light of lateral concrete confining effects, and it was found that larger shaft diameters provide increased footing capacities. Analyses performed to estimate the influence of concrete compressive strength showed that splitting of the strut controlled the concrete-governed failure mechanism of footings. Finally, the models developed with different amounts of reinforcement revealed that increasing bottom mat reinforcement leads to increased ultimate loads; however, the rate of strength increase decreases with increasing reinforcement ratio. Providing a minimal amount of top mat and side face reinforcement was estimated to impact the structural responses of the footings positively; however, increasing the ratios of the top mat and side face reinforcing bars beyond this minimum did not significantly impact footing strength.

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.

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.

In this paper, a novel arch structure—circular box arch with sinusoidal corrugated webs (CBASCW)—is presented. Through the methods of theoretical derivation and finite element simulation, we studied its in-plane elastic buckling and in-plane elastoplastic stability. Through theoretical derivation, a shear stiffness formula of the arch section is determined, and the elastic buckling load when the arch is in pure compression state is proposed considering the shear deformation. We also introduced a simplified model, which can simulate the deformation and internal forces conveniently. The failure mode and global elastoplastic instability mechanism are investigated under uniformly distributed full-span radial load, uniformly distributed full-span vertical load, and uniformly distributed half-span vertical load. Furthermore, by introducing a regular slenderness ratio and stability coefficient, the stability curve of the arch under the state of pure compression is plotted. Subsequently, based on the stability curve and the numerical simulation results of a simplified model, a design formula for the stability bearing capacity is proposed for situations where global elastoplastic instability occurs.

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.

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.

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.

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 $0.3A_g$$f_{cm,c}$ or $0.5A_g$$f_{cm,c}$, where $A_g$ and $f_{cm,c}$ 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, $(EI{)}_{test}/E_{cm,c}{I}_g$, 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 $(EI{)}_{test}/E_{cm,c}{I}_g$ ratio between approximately 0.3 and 0.6.

Interest in earthquake resilience has increased in recent years, and the use of building cluster performance objectives has been shown to be an effective method for evaluating the resilience of a built environment. A building cluster is a portfolio of buildings that share the same role in a community; its performance objectives are defined by considering earthquake scenarios, hazard levels, and individual building performance. The methodology presented in this paper employs performance-based assessments to estimate the probability of achieving building cluster performance objectives immediately following a seismic event. It can be used to assess the immediate post-earthquake community resilience in five steps: (1) hazard analysis; (2) conditional assessment of individual building performance; (3) conditional assessment of building cluster performance; (4) building cluster performance assessment by aggregation; and (5) earthquake resilience assessment of building clusters considering all hazard levels of interest. The design and extreme hazard levels are formulated using ground motion records selected based on the conditional spectra considering characteristics of earthquake scenarios and spatial correlation. Three performance objectives are defined for individual buildings and building clusters: (1) functionality; (2) safe and usable during repair; and (3) collapse prevention. Two engineering demand parameters, i.e., the maximum transient and the permanent interstory drift indices, are used to estimate individual building performance. The probability of achieving building cluster performance objective is calculated using the total probability theorem. The application of the proposed methodology is demonstrated using two clusters of reinforced concrete buildings, corresponding to ASCE 7 Risk Category II and IV structures, in San Francisco, California.

This study deals with the compressive performance of cold-formed steel semi-oval hollow section (CFS-SOHS) stub columns after exposure to a standard fire. An experimental program was carried out on 17 CFS-SOHS stub columns after four different fire exposure temperatures, namely 300°C, 550°C, 750°C, and 900°C. Details of post-fire test specimens, material properties, stub column test arrangements, and results are described and discussed in this paper. A finite-element model was established and then validated by the experimental compressive performance in terms of ultimate strength, load-end shortening response, and failure mode. Parametric analyses were then performed on 160 post-fire CFS-SOHS stub column specimens to furnish more numerical data. The acquired experimental and numerical compressive strengths were compared against the design predictions by the direct strength method (DSM) initially calibrated for open sections, and the modified DSM initially proposed for CFS-SOHS without fire. A reliability analysis was performed. Comparisons show that the modified DSM offers accurate and reliable post-fire residual resistance predictions for CFS-SOHS stub columns after exposure to the standard fire.

Implementation of existing stress–strain models for cold-formed steel requires the input of key material parameters determined from corner coupon tests on cold-formed portions. This paper proposes various approaches that can accurately describe the stress–strain responses of cold-formed steel by using corner material properties if known, or by using parent material properties and the corner geometry after cold-forming in the absence of corner material properties. First, a comprehensive database of coupon test results of cold-formed steel is assembled. A total of 483 corner coupon test results with 236 full stress–strain curves are collected from 31 sources, covering a large range of steel grades with nominal yield strength varying from 235 to $960\mathrm{MPa}$. The applicability of existing empirical models for determination of the enhanced yield strength, ultimate strength, and ultimate strain is carefully evaluated. New predictive expressions for the required input parameters (namely, 0.01% or 0.05% proof stresses for the use of the two-stage Ramberg-Osgood model, and the strain hardening exponent for the use of one-stage material model) are subsequently derived. Prediction performances of the two-stage Ramberg-Osgood model and the one-stage material model are then evaluated against experimental stress–strain curves under different availabilities of primary material parameters. According to the proposed approaches, the minimum required input parameter to utilize these models is only the yield strength of cold-formed steel or, alternatively, the yield strength of the parent metal and corner geometry after cold-forming. The developed models are proved to be accurate in predicting the monotonic stress–strain response (up to the ultimate point) of cold-formed steel, and they are suitable for use in parametric studies and advanced modeling of cold-formed structures.

A prefabricated seismic-resilient steel column base capable of accommodating bidirectional loading, enabling fast onsite construction and causing minimal disturbance to building function, is proposed. The column base consists of a lower circular column segment embedded in foundation, an upper box column segment placed above ground floor, four buckling-restrained steel plates (BRPs) as energy-dissipating devices to connect the column segments, and a pretensioned high-strength steel rod anchored between the column segments to secure self-centering. The upper column segment is supported on the lower one via a pair of circular base plates with protruded fillet edges to allow upper column rocking in any direction, and they are pretensioned in shop as a prefabricated column to expedite onsite construction. Theoretical models of the proposed column base under unidirectional and bidirectional seismic loading are developed, and design criteria for different seismic intensity levels are presented. A cyclic test program of a full-scale column specimen with the proposed configuration subjected to one unidirectional and three bidirectional loading phases is introduced. Global and local responses of the specimen are discussed, and test results confirmed effectiveness of the column base providing sufficient rigidity under service level earthquakes, repeatable hysteresis under bidirectional loading, avoiding rupture of the BRPs under series of strong earthquakes, and achieving self-centering, low-damage, and rapid postearthquake recovery. The theoretical models and design criteria to achieve the expected performance under bidirectional loading are validated.

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.

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.

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.

Many structures service in complex environments where multiple environmental factors (MEFs) coexist, and the coupling effects of MEFs often aggravate structural damage, thus increasing the risk of structural collapse and economic loss under seismic excitation. For structural damage caused by coupling effects of MEFs, previous studies have been mostly focused on one-way coupling analysis, such as the effect of structural pre-corrosion on its fatigue damage, and less attention to the interaction coupling effect of MEFs, which make it difficult to quantitatively calculate the interactive coupling damage due to the existence of MEFs. The large error of using one-way coupling damage calculation method to estimate the residual mechanical performance of the structure will reduce the reliability of seismic risk assessment of the structures suffering interaction coupling of MEFs. To solve such problem, this paper proposes a damage calculation method for structures considering the effect of interaction coupling of MEFs by establishing a multivariable interaction model, in which a coefficient $\beta (t)$ is introduced to characterize the time-varying mechanisms of the interaction coupling effect of MEFs (e.g., the acceleration of structural damage with service time). Then, the solution method for $\beta (t)$ is proposed by using Bayesian inference. Finally, a framework for analyzing the time-varying seismic risk of engineering structures considering the evolution of damage caused by interaction coupling of MEFs is established in which the uncertainty of environmental factors is also involved. The presented analysis framework is illustrated using a towering structure in a coastal area, and the results emphasize that the interactive coupling effect of MEFs can significantly increase the risk of structural collapse and economic loss.

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 $-20°\mathrm{C}$ 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.

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.

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 $P\text{-}\mathrm{\Delta }$ 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.

In December 2021, an EF-4 tornado swept through several Midwest states in the United States, with Kentucky being the worst hit. Among the impacted towns was Mayfield, KY, where the historic buildings in downtown suffered significant damage. In response to this disaster, the authors conducted a reconnaissance mission to digitally document the affected historic structures. This involved capturing a series of three-dimensional (3D) point clouds, providing detailed spatial data about the impacted buildings. The resulting data set includes both the original raw data and processed information, now accessible via the DesignSafe open-access repository. This paper outlines the data collection process for the impacted buildings, and the steps undertaken to process it. The final product of this endeavor are the point clouds generated for the historic building typology, which included 10 historic buildings and 2 comparable religious buildings. These point clouds serve as invaluable resources for further analysis, aiding in understanding a disaster’s impact, and guiding restoration endeavors.

This paper presents a data set of a fire-induced collapse on an existing building with a truss roof. The data set contains the thermal and structural responses of the tested building, the mass loss of the fuel, the heat release rates, and the videos of the entire test. The test building and basic test scheme are introduced first. Then, the monitoring points and corresponding equipment are presented. All data obtained have been converted to a unified format and uploaded to a published data set. Detailed data formats and processing methods are introduced, and metadata are provided. To the authors’ knowledge, this is the first open-access test data on fire-induced collapse of a real building, which is of great significance for further investigations on fire-induced building collapse and performance-based design for fire safety of buildings. This data set can be used to validate the existing temperature distribution models and develop deep-learning models in structural fire engineering. Moreover, the data set can validate and develop some cutting-edge theories and techniques in structural fire engineering, such as the approaches for the early-warning collapse of structures exposed to fire and the synchronous noncontact acquisition of structural deformation in fire.