Journal of Structural Engineering

This paper proposes a new mechanics-based model for the seismic design of beam-to-column panel zone joints in steel moment-resisting frames. The model is based on realistic shear stress distributions retrieved from continuum finite element (CFE) analyses of representative panel zone geometries. Comparisons with a comprehensive experimental data set suggest that the proposed model predicts the panel zone stiffness and shear strength with a noteworthy accuracy, even in panel zones featuring columns with thick flanges (thicker than 40 mm), as well as in cases with high beam-to-column aspect ratios (larger than 1.5). In that respect, the proposed model addresses the limitations of all other available models in the literature. If doubler plates are deemed necessary in the panel zone design, the CFE simulations do not depict any doubler-to-column web shear stress incompatibility, provided the current detailing practice is respected. Hence, the total thickness of the column web and doubler plates should be directly used in the proposed panel zone model. The panel zone shear strength reduction due to the axial load effects should be based on the peak axial compressive load, including the transient component due to dynamic overturning effects in exterior joints. It is found that the commonly used von Mises criterion suffices to adequately predict the shear strength reduction in the panel zone.

This paper investigates the relative effect of material properties and structural details in the joint panels on the seismic fragility of existing reinforced concrete (RC) frames. Five building classes with different structural details (particularly in the joint panels) and material characteristics are defined according to different past design codes, for a three-story and a six-story archetype geometry. Based on nonlinear static or nonlinear dynamic analysis procedures, results from the study show that the effect of structural details on seismic fragility of the considered structures is negligible for damage states involving an essentially elastic behavior. Conversely, it is much higher for life-safety and near-collapse damage states, and it is considerably higher than the effect due to materials. Therefore, in the diagnosis phase, higher emphasis should be given to on-site investigations of actual reinforcement content/layout rather than to invasive material testing. The uncertainty related to the structural details described here is practically related to exterior, rather than interior, joint panels. Cover removal for one of those joints may potentially eliminate this specific uncertainty. As a practical action, in situ testing of RC frames should involve the cover removal of at least one exterior joint panel regardless of the required target “level of knowledge” of the existing structure.

This paper proposes a uniform design (UD)-based Gaussian process regression (GPR) method for rapid damage assessment and fragility estimates of bridges. The core idea of the proposed method is that the GPR model was adopted to establish the relationship between the seismic damage and various parameters including bridge properties and earthquake attributes, and the UD method was implemented to enhance the training data set to improve the performance of the GPR model. An efficient method is proposed to improve the use of the UD method over empirical data to search the optimal training data set. Various empirical samples of damaged bridges from the 2008 Wenchuan earthquake in China were collected to validate the predictive ability of the proposed UD-GPR method. The ability and stability of the UD-GPR method for damage classification were evaluated using samples from other earthquakes that were not included in the training data set. The influence of different kernels for the GPR model, different sample sizes, and different discrepancies of training data sets on the predictions of the UD-GPR model was investigated. The empirical fragility curves for different bridge types were derived based on the results of damage classification. The efficiency and accuracy of the UD-GPR method for generating the fragility curves were validated by the actual fragility curves developed by the existing references. The effects of sample size and discrepancy on the median fragility and fragility dispersion were discussed. It can be concluded that the UD-GPR model is efficient and accurate for damage assessment and fragility analysis of bridges even when the training data set has a small number of samples, which can be helpful and beneficial for rapid postearthquake assessment of bridges.

This study presents the numerical investigation and design of cold-formed lean duplex stainless steel (CFLDSS) tubular sections subjected to concentrated end bearing loads, specifically end-one-flange (EOF), end-two-flange (ETF), and end loading (EL). Finite element models (FEM) were developed and verified against the test results of CFLDSS tubular sections subjected to the three loads. The FEM are able to predict the behavior of CFLDSS tubular sections in terms of ultimate strengths and web crippling failure. The verified FEM were used to perform an extensive parametric study that included a wide range of key parameters, including the ratios of flat web height to thickness, load bearing length to web thickness, and load bearing length to flat web height. Based on both the test and numerical results, new coefficients are proposed for the unified design equation and the direct strength method for the design of CFLDSS tubular sections subjected to the three concentrated end bearing loads. The strengths obtained from the tests and the parametric study were compared with the nominal strengths calculated using the design equations from current specifications and those in the literature, as well as those proposed in this study. Overall, the modified design rules provided more accurate predictions compared with the design rules in the current specifications and literature. The results showed that the proposed design methods are suitable for the web crippling design of CFLDSS tubular sections under the three concentrated end bearing loads.

Prescriptive design is a common practice in North America for low-rise light wood frame buildings. The prescriptive wood-based shear wall details provided in building codes to resist lateral loads were largely derived based on a combination of historical performance and engineering analysis. Inherent within the historical performance assumption is the presence of certain elements such as internal partitions that contribute to direct load resistance and structural redundancy. This inherent assumption is sometimes challenged by design engineers and proponents of alternative lateral load–resisting systems. In an attempt to showcase the contributions of the partition walls, a number of archetypes with various quantities of partitions were analyzed using a finite-element program. In the finite-element models, the wood-based structural shear walls and partition walls with gypsum wallboard were modeled as macroelements, with mechanical properties obtained from previous tests. Assumptions were made for the diaphragm and connection stiffness values. The results show a significant contribution of the partition walls to the lateral load resistance of light wood frame buildings. Partition walls accounted for 55%–71% of the overall lateral resistance of the evaluated buildings. Furthermore, diaphragms and wall-to-diaphragm connections contribute significantly to the overall behavior of the structures.

This paper presents the behavior of floor diaphragms of a shake-table experiment of a full-scale 2-story mass-timber building structure. The structure consists of glued-laminated timber beams and columns, and floors and walls were designed and built making use of cross-laminated timber panels. Two different floor systems were designed, where the roof consists of a topped cross-laminated timber (CLT)-concrete composite system, and the floor level consists of untopped CLT panels connected with plywood single-surface splines. The CLT floor systems were designed to remain essentially elastic over the whole series of shake-table tests, which included testing of three lateral force–resisting systems tested at three different seismic intensity levels (service level, design basis, and maximum considered earthquake) for a total of 34 shake-table earthquake tests. Results from the testing indicate that CLT diaphragms designed to remain essentially elastic based on basic principles of structural mechanics and existing test data can achieve desired seismic performance objectives. In addition, sources of overstrength in certain elements of the diaphragm need to be explicitly considered for a holistic diaphragm design.

This paper attempts to formulate an expression for the estimation of equivalent viscous damping (EVD) for cross-laminated timber (CLT) structural archetypes as a function of ductility. The paper aims at contributing toward the direct displacement-based design procedure (DDBD) of CLT structures, which makes use of equivalent viscous damping and secant stiffness estimations as proxies for the estimation of the nonlinear behavior of structures. The available hysteretic models of CLT structures are very elaborate, and the inelastic time-domain simulations using hysteretic models are not easily manageable. Hence, the adoption of equivalent viscous damping is a crucial feature of any DDBD method. In this paper, the authors estimate the EVD of a set of 16 typologies of CLT buildings with an increasing slenderness ratio. The minimum of the squared error between the maximum drift of the elastic time-history and the hysteretic response gives the EVD. The extended energy-dependent generalized Bouc Wen (EEGBW) model, calibrated on experimental data, is used to predict the inelastic seismic response of the single CLT shear wall. The correlation between EVD and ductility is compared to existing EVD formulations referring to concrete and steel structures.

Cold-formed steel (CFS) moment connections are often formed by bolting the webs of the connecting elements to a stiffened gusset plate, and local buckling of the web adjacent to the connection typically governs their capacity. This paper aims to study this failure mode in case the connection is subject to combined axial compression, shear, and bending moment. In a first step, the case of pure compressive loading was investigated. Validated geometric and material non-linear analysis with imperfections (GMNIA) finite-lement (FE) models were used to investigate the effects of different design variables, including the cross-sectional geometry and thickness, the bolt group configuration, and the bolt group length. The results were then used to develop design equations for the compressive capacity of CFS bolted connections. In a next step, the FE models were used to assess the capacity of CFS bolted connections subject to combined bending and shear, and combined axial compression, bending, and shear. Suitable interaction equations were proposed and reliability analyses were performed within the framework of both the Eurocode and the American Iron and Steel Institute (AISI) standards. It was concluded that a linear equation accurately captures the interaction between bending moment and axial force, while the effects of a shear force smaller than half of the shear capacity on the bending moment capacity can be neglected.

This paper presents a time-varying model-based method for estimating earthquake-induced displacement responses of building structures using limited acceleration data. First, a time-varying model which considers the variability of stiffness by a time-variant story local stiffness reduction factor and the variability of damping by formulating the Rayleigh damping model with a time-variant mass coefficient was developed. Then, a displacement estimation algorithm was derived on the basis of the state space representation of the time-varying model and the unscented Kalman filter. The effectiveness of the proposed method is numerically verified through nonlinear responses of a ten-story building model where the hysteretic restoring force is simulated by the Bouc–Wen model. In addition, numerical results indicated that a few sensors with low noise are more desirable for the measurement strategy. Finally, the applicability to realistic seismic monitoring of buildings was investigated through a $1:3\text{-}\mathrm{scale}$ 18-story steel frame test at the E-Defense shaking table facility, which tested collapse behavior and realistic damage of high-rise steel buildings constructed in the 1990s in Japan.

Considering the socioeconomic prominence of long-span cable-stayed bridges, it is important to ensure their normal operation after strong earthquake events. To this end, their seismic performance must be based on a proper understanding of the relationship between structural capacity and seismic demand. However, evaluating the seismic demands on cable-stayed bridges is challenging due to relatively long distances between supports and the complex composition of various structural elements. The large dimension in the horizontal direction inevitably leads to incoherent input ground motions at supports, while various structural components such as cables, decks, and pylons make it difficult to define the system’s performance limit-state or capacity using a single index or function. This work presents three main contributions to properly assess the seismic performance of a long-span cable-stayed bridge. First, an algorithm was proposed to generate a set of bidirectional spectrum-compatible ground motions for the multiple supports of a bridge. Second, two performance measures were proposed to quantitatively assess the seismic demands and capacity of a cable-stayed bridge: probabilistic comparison index and axial force-bending moment (PM) safety factor. Third, the impacts of the seismic motions on the long-span cable-stayed bridge were thoroughly examined using eight different scenarios in terms of the three aspects: (1) multisupport excitation, (2) assumed soil class, and (3) wave passage effect. For this purpose, the Incheon Grand Bridge was chosen as a reference structure. This bridge has a central span of $800\mathrm{m}$ and a total length of $\mathrm{1,480}\mathrm{m}$. The results demonstrate that the seismic demands of the long-span cable-stayed bridge vary along with different conditions of seismic motions, and the proposed performance measures and ground motion-generating algorithm enable quantitative investigation of the impact of different conditions on the long-span cable-stayed bridge.

This study investigated the seismic performance of welded stainless steel H-section columns. Ten columns were tested under cyclic horizontal load; their seismic performance was analyzed according to their hysteresis curves, degree of plasticity, and energy dissipation capacity. The test results obtained were used to validate the developed finite-element (FE) model, which was later utilized in parametric studies. In the tests, it was found that the final failure form of all test columns was local buckling. Slenderness of the component plates and axial load ratio were the governing factors which affected the development of plasticity within the cross sections, the energy dissipation density, and the ductility coefficient. The cross-section classification in the relevant European code is discussed in this paper. Based on numerical data, a ductility-based design approach is proposed, which can provide a reference for the seismic design of welded stainless steel H-section columns.

In recent years, falling-floor impact scenarios have been studied because they may generate disproportionate collapse. A series of impact tests was carried out at Nanyang Technological University to investigate the dynamic behavior and impact resistance of steel-framed structures. Ten specimens with five types of beam–column connections—i.e., a welded unreinforced flange-bolted web connection (WUF-B), a reduced beam section connection (RBS), a fin-plate connection (FP), a reverse channel connection with flush end plate (RC-FEP), and a reverse channel connection with extended end plate (RC-EEP)—and two typical impact locations—i.e., at midspan for tensile/bending failure, and at beam end for shear failure—were tested under impact loads. Finite-element models were developed and validated against the experimental results. Numerical and experimental results indicated that the numerical model is capable of predicting the dynamic behavior of steel-framed specimens subjected to impact loading in terms of the impact force, displacement, energy absorption, and failure mode. The results showed that all specimens had greater failure displacement under midspan impact. Except Specimen FP, the specimens had greater impact force under beam-end impact. Only Specimen RC-FEP had greater energy absorption under beam-end impact than under midspan impact. Specimen RC-EEP and Specimen FP had the best and worst impact resistance, respectively, which was attributed to the greatest and lowest energy absorption at both impact locations.

A full-scale 2-story mass timber building was tested on the University of California San Diego Natural Hazards Engineering Research Infrastructure (UCSD-NHERI) uniaxial shake table during the period from June 2017 to September 2017. The main objective of the experimental program was to test the performance of mass timber building designs with different seismic lateral force–resisting systems. The focus of this study is on a building configuration designed using self-centering post-tensioned cross-laminated timber (CLT) rocking walls with U-shaped steel flexural plate energy dissipators. The shake-table tests were designed to subject the building to a series of earthquake ground motions of increasing intensity, ranging from a service-level earthquake to 1.20 times the maximum considered earthquake intensity. Between each ground motion, low-amplitude white-noise excitations were applied to the building, which responded as a quasilinear system. In this paper, two output-only operational modal analysis methods are used to estimate the modal parameters (frequency, damping, and mode shapes) based on acceleration data collected during the white-noise shake-table tests. The correlations of observed damage and repairs performed during the experimental program with changes in estimated modal features are reported. The modal parameters estimated from the testing program are also compared with a linear finite-element model that is used to validate the modal identification results and study the performance of the two system identification methods for CLT rocking structures.

Damage assessment in postearthquake reconnaissance of civil structures has traditionally relied upon the judgment of experienced site inspectors. In a step toward eliminating the need for on-site inspections, this paper presents a method for automatic postdisaster structural damage assessment of reinforced concrete (RC) structures. The method uses digital image correlation to automatically detect cracks in RC structural elements and correlates the analyzed crack distributions to a damage index using fractal dimension. The method is applied in this study to track the progression of damage in a planar RC shear wall and a cylindrical RC containment vessel tested in a laboratory under reversed cyclic loading. The results from the proposed damage index are compared with quantitative and qualitative damage indices that have been used in the past to evaluate damage levels in RC structures. The results demonstrate the ability of the method to measure crack distributions and automatically correlate them to a damage index. The method is also applied to an RC shear wall tested under an actual earthquake ground motion record using hybrid simulation to evaluate its performance in a more realistic damage assessment scenario. The results show that the method is able to track the progression of damage to an RC structural element in a realistic earthquake damage scenario. Based on the results, damage grades are proposed that can be used to relate the automatically computed damage index to a specific damage level. The results show great promise for the automatic damage assessment method and is a first step towards automated postdisaster damage assessment of RC structures using digital image correlation.

This paper presents results from 21 large-scale experiments on steel columns that examined their collapse behavior as related to steel moment resisting frames (MRFs). The test specimens included wide-flange and square hollow structural shapes (HSS) and were tested until complete loss of their lateral load-carrying capacity. The test results suggest that the collapse rotations of steel columns under collapse protocols, representing near-fault events, are two to three times larger than those of their counterparts under standard symmetric cyclic protocols, regardless of the examined cross-sectional compactness. Conversely, when ground motion duration is an important seismic hazard characteristic, the collapse behavior of steel columns is reasonably traced with a standard symmetric cyclic protocol. It is shown experimentally that steel columns have an inherent reference energy dissipation capacity regardless of the employed loading history. Axial shortening attributable to local buckling is up to 10 times larger in interior than in end columns, which leads to differential axial shortening within a steel MRF story even at modest lateral drift demands during subduction zone seismic events. The test data underscore that the formation of local buckling at a column’s fixed end caps the strain demands at about 1% near complete joint penetration welds between the column and the base plate, even when the transient axial load demand becomes tensile. Simpler welds may provide adequate ductility in steel columns featuring cross sections near the compactness limits for highly ductile members according to current design standards. It is shown that the estimated rotations by current ASCE 41 acceptance criteria for collapse prevention are 5–10 times smaller than the measured collapse rotations, even for columns with moderately compact profiles.

This study investigated the compressive behavior of concrete-encased high-strength steel angle columns ($F_y=718\mathrm{MPa}$). Axial compressive tests were performed on six composite columns with different angle sections and confinement details. The results showed that the failure mode of the columns was local buckling of the angle legs and crushing of the confined core. Local buckling and concrete confinement significantly affected the compressive strength and ductility. The test strengths were compared with the theoretical strengths computed using the plastic stress distribution method. For analytical investigation, effective stress–strain models of the steel angle and concrete are proposed to account for the local buckling, spalling, and confinement. Through the strain-compatibility analysis based on the proposed models, the contributions of the angles, unconfined cover, and confined core to the compressive strength varying with deformation were investigated. Based on the investigation results, recommendations for the design and detailing of concrete-encased high-strength steel angle columns are given.

This paper presents the details of a numerical study aimed at investigating the fire performance of carbon-fiber-reinforced polymer (CFRP)-strengthened short square hollow section (SHS) steel columns with and without an insulation system. Steady- and transient-state finite-element (FE) models were developed to simulate the behavior of CFRP-strengthened columns exposed to uniform elevated temperatures and CFRP-strengthened and insulated columns exposed to standard fire conditions, respectively. They were validated using the results of the authors’ experimental study. A detailed parametric study was then conducted using the validated steady-state FE model to determine the influence of SHS steel grade and dimensions and CFRP strengthening configuration on the axial compression capacity deterioration at elevated temperatures, based on which suitable design equations were proposed to predict the elevated-temperature axial compression capacity of CFRP-strengthened columns. Fire resistance ratings (FRRs) of CFRP-strengthened and insulated SHS columns were determined based on the time-temperature profiles from heat-transfer analyses and the load ratio versus critical temperature profiles developed from steady-state FE analyses. In this study, two types of insulation materials (spray-applied CAFCO 300 and intumescent paint) were investigated, and both were found to provide satisfactory FRRs, where more than 60- and 120-min FRRs were achieved for most columns with CAFCO 300 and intumescent paint, respectively. The modeling and design methods presented in this paper can be used to conduct fire safety designs of CFRP-strengthened and insulated steel columns.

This paper focus on parameter identification of the main cables of cable suspension structures. Based on the dynamic stiffness theory, an inverse analysis characteristic function (IAC function) for identifying the main cable parameters (such as cable tension, moment of inertia, cable length, and mass per unit length) is established. This function allows for the consideration of cable flexural rigidity, sag, inclination, and additional lumped masses sustained by the suspender. The effects of the cable tension and moment of inertia on the IAC function are investigated via a numerical method. On this basis, a method for identifying the two parameters based on the peak-ridges of the IAC function is proposed. The method comprehensively utilizes measured multimode frequencies. It is unnecessary to determine the fundamental frequency and frequency order. A 20-m real cable test with suspended lumped masses is conducted to verify the correctness of the proposed methods. With the increase in the weight of suspended lumped masses, the advantages of the proposed method are more obvious. For operational cable tension less than 50% of the cable breaking tension, the cable moment of inertia is less affected by suspended lumped masses.

Laminated elastomeric bearings are used widely as seismic isolation devices. Most previous studies on the horizontal behavior of elastomeric bearings have assumed that the rotations of the top and bottom supports of the bearings are zero, mainly because in conventional practice, the superstructure and substructure above and below the isolation layer have very large rotational stiffness. However, in certain applications, including in bridges, in midstory isolation, and isolation of high-rise buildings, the support surfaces of elastomeric bearings may experience appreciable rotations. The main objective of this study was to investigate the effect of support rotation on the horizontal behavior of elastomeric bearings. For this purpose, an extensive experimental campaign on a circular isolator was conducted. Two experimental procedures were used. The first procedure investigated the behavior of the bearing under lateral quasi-static cyclic displacement, constant axial load, and constant rotation. The cyclic tests illustrated the effects of rotation on the hysteresis loops. The second procedure investigated the behavior of the bearing through monotonic lateral displacement under constant axial load and rotation. The experimental results were used to validate an advanced finite-element model (FEM) of the bearing. In addition, the experimental results were used to validate a mechanical model (MM) proposed by the authors in a previous study to account for the effect of rotation on the lateral behavior of elastomeric bearings.

Cross-laminated timber (CLT) panels with unbonded post-tensioning and a rocking mechanism can be used as a robust lateral load–resisting system (LLRS). The seismic performance of these systems can be improved further by incorporating external sacrificial energy dissipating elements. The additional damping provided by the energy dissipaters reduces the structural displacement demand during a design-level earthquake, and the unbonded post-tensioning provides recentering ability. This study developed a surface mountable, easily replaceable sacrificial oval metallic element specific to the CLT walls using aluminum was. This connector contributes to the wall system lateral load capacity. Laboratory testing of the aluminum connectors under cyclic shear loading was performed to characterize the force–displacement behavior and energy dissipating capacity. A detailed three-dimensional (3D) finite-element analysis (FEA) of aluminum connectors was carried out to replicate the observed experimental behavior. The experimental results, analytical modeling, and design equations for connector force–displacement response based on first principles are presented in this paper. The test results showed that the O-connectors can be used as an effective energy-dissipating element with equivalent damping ratio varying between 20% and 40%. The simplified design equations calculated the response within 90% of the measured values.

Documented evidence shows that anchor nut loosening on highway ancillary structures has been a problem in the transportation industry since at least the 1990s. There have been reported cases in the past, where loose anchor nuts were found to be partially responsible for the failure of ancillary structures. Resonant vibrations in ancillary structures as a result of variable frequency winds are believed to be one of the potential causes of loose anchor nuts. The current research primarily focused on investigating the effect of wind-induced vibrations on the loosening of anchor nuts in double-nut moment connections in ancillary structures. The research involved large-scale vibration testing of a traffic signal on the basis of vibration stress results from a 4-month field monitoring program. The purpose of the large-scale testing was to establish the relationship between the number of vibratory cycles, rod pretension, and nut loosening. A small-scale vibration test was also performed to validate the large-scale testing results. The testing results showed that anchor rods tightened in a double-nut moment connection above a pretension of 38 MPa (5.5 Ksi) do not experience nut loosening under vibrations.

This paper presents the procedure for the development of energy-absorbing connections (EACs) in glued-laminated timber (glulam) and cross-laminated timber (CLT) assemblies to resist the effects of blast explosions. A probabilistic approach, which ensures that energy dissipation occurs in the ductile connections prior to brittle flexure failure of the wood element, is presented and discussed. The design and detailing of the EACs was also based on the results from a preliminary numerical investigation. A total of 23 dynamic tests were conducted on full-scale glulam and CLT elements with EACs as boundary connections using a shock tube test apparatus. The behaviors of the assemblies were established and failure modes were characterized based on the observations of damage occurring in the connections and wood member. The results from experimental testing demonstrated that when properly designed, the EACs allow the assemblies to withstand a greater amount of blast energy than typical glulam and CLT connections as well as idealized simply supported end conditions. A two-degree-of-freedom (TDOF) analysis was conducted to model the assemblies through the discretization of the timber and connection components, and the results showed that TDOF modeling is capable of predicting the behavior of the full-scale assemblies with good accuracy.

This work studied the cyclic shear performance of connectors used for sidelap and structural connectors in bare steel deck roof diaphragms. Typical bare steel deck roof diaphragms include thousands of such connections, and knowledge of the connection shear performance is important for understanding and predicting diaphragm performance under seismic loads. The experimental program included four types of sidelap connectors: screw nestable, top arc seam weld, button punch, and the proprietary PunchLok II crimp. The testing included three types of structural connectors: power-actuated fasteners, arc spot welds, and arc seam welds. A total of 64 sidelap and 60 structural connector tests were performed under a cyclic loading protocol, to evaluate behavior at small deformations as well as under large excursions, providing the shear response up to and through the peak response, including postpeak response until material separation and failure. The connection test results were used to establish experimental multilinear backbone curves. From these backbone curves, average connection shear stiffness, strength, and ductility can be estimated and compared for all studied configurations. The connection response for the mechanical connections and welded connections exhibited significantly different behavior, particularly in terms of postpeak ductility and residual force. The connector backbone response is appropriate for use as nonlinear shear springs to model the response of the connections in high-fidelity models of bare steel deck roof diaphragms.

Nail connections, serving as critical nodes in the loading path of wood residential buildings, could play a crucial role in structural analysis and damage prediction when the structures are subjected to winds and floodings from natural hazards, such as hurricanes or tsunamis. To simulate the nonlinear behavior of the nail connections, nonoriented nonlinear spring elements usually are used for three translation degrees of freedom (DOFs). However, because the three DOFs are decoupled as three independent springs, their coupled effects can not be included in the modeling scheme, which leads to inconsistency for displacement trajectories. The equivalent parametrized beam element (EPBC) was proposed to avoid this inconsistency. However, the EPBC assumes the same response in two transverse directions, inducing inaccurate nail connection response predictions for three-dimensional (3D) problems. To include material nonlinearity and the coupled effects between different DOFs of the nail connections, this study proposes a three-dimensional equivalent parametrized beam element (3DEPBC). An algorithm of importance sampling for shear stiffness (ISSS) was developed to determine the optimal parameters for the 3DEPBC. Data from experimental tests were used to validate the accuracy of the proposed connector modeling scheme. The capability of loading coupling of the 3DEPBC was demonstrated by comparing the result with that of the equivalent nonlinear spring connector (ENSC), which uses nonlinear spring elements, and the EPBC with combined loadings. A case study was presented for the application of the nail model in a real roof. The investigation of shear stress suggested that shear stress has a limited influence on the total stress, indicating that ignoring the shear stress in the ISSS algorithm is reasonable, which also makes the algorithm more applicable. The proposed new connector significantly reduces the number of elements in the building model, and real nonlinear behavior of the building under complicated loadings can be captured carefully.

The use of cold-formed steel (CFS) elements in residential and industrial buildings is widely gaining popularity due to their ability to provide cost-effective and sustainable solutions. A high degree of flexibility in the manufacturing of various cross-sectional shapes provides a unique opportunity to further improve the load-carrying capacity of these elements through an optimization process, leading to more efficient and economical structural systems. This paper aims to offer a practical methodology for the optimum design of CFS beam-column members with different lengths and thicknesses, subject to various combinations of axial compression and bending moment, but with constant material use. The optimization process is carried out using a genetic algorithm and aims to maximize the resistances of CFS members, determined according to the European design guidelines (Eurocode 3). Six initial prototype cross sections, including both single and built-up channel sections, are selected and their relative dimensions and edge stiffener configurations are allowed to vary during the optimization process. To ensure practically relevant solutions Eurocode 3 slenderness constraints, as well as a range of practical manufacturing and construction limitations, are imposed on the cross sections. Standard commercially available single and back-to-back lipped channel sections are taken as the starting points of the optimization and used to benchmark the efficiency of the optimized sections. Significant gains in capacity (of up to 156% in the present study) can be obtained compared to the initial cross sections, while the optimization results also offer further insights on the material efficiency achievable with various cross-sectional shapes in combined loading scenarios ranging from pure bending to pure compression.

Numerical models of structural components that deteriorate primarily due to geometric instabilities under multiaxis cyclic loading are sensitive to both the assumed geometric imperfections and the nonlinear material model assumptions. Therefore, the accuracy of the constitutive model is a desirable feature in finite-element simulations. However, the classic Voce-Chaboche metal plasticity model, ubiquitous among commercial finite-element software, is found to underestimate the initial yield stress in structural steels by about 10%–30% when calibrated to minimize the overall difference in strain energy between the model and test data of load protocols representative of earthquake loading. This paper proposes a refined version of the Voce-Chaboche material model. When compared with the original model, the updated one improves the prediction of the initial yield stress, can simulate initial yield plateau behavior, and better estimates experimental cyclic stress-strain data. Constraints on the model parameters are established, a calibration procedure is developed, and model parameters are proposed for nine structural steels used worldwide. Source code for the material model is also made publicly available. A case study demonstrates that steel component behavior is sensitive to subtle differences in the material response that arise between the Voce-Chaboche and the proposed material models.

An ultrasonic shear wave-based nondestructive method is proposed in this paper to detect steel–concrete interface debonding owing to the top-bar effect. A concrete wall was cast with horizontal reinforcements at different heights in order to create interfacial defects underneath the top bars. Lead zirconate titanate (PZT) patches were surface mounted at the ends of the bars to excite and record shear waves. The ultrasonic results showed that the amplitude of the signals increased with the height of the bars. The specimens were cut open after the experiments and the top-bar effect was clearly discerned. Its increase with the height of the bar was clearly observed. An increasing difference between the high-frequency component (HFC) and the excitation frequency of the signal was observed between the bottom bar with a good bond and the top bars. This feature can be utilized for nondestructively monitoring the top-bar effect.

The axial capacity and force demand of a steel column are expected to change continuously during a fire incident. In assessing the structural performance in the event of a fire, it is important to monitor both the capacity and force demand at the entire temperature range. Although the axial capacity of steel columns at elevated temperatures can be calculated with closed form-equations in the design codes, limited information is available regarding the changes in force demand due to the time-dependent temperature load. This paper proposes a set of demand-capacity curves for steel columns at elevated temperatures with various initial force and constraint conditions. A series of full-scale steel columns are tested using the hybrid fire simulation (HFS) method to validate the developed demand-capacity curves. The hybrid fire simulation results are also replicated numerically using a finite element model. The test results match the developed curve with minimal calibration. The developed curves can be used as a quick tool to evaluate the axial capacity and force demand of a steel column at elevated temperatures.

In this study, glue-pressed engineered honeycomb bamboo (GPEHB) was prepared, and the dependence of the compressive properties of the produced GPEHB on the load–slenderness ratio, longitudinal strain–slenderness ratio, and ultimate strain–slenderness ratio was examined. The detailed failure modes were also investigated. The main failure modes of the short GPEHB specimens were squashing, crushing, and splitting, and the bearing capacity was mainly dependent on the compressive strength of the bamboo units. Buckling failure modes involving significant lateral deflection were observed for the long GPEHB specimens. With increasing slenderness ratio, the bearing capacities of the GPEHB specimens decreased significantly. The ultimate load of the GPEHB specimens decreased significantly as the slenderness ratio increased from 4 to 6 (GPEHB length increased from 736 to 1,104 mm). The ultimate deformation behaviors of the specimens were fit well by a quadratic function of the slenderness ratio. The GPEHB was also analyzed and modeled via finite element analysis (FEA). The experimental results, theoretical calculations, and FEA analysis results were compared.

The objective of this paper is to propose relationships for the reduction in mechanical properties of cold-formed steels at elevated temperature. Predicting the degradation of strength and modulus of cold-formed steels with temperature is critical to enable fire design of cold-formed steel members. Here, the properties of elastic modulus, 0.2% proof stress, 2% stress, and ultimate stress are studied for grades up to and including 550 MPa. Data are collected from the literature as well as from recent tests conducted by the authors at Johns Hopkins University. Steady-state and transient test results in the range of 20°C–1,000°C are analyzed. Retention factors are then proposed for the mechanical properties adopting a standardized format developed through committee work with the American Iron and Steel Institute.

This data paper reviews the experimental research on fully restrained beam-to-column connections for steel moment-resisting frames (MRFs) over the last $50\mathrm{years}$ worldwide and presents an experimental database consisting of 100 tests with an emphasis on those exhibiting inelastic panel zone behavior. The collected data, which is organized in a consistent format, includes full digitized histories of the local panel zone shear force–shear distortion as well as the global force–displacement hysteretic diagrams of each experiment. In most cases the original data was only available in paper format. The gathered dataset suggests that the existing panel zone models that are currently used for the seismic design of steel MRFs deviate, in some cases considerably, from the measured response quantities of an actual panel zone. These involve the panel zone stiffness and shear resistance at selected inelastic shear distortions of interest to the engineering profession. The assembled inelastic panel zone database provides ranges in which post-Northridge beam-to-column connections, which exhibit considerable inelastic deformations within the panel zone web, may achieve lateral drift demands larger than 4% without experiencing premature fracture. The assembled dataset constitutes an important source for validation of continuum finite-element models that could aid the simulation-based engineering design of steel MRF beam-to-column connections designed with a balanced design approach. The database is made available to the engineering and research communities through a publicly available data repository.

The present work proposes a new multituned mass damper inerter (MTMDI) system to reduce the wind-induced responses of linked high-rise buildings. In the proposed system, two high-rise buildings are linked to each other by two tuned mass-damper-inserters (TMDIs). Such a system exploits the large relative motion between two-linked buildings (TLBs) by using an inerter to reduce the individual building’s acceleration responses. In this paper, a model of the TLBs with the MTMDI under wind loads is proposed, and the model involves three additional scenarios, including a single TMDI in TLBs, each building separately equipped with TMDIs and tuned mass dampers (TMDs). Wind-induced responses of the TLBs are estimated based on wind loads obtained from wind tunnel tests of synchronous multipoint pressure measurements. The performance of the MTMDI system with optimal parameters obtained by the multiobjective optimization method is compared with that of the other three scenarios. The results demonstrate the effectiveness of the optimal MTMDI system in terms of mitigating acceleration responses with less requirement of total mass, which makes the MTMDI system more efficient and an attractive alternative to the other scenarios.

This technical note reports the results from a pilot testing program on the flexural behavior of cross-laminated bamboo and timber (CLBT) beams. The testing parameters include the combinations of two types of timbers, spruce-pine-fir (SPF) and poplar, as inner layers as well as two types of glubam, thin- and thick-strip glubam, as surface layers. The simply supported specimens were tested in flatwise and sidewise setups with three-point loading. The test results show that the CLBT beams exhibited an elastobrittle behavior and had adequate load-carrying capacity. The bending stiffness and capacity calculated from the test results were between those calculated by the two prediction models, i.e., a relative slip assumption model and a plane assumption model.