Journal of Structural Engineering

The progressive failure analysis of wood-frame structures under wind loads requires the resistances of each of the components (such as roof, walls, and connections) as input. The resistance functions should be able to account for the variability in the design parameters, support, and loading conditions. This study provides parametric models to calculate the in-plane (IP) and out-of-plane (OP) wind load resistances of wood-frame walls based on finite element analysis (FEA). The finite element model (FEM) of the walls are validated against experiments from published literature, and the IP and OP failure loads of the walls are determined for different length, height, stud spacing, sheathing nail spacing, sheathing thickness, presence of drywall and opening, and different support conditions. Based on a broad set of data generated by finite element calculations, two parametric models are developed to estimate the IP and OP wind load resistances of the walls by considering all of the variable parameters in this study. The parametric models demonstrate very good agreement with the FEM generated data and the available experimental results and will be useful to facilitate progressive wind failure analysis of wood-frame structures.

This paper presents an experimental investigation of bolt behavior in adjustable bolted steel plate connections during field installation and a numerical finite-element (FE) parametric investigation of the impact of (1) bolt diameter; (2) plate thickness; and (3) member flange thickness on the strains induced in the plates and bolts during field installation. The adjustable connection consists of prefabricated cold-bent plates that are further bent during field installation (via bolt tightening) to form moment-resisting joints between steel members. The connection is adjustable because the bolt-tightening field installation process changes the connection angle in situ to accommodate additional angles or manufacturing and erection tolerances. This paper presents the residual bolt surface strains, measured using the full-field photographic technique digital image correlation, providing unprecedented information on the behavior of high-strength bolts. A FE modeling approach for predicting strains in the plates and bolts is developed and validated against measured data. Parametric studies are then performed using the validated FE models with varying bolt diameter, plate thickness, and member flange thickness. Research results are relevant to any misaligned (i.e., nonflush) bolted connections, offering insight into strains from force fitting.

The seismic performance of four- and eight-story steel buildings with prepressed spring self-centering energy dissipation (PS-SCED) braces was evaluated using a proposed nonlinear mechanical model. Nonlinear dynamic analyses of conventional steel braced frames (CSBFs) were performed for comparison. Compared with CSBFs, PS-SCED braced frames experienced smaller peak interstory drift, less residual deformation, and lower peak floor acceleration. An orthogonal experiment was used to investigate the influences of three dimensionless design parameters of PS-SCED braces on structural responses. The results indicate that the variation in the ratio of friction slip force provided by the energy dissipation mechanism to the prepressed force of the self-centering mechanism had significant effects on interstory drift and residual deformation of the structure. Additionally, a change in the ratio of postactivation to preactivation stiffness of the PS-SCED brace could elicit significant changes in these two responses. An increase in contact friction between the combination disc springs resulted in a significant increase in peak floor acceleration; therefore, these contact frictions should be avoided when assembling PS-SCED braces.

An in-situ experimental campaign investigating the in-plane behavior of retrofitted timber floor diaphragms was undertaken on full-scale specimens located in a two-story clay brick unreinforced masonry building constructed circa 1913. The diaphragm retrofit strategies included renailing of board-to-joist connections, use of a fire-rated ceiling, use of steel chords, and the application of a plywood sheet overlay. When compared with as-built single straight-sheathed diaphragms, all tested solutions provided significant stiffening of the in-plane diaphragm response, with the sole exception being the configuration incorporating steel chords, where the chord influence was observed to be negligible. The fire-rated ceiling showed noticeable strength degradation due to cyclic loading while the plywood sheet overlay exhibited no strength loss between cycles to the same deformation levels, demonstrating the ability of the plywood-overlaid diaphragm to resist multicyclic loading. The subsequent phase of the study included comprehensive numerical modeling of the adopted retrofit strategies and their validation against the attained experimental results. A detailed parametric study on retrofitted timber floor diaphragms was also undertaken and is reported herein. These numerical investigations allowed evaluation of the most efficient overlay pattern, and also allowed the influence of aspects such as the plywood thickness and connection properties to be considered.

This paper presents experimental and analytical investigations on the structural behavior of horizontally curved ultrahigh-performance fiber-reinforced concrete (UHPFRC) beams subjected to concentrated loads applied normal to plane of the beam. Four fixed-ends supported UHPFRC beams with curvatures of 0°, 60°, 90°, and 120° were tested. The structural responses, including the deflection, out-of-plane rotation, and reaction forces of UHPFRC curved beams under all stages of loadings, were experimentally studied. A change in failure mechanism of a UHPFRC beam with the change in its curvature was observed, and the load-carrying capacity and ductility of a UHPFRC beam decreased slightly with an increase in the curvature of the beam. The experimental results also indicated that due to the strain-hardening behavior of UHPFRC materials under tension, a UHPFRC curved beam exhibited improved load-carrying capacity and ductility over conventional straight reinforced concrete beams because the ductility index of each of the UHPFRC curved beam tested was over 3. In addition, structural mechanics–based closed-form solutions were developed for horizontally curved UHPFRC beams using Castigliano’s second theorem to predict the values of bending moment, shear force, reaction force, and torsional moment of the beams under linear-elastic material conditions. Influence lines for bending moment, shear force, and torsional moment were also generated using the validated closed-form equations to show the influences of critical factors on the behavior of UHPFRC curved beams.

The cracked membrane model with fixed, interlocked cracks (CMM-F), whose basic concepts were already outlined in this journal more than 20 years ago, is the most general approach for cracked reinforced concrete members subjected to in-plane stresses as long as one set of uniformly spaced cracks is considered and steel and bond stresses are modeled by equivalent, uniformly distributed stresses. However, the CMM-F was not implemented so far, due to the numerical intricacy of the general solution procedure. In this paper, these issues are overcome by determining the variation of steel and concrete stresses and strains between cracks using the tension chord model (TCM), rather than by iteratively integrating over a crack element. After a discussion of the compression field approaches, the TCM and the CMM-F, including the constitutive relationships of concrete and reinforcement and aggregate-interlock models, response predictions obtained from the CMM-F are validated against experimental data. While the agreement is generally good, the predicted stresses at the cracks and the crack kinematics differ significantly between the different aggregate-interlock relationships. These values should be measured in future experiments, using appropriate instrumentation, to validate the aggregate-interlock models.

To quantify the monetary losses associated with damages induced by tornado wind storms, a numerical performance-based engineering framework complete with dynamic simulation of tornado-like wind fields, calculation of probabilities of structural performance for a point-like (monopole) structure and life-cycle cost analysis is presented. Within a Monte Carlo sampling environment, digitally simulated loads generated from five distinct tornado wind field models replicate aleatory and epistemic uncertainties concentrated in the aerodynamic load coefficients and turbulent wind velocities. Using random maximum displacements and base-bending moments as engineering demand parameters, the convolution of fragility functions with hazard curves for three intensity measures (maximum tangential velocity, core radius of the simulated tornado, and starting location of the tornado) yield probabilities of structural failure for selected limit states. The shapes of the integrand probability surfaces and the subsequent estimations of relative costs exhibit significant differences among the five models despite the parametrically equivalent simulations. This initial study, though limited through its case analysis of a point-like (monopole) structure, sets the stage for future investigations of life-cycle costs for other vertical structures (e.g., tall buildings) subjected to tornadic wind loads.

Steel castings have been increasingly used in building construction to enhance the seismic resistance of structures. Such castings are designed as yielding fuses that dissipate energy through large inelastic deformations, while the rest of the structure remains mainly elastic. Typically, the governing ultimate limit state of these yielding fuses is their ultralow-cycle fatigue (ULCF) life. This paper presents tests and finite-element analyses of small-scale coupons and full-scale tests of a variety of cast steel yielding connectors—devices that dissipate seismic energy through the inelastic deformation of cast steel triangular yielding fingers. This paper presents results of modeling improvements over previous numerical models of yielding connectors, an optimized material calibration procedure using an automated optimization algorithm and a device-specific ULCF model calibration process, the use of the stress-weighted damage model for fracture prediction that considers the Lode parameter along with the stress triaxiality, and an improved bolt friction model. These enhanced analyses provided good predictions of the onset of failure in full-scale steel castings across various specimen sizes and loading histories.

In this study, a novel method is proposed which allows for testing facilities to run hybrid simulations when the number of actuators is less than the number of the available controlled degrees of freedom. The method is based on coupling of a surrogate numerical model with a physical specimen such that the numerical model can supplement the response of a degree of freedom (DOF) that cannot be obtained from the physical specimen. This paper presents the analytical study and the theoretical framework of the proposed methodology. Additionally, a parametric study is conducted for defining the method’s applicability to various frame elements whose structural characteristics represent common frame elements. The proposed methodology of this paper is numerically verified by performing the seismic performance assessment of a typical 3-story moment resisting frame (MRF). This article concludes with the applicability figures of the proposed simulation method and the summary of the parameters that influence the applicability of the simulation method.

Base isolation is a powerful technique to prevent damage in low- and medium-rise structures during an earthquake. Nowadays, the extensive use of high-damping viscoelastic (VE) materials in base isolators has motivated the necessity to model its mechanical behavior more accurately. Traditional approaches, such as Maxwell and Kelvin models, are often used to predict VE properties. However, these models cannot precisely represent the material’s frequency-dependent behavior. Mathematical models using fractional derivatives (FD) have been shown to have the features needed to capture and predict the salient VE characteristics. Despite the possibility of such accurate descriptions using FD models in VE material applications, their implementation has been limited because of the complex computations needed to obtain the mathematical solution. This is especially true in a base-isolated (BI) building, when the bearing-superstructure coupled system includes both fractional and integer differential equations. In this study, a novel framework is developed based on dynamic substructuring to analyze a hybrid BI system with both integer and fractional order differential equations. To demonstrate the framework, the seismic response of a multidegree of freedom building model coupled with a FD state space model governing the base isolators is obtained. The structural response of the asymmetric-plan 8-story benchmark building with 92 high-damping VE bearings, governed by the fractional derivative Zener (FDZ) model, is calculated and evaluated. Using this well-known benchmark structure, a numerical comparison is performed considering the seismic response of the building fixed to the ground, the BI building with traditional elastomeric bearings, and the BI building with FDZ bearings. The results demonstrate that the framework developed provides an effective and reliable approach to evaluate the hybrid base-isolated system equations.

In modern seismic design of reinforced concrete structures, areas designed to form plastic hinges are reinforced with ASTM A706 steel because of its ability to sustain large elongations, as well as its tightly controlled specifications on yield and ultimate strength. The A706 standard now includes reinforcing steel with a nominal yield strength of 550 MPa (80 ksi), but its use in seismic applications is limited given the lack of experimental data on its behavior in members forming plastic hinges. In this paper, the results of four circular Grade 80 (550) reinforced columns tested under reverse cyclic loading are discussed and compared with companion Grade 60 (420) reinforced columns. The results showed that columns reinforced with Grade 80 (550) steel exhibited rebar fracture at lower levels of column deformation, although the onset of bar buckling, plastic hinge lengths, and energy dissipation were similar to columns reinforced with Grade 60 (420) steel.

This paper presents and discusses experiments examining the responses of mass-timber floor systems under idealized removal of an interior load-bearing wall. Testing was performed on continuous double-span ($2\times L$) and discontinuous single-span ($L$) floor assemblies with both conventional (lap-joint and self-tapping screws) and novel (additional internal steel tubes) floor-to-floor panel connection detailing. The continuous floor systems depended solely on the panels’ bending resistance, and brittle failure occurred at a deflection of 6% of $L$. Improved performance associated with ductile behavior was obtained with the introduction of floor-to-floor connections with maximum deflections of 8% and 12% of $L$ for conventional and novel detailing, respectively. For the floors with conventional connection detailing, failure was observed after compressive arching due to the low axial strength and ductility. The addition of steel tubes enabled catenary action, in which the floor systems maintained high load-carrying capacity while undergoing large deflections. This study demonstrated that adequate connection detailing can ensure structural robustness of mass-timber floors for disproportionate collapse prevention.

Precast prestressed concrete beams present camber after prestressing and early-age imperfections like initial sweep and rotations. Because there have been many reported cases of collapse with this type of element when supported only by bearing pads and during transport, its nonlinear behavior must be understood for a possible improvement in safety during handling and erection. From this observation, it should be pointed out that there have been no analytical studies on the nonlinear response of the problems. Also, no analytical solution accounts for the initial rotation of the elements on stability analysis. Thus, the purpose of the present research is to present nonlinear solutions for prestressed concrete beams resting on elastomeric bearing pads as well as truck and trailer during transport while considering initial imperfections and camber. The equations are obtained by using the Rayleigh-Ritz variational method. From the results, the nonlinear study demonstrates that the problem is highly sensitive to initial imperfections due to the unstable trajectory after peak load. The most critical imperfection for rollover of beams is the initial rotation, compared with initial camber and initial sweep. However, all misalignments influenced the maximum load. Furthermore, the proposed formulation can determine the nonlinear rollover behavior combining all these factors.

The performance of tall reinforced concrete core building archetypes in Seattle, Washington, was evaluated for 30 simulated scenarios of a magnitude 9 (M9) Cascadia subduction zone interface earthquake. Compared with typical risk-adjusted maximum considered earthquake (${\mathrm{MCE}}_R$) motions, the median spectral accelerations of the simulated motions were higher (15% at 2 s) and the spectral shapes were more damaging because the Seattle basin amplifies ground-motion components in the period range of 1.5–6 s. The National Seismic Hazard Maps do not explicitly take into account this effect. The significant durations were much longer ($\sim 115\mathrm{s}$) than typical design motions because the earthquake magnitude is large. The performance of 32 building archetypes (ranging from 4 to 40 stories) was evaluated for designs that barely met the minimum code requirements as well as for more rigorous designs that were typical of current tall building practice in Seattle. Even though the return period of the M9 earthquake is only 500 years, the maximum story drifts for the M9 motions were on average 11% larger and more variable than those for the ${\mathrm{MCE}}_R$ design motions that neglect basin effects. Under an M9 event, the collapse probability for the code-minimum archetypes averaged 27% for code minimum-designed archetypes. In contrast, the collapse probability for the archetypes designed according to current tall-building practice in Seattle were lower and averaged 14%. These collapse probabilities for an M9 earthquake, which has a return period of about 500 years, exceeded the target 10% collapse probability in the ${\mathrm{MCE}}_R$, which has a longer return period.

This paper presents a new 4-node finite element model, developed from a 2-node rocking beam element that can predict the rocking behavior of post-tensioned panels and columns. The stiffness matrix of the 2-node beam element was derived from the flexibility method. Then, the stiffness matrix of the 4-node beam element was obtained through the use of transformation matrices. The 4-node element model allows for the prediction of not only the global behavior of the rocking element (e.g., nodal displacements and nodal loads) but also the local behavior (e.g., the contact length, the vertical displacement, and the strain and stress at the rocking interface). The numerical results from the 4-node element model were compared to that from 3D finite element method (FEM) models in MATLAB 2016 and ABAQUS programs and showed a high accuracy. Moreover, the 4-node element model can be combined with the other types of elements in order to analyze building structures at a global level, especially for mid-rise and tall buildings where the nodal displacements at panel corners are vital to correctly predict the behavior of the other structural elements (e.g., light-frame shear wall elements). An example of a six-story building that included a hybrid system of post-tensioned cross-laminated timber (CLT) walls and light-frame wood shear walls was presented.

In this study, the buckling-resistant antispring-clad reinforcing bar (BRASR) for improving the performance of the longitudinal reinforcing bars embedded in concrete columns is presented. BRASR is formed using a set of springs wound in opposing directions and clad on the rebar with a groutable gap. In an experimental program, the performance of the BRASR is compared with the conventional longitudinal rebar in a typical column reinforcement cage. Short reinforced concrete (RC) square column elements with parametric variations in the ratio of tie spacing to the diameter of longitudinal bar ($s/d$) and the influence of tie restraint are evaluated under applied uniaxial compression. RC columns with spring clad bars exhibited improved buckling resistance of the rebar, which enhances the load capacity and the ultimate displacement ductility. In columns with BRASR, there is an increase in the strain energy and the resistance of the concrete core is improved. While the conventional specimens failed by a decrease in load resistance, the BRASR specimens showed better post-peak behavior and ductility.

The seismic performance of exterior beam-column joints in low-rise buildings with limited ductility details was investigated. Seven exterior beam-column connection specimens were prepared for cyclic loading tests, and the major test parameters were the column depth and joint shear reinforcement details. In the specimens, joint shear failure occurred before beam or column yielding. The shear strength of the exterior joints increased as the column depth (i.e., joint depth) and the area of shear reinforcements increased. Despite the nonseismic reinforcement details, U-shaped bars and 90°-hooked hoops with a spacing of one-third of the column depth increased the joint shear strength. As a result, flexural beam yielding occurred in several specimens. The joint shear strengths were compared with the predictions by current design codes, and the effects of the test parameters were investigated. Based on the results, a shear strength equation for exterior joints was proposed that is applicable to nonseismic details.

The uniaxial Giuffrè-Menegotto-Pinto (GMP) constitutive steel model is widely used in nonlinear modeling of reinforced concrete components. However, the parameters characterizing this constitutive law are not easily identifiable from mechanical tests. An extensive literature review showed that most authors use the parameter values recommended during the early development of this constitutive model. Therefore, a calibration of the model parameters to steel manufactured in accordance to modern standards represents an important contribution to researchers and engineering professionals. A series of cyclic stress-strain tests were performed on 36 reinforcing steel Grade 60 coupons. To obtain data about statistical variability, the bar specimens were sourced from three different manufacturers. The test results were used to calibrate the model parameters, which were then verified using a set of validation reversed cyclic stress-strain tests. The strain-rate effects were analyzed using equivalent cyclic coupon tests at rates of $0.001/\mathrm{s}$ and $0.02/\mathrm{s}$. The final calibration results are presented in terms of recommended model parameters for Grade 60 steel reinforcement complying with two commonly used standards.

This paper formulates an analytical calculation model for predicting the cracking behavior of reinforced concrete ties to provide more consistent crack width calculation methods for large-scale concrete structures in which large bar diameters and covers are used. The calculation model was derived based on the physical behavior of reinforced concrete ties reported from experiments and finite-element analyses in the literature. The derivations led to a second order differential equation for the slip that accounts for the three-dimensional effects of internal cracking by using a proper bond-slip law. The second order differential equation for the slip was solved completely analytically, resulting in a closed-form solution in the case of lightly loaded members and in a non-closed-form solution in the case of heavily loaded members. Finally, the paper provides a solution strategy to facilitate a practical and applicable method for predicting the complete cracking response. Comparison with experimental and finite-element results in the literature demonstrated the ability of the calculation model to predict crack widths and crack spacing consistently and on the conservative side regardless of the bar diameter and cover.

Superelastic shape memory alloys (SMAs) have inherent properties of complete recovery of large deformation and satisfactory energy dissipation under cyclic loadings. Such properties have attracted wide attention within the earthquake engineering community, especially for the perspective of developing self-centering (SC) structures. SMA braced frames (SMABFs) have emerged in recent years as one of promising SC frames. This paper presents a seismic design methodology for SMABFs using the hysteretic energy spectrum. The underlying principle for the proposed design methodology is that both the total hysteretic energy and accumulated ductility demands in earthquake resistant structures are correlated with the maximum endured deformation. With the quantitative relationship, the seismic performance target, such as the maximum interstory drift ratio, can be readily achieved. The spectra of hysteretic energy and accumulated ductility demands are first constructed in this study for the single-degree-of-freedom (SDOF) systems which represent the global behavior of SMABFs. The SDOF system based results were then utilized for the development of an iterative design procedure for multistory SMABFs. Both 3- and 6-story SMABFs are designed for representative low-to-medium rise building structures and subjected to a suite of earthquake ground motions scaled to the design basis earthquake (DBE) and maximum considered earthquake (MCE) seismic hazard levels. Computational simulation results show that the designed SMABFs satisfy the performance target very well. The proposed methodology is demonstrated to be effective and efficient for seismic design of SMABFs, but could also shed light on other SC structures.

In this study, a bridge seismic monitoring system was developed based on smartphones connected together in the same project as a sensor network using a cloud server for easy upload and access to data. Thus, a decentralized structural seismic monitoring network was established using easy-to-install smartphones as both sensing cells and intelligence neurons. A long-term field test of this system was performed on Japan’s Takamatsu bridge. Smartphones with the monitoring application were deployed at six different locations inside the bridge’s concrete box girder. The system was connected to a cloud server for real-time data uploading and remote control. Inconsistent sampling rates and faulty sensor readings were identified to be two major problems with the use of the proposed system; however, correction methods were also proposed accordingly. A few seismic acceleration response records of the Takamatsu bridge were captured during the more than one-year operation period. Dynamic properties extracted from this system were compared with those of reference seismometers to verify its viability and accuracy.

An analytical model for predicting the strengths of exterior reinforced concrete wide beam-column joints is developed in this paper. In the proposed model, the shear strength of the joint core is derived based on the softened strut-and-tie concept and the torsional strength of the outer joint is determined using the thin-walled tube space truss analogy. Integration and iteration in the computation processes are minimized to enable easier applications in the design practice. Compared with the predictions by current standards, the model shows high accuracy through experimental verification, with an average strength ratio of 1.04 and a coefficient of variance of 0.14. Owing to its superior accuracy, simplicity, and conservativeness, the proposed model is considered as a suitable tool for the practical design of reinforced concrete wide beam-column joints for seismic resistance in practice.

Flexural buckling is one of the main problems steel structures are faced with in ensuring an economic design. In Europe, the buckling resistance is calculated using an imperfection factor based on the section type, fabrication method, and steel grade. The current European design standards contain guidelines for the imperfection factor for sections made of steels with yield strength up to and including 700 MPa. However, the current design codes are based mainly on tests performed on steels with yield strength below 460 MPa. Therefore, the applicability of the methodology was reassessed. This paper reviewed the background documentation of the European flexural-buckling design methodology and discussed the current design practice described in the American National Standard. A total of 72 flexural-buckling experiments performed on cold-formed, hot-finished, and welded sections made of steel with yield strength in the range 690–960 MPa were collected and analyzed. Four models for estimating the resistance of high-strength steel struts subjected to pure compression were statistically evaluated based on the collected data. Finally, a recommendation for the estimation of flexural-buckling resistance of high-strength steel members is presented.

In studying the environmental impacts of buildings, earthquake hazards are rarely considered, but their environmental impacts can be significant. This case study paper demonstrates how the US Federal Emergency Management Agency’s Performance Assessment Calculation Tool (PACT) can be used to analyze the environmental impacts of buildings using probabilistic seismic hazard assessment. PACT was used to evaluate 10 case study buildings that varied by five types of lateral systems and two risk categories. For each building, PACT generated 1,000 realizations at five earthquake intensities. The resulting environmental impacts were analyzed according to their distribution, median, and average values, and the differences among building component types, risk categories, and lateral force-resisting systems were explored. In this study, building components that were categorized under Exterior Enclosures, Interior Finishes, and Heating, Ventilation, and Air-Conditioning (HVAC) produced notably higher environmental impacts in response to seismic damage, and their vulnerability to displacement- or acceleration-induced damage could be attributed to the characteristics of the lateral systems. Although these observations are notable, they should not be taken as universally applicable to all buildings. Instead, these findings exemplify how the environmental impact results from PACT can be analyzed and interpreted to address both the seismic and environmental aspects of building design.

The dynamic properties of seven supertall buildings that are currently among the world’s 30 tallest are evaluated using field measurements collected during tropical cyclone events. In this study, the natural frequencies and damping ratios of the skyscrapers under violent wind excitations are estimated using the random decrement technique and the Bayesian spectral density approach, existing prediction models for the building modal parameters are validated, and new empirical models for supertall buildings are proposed. This research aims to further understand the structural dynamic properties of supertall buildings (taller than 300 m) and provide useful information for wind-resistant design of future skyscrapers.