Journal of Structural Engineering

This paper investigates the bearing resistance of bolted connections with consideration of bolt hole elongations. Based on the test results of 27 single-bolt connections and 36 two-bolt connections fabricated from three grades of high strength steels, Q550, Q690, and Q890, with nominal yield stress of 550 MPa (80 Ksi), 690 MPa (100 Ksi), and 890 MPa (129 Ksi), the applicability of existing rules to limit the excessive elongation of bolt hole is evaluated. The comparison shows that current limitations of bolt hole elongation may overestimate the deformation capacity of connections with small end distance or with small bolt hole diameter. To find the balance between the bearing strength and the bolt hole elongation of bolted connections, a quantified load-displacement model is proposed based on a growth model. The key parameters affecting the shape of the curve are identified and analyzed. Based on the test results and the numerical simulations, global and local behavior transition states are identified. Related resistance formulae are established for these two behavior-transition states. A three-stage process for the development of bearing resistance is proposed. This three-stage bearing process describes the development of bearing resistance in relation to bolt hole elongation. A behavior-based resistance model with the flexible adjustment of reserved safety is proposed. According to the proposed resistance model, a reasonable bearing resistance design with consideration of the bolt hole elongation can be achieved.

This study investigates the high-temperature mechanical response of deformed steel bars used in the United States (ASTM A615 and A706, all grades) for the construction of reinforced concrete structural members that are at risk of fire exposure. Bars meeting both ASTM standards with nominal yield ranging from normal (420 MPa) to high strength (up to 690 MPa) were tested to fracture using a universal testing machine in combination with an electric split-tube furnace. A full stress–strain characterization at temperatures from ambient to 800°C was obtained, and all grades exhibited similar reductions in strength and stiffness as well as strain ductility at ultimate and fracture as a function of increasing temperature. Based on the experimental results, a modified version of the Eurocode 2 stress–strain model for hot-rolled steel rebar at elevated temperature is proposed. The reductions in steel ductility that are introduced by the proposed model are examined in a numerical study. A simple prototype floor beam, designed to have the same nominal strength using each grade of rebar, is analyzed for fire resistance according to ASTM E119 thermal and deflection criteria. The numerical results indicate that the reductions in strain ductility in the proposed model can reduce flexural performance for fire-exposed sections that use higher strength rebar grades. Also, reduced minimum cover requirements that are enabled by the use of higher strength bars with smaller diameter will allow faster temperature increases in the steel reinforcement. As a result, the fire resistance of the floor beam may be reduced in some cases below standard predictions based on nominal strength.

Double-web-angle beam–column connections are used extensively for gravity framing in steel buildings. Although they are designed to resist shear and to allow rotation, they still possess moment capacity that may contribute to lateral resistance, particularly in extreme-load scenarios. To characterize the nonlinear hysteretic behavior of bolted angle connections subjected to simultaneous gravity shear and rotational demand from the moment frame action, a comprehensive test program was conducted. Eight full-scale beam–column subassemblages of two different geometries were tested to characterize their hysteretic behavior and failure modes in relationship to the following parameters: angle geometry, beam and column section properties, gravity shear load, and loading history. The backbone curve of each test was calibrated numerically to reproduce the connection behavior. Double-web-angle connections exhibited large rotational capacity and stable hysteretic behavior. Their stable hysteretic behavior may be of interest in terms of a reserve capacity because it can provide sufficient rotational capacity to the gravity frame and mitigate building collapse in low-ductility braced frames.

Two full-scale Howe trusses were instrumented and posttensioned to study their time-dependent behavior in outdoor conditions. Force, relative humidity, and temperature data were acquired for more than 2 years. In addition, a single $8\times 8$ (nominal size in inches) Douglas fir member was also instrumented, posttensioned and data were acquired for more than 5 years. The data indicated that a permanent prestress state can be achieved in Howe trusses posttensioned using current technologies. Wood viscosity caused some prestress losses, which occurred primarily in the first few months for the Douglas fir members. Linear viscoelastic analyses reliably predicted observed behavior. Because wood and steel have different coefficients of thermal expansion, there were daily and seasonal prestress force fluctuations, which can be predicted using linear elastic structural models. The data showed that extended periods of very high relative humidity did not significantly change member forces. Nevertheless, Fickian diffusion analyses were performed to predict wood moisture content within a cross-section under atmospheric equilibrium moisture content boundary conditions.

Estimating seismic response of reinforced concrete (RC) structures under bidirectional excitation covering admissible incidence angles is computationally challenging and time-consuming for routine design. Further, such responses are widely scattered because of inherent variability in the characteristics of real records, especially owing to the degradation of RC members under cyclic loading. Hence, to obviate the complexity and tedium of the task, this paper suggests an approach to making an advance estimate of response under both unidirectional and bidirectional shaking for all incidence angles. To this end, response of a RC bridge pier has been computed under a set of near-fault and far-fault records. Important response indices (peak deformation and hysteretic energy) have been presented in nondimensional Π-terms choosing simple structural parameters (yield force and yield displacement) and ground motion characteristics (peak ground acceleration, root mean square acceleration, and mean period of ground motion). Representation of responses in dimensionless form reveals a shape-similar pattern. A regression model developed using these nondimensional Π-terms has been found to perform reasonably well in the statistical sense and hence can be used in practice.

Posthurricane surveys have shown that building interior damage often results from water intrusion into the building interior. The interior damage can make up 50%–100% of the total building loss; therefore, its accurate evaluation and quantification are necessary for estimation of hurricane losses. In this research, water propagation into a building’s interior was experimentally investigated. Large-scale building models with gable and hip roofs were tested for three exterior damage states. The results showed that for the light damage state, the very small area of the roof and wall defects and breaches does not allow wind circulation inside the building, and as a result, the rain affected only localized areas with defects. However, for the more severe damage states, the areas of breaches were large enough to allow wind circulation inside the building, and the water propagation path is highly affected by the internal wind flow. The findings from the current study can be implemented in hurricane loss models and improve their accuracy by estimating the water distribution inside the building.

Sudden extreme loads acting on a marine structure can seriously damage components; thus, a structural module is beneficial for simultaneously load bearing and energy dissipating. However, the low damping characteristic of metal members allows a lasting dynamic response. In this paper, a specially designed metal module is proposed. In this module, the postbuckling transition of the inner eccentric columns in the elastic state creates a hysteresis relation with an initial stiffness that is close to that of the metal material under a tension-compression load. The hysteretic characteristics of this module are simulated via finite element modeling (FEM). Theoretical models are deduced to determine the critical buckling and postbuckling transition; this work results in a piecewise equation that approximately describes the system dynamics. Using an averaging method, the constitutive relation between the structural slenderness parameter and dissipation performance is delineated by obtaining analytical expressions for the time-domain variation in the response amplitude. Analyses of different geometric parameters illustrate the damping and stiffness design of the nonlinear module. The hysteresis module is integrated as a bracing member and embedded in a representative jacket platform. In the simulation, a three-dimensional FEM and a user-defined material (UMAT) subroutine are combined in ABAQUS such that the hysteretic bracing member mitigates the wave impact response of the structure within the elastic range. The simulation results demonstrate the potential of the hysteretic module with a postbuckling transition mechanism to ensure high stiffness and to enhance damping in marine structures.

The bearing boundary conditions in bolted connections can be classified either as open. when end tear-out is possible, or as closed, when end tear-out is physically impossible. In this study, comprehensive tests of single-bolted bearing connections were conducted and analyzed considering the two bearing boundary conditions. The primary objective was to develop a generalized load–deformation relationship that can be used when designing group-bolted connections based on the instantaneous center of rotation method (ICRM). A new bearing-strength formula, permissible deformation limits, and new load–deformation relationship covering high-strength steel were proposed.

The coupled effect of corrosion and fatigue deteriorates the performance of reinforced concrete (RC) structures. This paper proposes a novel framework for the probabilistic life prediction of aging RC structures under seasonal corrosion-fatigue damage based on the fracture mechanics and equivalent initial flaw size concept. A series of fatigue crack growth tests of steel bars in air and solution environments are conducted to simulate the fatigue crack growth behavior of rebar in different seasons. The framework includes three critical deterioration stages: corrosion initiation–pure fatigue crack growth, competition between corrosion pit growth and fatigue crack propagation, and structural failure. The chloride ingress, cyclic load, corrosion pit growth, concrete cracking, seasonal environmental variation, and corrosion pit-induced stress concentration are considered. Following that, an uncertainty model is established to incorporate various uncertainties associated with the load and environment. The characteristics of different stages are discussed. A parametric analysis is also performed to illustrate the influence of stress concentration, concrete severe cracking, and seasonal environmental variation on the life prediction results. Several conclusions are drawn and future work is discussed based on the proposed study.

As proven by several past earthquakes, seismic losses associated with nonstructural damage in modern buildings are likely to significantly exceed those associated with structural damage. Hence, to satisfactorily assess the overall seismic performance of a building and consequently the associated losses, it is paramount to properly account for the nonstructural damage through the adequate estimation of acceleration demands that are imposed on its acceleration-sensitive nonstructural elements in any one-floor level during an earthquake. Component acceleration amplification factors, ${\mathrm{a}}_{\mathrm{p}}$, which measure how much the acceleration of a component is amplified relative to the peak floor acceleration are evaluated by floor motions recorded during earthquakes on instrumented buildings in the United States. The study shows that component amplification factors currently used in codes significantly underestimate acceleration demands for components whose periods are tuned or nearly tuned to modal periods of the supporting structure. Simplified equations are proposed to estimate component acceleration amplifications. The study also evaluates inelastic floor acceleration spectral ordinates. As a result of the filtering and amplification of the ground motion by the structure, the results show that even small levels of nonlinearity in the nonstructural element or its attachment to the structure lead to significant reductions in acceleration demands.

Footbridges often have a lightweight and slender design. As a result, they tend to be susceptible to human-induced vibrations. In this paper, the application of the twin rotor damper (TRD), an active mass damper consisting of two eccentrically rotating masses, for the control of human-induced footbridge vibrations is presented. A proof-of-concept prototype is developed for a real-world slender steel footbridge that is sensitive to human-induced vibrations. First, a numerical study is performed to design a TRD to mitigate human-induced vibrations. Based on these results, a TRD prototype was designed and built. Second, the performance of the TRD is evaluated on-site. The response of the footbridge to human-induced loading is measured under both uncontrolled and controlled conditions and compared to corresponding numerical simulations. The measurements confirm the results of the numerical simulations. They show that the TRD prototype is able to effectively damp human-induced vibrations of a real-world footbridge and validate the TRD design.

An experimental investigation was conducted with thin-sheet steel (TSS) double shear-bolted connections at elevated temperatures. The connection specimens were fabricated by TSS 0.42-mm G550 and 1.90-mm G450. The specimens were designed with variation in end distance. The tests were conducted at five different nominal temperature levels up to 900°C using the steady-state test method. The variation of the end distance and temperature on the behavior of the connection specimens was investigated. The increment of the connection ultimate load was found as the end distance increased up to five times the diameter of the bolt. It was also found that deteriorations of connection strengths occurred in a similar manner to the corresponding material properties at elevated temperatures. At each nominal temperature level, as the end distance increased, the failure modes of specimens changed from tearout to bearing. The experimental results were compared with predictions by using international design codes for cold-formed steel structures, including NAS 2016, EC3-1.3, and AS/NZS 2018. In calculating the nominal strengths of the connections, the reduced material properties of TSS obtained at elevated temperatures were used. Overall, the predictions from NAS, EC3-1.3, and AS/NZS were found to be conservative, with AS/NZS providing the least conservative and least scattered predictions. In general, NAS and AS/NZS could accurately predict the failure modes for TSS connection specimens that failed in tearout and bearing failure at different temperature levels.

Probabilistic methods, such as fragility analysis, have been developed as a promising alternative for the seismic assessment of dam-type structures. However, given the costly reevaluation of the numerical model simulations, the effect of the model parameters likely to affect the seismic fragility of the system is frequently overlooked. Acknowledging the lack of the thorough exploration of different machine learning techniques to develop surrogates or metamodels that efficiently approximate the seismic response of dams, this study provides insight on viable metamodels for the seismic assessment of gravity dams for use in fragility analysis. The proposed methodology to generate multivariate fragility functions offers efficiency while accounting for the most critical model parameter variation influencing the dam seismic fragility. From the analysis of these models, practical design recommendations can be formulated. The procedure presented herein is applied to a case study dam in northeastern Canada, where the polynomial response surface of order 4 (PRS ${\mathcal{O}}^4$) came up as the most viable metamodel among those considered. Its fragility is assessed through comparison with the current safety guidelines to establish a range of usable model parameter values in terms of the concrete-rock angle of friction, drain efficiency, and concrete-rock cohesion.

This paper investigates a novel retrofit strategy for code-deficient reinforced-concrete (RC) shear walls that are vulnerable to undesirable failure modes. The strategy combines weakening by partially cutting the wall base and self-centering by adding post-tensioning. RC walls in need of retrofit were analyzed under lateral cyclic loading using three-dimensional (3D) finite element (FE) modeling. Analyses were validated using test data from the literature on conventional walls that failed in flexure/shear and pure shear. These analyses were used to study the retrofit strategy. A parametric study was conducted to determine the working details of the retrofit method. A method was proposed to select retrofit parameters preliminarily. Retrofitted and original walls were compared. The sequence in which wall components failed was documented to identify changes in failure modes. Results of the analyses showed that although retrofitting reduced energy dissipation capacity, flexural displacements increased due to retrofit of poorly designed RC walls suffering from partial or pure shear failure. Retrofit resulted in fewer cracks, less intense concrete crushing, and a delayed fracture of transverse reinforcement.

Nonlinear time history analyses were conducted for 5-story and 12-story prototype buildings that used post-tensioned cross-laminated timber rocking walls coupled with U-shaped flexural plates (UFPs) as the lateral force resisting system. The building models were subjected to 22 far-field and 28 near-fault ground motions, with and without directivity effects, scaled to the design earthquake and maximum considered earthquake for Seattle, with ASCE Site Class D. The buildings were designed to performance objectives that limited structural damage to crushing at the wall toes and nonlinear deformation in the UFPs, while ensuring code-based interstory drift requirements were satisfied and the post-tensioned rods remained linear. The walls of the 12-story building had a second rocking joint at midheight to reduce flexural demands in the lower stories and interstory drift in the upper stories. The interstory drift, in-plane wall shear and overturning moment, UFP deformation, and extent of wall toe crushing is summarized for each building. Near-fault ground motions with directivity effects resulted in the largest demands for the 5-story building, while the midheight rocking joint diminished the influence of ground motion directivity effects in the 12-story building. Results for both buildings confirmed that UFPs located higher from the base of the walls dissipated more energy compared to UFPs closer to the base.

The relationships in ASCE 7 for the determination of roof snow drift size are functions of the ground snow load and the upwind fetch of the snow source area. In a 2019 paper, O’Rourke and Cocca propose a new relationship for snow drift size that includes a new winter wind parameter along with current ground load and fetch parameters. An inclusion of the winter wind parameter would improve the accuracy of snow drift estimates. The O’Rourke and Cocca paper presents the winter wind parameter for about four dozen sites across the United States. For potential use in ASCE 7, one needs a map of the winter wind parameter for the whole United States. In the current paper, the winter wind parameters for 272 locations in the United States are used to develop a map suitable for use in the ASCE 7 standard. The paper also provides information of the expected change in the design drift size if the winter wind relationship were to be used in ASCE 7. It is shown that, on average, there would be a 15% reduction for an upwind fetch of 250 ft (1 ft = 30.48 cm).

The paper presents the development of a three-dimensional (3D) beam element for the analysis of steel structures in fire that properly accounts for the degradation of the torsional strength and stiffness owing to thermal exposure. The element is well-suited for the analysis of members that are subjected to significant torsional effects, as steel members with open cross-sections subjected to torsion, lateral-torsional buckling, and torsional buckling. The element is based on a corotational formulation and small strains assumption, while the local formulation was developed according to both the Timoshenko and Bernoulli beam theories. The stress-strain relationship and thermal expansion of steel were implemented according to Eurocode EN 1993-1-2 (CEN 2005). A comprehensive numerical analysis was performed and results for several case studies are presented in the paper to assess the performance of the 3D beam element. The outcomes indicated very good agreement when compared with shell-based models, highlighting promising capabilities of modeling steel structures in fire. Moreover, the proposed element showed more accurate results with respect to beam elements included into two commercial software, i.e., ABAQUS and SAFIR.

This paper describes a comprehensive experimental program on cold-formed steel built-up beams with two different cross-sectional geometries. The work aimed to experimentally investigate the interaction between the individual components under increasing loading and to quantify the effect of the connector spacing on the cross-sectional moment capacity and the behavior of the beams. In total, 12 specimens were tested in a four-point bending configuration, with lateral restraints provided at the loading points in order to avoid global instabilities. The built-up specimens were composed of three or four plain channels with nominal thicknesses of 1.2 and 1.5 mm, which were joined together using M6 bolts. Each built-up geometry was tested with three different connector spacings. The specimens were designed to fail by local buckling of their components. Additionally, strut buckling of the channel comprising the top flange in between connector points was observed. The local buckling deformations and the beam deflections were recorded during the tests. The material properties of the test specimens were determined by means of coupon tests and the geometric imperfections were measured prior to testing. The experimental results showed clear evidence of interaction between the local buckling patterns of the components, with the interaction being affected by the connector spacing and the type of geometry. However, the connector spacing showed a less significant effect on the ultimate capacity when failure was governed by local instabilities of the components.

This study developed a coupled thermomechanical damage model for structural steel at elevated temperatures. The need for adequate modelling of steel deterioration behavior remains a challenging task in structural fire engineering because of the complexity inherent in the damage states of steel under combined actions of mechanical and fire loading. A fully three-dimensional damage-coupled constitutive model was developed based on the hypothesis of effective stress space and isotropic damage theory. The new coupling model, adapted from an enhanced Lemaitre’s ductile damage equation and taking into account temperature-dependent thermal degradation, is a heuristic approach which retains the underlying mechanisms that govern the damage processes. The proposed damage model comprises a limited number of parameters that can be identified using unloading slopes of stress–strain relationships through tensile coupon tests. The proposed damage model was successfully implemented in finite-element software and validated against a comprehensive range of experimental results. The damage-affected structural response was accurately reproduced under various loading conditions and a wide temperature range, demonstrating that the proposed damage model is a useful tool in giving a realistic representation of steel deterioration behavior for structural fire engineering applications.

This paper experimentally and numerically investigates the service and ultimate behavior of adjustable bolted steel plate connections—slip-critical, splice plate connections that can join wide flange sections at a range of angles as well as adjust in situ to achieve additional angles or compensate for erection and fabrication tolerances. The connection is comprised of plates that are cold bent by a press brake to a specific set of angles, forming a prefabricated, kit-of-parts. Adjustability is achieved by further cold bending the plates in the field through bolt tightening. The slip and bolt shear behavior of the connection was experimentally tested by applying an axial force on a wide flange member (via a servo-controlled hydraulic actuator in displacement control) joined by the tested connection to another wide flange member (restrained by a rigid reaction frame). A total of 18 scenarios were tested to investigate the effect of (1) the direction and amount of cold bend via bolt tightening, (2) tightening approaches, (3) the direction of loading, and (4) the plate and member angle on the behavior. A finite-element numerical modeling approach was developed and validated, offering additional understanding of bolt behavior in the adjustable bolted steel connection. A degradation in slip capacity was observed due to a reduced clamping load. During bolt tightening, the bolts deform nonflush plies into contact with the flanges and are simultaneously being bent by contact with the plates, leading to this reduced clamping load. The bolt shear capacity can also be degraded due to the connection geometry, which can reduce the engagement of the shear planes. Recommendations for reductions in slip and bolt shear capacity are developed. Importantly, findings also offer insight into the behavior of bent connections, as well as misaligned or nonflush connections that are force-fit in the field.

This paper proposes novel self-centering (SC) seismic base isolators by utilizing shape memory alloy U-shaped dampers (SMA-UDs) with favorable superelastic behavior. Two different designs, which incorporate the SMA-UDs into a conventional laminated rubber bearing with a lead core or that with steel-UDs, are investigated. In both designs, four groups of superelastic SMA-UDs are arranged symmetrically around the rubber bearings. In the SC seismic base isolators, the laminated rubber bearings withstand the high vertical loads from superstructures, and the lead cores or the steel-UDs provide the majority of energy dissipation through hysteresis behavior under cyclic loading. Moreover, the superelastic SMA-UDs spontaneously offer excellent SC force, which can effectively minimize residual deformations and reduce downtime after earthquakes. This study first illustrates the working mechanism and performance of the SMA-UDs in the base isolators through a series of component tests under loadings with different directions (i.e., in-plane and out-of-plane directions), protocols, and frequencies. Subsequently, the principles and performances of the SC base isolators are examined systematically through the quasistatic cyclic loading tests of the conventional and proposed base isolators. Test results demonstrate that these SC base isolators can exhibit satisfactory SC capability and stable energy dissipation. Moreover, the hysteresis characteristics of the SC base isolators are nearly isotropic, thereby enabling the SC base isolators to resist seismic actions in any horizontal direction. In comparison with conventional seismic base isolators, the proposed SC base isolators will provide a promising type of high-performance seismic-resilient devices required by modern civil infrastructure.

Although toenailing has been common practice in light-frame residential construction, using toe screws in cross-laminated timber (CLT) shear walls has not been investigated. CLT shear walls with inclined washer-headed, self-tapping screws installed along the wall’s bottom edge into a floor plate were tested to evaluate the shear wall connection. The tested geometry represents platform construction wall-to-floor conditions at the top and bottom of walls in multistory timber buildings. Three CLT shear wall connections—equally spaced toe screws, grouped toe screws, and a combination of toe screws and hold-downs—were tested under monotonic and cyclic loading. The full-scale CLT walls had a $2:1$ aspect ratio; their performance was compared to that of other CLT metal connections, light-frame-shear walls (LFSWs), and the presented design method. Wall properties, backbone curves, ductility, equivalent-energy-elastic-plastic (EEEP) curves, and standard idealized-component backbone, nonlinear modeling parameters, and acceptance criteria were extracted for nonlinear static pushover analysis. Toe-screwed (TS) CLT shear walls exhibited significant energy dissipation due to the head pull-through failure mode found in connection assembly testing. All tests had significant hysteretic pinching and CLT damage. Walls displayed 2.6%–3.7% drift and good strength with rapid secondary backbone degradation. Toe-screwed CLT shear connections using partially threaded, washer-head screws exhibited high strength, stiffness, large hysteresis loops, and ductility compared to other CLT metal connections and LFSWs. The equally spaced and grouped toe-screw connection conditions exhibited 3.4% drift capacity and strength and energy dissipation comparable to those of the wall connections in the reviewed literature. Walls with toe screws and hold-downs exhibited higher strength, lower drift capacity, and good stiffness compared to the equally and grouped toe-screw walls. The results suggest that washer-head, partially threaded toe screws are a viable connection in lateral-force-resisting systems.

Sliding-base (SB) systems are efficient for protecting low-rise buildings in high-seismicity rural areas. The normalized peak pseudoacceleration (NPPA) of one-story SB structures under three-component earthquake excitation and its dependency on various structural and ground motion characteristics are investigated herein. The relationships between the NPPA and the normalized peak ground acceleration (PGA) are basically identical for both orthogonal horizontal directions. The vertical earthquake component can either increase or reduce the horizontal superstructure response; for most cases, its effect is negligible. The NPPA first increases and then decreases as the natural period of the superstructure increases; the responses at the period of the maximum mean NPPA can be used to represent the responses of possible SB structures. The ratio of the natural periods in the two orthogonal horizontal directions and the difference between the static and dynamic friction coefficients affect the superstructure responses of SB structures little. The earthquake magnitude and source-to-site distance also exhibit negligible effects. The superstructure responses under pulse-like ground motions are generally smaller than those under non-pulse-like ground motions. Local site conditions affect the superstructure response; sites on softer soils display larger NPPAs. However, this effect decreases rapidly as the normalized PGA increases. For a given site class, mass ratio, and normalized PGA, the NPPA probability distribution approximately follows a normal distribution. Simplified equations with associated regression coefficients were proposed to estimate the mean values and coefficients of variation (COVs) of NPPAs. These equations can be further used to predict the NPPA corresponding to any probability of nonexceedance.

Shear-acting structural fuses rely on steel plates subjected to in-plane lateral displacements that dissipate energy through shear yielding or may have cutouts that result in shear or flexural yielding of ductile local mechanisms. However, the relatively high slenderness of the plates makes them prone to buckling, reducing the strength and energy dissipation capacity. The current study aims to facilitate local yielding mechanisms in shear structural fuses while resisting buckling. First, a genetic algorithm is implemented to find optimized topologies for structural fuses with a square domain and constant thickness. An objective function is formulated using the elastic shear buckling load obtained from a 3D eigenvalue analysis and the shear yield load obtained from a material nonlinear, but geometrically linear 2D plane-stress analysis. The ratio of shear yield load divided by shear buckling load is used as a way to control the amount of yielding expected before buckling. The set of new optimized topologies are interpreted into smooth shapes and analyzed using finite element models to evaluate their effectiveness. The finite element simulations show that the optimized geometries can resist buckling through inelastic displacement cycles with up to five times larger displacements than those that cause buckling in previously studied structural fuse shapes.

The shear transfer strength (STS) of uncracked concrete at ambient and after elevated temperatures of 350°C, 550°C, and 750°C is investigated. Forty-eight uncracked push-off specimens with different confinement levels were cast with a constant concrete mix having a target compressive strength of 40 MPa. Specimens were heated at different temperatures in an electric furnace and tested for STS after natural cooling. Results revealed that loss in STS was at its maximum for specimens without transverse reinforcement. An increase in transverse reinforcement resulted in a decrease of loss in STS after exposure to elevated temperatures. Elevated temperatures resulted in the reduction of stiffness of the shear stress-crack deformation curves and also increased the crack deformation corresponding to peak shear stress. An equation for the prediction of STS after elevated temperature is also suggested from the experimental results and validated on the specimens reported in the literature.

The supportive structures of power grids are vital but susceptible to weather-related events, such as extreme wind and icing rain with concurrent wind. The objective of this paper is to assess the reliability of the power grids subjected to high wind and ice accretion. The material and geometry uncertainty and the strength deterioration of poles due to decay are included in probabilistic models considering the bending failure of the poles and tensile failure of the wires. The extreme wind speed and icing accretion thickness are modeled with the Weibull distribution and generalized Pareto distribution, respectively. The fragility and reliability are analyzed with a Monte Carlo simulation for the comparison of two example locations with different hazard conditions. Case studies are implemented with a notional system and the system of Centerville, a fictitious study domain. The results illustrated that the fragility of wires is noteworthy in icing hazard reliability assessment. During icing rain, the concurrent wind speed significantly impacts the reliability of the power grids. The system reliability subjected to wind hazards is more sensitive to pole strength deterioration than in icing scenarios. The presented analysis framework will be beneficial for the design and maintenance of power grids subjected to both wind and icing hazards.

This study conducted experimental research on inelastic behavior of RC beams under cyclic loading. The experimental results were investigated and compared for two types of plastic behavior, ductile and nominally ductile, and for two types of plastic hinge mechanism, unidirectional (nonreversing) and bidirectional (reversing) behavior. For test samples with different transverse reinforcement detailing and inelastic demand, displacement capacities, curvature ductility ratios, longitudinal reinforcement strain capacities, plastic hinge lengths, concrete contribution to shear force, and cumulative dissipated energy capacities were obtained for various damage limit states. A new cumulative damage index is proposed based on plastic hinge behavior of RC beams taking into account the low-cycle fatigue behavior of longitudinal reinforcing steel. The proposed damage model was compared with experimental results.

A new type of concrete-filled steel plate (CFSP) composite shear wall that employs high-strength concrete (HSC) and square spiral-confined concrete-filled steel tube (SCCFST) boundary elements was proposed to reduce the core wall thickness of skyscrapers. Since the axial compressive behavior of the SCCFST boundary elements is essential to the overall seismic performance of the proposed composite shear wall, studies on square SCCFST members with HSC were first conducted to lay a foundation for further studies on the composite shear walls. Twelve SCCFST specimens and two conventional concrete-filled steel tube (CFST) specimens with the concrete compressive strength of 112 MPa were tested. The test variables included the amount and yield strength of the spiral and the ratio of the spiral-confined area to the total concrete area. The axial load capacities of the SCCFST specimens were essentially not increased, whereas the postpeak performances of the SCCFST specimens were significantly improved in comparison with the corresponding CFST specimen. The spirals in all the SCCFST specimens ruptured several times during the test, and each spiral rupture induced a considerable drop in the axial load of the specimens with high-strength spirals. The trend of the ductility of the concrete in SCCFST columns can be well captured by the spiral confinement index which reflects the effects of both the amount and strength of the spiral. Design expressions were derived based on the test results to determine the amount of spirals required for the boundary elements of the proposed composite shear wall using 110 MPa concrete.

This paper presents a detailed study on an E-plan-shaped (asymmetry about both plan axes) building under wind excitation (wind angles varied from 0° to 330° at an interval of 30°). This study is conducted by the wind-tunnel procedure and by utilizing the computational fluid dynamics (CFD) technique numerically. The numerical study is performed using the $k\text{-}\epsilon$ and shear stress transport (SST) $k\text{-}\omega$ models. The pressure contours and mean pressure coefficients of all the faces are computed by both approaches. The results show a good agreement between the experimentally and numerically computed results. The SST $k\text{-}\omega$ model performed better in comparison with the $k\text{-}\epsilon$ model for computing the mean pressure coefficients. The maximum positive and negative mean pressures of some faces of the building are found at skew wind angles. Additionally, a comparative study of the pressure variation with a symmetrical E-plan-shaped building (having the same cross-section area) is conducted in this paper. This study has shown that a drastic increment in the pressure variation is noticed for both the maximum positive and negative mean pressure coefficients due to a small aerodynamic modification.

The nonstationarities observed in extreme winds (e.g., tropical cyclones and downbursts) are typically characterized by the time-dependent second-order statistics (e.g., power spectra and correlations) for engineering applications. In the conventional simulation of nonstationary winds, however, only the time-varying spectra are addressed, for example, through the evolutionary power spectral density approach. The spatial correlation (zero time lag) is usually treated as time-invariant. In this study, the Hilbert transform, together with the wavelet packet decomposition technique, is utilized to simulate nonstationary wind fields with time-varying spatial correlation. The Hilbert-wavelet scheme first decomposes the original broadband wind process into a series of monocomponent subsignals, and then the corresponding instantaneous amplitudes, phases, and frequencies are obtained. Hence, it actually requires the simulation of time-varying multiscale spatial correlation between subsignals at various decomposition levels. It turns out that the correlation coefficients for each scale (decomposition levels) can be determined by the time-dependent probability density function (PDF) of the instantaneous phase difference between corresponding subsignals. In addition, the bounded Gaussian-like distribution of the instantaneous frequency indicates that the power spectral density (PSD) of the instantaneous phase difference should possess a low-value upper bound. The widely used translation process theory is employed to ensure that the generated instantaneous phase difference sequences satisfy both target PDF and PSD. A numerical example of the downburst wind field is used to demonstrate the high simulation fidelity of the proposed synthesis scheme for nonstationary winds with time-varying multiscale spatial correlation, and a tall building with various natural frequencies and damping ratios is utilized to show the significance of the time-varying multiscale spatial correlation in the estimation of the wind loading of structures.

Axially loaded elements play an important role in various civil structures. Knowledge of these crucial members is critical to health monitoring and performance assessment of a structure system in daily service or after a disaster. In the framework of substructure identification, a vibration-based method is proposed to evaluate the mechanical performance of a beam-like structural member by using multipoint dynamic measurements from acceleration, velocity, or displacement sensors. The major advantage of this method is its ability to simultaneously identify axial force, bending stiffness, and boundary conditions of the beam based on the local modal parameters of two or more modes, which is particularly favorable in the case that anchorage devices become complicated and uncertain through long-term service or after disasters like earthquakes. A laboratory experiment is conducted to validate the feasibility and effectiveness of the proposed method.