Journal of Structural Engineering

Two modeling approaches with different levels of refinement were used to numerically investigate the influence of different parameters on the response of straight sheathed timber diaphragms when subjected to in-plane loading. The investigated parameters included diaphragm aspect ratio, scale factor (i.e., diaphragm size), impact of board-to-board contact phenomena, and the effects of board-to-board shear force exchange. The aim of the work presented herein was to use numerical modeling to investigate the aspects that potentially contribute to the difference in experimental behavior reported in literature and that consequently might have influenced provisions encompassed in the most recent standards for the assessment of timber diaphragms. The modeling strategies were validated against a wide range of available experimental data on newly constructed and vintage timber floor specimens. Analysis results confirmed that the in-plane behavior of straight sheathed diaphragms is significantly influenced by parameters that are often neglected by numerical studies and assessment procedures.

Cables of parallel wires are idealized as laminated beams including interlayer slips to consider the effect of interfacial slips among wires on their bending stiffness. The governing differential equations for the bending of laminated beams are then derived and solved analytically under either uniformly distributed load or midspan concentrated force. Consequently, the equivalent bending stiffness (EBS) of the cable is obtained analytically, which is significantly dependent on the slip rigidity between the layers. Using the experimental results of bending tests of cables of parallel wires in the literature, the relationship between the slip rigidity and the average tensile stress of cable is established. The factors influencing the EBS of cables are studied and the EBS of cables with common cross sections is provided to demonstrate the presented method.

Although dynamic torsional responses are often regarded as secondary effects in the seismic design of symmetric-plan buildings, torsional effects arising from plan asymmetry can be substantial in some cases. In RC wall buildings, a combination of flexural, shear, and torsion dictates the type of failure, which needs to be addressed in the design of RC walls. This study investigates two aspects of building structures with C-shaped RC walls: (1) evaluation of seismic force demand at different levels of torsional sensitivity, and (2) effectiveness of using the dual plastic hinge method in controlling the seismic shear force demand. A macroscale modeling approach using the wide column analogy captures the inelastic response of C-shaped RC wall buildings, including torsional effects. The numerical model of the wall is validated against available experimental data. Nonlinear time history analyses of typical multistory buildings located in eastern North America (8-, 12-, and 16-story) are performed. Four different levels of torsional sensitivity ($B=1.3$, 1.7, 2.0, and 2.5) are considered for each building configuration. Although the studied range of torsional sensitivity has no substantial effect on the bending moment envelope of the building, it significantly increases the story shear force demand during an earthquake. The shear force envelopes in torsionally sensitive buildings ($B>1.7$) exceed the capacity design envelope predicted by the response spectrum analysis of a large number of selected ground motions. The dual plastic hinge design method recently proposed by other researchers is adopted and is found to be an efficient method, resulting in lower shear force demand along the height of the structure, especially when high torsional flexibility is expected.

Nonlinear finite-element analyses are used to numerically investigate the punching shear resistance of reinforced concrete flat plate structures. Material nonlinearity is based principally on the formulations of the disturbed stress field model, a smeared crack reinforced concrete modeling procedure. Low-cost three-dimensional solid finite elements and one-dimensional truss bar finite elements are used to represent concrete and steel reinforcement, respectively. Requiring only easily defined concrete material properties and employing fundamental finite-element meshing techniques, the modeling approach was found to provide good response estimates for slab–column connection assembly tests under concentric shear loading conditions and was shown to effectively capture the effects of design parameters on slab punching shear performance: reinforcement ratio, column size, and slab thickness. The validated modeling approach was used to perform a brief numerical investigation on the effects of boundary conditions on the punching shear capacity of multibay flat plates. The results from the investigation were compared to the response obtained for an equivalent isolated slab–column assembly specimen and to existing code provisions and two-way shear analysis procedures.

A large number of existing reinforced concrete structures, constructed before the 1970s, are poorly designed and inadequately detailed. The design and detailing of these structures are based on the prevailing guidelines and practices to cater for the gravity load demand. Such structures are extremely vulnerable during seismic events. An efficient, easy to implement, and cost-effective intervention to those structures is the immediate requirement to mitigate the damage due to possible seismic events. The present study deals with the development of an innovative single metallic bracing system fixing to the bottom of the beam-column subassemblage. This is made to protect the week joint region of gravity load designed (GLD) structures by allowing the force path to bypass from beam to column. A steel haunch system was developed and implemented in beam-column subassemblages representing the GLD scenario. Analytical formulations were developed for evaluating the force flow mechanisms in rigid and flexible systems. Experimental studies on upgraded beam-column subassemblages were carried out to check their performance under reverse cyclic loading. The key behavioral parameters such as hysteresis behavior, energy dissipation, and stiffness degradation were evaluated. It was found that the single steel haunch system was very effective in improving the performance of the subassemblages. The steel haunch system was further improved by introducing a strut relieving mechanism, which showed encouraging performance. At drift corresponding to the 20% reduction in the strength, it was found that the single haunch and strut relieving bracing systems were capable of dissipating almost 46% and 60%, respectively, more energy than that of the GLD specimen. The study points out the feasibility of seismic damage mitigation of poorly designed building stock using the innovative steel haunch system.

A unified model that can be used to study both distortional buckling and global lateral buckling of cold-formed Z-purlins with sloping lips is presented. The model is composed of the compressive lipped flange and part of the web, upon which two interactive springs are attached, representing the restraints of remaining part of the cross section. The distortional and lateral buckling capacities are obtained by the Ritz method. The inclination angle of the lip, as well as widths of the flange and lip, are varied in the parametric study. The results show that the inclination angle has a significant influence on the distortional buckling coefficient but relatively less influence on lateral buckling. The distortional buckling coefficients increase as the flange and lip widths become larger. The results are also used to predict the load-carrying capacity of available tests, and good agreement is achieved with the test results. Formulas for distortional buckling coefficients of Z-purlins with sloping lips are presented and have been verified to have high accuracy compared with the numerical results.

The conventional restraining ratio approach is not suitable for a straightforward design of the pre-tensioned cable-stayed buckling-restrained brace (PCS-BRB) because of its complicated buckling-restrained system. This study uses an adequate bracing approach to establish a more rigorous design procedure for the PCS-BRB by analyzing and designing the PCS-BRB as a braced system; a simplified midspan braced column with translational and rotational springs. Based on the results from an elastic buckling analysis, the influences of the midspan translational and rotational spring stiffnesses on the buckling axial loads associated with symmetric and antisymmetric buckling modes, respectively, are discussed. In a second-order analysis, the solution for the column differential equation of equilibrium is derived considering both symmetric and antisymmetric initial imperfections. The inverse interrelationship between the bracing strength and stiffness requirements is investigated. Then, using the results from these analyses for the midspan braced column, the adequate bracing approach is followed for the design of the PCS-BRB. The strength limits of the cable-stayed system are formulated for its effectiveness, and its adequate stiffness requirements are determined based on examination of these strength limits. A detailed design procedure and an elementary design example are presented.

In coupled shear wall or core wall systems, reinforced-concrete (RC) coupling beams are crucial to the seismic performance of the overall structure. These coupling RC beams, however, tend to undergo brittle shear failure, especially those with a small span-to-depth ratio (i.e., deep coupling beams). In this paper, an alternative RC coupling beam with high seismic resistance and high ductile behavior is proposed. The coupling beam is made of high-toughness concrete reinforced with an embedded vertical steel plate as well as steel bars. Three proposed steel plate–reinforced high toughness–concrete (PRHTC) coupling beams with different span-to-depth ratios ($l/h=1.0$, 1.5, and 2.0) were tested. All three PRHTC coupling beams behaved in a ductile manner with good hysteretic behavior and large energy-dissipating capacity. Both the embedded steel plates and the high-toughness concrete contributed greatly to the high performance of the PRHTC coupling beams. The test results also show that load-carrying capacity of the PRHTC coupling beams increases as the span-to-depth ratio decreased whereas deformation ductility remains stable.

A macroscopic global seismic damage model is proposed for reinforced concrete structures by considering the dynamic modal contributions. Modal damage is defined using the concepts of dynamic modal stiffness and modal mass. Based on the kinetic energy inequality for damaged systems, a normalization method is chosen for the proposed modal mass contribution factor, which reflects the fluctuation of modal damage caused by a change in modal shape. Assuming an in-series independence between the modal damages, a customized combination rule is suggested. Global damage curves generated from the proposed model (PM) tend to have a segmented evolution, composed of a zero-damage segment, an acceleration segment, a constant velocity segment, a deceleration segment, and a converged segment, following the general damage evolution rule. The results from a case study indicate that the PM can explain the dynamic transition in the modal damage and exhibits a distinct convergence with the increasing peak ground acceleration level and number of modes included. The proposed damage model is proven to have a good correlation with the results from the incremental dynamic analysis at the collapse-critical point, indicating a potential application as a promising collapse criterion. The results have also confirmed the effectiveness of the five-segment damage evolution curve proposed previously.

The steel–concrete–steel (SCS) sandwich composite structures with orthogonal longitudinal and transverse (bidirectional) steel webs exhibit superiorities in strength, ductility, impact resistance, blast resistance, and construction efficiency compared with the traditional engineering structures, offering a competitive alternative for applications such as submarine tunnels, nuclear shells, protective structures, offshore structures, etc. While there were several practices in engineering, the current design method is an application of the concrete code and there are few experiments that could support the design theory especially for the shear resistance. Unlike RC beams or steel beams, the SCS composite structures with bidirectional steel webs have multiple shear force transferring mechanisms, and it is of importance to investigate the contributions of the different mechanisms and how they work together as a composite structure. To address this problem, 16 shear tests of SCS composite structures with bidirectional steel webs were carried out and theoretical analysis was conducted. The shear resistance is categorized into three mechanisms: the composite truss, the pure shear of the axial web, and the dowel action of the flange. Then the theoretical method to predict the shear resistance considering the coworking of different mechanisms is proposed and compared with existing methods. It is proved that the proposed method reveals the antishear mechanism and is of satisfactory accuracy.

This paper proposes a general approach for topology optimization of tensegrity structures. The optimization problem is formulated in the framework of a mixed-integer linear programming. Compared with previous approaches, more practical issues such as member overlapping, strut buckling, displacement limits, and multiple load cases are considered in the proposed approach. The member connectivities, internal forces, and cross-sectional areas are used as independent variables. The total weight of the final structure is used as the objective function. The maximum allowed number of struts connected to each node, the maximum allowed number of cross-sectional sizes for each type of members, and the minimum number of nodes used in the final structure can be actively controlled. A novel constraint formulation is proposed to avoid the member overlapping problem. Numerical examples are carried out to verify the proposed approach. The tensegrity structures found by the proposed approach are much more suitable for practical applications, and the approach can be used as a general generator for new types of tensegrity structures for specific application scenarios.

Form-finding analysis is very important for developing innovative tensegrity structures. Nevertheless, it is frequently difficult to determine simultaneously the prestress mode and the exact nodal coordinates for a given geometry. This paper presents an improved symmetry method for analytical form-finding of tensegrity structures. The method is based on group representation theory and the force density method, and requires only the specified symmetry type and connectivity of a structure. The force densities of a $d$-dimensional tensegrity structure can be accurately determined using the zero determinant of $d$ small-sized block matrices of a symmetry-adapted force density matrix. The nodal coordinate vectors can be obtained from the null spaces of the blocks through symmetry spaces for rigid-body translations along $d$ directions. A number of geometries with cyclic symmetry, dihedral symmetry, or tetrahedral symmetry are investigated. Illustrative examples show that the proposed method allows significant simplification of the form-finding process. The analytical solutions offer all feasible stable or superstable tensegrity structures with expected symmetries. The obtained prestress modes for each independent structural configuration necessarily retain full symmetry.

The direct strength method of cold-formed steel member design uses local, distortional, and global cross-section elastic buckling analysis with empirically derived direct expressions to predict member strength. The direct strength method is an accepted design method in national design specifications and enables a unified, robust, and flexible design approach. However, for beam-columns the direct strength method in current design specifications uses simplified linear interaction expressions based on combining the pure axial and bending elastic buckling and strength response. Today, local, distortional, and global elastic buckling under any combination of axial load and bending moments may be readily found using elastic buckling analysis tools such as the finite strip method. Thus, stability may be assessed under the actual combined actions, but new direct strength method expressions are needed to utilize this explicit stability information in determining beam-column strength. In this paper, new strength expressions for each limit state are developed. In addition, the results of beam-column tests performed by the authors and those available in the literature are used to validate the performance of the new proposed direct strength method for beam-columns. The development of the direct strength method for beam-columns has the potential to provide a more mechanically sound solution to the strength of cold-formed steel beam-columns, eliminate excessive conservativeness, and at the same time encourage the next generation of optimized, high-strength cold-formed steel shapes.

Field measurements of wind effects on a 420-meter-high supertall building in Hong Kong were analyzed during the passages of 14 tropical cyclone (TC) events, from 2008 to 2016, with a total recording time duration of 360 h. In this paper, statistical results of wind characteristics of these TCs are presented and discussed; modal parameters of the building such as natural frequencies and damping ratios are estimated using the random decrement technique, which is a deterministic time domain method, as well as the Bayesian spectral density approach, which is a recently proposed probabilistic frequency domain method; and the serviceability of the skyscraper during these violent TC events are evaluated against three comfort criteria. This study uses a substantial amount of field data to yield accurate estimations of the modal parameters of the building to further the understanding of wind effects on supertall buildings in TC-prone regions to provide useful information for their wind-resistant designs.

Earthquake engineers lack well-founded consensus guidelines for selecting ground motion time series for sequential mainshock-aftershock events for use in seismic performance assessment. Past practice has seen sequences formed by coupling as-recorded mainshock and aftershock records and by using repeated mainshock records for both event types. Using mainshock-mainshock versus mainshock-aftershock record pairs, this paper assesses the structural performance of five ductile reinforced concrete frames with varying heights using sequential nonlinear response history analyses. Systematic differences are found in the frequency content of mainshock and aftershock records, which in turn produce expected differences in structural responses conditional on the dynamic characteristics of each structure. The outcome is measurable differences in the structural response, with mainshock-mainshock sequences potentially overestimating or underestimating seismic demand and risk relative to the use of more-appropriate mainshock-aftershock record pairs. This finding holds true even when mainshock-mainshock sequences are formed by preserving the magnitude and distance relationships between as-recorded mainshocks and aftershocks. The correlation between event terms of mainshock and aftershock ground motions recorded from the same sequence is found to have a significant impact on maximum story drift ratio. This paper provides recommendations for aftershock record selection that draw upon these results.

This paper presents an experimental investigation of concrete-filled high-strength steel tubular X joints. The high-strength steel tubes were cold formed into square and rectangular hollow sections with nominal 0.2% proof stresses of 700 and 900 MPa. The cold-formed high-strength steel tubes were infilled with normal and high-strength concrete with nominal concrete cylinder strengths of 35 and 100 MPa, respectively. A total of 31 tests was conducted, covering chord sidewall slenderness ratios varying between 12.6 and 40.6. Two different types of load–deformation behavior were observed and are discussed in this paper. The obtained test strengths were compared with the nominal strengths calculated using Comité International pour le Développement et l’Étude de la Construction Tubulaire (CIDECT) design provisions. Overall, the nominal strengths predicted by the CIDECT design provisions are quite conservative for concrete-filled high-strength steel tubular X joints with chord sidewall slenderness ratios up to 40. However, the predictions for specimens with ductile load–deformation behavior are found to be overly conservative. Hence, modifications to CIDECT provisions are suggested for the design of concrete-filled high-strength steel tubular joints under transverse compression.

Due to their aesthetics and structural advantages, diagrid structures have been used for several mid- to high-rise buildings around the world. However, their seismic performance, collapse fragility, and resilience are yet to be studied. This paper presents a comprehensive investigation into the nonlinear performance of steel diagrid structures using static, time-history dynamic, and incremental dynamic analyses. A framework for seismic performance assessment and loss estimation of steel diagrid buildings is developed. Illustrative and quantitative criteria for performance and damage assessment of diagrid frames are introduced and employed to estimate the seismic loss of archetype diagrid buildings. The diagrids are found to have a substantial collapse capacity and lateral stiffness. Nonetheless, the nonstructural loss due to large maximum absolute floor acceleration experienced by stiff diagrid frames may adversely impact the expected total loss. Due to the shear lag effect, the corner diagonal members are the key elements in their behavior. Further, the effects of building height, diagonal angle, and incomplete diagrid modules on performance and loss are studied.

A seismically deficient 10-story chevron-braced frame located on the west coast of Canada is retrofitted using different schemes. The building was designed in accordance with the Canadian codes applicable in the mid-1980s, prior to the implementation of the special seismic design provisions in the steel design standard. The ASCE 41 nonlinear dynamic procedure (NDP) was used to develop and validate the retrofit schemes. The performance objective was collapse prevention under seismic hazard with probability of exceedance of 2% in 50 years. Three retrofit solutions developed to satisfy the ASCE 41 component-based criteria and achieve uniform demand-to-capacity ratios over the structure height exhibited inadequate global inelastic seismic response characterized by soft-story mechanisms and structural collapse. The same behavior was observed after having increased the lateral strength of the system by 80%, clearly indicating that ASCE 41 should include acceptance criteria aimed at verifying overall seismic response. Story drift concentration and structural collapse could be avoided by combining the retrofitted braced frame with a moment frame or elastic vertical truss installed from outside along the perimeter walls. A vertical truss with a flexural hinge at midheight was found to be the most cost-effective option. The exterior frames can serve as temporary lateral system during the repair of the existing braced frame.

The estimation of building fragility, i.e., the probability function of seismic demand exceeding a certain limit state capacity given the seismic intensity, is a common process inherent in any seismic assessment study. Despite this prolific nature, the theory and practice underlying the various approaches for fragility evaluation may be opaque to their users, especially regarding the handling of demand and capacity uncertainty, or the generation of a single fragility curve for multiple failure conditions, using either an intensity measure or engineering demand parameter basis. Hence, this paper provides a comprehensive guide that compiles all necessary information for generating fragility curves of single structures based on the results of nonlinear dynamic analysis. Although various analysis methods are discussed, incremental dynamic analysis is invoked to clearly outline different methodologies that rely either on response parameter or intensity measure ordinates. Step-by-step examples are presented for each case, under both a deterministic and an uncertain limit state capacity framework, using limit states that range from simple structural damage to the global collapse of the structure.

Several standards and guidelines allow the use of the equivalent rectangular stress block (ERSB) as a simple concept to accurately predict flexural strength with or without axial force. North American codes (ACI 318 and CSA A23.3) allow the use of the ERSB as an alternate approach to stress-strain relationships in predicting the strength of high-strength concrete (HSC) reinforced with steel bars (steel-HSC-RC). The strength of high-strength concrete specimens reinforced with fiber-reinforced polymer (FRP) bars (HSC-FRP-RC) could be predicted similarly to steel-RC specimens. This research represents an early attempt to investigate the applicability of several ERSBs proposed by different associations to predict the strength of HSC-FRP-RC specimens subjected to combined flexural and compression loads. An experimental database was assembled from 92 specimens studied by the authors and others. The test parameters included concrete strength, level of eccentricity, reinforcement type, glass fiber–reinforced polymer (GFRP) reinforcement ratio, and confinement configuration. Extensive analyses were integrated into the test results to investigate the impact of each test parameter on ERSB parameters. The accuracy and conservativeness of several models were assessed. Comparing the predictions for the tested FRP-RC specimens made with normal-strength concrete (NSC) and HSC revealed that the level of conservatism dramatically decreased for all models, leading to overestimations for some specimens. The American Concrete Institute model always had the lowest level of conservatism, which led to overestimations of some specimens for steel and FRP-RC specimens made with HSC among all the other models. Modified expressions of the ERSB given in ACI 440.1R and CSA S806 were developed. The results indicate good and safe correlation of predicted and measured strength values with reasonable levels of conservatism.

Some steel structures, such as hydraulic navigation and marine structures, operate in harsh wet and corrosive environments and can suffer significant deterioration. The deterioration manifests itself in the form of corrosion, fatigue cracking, or a combination of both. Although typically viewed as a nuisance, if left unrepaired, the deterioration can threaten the integrity of the structure. Repairing these cracks using conventional repair methods has proven to be not only time-consuming but also ineffective. Recent advances in the use of carbon fiber–reinforced polymers (CFRPs) to retrofit structures have demonstrated its viability as a solution for increasing fatigue life of metal structures. However, the applications have been primarily focused on the aerospace and bridge industries, and very few studies have been concerned with retrofitting metallic structures under wet and corrosive environments. Therefore, there is a clear need to evaluate the possibility of using CFRP to repair underwater metal structures. To this end, this paper devises a new experimental setup to allow for underwater testing of large-scale steel panels retrofitted with CFRP patches. The purpose of this experimental study is to provide a first-of-its-kind benchmark data by which the potential for using CFRP for underwater fatigue repair of metallic structures can be assessed. Five large-scale steel panels are tested, three of which are repaired with CFRP patches, under different environmental conditions. The study evaluates the effect of CFRP retrofit on crack growth rate. Because the application in this study pertains to water navigation structures used in rivers, the effect of fluvial sediments and salt are considered. The use of salt allows for accelerated corrosion in the specimens to represent the actual condition of deteriorated panels. Test results for dry and underwater specimens show an increase in fatigue life with the use of CFRP compared with bare specimens. The results also show an increase in debonding susceptibility of the CFRP when the CFRP/adhesive system is subjected to corrosion, turbulence, and sediment particles.

Seismic fragility analysis involves probabilistic assessment of the seismic performance of structures. A large amount of uncertainty is involved in the estimation of seismic fragility. The probabilistic modeling framework for performance assessment requires specifying the uncertainties in key input parameters in terms of probability distributions, sampling the distribution of the specified parameters in an iterative fashion, and propagating the effects of uncertainties through the model. The objective of this work is to identify and statistically predict the influence of uncertainty in the independent input parameters on which the seismic performance of RC buildings (with and without infill walls) depends. Random samples of the uncertain parameters are used in parametric nonlinear dynamic analyses of three variants of typical three-bay, four-story reinforced concrete (RC) frames, namely, bare frame, open ground story frame, and fully infilled frame. The relative importance of the uncertainties in different input parameters on response sensitivity is discussed using different statistical and graphical methods, such as displacement sensitivity radar charts, response sensitivity bar diagrams, tornado diagrams, Sobol′ indices, least absolute shrinkage and selection operator (LASSO) regression, and weighted pie charts. The seismic response of the bare and the open ground story frames is found to be most sensitive to the compressive strength of concrete and the column dimensions. Whereas the response of the fully infilled frames is sensitive to the infill properties, it is also observed that input variables with high uncertainty do not necessarily yield the highest sensitivity in the response.

The precast wall with end columns, known as the PreWEC, was developed as a solution for resisting earthquake lateral loads and validated using quasistatic testing. This paper presents a shake table investigation of this system, which evaluated the performance of four PreWEC test units with total damping varying between 9 and 16% using multiple-level earthquake input motions. Different amounts of lateral resistance were targeted for the four test units by varying key design parameters, including the posttensioning area, location of the end columns, and number of the connectors joining the end columns to the wall panel. Results from this study: (1) confirmed the ability of using PreWECs with different locations for the end columns; (2) validated good seismic performance for all four systems in terms of the maximum transient drift, absolute acceleration, and residual drift; and (3) enabled the response modification coefficient (or $R$ factor) to be expressed for the PreWEC system as a function of available damping. Based on the test outcomes, the procedure for designing PreWEC systems is presented.

The torsional behavior of braced frames can be significantly influenced by the sequence of brace buckling, hinge development in beams or columns, and in-plane deformation of the diaphragm, even for the case of symmetric configurations. To understand these effects, six four-story steel braced structures with different diaphragm in-plane stiffness and configurations of vertical force resisting systems are investigated in this paper. The analyses indicate that (1) the torsional coefficient used to define the levels of torsional irregularity in the current design provision can significantly underestimate the real torsional behavior in the inelastic range, (2) the ultimate strength of structures with rigid diaphragms is higher than that of structures with semirigid diaphragms, (3) asymmetric structures with extreme torsional irregularities and semirigid diaphragms evidenced the highest ductility demands, and (4) higher modes significantly affect behavior after the onset of inelasticity due to buckling of the braces. Two new measures of torsional behavior, a maximum rotation angle and a maximum interstory rotation angle, are proposed and found to give better insight than current measures based on the displacement used in the current design provision.

This paper presents the test results of three $1/2$-scaled Chinese traditional mortise-tenon jointed beam-column frames, initially loaded to damage and retrofitted by use of self-tapping screws and retested under a constant vertical load and cyclic lateral loading. The retrofitting effect on a bare frame and two otherwise the same frames with partial (with a window opening) and full infill is discussed in terms of the damage distribution, envelope curve properties, strength degradation, and equivalent viscous damping ratio. The results indicate that the retrofitted frames exhibited smaller stiffness (27% the least), large deformability (155% the most), higher damping ratios (118% the most), and similar strength degradation (less than 40% decrease) from primary cycles to trailing cycles. The maximum loads of the rested bare frames, partially infilled frame, and fully infilled frame reached 55%, 85%, and 125% of those from the initial testing, respectively. It is also believed that the retrofitting of the fork-leg joints of the columns to the bottom beams was unsuccessful using screws and may be unnecessary for the better function of the infill panels. The retrofitting of the mortise-tenon joints next to the main and secondary beams above the infill panels are, however, very important, especially in terms of preventing pulling-out deformation of the joints because it is closely related to the shear stiffness of the infill panels.

Strategies used to simulate the response of ductile cementitious materials, such as high-performance fiber-reinforced cementitious composites (HPFRCCs), have primarily focused on simulating the ductile cementitious composite material-level response in tension, compression, and shear. However, recent experimental research has shown that the interaction between steel reinforcement and HPFRCCs is critical to the structural performance and deformation capacity of reinforced HPFRCC members. In this paper, an emphasis is placed on predicting reinforced HPFRCC component deformation capacity by studying the reinforcement strain causing fracture in monotonic and cyclic simulations with different reinforcement ratios. All simulations are compared with experimental results from testing of reinforced engineered cementitious composite (ECC) flexural members. A cyclic bond-slip interface material model for reinforced ECC components is developed from experimental data and implemented in a finite-element framework. Numerical simulations of reinforced ECC structural components modeled with perfect bond were compared with the proposed interface bond-slip material model. The results show that including bond-slip behavior in simulations improves predictions of component strength, stiffness, and deformation capacity when the simulations are compared to perfect bond models and experimental results. The sensitivity of simulations to tensile strength and fracture energy is explored, and recommendations for using a damaged fracture energy parameter based on cyclic uniaxial material experiments are discussed. Considerations for understanding factors influencing predicted fracture in reinforced HPFRCC structural components is presented by analyzing reinforcement strain, including bond-slip interface elements, and by using a cyclic fracture energy material parameter.

This paper experimentally studies the low-cycle fatigue (LCF) behavior of shear links in eccentrically braced frames (EBFs) with the aim of calibrating a convenient damage law for estimating the exhausted as well as remaining life of these members under any loading history. A total of 14 specimens are tested using a nearly full-scale EBF setup under constant-amplitude cycles as well as proportional and arbitrary loading histories. A generalized damage law is subsequently calibrated using results of the present study as well as a comprehensive data compilation of previous experiments for predicting the occurrence of link fracture under earthquake-induced loading histories. The approach forms a basis for the development of acceptance criteria based on cumulative measures which can be incorporated into the current performance-based design and evaluation procedures. For further validation, the procedure is applied to the case of EBF links fractured during the Christchurch earthquakes. Finally, the current standards for EBF shear links are discussed based on the findings of the LCF tests.

The objectives of this study were to evaluate the capacity of thin-autoclaved aerated concrete (AAC) panels used as an external cladding system using either timber or cold-formed steel framing as a backup system and develop predictive models. Both out-of-plane and in-plane loads were applied to wall segments. Out-of-plane pressure testing was completed on 12 wall specimens using a vacuum test setup to load the walls. The primary variable was the type of backup system, wood or cold-formed steel. Strong correlation was achieved for pressure specimens based on applying one-way slab theory using tested mechanical properties and flexural cracking. Leeward winds were simulated by flipping the specimen. Suction tests that failed at the fastener locations were effectively modeled based on direct shear and tested material properties. A total of four light-frame, AAC-sheathed shear wall specimens were built and tested under in-plane, monotonic-racking loads. In all cases, damage was initiated by cracking or crushing at the fastener-AAC interface. Following the completion of the shear wall testing suite, a model based on elastic fastener forces was applied and is proposed as an analysis tool for AAC-sheathed shear walls. Experimental test results were compared with the model with ratios of observed to predicted capacities ranging from 1.14–1.33, indicating conservative results.

Wood–concrete composites are structural deck systems that benefit from the use of wood as a lightweight, sustainable substructure and concrete as a wear-resistant, vibration-damping top element. These systems employ shear connectors to transfer shear stresses between the wood and the concrete leading to full or partial composite action for strength and stiffness benefits. This paper presents results of finite element (FE) analyses and a parametric investigation for one type of connector: a perforated steel plate of which half is epoxied into a route in the wood member while the other half is embedded in a concrete slab. The FE model was first validated against experimental push-out tests performed on a commercial product and then employed to examine the effect of several parameters of the connection: thickness of plate; insulation gap between concrete and wood; depth of embedment in concrete; and depth of embedment in wood. Within the range of thicknesses studied (between 1 to 3 mm), the results showed that thickness predictably affects shear capacity as well as ductility and stiffness (slip moduli) of the connector. Surprisingly, however, the results indicated that a gap of up to 25 mm has no significant effect on the slip moduli, although it would reduce shear strength by about 15%. In terms of depth of embedment of the connector, it was discovered that higher stresses predominantly developed within about 30 mm of the depth of embedment in both the concrete and wood, indicating a possible lower value, closer to 60 mm, on the required embedment of the steel connector into the wood and concrete components.

Fiber-based elements are commonly used to simulate steel beam–columns because of their ability to capture $P\text{-}M$ interactions and spread of plasticity. However, when mechanisms such as local buckling result in effective softening at the fiber scale, conventional fiber models exhibit mesh dependence. To address this, a two-dimensional (2D) nonlocal fiber-based beam–column model is developed and implemented numerically. The model focuses on hot-rolled wide flange sections (W-sections) that exhibit local buckling-induced softening when subjected to combinations of axial compression and flexure. The formulation upscales a previously developed nonlocal formulation for single-fiber buckling to the full frame element. The formulation incorporates a physical length scale associated with local buckling along with an effective softening constitutive relationship at the fiber level. To support these aspects of the model, 43 continuum finite element (CFE) test problems are constructed. These test problems examine a range of parameters, including the axial load, cross section, and moment gradient. The implemented formulation is validated against CFE models as well as physical steel beam–column experiments that exhibit local buckling-nduced softening. The formulation successfully predicts postpeak response for these validation cases in a mesh-independent manner, while also capturing the effects of P-M interactions and moment gradient. To enable convenient generalization, guidelines for calibration and selection of the model parameters are provided. Limitations are discussed along with areas for future development.

Effective force testing (EFT) is a dynamic testing method that can consider the rate-dependent behavior of a structure. Because of the lack of knowledge of real-time force control for a servohydraulic actuator, however, EFT has seldom been used within the testing community. Recent advances in force control enable the force application to nonlinear structures in real-time and effectively resolve the natural velocity feedback issue of servohydraulic actuators. With the aid of the new real-time force control method, this paper demonstrates EFT conducted for a small-scale nonlinear concrete mass block system combined with a rubber bearing and a frictional slider, which was a challenging task to implement with the previous knowledge of EFT. This study uses two different earthquake ground motions with different frequency contents for the EFT. The accuracy of the applied effective force is evaluated by comparing the time domain data and the response spectra. In addition, a nonlinear numerical model for the test structure is constructed and used for numerical simulation to compare its result with the EFT result. Overall, satisfactory results are obtained, which show that this study successfully conducted the EFT.

Elastic buckling and second-order analyses are conducted using the matrix structural analysis approach for the in-plane and out-of-plane stability and adequate bracing design of a new type of Ferris wheel support system that can be used to allow a large span: the pretensioned cable-braced inverted-Y-shaped support system (PCB-IYSS). First, the global structural stability stiffness matrix is formulated by combining the element stability stiffness matrices and considering the lateral bracing stiffnesses of the cable system. In the elastic buckling analysis, the eigenproblem is solved by setting the determinant of the global structural stability stiffness matrix to zero. The influence of the lateral bracing stiffness on the buckling load and economical efficiency of the columns are discussed. In the second-order analysis, the element end displacements and reaction forces are determined considering the lateral loads at the top of the column. Finally, using the results from these analyses, the adequate bracing approach is followed for the design of PCB-IYSS. The strength limits of the cable system (as column-top lateral bracing) and supporting columns (as column-base in-plane rotational spring-supported bracing) are formulated, and their adequate stiffness requirements are determined based on examination of the strength limits. A detailed design procedure and an elementary design example are presented.

This paper presents an experimental study on the seismic performance up to fracture of gusset-plate brace connections. During the inelastic behavior of a bracing member (e.g., buckling), weak-axis bending in the gusset is induced by brace-end rotation and a plastic hinge is formed in a predefined inelastic zone (clearance distance) of the gusset. Five gusset-plate connections that can develop restraint-free plastic rotations to accommodate the brace-end rotation demands are tested. The test parameters include the plate thickness, length of clearance distance, and several inelastic rotation demands. The connections are tested using an innovative substructure-based hybrid test method that simulates the complex boundary and load conditions that exist between the gusset-plate connections and brace member. The tests quantify the maximum rotation ductility and strength capacity of the gusset-plate connections under actual cyclic inelastic rotations and varying axial loading. The test results also provide a basis for developing a ductility-based design methodology that determines the rotation ductility of gusset-plate connections using the brace-end rotation demand at a given axial deformation capacity of the brace. A design application example demonstrates the necessity of considering explicitly in the seismic design of steel braced frames the gusset-plate fracture capacity.

In this study, four $1/3$-scaled enhanced steel frame–composite floor specimens were tested quasi-statically under a column-removal scenario. One specimen was the control test and the other three were different in terms of aspect ratio, degree of composite action, and boundary condition. The objective of this paper is to study the effects of these three parameters through comparing experimental results of the four specimens. The comparisons revealed the effects on load-carrying capacity, ductility, failure mode, deformation characteristics, and load redistribution among the remaining columns and reaction forces from surrounding structures. First, the load-carrying capacity of the specimen with slab panel dimensions of $2\times 2\mathrm{m}$ was around twice as great as those of specimens with slab panel dimensions of $2\times 3\mathrm{m}$, while the deformation capacity of the former was much smaller than those of the latter. Second, weaker composite action decreased flexural resistance but improved ductility significantly, which was beneficial for development of tensile membrane action. Third, more flexible boundary conditions could not increase applied load beyond the stage dominated by flexure. For composite floor systems, flexural rigidity of steel columns was sufficient to support development of compressive arch action (CAA) so that additional horizontal restraints from surrounding structural members were not so beneficial at the CAA stage. However, the stiffness of additional restraints significantly affected the floor system at the catenary action stage. Finally, the typical yield pattern of composite slabs comprised negative yield lines that were formed around the perimeters and positive yield lines along the double-span girder, the double-span beam, and the paths connecting corner columns to the nearest loading points.

Oriented strand board (OSB) sheathing-to-wood framing connections, as typically used in light-frame shear walls, were experimentally examined in a novel biaxial test setup with respect to possible path dependence of the load-displacement relation. The connection with an annular-ringed shank nail was loaded under displacement control following nine different displacement paths within the sheathing plane, which coincided at a number of points. At intersection points, the resultant connection force, its orientation, and work performed on the connection system to reach the specific point were calculated and compared. Evaluation of experiments revealed significant path dependence with respect to the orientation of force resultants at path intersection points. However, the magnitude of the forces and the work carried out showed relatively small dependence of the displacement path undertaken. Comparison of uniaxial connection tests with the European yield model demonstrated a strong contribution of withdrawal resistance of the ringed shank nail to its lateral strength. Results of this type are a valuable basis on which to build better models when simulating such connections in wood structures.

The dependency of wind forces and responses on the outer shape of tall buildings provides a unique opportunity to reduce wind effects through the aerodynamic optimization of the outer shape. The current study presents a multiobjective aerodynamic optimization procedure (AOP) by introducing horizontal openings to reduce wind load. The adopted method joins an optimization algorithm, large eddy simulation (LES), and an artificial neural network (ANN) surrogate model. The base building geometry is the Commonwealth Advisory Aeronautical Research Council (CAARC) building. The present optimization process is carried out by introducing three openings along the height of the building. However, the adopted method is useful for any shape modifications. In all cases, opening volumes are maintained at 10% of the total building volume to enable a simple comparative performance assessment. The objective of the optimization process is to identify the optimal aspect ratio and distances between the openings that produce the best aerodynamic performance. Three optimization problems are presented. The first two follow single-objective optimization to reduce the peak base moment coefficients about the $x$- and $y$-directions, respectively. Reductions of 47% and 42% are achieved for the moments about the $x$- and $y$-directions, respectively. The third optimization is a multiobjective optimization problem, which aims to simultaneously reduce the two base moments.