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A steel brace is effective to retrofit old reinforcement concrete (RC) buildings by increasing the horizontal load capacity of structures. However, concrete cracks that easily occur in the surrounding RC members under tension initiate early strength degradation, so this research aimed to develop a new self-centering brace (SCB) with the compression-only capacity such that no tension force is developed in the brace or to the adjoining RC members. Original SCBs have been developed to reduce the residual deformation of structures with a symmetrically flag-shaped hysteretic response. By altering the force transfer mechanism in the original SCB, a compression-only self-centering brace (C-SCB) can be developed under a symmetrically reversed cyclic loading, providing an alternative for the RC building retrofit. This paper first introduces the mechanics and deformation mechanism of the proposed C-SCB. A test program is then conducted on the cyclic tests of a buckling-restrained energy dissipating bar (EDB) to evaluate the energy dissipation. A 3,695-mm-long C-SCB is composed of posttensioning high-strength steel tendons, steel compression members, and buckling-restrained EDBs for the energy dissipation. The C-SCB in tests showed a good compression-only self-centering capability up to an axial displacement of 31 mm, with a maximum axial force of 1,530 kN. No damage of the steel tendons, compression members, or EDBs was found after three phase tests. Finite element analysis further validated the compression-only hysteretic response and mechanics of the C-SCB in a symmetrically reversed cyclic loading. [ABSTRACT FROM AUTHOR]

This paper presents the experimental results of a study investigating the behavior of bolted glued-laminated (glulam) timber brace connections with slotted-in steel plates under monotonic and cyclic loading. A total of 12 brace specimens with one or two slotted-in steel plates and two different bolt sizes were studied with the aim to determine the ductility of the connections and brace assemblies. The use of self-tapping screws as perpendicular-to-grain reinforcement to prevent splitting and enhance brace ductility was also investigated. The results of the study showed that both connections in a brace can experience significant plastic deformations if the connections exhibit a postyield hardening response. In braces with connections that exhibited postyield softening, plastic deformations were limited to one of the brace connections, resulting in lower brace ductility ratios. The use of self-tapping screws was found to be effective at preventing splitting and increasing the connection yield and ultimate strengths, while also increasing the brace ductility when compared with an identical connection without reinforcement tested under cyclic loading. [ABSTRACT FROM AUTHOR]

Thick rubber bearings (TRBs) have been proven to be effective in mitigating horizontal shaking induced by earthquakes as well as railway-induced vertical vibration. During earthquake excitations, TRBs might be subjected to tension, which should be carefully assessed during design. This paper presents experimental and numerical studies on the behavior of TRBs under tensile loading. Four full-scale thick natural rubber bearing (TNRB) and lead thick rubber bearing (LTRB) specimens were designed and tested under tension, with and without lateral offset. The test results showed that increasing the applied lateral offset decreased the tensile stress and stiffness of the TNRBs, while the LTRBs did not exhibit any reduction. In addition, the test results were compared with design specifications in current codes for conventional rubber bearings. Finally, finite element (FE) models of TRBs were built and validated against the results of uniaxial and offset tensile experiments, and the cavitation of rubber was modeled via a two-phase model. To further estimate the damage due to previous tensile loading, damage variables under cyclic tensile loading were also taken into account. The experimental and numerical results showed that the lead core only slightly increased the initial tensile stiffness of the bearing under uniaxial testing, while it had a significant influence on the tensile properties of the LTRBs under offset displacement. [ABSTRACT FROM AUTHOR]

The mechanical behavior of mortar joints can be described by means of the cohesive interface element in the mesoscale modeling of masonry structures. In this paper, a novel three-dimensional (3D) constitutive model for the cohesive interface element under cyclic loading is presented. The proposed constitutive model is formulated in the damage-plasticity theoretical framework with the following unique features: (1) two smooth hyperbolic yield surfaces, capable of capturing various failure modes of mortar joints; (2) two damage scalars Dt and Dc to characterize the stiffness degradation; (3) two damage functions ξt(Dt) and ξc(Dc) to describe the strength softening; and (4) an unassociated flow rule to capture the dilatancy behavior. The proposed constitutive model is implemented in the general-purpose finite-element package Abaqus using the user subroutine UMAT. The developed model was validated at the masonry-component level using a mortar-jointed specimen under indirect cyclic tensile loading and three masonry couplets under compressive-shear loading, and then at the structural level using two unreinforced masonry walls characterized by two distinct failure modes. The validation results show that the developed constitutive model is capable of modeling mortar joints and masonry structures with good performance. [ABSTRACT FROM AUTHOR]

Steel fibers in ultra-high performance concrete (UHPC) have been demonstrated to improve resistance to crack growth, decrease deflection, and increase fatigue life under cyclic loads. Using steel fibers as shear reinforcements, this paper investigates its effect on the postcracking shear fatigue behavior of nonstirrup UHPC beams. The study involved five UHPC beams comprising two static and three fatigue specimens to test the effects of the upper fatigue load, steel-fiber ratio, and stirrup ratio on the shear fatigue response. The test results showed that increasing the initial crack width in the nonstirrup UHPC beam from 0.05 to 0.2 mm (the equivalent of doubling the upper fatigue load) decreased the fatigue life from over two million to 24,875 cycles. The use of steel fibers in place of stirrups increased the residual-to-static strength and residual-to-initial stiffness ratios by 5% and 16%, respectively, after two million cycles. Compared with the specimen with stirrups, the steel-fiber-reinforced specimen had a lower midspan fatigue deflection-to-ultimate static deflection ratio owing to the relieved fatigue strain localization and increased tensile steel reinforcement-UHPC bond fatigue strength. The current codes predict the shear fatigue strength conservatively. A calculation model for accurately predicting fatigue deflection was proposed and compared with the existing test results. A future study on the wider parametric analysis and large-scale beam tests on the fatigue performance of these beams should be conducted. [ABSTRACT FROM AUTHOR]

This paper presents an experimental study of the seismic behavior of steel gravity frames with concrete on metal deck floor systems using multibay test specimens subjected to cyclic lateral loads. Fully bolted double-angle connections were used for the primary gravity connections under investigation. Key design variables and construction details under investigation include metal deck orientation, positioning of metal deck seams, and increased deck reinforcing ratios around the columns. Test specimens were simultaneously subjected to gravity loads and quasi-static displacement-controlled cyclic lateral loads. Results show that composite gravity connections exhibit substantial flexural stiffness, strength, and ductility, with some differences in response depending on connection design variables and construction details. Results from the system-level experiments using multibay test specimens demonstrate significant differences compared to previous subassembly tests, which indicates that the moment-resisting capacity of connections may potentially be underestimated in subassembly level tests. [ABSTRACT FROM AUTHOR]

This paper presents an experimental study on the multidirectional cyclic lateral-load response of post-tensioned self-centering (SC) cross-laminated timber (CLT) shear walls. SC-CLT shear wall damage states are introduced and qualitatively defined in terms of the repairs needed to restore the lateral-load response of the SC-CLT wall. A comparison between SC-CLT wall damage states under unidirectional (in-plane) and multidirectional (in-plane and out-of-plane) lateral loading is presented. The experimental results show that the initiation of SC-CLT wall damage occurs at smaller story drifts under multidirectional loading compared to unidirectional loading. Engineering demand parameters (EDPs) are used to quantify the SC-CLT wall damage states. Uncertainty in the EDP value when a damage state occurs is considered and quantified. Using the experimental results, component (i.e., a CLT wall panel corner) and system (i.e., an entire SC-CLT wall) fragility functions are developed and presented. [ABSTRACT FROM AUTHOR]

This paper presents experimental investigations on the lateral performance of cross-laminated timber (CLT) shear walls with customized self-tapping screw (STS) connections. The panel-to-base (hold-downs and shear brackets) and panel-to-panel (spline) connections were tested under quasi-static monotonic and reversed cyclic loading to derive design values of STS, which were shown to be 2.8–3.6 times higher than those calculated using the current Canadian timber design standard. Then, a total of 26 CLT shear walls, including single-, double- and triple-panel configurations, were tested, again under quasi-static monotonic and reversed cyclic loading. The shear walls consisted of five-ply, 139-mm-thick and 3-m-high CLT panels with aspect ratio of either 2∶1 or 3∶1 , and different numbers of STS in the connections. The shear wall strength and corresponding displacements increased with the number of screws in hold-downs and spline joints; further, it increased with number of connected panels and decreased as a function of aspect ratio. The data can be used for developing and calibrating numerical models to investigate the lateral responses of CLT shear walls with different configurations. [ABSTRACT FROM AUTHOR]

Protecting critical equipment in seismically excited buildings is essential to ensure functionality after an earthquake. Individual equipment or equipment sets can be seismically isolated from the building motion. Special isolators can be employed to mitigate the most severe accelerations that occur in the horizontal direction of a building. This paper presents the results of an investigation of the performance of an uncoupled bidirectional isolation system for horizontal isolation using a novel adaptive restoring force (ARF) device. The device changes the structural response transmitted to floor-mounted equipment by filtering the most intense portions of input floor acceleration histories to minimize the acceleration of the equipment and the stress demands imposed by the supporting structures. The ARF device utilizes restoring and damping elements to generate restoring forces that vary nonlinearly with displacement, resulting in a force–displacement curve with varying slopes and loading and unloading paths. The force–displacement relationship of the ARF device is characterized by high stiffness at small and large displacements, and low stiffness in between. A small-scale prototype was constructed to validate the ARF concept, and its force–displacement properties were observed for cyclic loading. A numerical model was developed that accurately predicted the relationship between the device force and displacement. The system's performance was evaluated through numerical analysis of equipment installed on different levels of multistory buildings subjected to measured floor accelerations. The results showed that the horizontal isolation system effectively limited the transmission of the floor accelerations to the equipment. Furthermore, the results showed that the isolation system transformed the seismic acceleration profile from a high-amplitude and -frequency signal to one with a low quasi-constant amplitude and low frequency, acting as a low-pass filter under the most intense time window of the floor acceleration. Protecting critical equipment can be a significant concern for those who manage or work in facilities vulnerable to earthquakes. This study presents a new technology for horizontal seismic isolation of equipment, the adaptive restoring force device, that effectively minimizes the damaging effects of earthquakes on floor-mounted equipment in multistory buildings. The ARF device protects equipment by filtering out the most intense and destructive vibrations accompanying earthquakes, thus reducing accelerations on the equipment and its supporting structures. It transforms high-amplitude and -frequency vibrations to lower, more-constant levels. Unique to the ARF device is its adaptability to work effectively on any floor of a building, even on rooftops, while allowing considerable relative movement between the equipment and the floor. The results of this study are promising—equipment experienced reduced and nearly constant low-frequency accelerations during simulated seismic events. Although further research is required to address more complex problems, such as building torsion and vertical seismic effects, preliminary findings suggest that the ARF device offers a practical solution for preserving vital floor-mounted equipment in multistory buildings in earthquake-prone regions. This device can prove invaluable as a tangible solution for businesses, industries, and hospitals dependent on critical equipment. [ABSTRACT FROM AUTHOR]

Steel plate shear walls (SPSWs) often need to accommodate rectangular openings in their infill plates. When subjected to lateral loadings, such as wind and earthquake, unstiffened SPSWs with rectangular openings may experience large deformations around the openings. This paper presents a stiffener layout to limit the deformations around the rectangular openings in the SPSW system. The effectiveness of the proposed stiffener layout is investigated by conducting experimental tests on two one-third-scale single-story SPSWs with rectangular openings at the center of the infill plates. The two specimens have the same aspect ratio but have different rectangular opening sizes. To prevent deformations around the rectangular openings, the infill plates of the two test specimens are stiffened with the proposed stiffener layout. Quasi-static cyclic loading tests are performed on the specimens, and the deformations around the openings are measured at different loading stages. Tests showed that the proposed stiffener layout can successfully restrain the deformations around the rectangular openings. The specimens also showed stable hysteresis curves and good energy-dissipation capacity. To further examine the inelastic performance of the proposed stiffener layout, finite-element analysis of stiffened SPSWs is conducted. Seismic analyses are also performed for 4-story stiffened and unstiffened SPSWs with rectangular openings to investigate the seismic response of SPSWs with the proposed stiffener layout around the openings. Seismic analyses showed that the proposed stiffener layout around the rectangular openings can prevent the out-of-plane and in-plane deformations around the openings in the SPSW system. [ABSTRACT FROM AUTHOR]

This paper presents the experimental results of two welded unreinforced flange-welded web (WUF-W) beam-to-column connections that defy the current design paradigm of prequalified welded connections. The proposed WUF-W connections feature customized beveled backing bars that are intentionally left in place after the completion of the beam flange-to-column face complete joint penetration welds. The connection design aims at a stable hysteretic response by exploiting the beneficial aspects of appreciable panel zone shear yielding (i.e., inelastic shear distortions of at least 15γy , where γy is the panel zone shear distortion at yield), by considering a shear strength-to-demand ratio of 0.8. To prevent divot fracture in the column, minimum through-thickness toughness requirements were imposed for the steel column material. The experimental results suggest that the proposed WUF-W connections achieve a stable hysteretic response up until lateral drift demands of at least 7% rad, while a non-softening response was assured up to 9% rad. The beveled backing bars minimize the associated fracture potential near the beam web centerline, which is a primary concern in prequalified field welded moment connections when conventional weld backing bars are employed. The tests suggest that, under a symmetric cyclic loading protocol, local buckling near the steel beams is prevented up until a lateral drift demand of 6% rad, which is an important finding from structural repairability and stability standpoints. The ultimate failure modes of the welded connections, which are attributable to ductile crack initiation and propagation, are consistent regardless of the employed lateral loading histories, which involved standard symmetric cyclic and collapse-consistent loading protocols. The implications for the seismic design of steel moment resisting frames (MRFs) and the limitations of the present work are discussed. [ABSTRACT FROM AUTHOR]

Unbonded fiber-reinforced elastomeric isolators (UFREIs) are a potentially low-cost and viable alternative for application as base isolators in low-rise buildings due to their adaptive characteristics. The behavior is denoted adaptive because the device exhibits well-defined lateral softening and subsequent substantial stiffening responses depending on the loading level. Since adaptive characteristics could have a significant effect on the seismic response of base-isolated structures, proper modeling of adaptive devices is crucial. There are several numerical modeling techniques for considering the adaptive characteristics of UFREIs. However, to date, none accurately fit the experimental hysteresis loops of UFREIs at large displacements where there is more dissipated energy due to full rollover. In this paper, an impact model is added to the leading numerical models of UFREIs (i.e., the Bouc–Wen model with a fifth-order polynomial and the algebraic model) to accurately capture the force-displacement hysteresis in lower and larger displacement amplitudes. The proposed impact model is then validated using prior experimental cyclic loading tests for square and rectangular specimens and shake table tests for different earthquake records. The effect of the impact model was also investigated through comparison with the response of the existing phenomenological models (e.g., the Bouc–Wen model with a fifth-order polynomial, the algebraic model, and the elastomeric bearing (Bouc–Wen) element). The results show that incorporating the impact model will improve the ability of the current numerical models to capture the behavior of UFREIs, particularly at larger amplitudes. [ABSTRACT FROM AUTHOR]

This paper presents the results of an experimental investigation on the performance of half-scale, unbonded, post-tensioning, precast concrete walls subjected to fully reversed cyclic loads. Moreover, this paper discusses the damage progression and failure mechanism of each specimen, associated with their construction details (damper types and confinement details of the boundary elements). Five isolated walls were tested, each consisting of precast concrete panels joined only by unbonded post-tensioning strands. The bottom joint of the walls featured two kinds of dampers: Three specimens had mild steel reinforcement, crossing the bottom joint, and the other two specimens had external replaceable hysteretic dampers, attached to the wall sides. Different types of confinement details at the boundary elements were used among the specimens. Steel fibers were mixed into the concrete of one specimen. The prestressing load ratio was 0.05 in most of the specimens. An additional axial load of 468.5 kN was applied to each specimen (additional axial load ratio of about 0.04), before any lateral loading. Quasi-static, displacement-controlled loads were applied to the specimens until a significant strength reduction was observed. Although only moderate axial loads were applied, most of the specimens sustained drifts above 3% while maintaining their lateral strength, gravity load stability, and self-centering. A better performance was observed in the specimens with external dampers, with drifts above 4%, less residual drifts and less cover concrete spalling, particularly in the specimen with steel fibers. The external dampers were very effective in dissipating energy before fracture, until 3% drifts. On the other hand, the specimens with internal dampers sustained unexpected damage at their bottom joint, after reaching their peak strength. For instance, the gravity load-carrying capacity of one specimen with internal dampers was compromised after 4% drifts. Then, the use of external replaceable dampers provided higher performance and post-earthquake recovery for unbonded post-tensioned precast walls. Additional design recommendations are provided based on the test results. [ABSTRACT FROM AUTHOR]

Wide-flange columns are commonly used for the construction of special moment frames and braced frames. For special moment frames, design engineers routinely use deep sections to meet the stringent code-specified story drift limits in order to achieve economy in recent years. Columns with shallow and stocky sections are common for braced frame construction. Observation made from two recent experimental studies involving both deep and shallow columns under axial compression and cyclic drifts showed a variety of buckling modes. A classification with three cyclic buckling modes is proposed in this paper; subsets of each buckling mode are also presented. A parameter measuring the relative rotational restraint that the web provides to each flange is derived. After calibrating this parameter with the test results, a practical procedure that can predict the governing cyclic buckling mode is proposed. [ABSTRACT FROM AUTHOR]

An experimental and numerical investigation on the behavior of a new replaceable steel device (RSD), is presented in this paper. The RSD consists of a steel pipe with two circular steel plates that close the ends of the tube, four stiffeners, and an added damping and stiffness (ADAS)-type steel plate that functions as a fuse element. This RSD is characterized by its compressive strength, which is much higher than its tensile strength and is compatible with the rocking behavior of a self-centering prefabricated shear wall (SCPSW), and also by its ability to dissipate energy. Three-dimensional finite element analyses were carried out to investigate the behavior and performance of the RSD, both individually and in the case where they were installed at the bottom of the toe and heel of a SCPSW. The results show that the RSD has stable behavior and is compatible with the gap opening in the corner of the SCPSW. The combined specimen of SCPSW and RSD (SCPSWR) remains stable under cyclic loading, with a maximum drift ratio of 3.98%, demonstrating that the RSD could be a viable candidate for practical use in seismic-prone areas. The behavior of the RSD was assessed by conducting two sets of cyclic tests, which provided good agreement with the numerical results. The results indicate that the RSD's performance is influenced by the plastic behavior of the fuse element, plastic buckling of the disks, and pipe deformation. If the RSD is damaged, it can be easily replaced, because fabrication and installation of the proposed RSD is easy and cost-effective. This article proposes a replaceable steel device (RSD) that can be installed at the lower corners of a self-centering prefabricated RC shear wall (SCPSW) in order to prevent damage to the wall. The RSD consists of a steel pipe with two circular steel plates that close the ends of the tube, four stiffeners and an added damping and stiffness ADAS-type steel plate functioning as a fuse element. This device is easy to fabricate, install, and replace, and is inexpensive compared to other types of yielding dampers. One of the characteristics of this RSD is that its compressive strength is much higher than its tensile strength, which makes it compatible with the rocking behavior of a SCPSW. Another feature of this device is its ability to dissipate energy by tensile deformation. In case of damage, the RSD can be quickly and easily replaced. The contribution of the RSD in resisting the lateral load induced by an earthquake to the SCPSWR is another excellent feature of this device. Its resistant to compressive force exerted to the system is noticeable. Finally, the proposed RSD is a convenient device to prevent damage to a SCPSWR and would be a desirable candidate for practical use in earthquake-prone areas. [ABSTRACT FROM AUTHOR]

This paper presents findings from experiments conducted on four large-scale T-shaped concrete filled composite plate shear walls (C-PSW/CF) specimens subjected to axial force and flexure. A C-PSW/CF is a sandwich type of construction by which concrete (without rebars) is enclosed between steel plates connected by tie bars. One of the walls was subjected to a cyclic wind loading protocol and the other walls were cycled with a seismic loading protocol. Their dimensions were identical, but different axial loads (up to 30% of the crushing load of the infill concrete, Acfc′) were applied. The plastic hinge development was investigated along with the composite behavior and compared with the calculated plastic moment of the corresponding cross section. These tests along with the results on C-shaped wall tests were conducted to establish the development of design guidelines for high-rise core-wall steel buildings having C-PSW/CF as the primary lateral force resisting system. [ABSTRACT FROM AUTHOR]

Rebar buckling and fracture have been experimentally observed to cause significant degradation of the mechanical properties of reinforced concrete (RC) elements and should be accounted for in the analysis of RC structures. While data on the material properties of steel rebar are widely available, test data on rebar buckling remain scarce. This paper proposes a macromechanical model capable of predicting rebar buckling responses solely on the basis of steel material properties and the rebar geometry, even when rebar buckling experimental data are not available. This is achieved by computationally building the uniaxial stress-strain constitutive response at each analysis step through the equilibrium in the deformed configuration of the buckled rebar and through the cross-sectional constitutive response. The equilibrium in the deformed configuration is treated in a manner consistent with the corotational formulation, while the cross-sectional constitutive response is built through integration of a uniaxial damage plasticity model over the cross-section area. Rebar buckling is triggered by an initial imperfection, while low-cycle fatigue effects are reproduced through the uniaxial damage plasticity steel material model, without the need for cycle-counting algorithms. The proposed model is translated to a computer code, calibrated to a set of experimental data, validated to separate test data, and subsequently used in the analysis of an experimentally studied RC column that experienced rebar buckling under cyclic loading. Using the proposed model, the analysis captured the response of the RC column and the experimentally observed strength deterioration due to rebar buckling. [ABSTRACT FROM AUTHOR]

This paper presents an experimental investigation on the evaluation of the seismic performance of a new hybrid buckling restrained brace (HyBRB) under cyclic load. Detailed design steps adopted for the HyBRB design are reported in this paper. The analytical method for estimation of critical loads corresponding to buckling mode formation of the steel core inside the restrainer has been presented. The design targets achieved for the HyBRB are ease of inspection of the detachable BRB core to facilitate replacement of the steel core after a seismic event, if necessary, and enhanced energy-dissipation capacity through restrained buckling about both weak and strong axes of the core. The proposed HyBRB has displayed stable hysteretic behavior with good energy-dissipation capacity in low to high levels of the core strain range. Permanent deformation about the strong axis of the core was observed on unfastening of the restrainers, although restrained buckling of the core was observed about the weak axis in lower displacement amplitudes. Analytical simulation was carried out using a phenomenological model to simulate the experimental behavior. The simulated axial force-deformation hysteresis loops were found to be in close agreement with those obtained from experimental investigation. [ABSTRACT FROM AUTHOR]

The self-centering technical approach is used widely to improve building resiliency. This paper presents a double activation self-centering brace (DA-SCB) with two groups of disc springs activated successively. Compared with current self-centering braces (SCBs), the DA-SCB is first activated under small displacement excitation to dissipate energy, and reactivated under large displacement excitation, leading to a higher bearing capacity. Cyclic loading tests were conducted on the SCB and the DA-SCB in order to comparatively study their energy dissipation and the self-centering behaviors and to validate the hysteretic performance of the DA-SCB. Moreover, the double flag–shaped model was developed to predict the hysteretic behavior of the DA-SCB. Fifteen-story steel frame models with SCBs (SCBF) and DA-SCBs (DA-SCBF) were analyzed to study the influence of the reactivation behavior on the seismic resilience of these structures. The test results showed that the bearing capacity and the energy dissipation ability of the DA-SCB were highly consistent with those of the SCB within the same design parameters. Comparisons of the prediction and test results indicated that the proposed model can accurately replicate hysteretic responses of the DA-SCB and the SCB. The DA-SCBF and SCBF have equivalent self-centering behavior. However, the seismic performance of the DA-SCBF is higher than that of the SCBF, and the economic loss of the DA-SCBF after earthquakes decreased by 8.08% compared with the SCBF. Moreover, compared with the SCB, the DA-SCB uses fewer disc springs and can attenuate the weak story effect. To sum up, the seismic resilience level of the DA-SCBF first increases and then decreases with an increased gap length. [ABSTRACT FROM AUTHOR]

Links in eccentrically braced frames (EBFs) are designed with transverse web stiffeners to achieve the desired seismic performance targets established in current design standards. Prior studies have suggested that stiffener spacing requirements in the standards may be conservative. This paper proposes new stiffener spacing design requirements for short EBF links. The proposed limits were established on the basis of a methodology that combines a numerical solution of the classical problem of inelastic plate buckling of a thick plate under shear thrusts along with comparisons with available experimental data. The resultant design equation was verified through complementary continuum finite-element simulations of 18 wide-flange short links under symmetric cyclic loading. The finite-element simulations suggested that the proposed design equation reduce the stiffener requirements by about 35%, on average, relative to the current stiffener spacing requirements for short EBF links. Limitations and suggestions of future work are discussed. [ABSTRACT FROM AUTHOR]

A new precast concrete (PC) shear wall system with diagonal-shaped or cross-shaped concealed bracing was developed and experimentally validated, owning sufficient energy-dissipation capacity, in a previous study. Given that the seismic performance of such precast braced concrete shear (PBCS) walls is not comprehensively understood, this paper numerically investigates the influences of axial load ratio (ALR) and various reinforcement ratios (RRs) on the mechanical behavior of PBCS walls under cyclic loading. For this purpose, the numerical models based on the layered-shell element are developed to analyze the PBCS walls and validated regarding the deformation capacity of experimental results. A total of 156 PBCS wall models with different ALRs, longitudinal RRs of the boundary columns and bracing, and horizontal and vertical web RRs are established and tested under cyclic loading. It is concluded that the effects of bracing RR and horizontal web RR on the hysteretic responses are negligible and thus can be designed as the minimum suggested by the codes. However, the ALR, boundary column RR, and vertical web RR can significantly affect the lateral bearing capacity and displacement ductility of PBCS walls. In addition, the ALR limits for both types of PBCS walls are presented to satisfy the ductility requirements. Moreover, the simplified formulations regarding the bearing capacity and ductility of PBCS walls are proposed, respectively, which show good agreement with the numerical results. The outcomes of this research not only provide an in-depth understanding on the seismic behavior of the PBCS walls, but also promote the design code expansion and potential engineering application of such new types of PC shear walls. [ABSTRACT FROM AUTHOR]

This paper, which is the second of two companion papers, presents the results of a large-scale testing program on a novel bridge column design, termed polyurethane (PU)-enhanced rocking column with energy dissipation (ED) links. The experimental program included cyclic testing of large-scale (approximately 1∶2.5) cantilever bridge columns, including (1) a rocking-only precast concrete column, which served as the reference column, (2) a PU-enhanced rocking column with a solid PU segment, and (3) a PU-enhanced rocking column with an axisymmetrically bilayered segment with an exterior PU layer to withstand seismic loads, an internal reinforced concrete core to sustain long-term gravity loads, and external ED links to provide energy dissipation and flexural stiffness and strength. The specimens were subjected to displacement-controlled lateral cyclic loading of increasing amplitude (exceeding a 10% drift ratio) at several drift ratio rates (up to 1 s−1). The tested PU column with ED links was further repaired via ED link release and retightening—the yielding of the ED links was small and did not justify replacement—to demonstrate its rapid reparability characteristics. The repaired column was subsequently retested to demonstrate that the original column properties had been practically recovered. This second companion paper experimentally quantifies the performance of all designs in terms of strength, ductility capacity, self-centering and energy dissipation capabilities, posttensioning losses, and ED link fracture capacity. It also quantifies the capability of ED link release and retightening (and, by extension, ED link replacement) in eliminating residual deformations and recovering the mechanical properties of the original/undamaged system. Compared to conventional RC rocking-only columns, the proposed PU-enhanced column design with ED links demonstrated higher energy dissipation and self-centering capabilities, while release and retightening of the ED links eliminated the residual deformations and resulted in the recovery of the mechanical properties of the original/undamaged column. While ED link release and retightening (i.e., ED link reuse) is adopted in this study, because the yielding of the ED links was small, as verified herein by the practically identical response of the original and repaired column, it can be deduced that ED link replacement (i.e., use of new/pristine ED links) would also restore the original column properties and eliminate residual deformations. [ABSTRACT FROM AUTHOR]

This paper, which is the first of two companion papers, investigates the performance of a novel bridge column design, termed polyurethane (PU)-enhanced rocking column with energy dissipation (ED) links, through a large-scale testing program. The proposed column design offers explicit damage control via damage-resistant end segments made of PU, ED and flexural strength/stiffness through ED links, and self-centering through internal unbonded post-tensioning. The PU segments have high deformability, allowing large lateral column deformations with negligible damage. The ED links are in the form of buckling-restrained bars made of high-performance steel and offer hysteretic damping and flexural stiffness and strength to reduce the seismically induced displacement demands. The experimental program included cyclic testing, at various loading rates, of large-scale (approximately 1:2.5) PU-enhanced cantilever rocking columns with two designs for the PU segment: (1) solid PU segment, and (2) axisymmetrically bilayered segment with an exterior PU layer to withstand seismic loads and an internal reinforced concrete core to sustain long-term axial service loads and provide resistance against creep. The specimens are subjected to displacement-controlled lateral cyclic loading of increasing amplitude (exceeding a 10% drift ratio) at several drift ratio rates (up to 1/s). A tested column is repaired via ED link release and retightening to demonstrate their rapid reparability characteristics and are retested to demonstrate the recovery of the original column properties. While ED link release and retightening (i.e., ED link reuse) is adopted in this study, because the yielding of the ED links was small as verified in the second companion paper by the practically identical response of the original and retrofitted column, it can be deduced that ED link replacement (i.e., use of new/pristine ED links) would also restore the original column properties. A rocking-only precast concrete column is also tested under the same loading protocols to serve as reference for comparisons. This first companion paper outlines the experimental program, quantifies the observed damage of the proposed column design for a range of seismic hazard intensities and compares it with that of the rocking-only column, and validates the capability of ED link release and retightening (and, by extension, ED link replacement) as a repair method that recovers the damage resistance/avoidance properties of the original system. Compared to conventional RC rocking columns, the proposed column design demonstrated significantly higher resistance against damage in terms of concrete spalling and crushing. [ABSTRACT FROM AUTHOR]

Self-centering heavy timber frames rely on the self-centering beam-column timber connections to limit damage and provide the recentering capability. However, low compressive strength and stiffness perpendicular to the grain of the timber columns have long been a design challenge, which yields low initial post-tensioning forces and possibly a significant loss of post-tensioning forces over the building service life. To address this issue, this paper proposes a new design solution for the self-centering steel-timber hybrid beam-column connections, in which the timber column is replaced by a steel-timber composite column. Cyclic tests were conducted on four beam-column connection specimens with post-tensioning. During the gap-opening, the composite column provided a stiff foundation to the timber beam. The hysteretic curves of all four connections were in a flag shape. Compared with self-centering beam-column timber connections that had the same geometry and material properties, the proposed connection had a larger connection stiffness and an improved efficiency of dissipating energy. After the cyclic loading, the loss of post-tensioning force of the proposed connection was also lower than that of the counterpart timber connections. [ABSTRACT FROM AUTHOR]

To satisfy the easy-repair demands of precast concrete (PC) frames after an earthquake, a PC frame with replaceable artificial controllable plastic hinges (ACPHs) is proposed in this paper. ACPHs were installed at each beam end on both sides of the frame, which concentrated the structural deformation to avoid any damage of precast reinforced concrete members. In this study, to explore the seismic behavior and ACPH location factor on the seismic performance of the frame structures, cyclic loading tests were conducted on two precast concrete frames with different positionings of the ACPH and cast-in-situ frame. The test results indicate that the ACPH frame exhibited favorable seismic performance, and the bearing capacity and energy dissipation capacity can be improved by appropriately extending the distance from the ACPH to the cylinder. Based on the principle of maximizing the elastic range resistance of precast reinforced concrete beams, the formulas for calculating the optimal locations of ACPHs were established. [ABSTRACT FROM AUTHOR]

Peridynamics (PD) has been increasingly used to study the damage behaviors of reinforced concrete (RC) structures due to its strong capacity in analyzing discontinuous problems. In this paper, bond-based peridynamics (BPD) is enhanced for refined analysis of bond-slip behaviors between concrete and ribbed steel rebar in the pullout test. The enhancement of BPD includes the following: (1) an axial-shear interaction (ASI) model for refined simulation of bond-slip behaviors between steel ribbed rebar and concrete; (2) a nonlinear uniaxial concrete model to avoid excessive compression of concrete bonds; (3) a novel gradually weakening fictitious element (GWFE) approach to improve the stability and convergence of the Newton algorithm in solving the PD equations, e.g., in case of negative concrete stiffness; (4) a horizon updating approach for rebuilding bond interactions when large displacements occur in the bond-slip process; and (5) a parallel computing approach to improve the computational efficiency of refined analysis. The enhanced BPD method is implemented in an open-source finite-element software, OpenSees, and verified by a rebar pullout test. The type of steel rebar rib, strength of concrete, cross-area of steel, and cyclic loading condition are investigated in detail regarding their effects on the stress redistribution and mesoscale crack propagation of the RC members. The results demonstrate that the enhanced BPD modeling method presented herein is capable of fine simulation of bond-slip behaviors in the pullout test, e.g., the strength deterioration, stiffness degradation, and cyclic response. [ABSTRACT FROM AUTHOR]

Pinching characterizes the hysteretic response of several structural systems. It is associated with a reduced dissipated hysteretic energy under cyclic loading and can significantly affect seismic performance, especially under repeated earthquakes. Although several scholars proposed advanced joint arrangements with reduced pinching, ordinary timber structures present pronounced pinching effects due to the local damage to the timber joints. This paper quantifies the impact of variable pinching on the seismic performance of a timber structural archetype. The authors modeled the hysteretic response of a light-timber framed assembly using an empirical hysteresis model and assessed the sensitivity of the displacement demand of the chosen archetype to pinching, number of earthquake repetitions, and spectral acceleration. The choice of an elementary structural archetype, rather than a more complex system, allows isolating the effects of pinching, which could otherwise be disguised by other phenomena, like force redistribution between structural assemblies due to plasticization. [ABSTRACT FROM AUTHOR]

Recent editions of Canadian national building codes increased the height limit for wood-frame construction from four to six stories. In addition, the seismic loads have also been increased. These increases in building height and seismic loads have raised the demand for a stronger shear wall system for construction of midrise wood-frame buildings, especially for those located in high seismic zones. In collaboration with FPInnovations, a new high-capacity shear wall system with multiple rows of fasteners along sheathing edges was developed. This paper presents the test results of shear walls with two rows of nails. A total of 10 specimens were tested under cyclic loading. Test results show that shear walls with two rows of nails have 1.8–2.0 times the lateral load resistance of a standard shear wall with the same sheathing thickness, nail diameter, and nail spacing. The initial stiffness and ultimate displacement of the high-capacity shear wall are also greater than that of the comparable standard shear wall. Based on seismic equivalency criteria, shear walls with two rows of nails can be assigned a design value of the comparable standard shear wall multiplied by a factor of 1.7. [ABSTRACT FROM AUTHOR]

To overcome the shortcomings of traditional shear walls, structure systems have been proposed and investigated. One such structure system is a steel-reinforced concrete shear wall, which has certain desirable properties such as good load-bearing capacity, stiffness, and seismic performance. This paper proposes an M-section cold-formed thin-walled steel reinforced concrete (MCTSR) shear wall, which uses M-section cold-formed thin-walled steel to function as reinforcements. Six specimens with different permanent formwork types, axial compression ratios, reinforcement diameters, and other parameters were tested under cyclic loading to investigate seismic performance. The results demonstrate that various types of permanent formwork, including cement fibrolite plate, metal lathing, and polystyrene board can meet the requirement of related seismic design codes, construction demand, and assembly requirements, and have no obvious impact on the ultimate load-bearing capacity, lateral stiffness, and stiffness degradation rate. However, it changes the energy dissipation capacity and ductility, which are two important indexes to evaluate seismic performance in engineering practice. The failure mechanism and the influence of axial compression ratio, reinforcement diameter, and space between reinforcements are discussed. The shear-strength equations proposed by various countries' or regions' codes were analyzed, which can be used as a reference for related engineers and designers. Finite-element models for MCTSR shear walls were established for further investigation. [ABSTRACT FROM AUTHOR]

This paper reports the shear performances of steel wedge block–crossed inclined stud–ultrahigh performance concrete (UHPC) connections for application to steel-concrete composite bridges. The study entailed 36 pushout tests based on the studs with 1.0, 1.5, and 2.0 aspect ratios, inclined 0°, 30°, 45°, and 60° from vertical. The test results show that in studs with aspect ratio less than 1.5 (ultrashort studs) and inclined at either 30° or 45°, shear strength increases 12% with initial slip increase of 47% and 110%, respectively, relative to the 0° connection. Also, the specimen comprising studs at 45° inclination showed a 1%–91% increase in secant shear stiffness at the elasto-plastic stage, implying less nonlinear sectional flexural stiffness response for such inclined connections. As the stud aspect ratio increased from 1.0 to 1.5, the shear strength increased by 13%, 25%, and 18% for studs inclined 30°, 45°, and 60°, respectively. Increased stud aspect ratio from 1.5 to 2.0 had only a minor influence on shear strength. During the test, the local embedment (UHPC over the stud head top) and UHPC slab shear failure with many subtle cracks showed pronounced ductility (continuous clear snapping sounds from steel fibers and major cracks observed approaching failure) for a stud aspect ratio less than 1.5. Furthermore, the reduced rigidity method, used in a given section under the service load, showed 10% lower deflection than 0° stud connections and a within-5% increase of the rigid connections for ultrashort studs. These results show that this type of shear connector exhibits good stiffness and strength performance, especially for ultrashort studs. In future research, low cyclic loading and high cycle fatigue tests should be performed on these connections. [ABSTRACT FROM AUTHOR]

This paper proposes a novel, cold-formed portal framing system that comprises tapered box members formed from two cold-formed nested channel sections. The proposed method possesses structural and nonstructural advantages, such as improved seismic performance, enhanced building hygiene through bird and dust resistance, further corrosion resistance, and aesthetic improvement, as a result of fly bracing removal. The novelty of the box member lies in the tapering ability of the section, leading to material and paint savings. To examine the failure mechanisms and structural performance of the tapered box portal frame and to investigate the adequacy of the design method, two full-scale portal frames with an 18.16-m span were built and tested to failure under two common loading scenarios. The first was lateral cyclic loading into the inelastic range in conjunction with a vertically acting permanent load. The possibility of ductile plastic hinge formation in a severe earthquake was investigated using lateral cyclic testing. The second was vertical loading to failure. A novel economic loading setup was used to apply the gravity load on the frame. For the seismic design of this section type, slenderness limits are proposed for seismic applications along with the design ductility. A rotational stiffness value for a nominally pinned portal frame column base was also suggested in this study. [ABSTRACT FROM AUTHOR]

Masonry-infilled wood frame walls are widely used in vernacular buildings all over the world. Based on traditional European wood frame walls, this paper proposes wood bracing as reinforcement for traditional Chinese masonry-infilled wood frame walls to compensate for premature cracking of masonry infill and the resulting performance degradation of the walls. Five wall frames were prepared and loaded cyclically in lateral direction. Wood bracings of different forms and their contribution to the wall performance were studied. The hysteretic curves, stiffness and strength degradation, energy dissipation, and equivalent viscous damping coefficient were determined and discussed for their relationship with the bracing provisions. It was found that the bare frame was flexible and resilient and the masonry-infilled frame was stiff and prone to brittle failures, while the frames reinforced by wood bracing exhibited good load-carrying capacity, deformability, and energy dissipation capacity. The peak load and the ultimate displacement of the frame reinforced by X-bracing were 49% and 85% higher than those of the masonry-infilled frame, and the equivalent viscous damping coefficient was increased by 81% at most. The asymmetric Z-bracing and double crossing bracing led to a slight decrease in the initial stiffness compared to the masonry-infilled frame due to the pull-out of the intermediate mortise-tenon connections. [ABSTRACT FROM AUTHOR]

This paper presents analysis of fracture in structural steel subjected to cyclic loads, which is of paramount importance for evaluating the safety of steel buildings exposed to extreme events such as strong earthquakes. The analysis relies on the phase-field concept to describe the formation and propagation of cracks in a solid body, in conjunction with a large-deformation description of the motion and an elastoplastic constitutive law having nonlinear isotropic and kinematic hardening to account for the material hysteretic response. The evolution of the phase-field is driven by a low-cycle fatigue criterion, aimed to phenomenologically describe the effect of irreversible processes ultimately leading to ductile fracture. The proposed modeling scheme is used in the simulation of experimental tests on circumferentially notched steel coupons tested by the authors, and its capability to capture fracture occurrence, as well as cyclic crack opening and closing, is demonstrated. [ABSTRACT FROM AUTHOR]

This paper presents the full-scale shake-table test and numerical simulation study results of a 2-story beam-through steel frame (BTSF) equipped with self-centering modular panels (SCMPs) subjected to near-fault ground motion records. A SCMP is a portable self-centering device that can be inserted and bolted to steel frames to provide lateral force resistance with recentering capability and replaceable seismic fuse devices for energy dissipation. Previous research works have been done on the analytical study, quasi-static cyclic loading testing, and numerical study of the general seismic behavior of the SCMP systems with different energy dissipation components including tension-only braces, slit steel plate shear walls (SWs), and hysteretic dampers. An important aim of this study is to experimentally verify the seismic performance of full-scale steel frame structures with SCMPs via shaking-table tests capable of applying pulselike ground motion. A literature review of previous research works suggested that near-fault ground motions can amplify the dynamic response of structures and cause more extensive damage compared with far-fault ground motion records. To achieve this goal of studying the effect of near-fault ground motion records on the test structure installed with SCMPs, a nonlinear finite-element (FE) model has been developed for a parametric study in which a set of near-fault ground motion records were used as base excitation to the structure model. The nonlinear dynamic analysis results showed that the test structure exhibited self-centering capability under both design-basis earthquake (DBE) and maximum considered earthquake (MCE) cases. Additionally, the effect of energy dissipation capacity on the test structure's response is also discussed. [ABSTRACT FROM AUTHOR]

The seismic vulnerability of existing RC framed buildings in seismic-prone areas requires affordable and practice-oriented solutions for their retrofitting. In this paper, the authors present a retrofitting solution for RC buildings based on the combined use of cross-laminated timber (CLT) panels and asymmetric friction connections (AFCs). The AFC connection is activated when the force level reaches the design threshold. The energy dissipation of the AFC increases the structural dissipation capacity and reduces the displacement demand. This research presents the outcomes of an experimental campaign on selected prototypes of these AFC connectors. The authors assess their dissipative capacity from cyclic load tests in four different connector arrangements and examine the contribution of aluminum shim layers. The first results highlight the significant dissipation potential of the AFC, although they also provide evidence of the notable sensitivity on the design and constructive details. The authors present a modeling approach to simulate the experimental results. [ABSTRACT FROM AUTHOR]

This paper introduces a novel technique called arched steel haunches with rib element (ASHR) for seismic retrofitting of RC frames. In this approach, the arched haunch is equipped with a steel ring or link, as the rib element (RE). A simplified physical model was proposed to approximate their behavioral curves. To evaluate the model's accuracy, a series of cyclic load tests on arched steel haunches, with and without RE, were conducted. The experimental responses showed that by increasing the RE stiffness, the maximum damping ratio decreased conversely, while the strength, plastic stiffness, and even dissipated energy increased. Accordingly, the tensile and compressive strength increased up to 1.5 and 1.35 times, respectively. However, the elastic stiffness did not vary compared to the reference specimens; the tensile plastic stiffness increased up to three times and, the ultimate secant stiffness in tension and compression enhanced up to 1.56 and 3.9 times, respectively. Moreover, the total energy dissipation upgraded up to 1.39 times with the fusing of the rib elements. It should be noted that the results of this pilot study will be used in future research on the experimental behavior of the reinforced concrete beam-column joints. [ABSTRACT FROM AUTHOR]

Reliable and robust numerical modeling of RC columns under lateral load is commonly performed using one-dimensional elements. Although the strain is assumed to vary linearly through the section, bond-slip and buckling of reinforcing bars at the joints/connections contribute substantially to the column response. This paper presents a three-dimensional (3-D) fiber-based model with explicit representation of the bond-slip that occurs at the column-footing interface for cast-in-place columns and at the interface between bars and mechanical couplers for precast columns with grouted sleeve (GS) connections. The model contains beam elements with fiber sections for concrete, beam elements for longitudinal steel bars and sleeves, and spring elements for interfacial bond-slip behavior. The novelty is that the model can be achieved using existing software implementations, retains the efficiency of fiber-based elements under cyclic loading, and parameters are calibrated based on component-level testing, unlike other resultant or hybrid models that require arbitrary backbone and cyclic property specification. An extensive experimental program was conducted to investigate the behavior of GS couplers and calibrate the bond-slip models. Four large-scale RC columns were then used to verify the proposed model by comparing the measured load-displacement, energy dissipation, curvature, and failure mode with the numerical responses. [ABSTRACT FROM AUTHOR]

Heavy glulam timber framed structures are facing a growing inadequacy in resisting lateral actions from earthquakes and winds due to the increasing building heights. This paper presents the experimental and numerical analysis results on the hysteretic behavior of newly developed carbon fiber reinforced polymer (CFRP) confined timber-steel buckling-restrained bracings and the lateral performance of bolted glulam timber frames with such bracings. Ten timber-steel bracings and four frames with different bracing provisions were tested via reversed cyclic lateral loading. A finite-element method based model was developed, verified, and used for parametric studies. The bracing test results indicated that the design requirements for ordinary buckling restrained bracings on the confinement ratio and the transverse bulging force are adequate for the proposed timber-steel bracings. A confinement ratio no less than 4.6 is suggested. Compared to an otherwise similar bare frame, two frames with the proposed bracings were found to be 132% and 176% higher in the peak loads, more than 10 times higher in the elastic stiffness, 40% and 43% higher in ductility ratio, and on average 106% higher in the equivalent viscous damping ratio. The two frames also exhibited higher stiffness and energy dissipation than a frame braced by timber bracings, which are prone to buckling failure. Parametric studies indicated that the secant stiffness and the damping ratio of the frames at small drift can be substantially affected by the bolt slippage of the bracing-frame connections. The increased lateral stiffness ratio will lead to increase in the peak load and stiffness, but the equivalent viscous damping ratio remains nearly constant for lateral stiffness ratios larger than 2.5. The frame stiffness and peak load increase with increased rotational stiffness of the beam-column connections while the equivalent viscous damping ratio decreases. [ABSTRACT FROM AUTHOR]

Hysteretic lateral force-displacement (HLFD) models are important for efficient structural analysis under cyclic loading (e.g., earthquakes). This paper proposes a novel machine learning (ML)-based HLFD model, referred to as ML-HLFD, to characterize the relationship between lateral force and displacement of reinforced concrete (RC) columns with different properties (e.g., geometry, and material properties). To this end, a database including 498 experimental results is collected for model training, validation, and testing purposes. The ML-HLFD first uses a support vector machine (SVM) to classify the different failure modes (i.e., flexure failure, flexure-shear failure, and shear failure). After that, an artificial neural network (ANN) is trained for obtaining the implicit mapping between inputs (i.e., the properties of RC column) and outputs (i.e., the crucial parameters of selected HLFD models). The performance of the ML-HLFD models is studied by (1) cross-validation; and (2) comparisons with experiments, a classical fiber-element model, and an existing analytical model, which demonstrate the accuracy and efficiency of ML-HLFD models under a wide range of scenarios. [ABSTRACT FROM AUTHOR]

This paper presents the results of a series of unidirectional quasi-static cyclic tests on 1/3-scale post-tensioned rocking steel bridge column specimens designed to rock at the interface with the foundation. The objective was to examine the effects of column diameter-to-thickness ratio, base plate, and energy dissipaters and their locations on the lateral cyclic behavior of the system. Site-specific cyclic displacement loading protocols were developed by performing time-history analyses of the pier. Emphasis was placed upon the sources of lateral response degradation including elastic restoring force reduction, local buckling, and energy dissipater failure. Strain distribution at the rocking plane and along the height, local bulging of the column, and uplift profile are discussed. The influence of multiple loading on the lateral response was also investigated. A component testing program was conducted to characterize the cyclic loss of post-tension force due to wedge seating in a typical industry monostrand anchorage system. The column test results demonstrate that a stable and robust self-centering response can be achieved with minimal damage to the column and most of the hysteretic energy is confined within the replaceable elements. [ABSTRACT FROM AUTHOR]

Brittle failure of lightly reinforced concrete columns is one of the primary reasons for partial or total collapse of substandard existing buildings subjected to earthquake loading. This study presents collapse performance of a full-scale building that was performed to gain insight into the seismic behavior and the collapse mechanisms of nonductile buildings with lightly reinforced concrete columns. The three-story building was tested under displacement-controlled quasi-static reversed cyclic loading followed by a lateral pushover loading up to realization of the total collapse. In addition to the poor reinforcement details, columns had high axial load–to–axial capacity ratios as also observed in many existing substandard buildings. During the test, severe structural damage was observed at 0.9% first-story drift ratio in the cyclic part of the lateral loading and the brittle total collapse of the building took place during the pushover loading at 1.45% first-story drift ratio. In this paper, after the introduction of the test campaign, the formation of structural damage and collapse mechanisms are discussed. In addition, an attempt to predict the behavior and performance of the test building is made by using a column model that considers flexural, slip, and shear deformations. Finally, the obtained analytical results are compared with the experimental observations and results. [ABSTRACT FROM AUTHOR]

This paper aims to investigate the seismic performance of a steel frame with an external diaphragm joint between a concrete-filled steel tube (CFST) column and H-shaped steel beam through experiments and finite-element (FE) analysis. A quasistatic test was conducted on five steel frame specimens. The parameters involved in the test were joint stiffness, beam-to-column stiffness ratio and concrete strength. Based on the experimental results, failure mode, lateral load versus displacement hysteretic curve, skeleton curve, strength and stiffness degradation effects, ductility, and energy dissipation capacity were analyzed. The experimental results show the hysteretic curves have a plump shuttle shape; the strength degradation effect and stiffness degradation effect are relatively feeble; and the ductility and energy dissipation capacity are excellent. Therefore, the tested specimens have good seismic performance. Also, this suggests that larger joint stiffness brings about superior seismic performance; a stronger column leads to higher bearing capacity as well as inferior ductility and energy dissipation capacity; and a CFST frame performs better than a hollow steel tube column frame under cyclic loads. On the basis of the experimental results, the ABAQUS software version 6.14 was adopted to establish the FE models. The applicability and accuracy of FE simulation were first verified by experimental results. Then, quantitative parametric analysis was carried out to study the effects of different parameters on seismic performance of the CFST frame with an external diaphragm joint. [ABSTRACT FROM AUTHOR]

This study developed a special energy dissipation X-bracing for cold-formed steel (CFS) shear walls to improve the ductility of the corrugated steel sheathing. In previous research, CFS shear walls with corrugated sheathing demonstrated poor ductility under cyclic loading. The paper presents a potential solution by adding a special energy dissipation bracing (EDB) to improve the ductility of the corrugated sheet–sheathed shear walls. The EDB can be tuned according to the CFS shear wall base performance to achieve the highest postpeak deflection capacity, thereby significantly improving the seismic ductility. To prove the concept and analyze the feasibility of the new EDB, a test program of nine full-scale shear walls was conducted. The experimental results showed that with the tuned EDB, the corrugated steel sheet–sheathed shear walls had improved ductility with no considerable reduction in the initial stiffness and shear strength. Installing the proposed EDB can be an efficient approach to enhance the seismic performance of CFS-framed shear walls. Details of the test program and discussion are presented. [ABSTRACT FROM AUTHOR]

This paper presents a test campaign concerning the fatigue behavior of the bird-beak square hollow section (SHS) gap K-joints subjected to brace in-plane force. A total of four bird-beak SHS gap K-joint specimens were tested. Prior to the high-cycle fatigue tests, static in-plane force was applied to the braces of K-joint to determine the hot-line strain distributions and the stress concentration factors (SCFs) via extrapolation. Based on the results of static loading tests, the amplitude of cyclic load can be further determined. Subsequently, high-cycle fatigue tests were performed on the square and diamond bird-beak SHS gap K-joints to investigate the fatigue behavior from different perspectives, such as failure mode, fatigue life, crack propagation, and stiffness degradation. The test results demonstrate that the brace crown region always possessed the most severe stress concentration, which coincided with the location of crack initiation. This implies that the experimentally obtained SCFs can accurately predict the crack initiation location. The test fatigue lives of bird-beak gap K-joints were compared with the predictions by the International Institute of Welding (IIW) Srhs–N design curves originally developed for the conventional joints. [ABSTRACT FROM AUTHOR]

Planar composite plate shear walls/concrete filled (C-PSW/CF) consist of two steel web plates and two flange (or closure) plates making up a long hollow box section that is filled with concrete. The web plates are connected to each other using regularly spaced steel tie bars. Steel headed stud anchors (shear studs) may be added to reduce the steel plate slenderness for local buckling considerations in the composite phase. This paper presents the results of experimental investigations conducted to evaluate the behavior of five planar C-PSW/CF specimens subjected to constant axial compression and cyclic lateral loading. Parameters included are the axial load level, steel plate slenderness ratio, and tie reinforcement ratio. The cyclic lateral load-deflection responses of the composite wall specimens are discussed along with their lateral stiffness, strength, and deformation capacity. Experimental results indicate that the lateral load capacity of composite walls is governed by flexural yielding of the steel plates followed by plate inelastic local buckling and concrete crushing. All the wall specimens developed and exceeded the flexural capacity calculated using the plastic stress distribution method (while including the effects of axial compression). The post-peak strength degradation of wall specimens is governed by the initiation and propagation of fracture through the steel flange plates and web plates. A fiber-based model was developed and used to calculate the section moment-curvature response of the specimens. Comparing the experimental and numerical moment-curvature responses indicates that the section flexural stiffness and flexural capacity can be estimated using the fiber-based analysis method. [ABSTRACT FROM AUTHOR]

This paper presents the structural performance of jacketed concrete columns subjected to cyclic lateral loading using ultrahigh-performance fiber-reinforced concrete (UHPFRC) with various advantages as construction materials of high strength and durability with self-compacting. The UHPFRC jacketing with/without textile reinforcement for concrete columns for the seismic retrofitting demonstrates its strengthening efficiency and reduction of jacket thickness through the experimental program in this study. Especially, textile-reinforced UHPFRC (TR-UHPFRC) jacketing has enhanced ductility compared with that of UHPFRC jacketing by changing critical failure crack patterns in jackets. The satisfactory interface shear strength between UHPFRC jackets and substrate concrete of columns was confirmed by a series of slant shear test programs provided that required roughness on substrate with moisture were prepared according to current design guidelines. This study also investigates the effects of discontinuity of tension forces in jackets at the floor level of columns on shear load paths, which are intended to alleviate jacketing construction for columns in existing buildings as a member intervention technique. Shears and axial forces induced in jacketed columns under lateral loading are mainly resisted by compression forces in diagonal struts through the jacket with substrate concrete columns and are explained by arch actions for enhancement of shear strength after jacketing. [ABSTRACT FROM AUTHOR]

This paper presents experimental investigations on the seismic behavior of cross laminated timber (CLT) shear walls in a balloon frame configuration with various ledger assemblies attached at midheight. The tested system consisted of two seven-ply 191-mm-thick CLT panels with generic hold-downs, steel angle brackets, plywood surface splines, and nails as fasteners. A 2-story system was tested with a panel aspect ratio of 3∶1 with different steel and wood ledgers under monotonic and quasistatic reversed cyclic loading. Three ledgers were subsequently tested under vertical quasistatic monotonic loading to determine their remaining load-carrying capacity. The tests showed that the shear wall displacement was due to the rocking of the wall panels, which themselves behaved as rigid bodies with negligible in-plane deformations. When compared to the monotonic tests, the strength in reversed cyclic tests was up to 21% lower. The ledger did not impede the desired rocking behavior of the wall, nor did the rocking of the wall reduce the remaining gravity load-carrying capacity of the ledgers by more than 7%. Balloon-framed CLT shear walls can be detailed and designed using the Canadian standard specifications for platform-type construction. [ABSTRACT FROM AUTHOR]

This paper studies the rotational behavior of beam-to-column bolted connections in bamboo scrimber structures. Three types of beam-to-column connections, including bolted connections with outer-clamping steel plates, bolted connections encased with T-shaped steel plates, and bolted connections encased with double L-shaped steel plates, were designed and tested under monotonic or reversed cyclic loads. The influence of bolt arrangement on the mechanical properties was also studied. Failure of the connections was mainly caused by cracking of the adhesive interface near the bolt at the tensile side of the beam, which was a weak point that needs further attention. The elastic stiffness, capacities, ductility coefficient, and energy dissipation capacity of the T-steel connections improved compared with the I-steel connections. The load-carrying capacities of the connections were calculated according to common standards. Results showed that for the I-, T-, and double L-steel connections, the different standards had different safety margins. [ABSTRACT FROM AUTHOR]

This paper presents the experimental calibration and validation of the analytical wall model that incorporates interaction between shear and flexural responses under cyclic loading conditions described in the companion paper. The model is calibrated and validated against detailed experimental data obtained from tests on five moderately slender reinforced concrete wall specimens that experienced significant levels of shear-flexure interaction. Test measurements were processed to allow for detailed comparisons between the predicted and measured wall responses at various locations and response levels. Response comparisons reveal that the proposed analytical model captures the experimentally measured nonlinear shear deformations and their coupling with flexural deformations throughout the cyclic loading history. In addition, the analytical results successfully represent various experimentally measured responses, such as lateral-load versus wall-topdisplacement relations, magnitudes and distributions of deformations associated with shear and flexure, and local responses including flexural rotations, vertical strains, and concrete crack orientations. Based on the comparisons presented, model capabilities are assessed and future model improvements are suggested. [ABSTRACT FROM AUTHOR]

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