Self-centering Capacity Research Articles

Development and performance assessment of a novel self-centering damper for slotted RC walls

Slotted RC walls exhibit better ductility compared to conventional RC walls, but inevitably lead to a reduction in lateral stiffness and load-bearing capacity. In order to improve the seismic performance and reduce the residual deformation of slotted RC walls, a novel self-centering damper (SCD) suitable for the connection of slotted RC wall is proposed. The novel SCD is composed of two diagonally intersecting disc spring devices (DSD) and multiple slit steel plate (MSSP) arranged in parallel. The construction and working principle of the novel SCD were thoroughly explained, and its theoretical model was established. Through cyclic loading tests and numerical simulations, the collaborative working mechanism of the two components was analyzed. The influence of the pre-pressed force and arrangement angle of the DSD on the energy-dissipating and self-centering capacities of the SCD was investigated. It was found that increasing the pre-pressed force and arrangement angle of the DSD would reduce residual deformation and equivalent viscous damping ratio. Then, the seismic performance of the slotted RC wall with the novel SCDs was analyzed. The results demonstrated that the slotted RC wall incorporating the SCDs exhibited superior deformation and energy-dissipating capabilities, while maintaining a relatively high level of load- bearing capacity and stiffness. Notably, the residual deformation rate of the SCDs was only 0.4 % at the design threshold, enabling disassembly and replacement after seismic events.

Development and application of replaceable self-centering energy dissipative braces

Aiming to enhance seismic resilience of steel frames, this paper proposes a novel replaceable self-centering energy dissipative brace (RSCEDB), in which the combined disc springs act as self-centering (SC) system and the replaceable slit dampers act as energy dissipating (ED) system. Initially, the configuration details, assembly process of RSCEDB are introduced. Based on the numerical simulations, the working mechanism and hysteretic model of RSCEDB are discussed in depth. After that, a steel frame equipped with RSCEDB (SF-RSCEDB) is presented, and the effect of RSCEDB with various parameters on the performance of the SF-RSCEDB is investigated by numerical simulation. The results indicate that the damage is concentrated in the ED system, while the remaining parts of the RSCEDB remain elastic. The self-centering and energy dissipation capacity of RSCEDB can be flexibly modified by pre-pressure and stiffness of combined disc springs, as well as yield strength of dampers, which is consistent with the prediction of the hysteretic model. Benefiting from the contribution of RSCEDB, the SF-RSCEDB has satisfactory self-centering capacity. Before activation, the RSCEDB serves as a structural component, providing larger lateral stiffness. After activation, the RSCEDB serves as a structural fuse, dissipating most of the seismic energy. With favorable self-centering performance, the damaged dampers can be easily identified and replaced, demonstrating that the SF-RSCEDB possesses excellent seismic resilience. Finally, a resilient design method is proposed for SF-RSCEDB.

Experimental study on seismically isolated systems using a novel roller-type bearing with energy dissipation capacity

The roller-type isolation bearing is highly effective in limiting the transmission of lateral seismic forces to the superstructure. This paper introduces a novel roller-type bearing with energy dissipation capacity (RB-EDC), which includes flat bearing seats, rollers, limit plates with energy dissipation capability, and limit rings. The RB-EDC is characterized by its excellent energy dissipation capacity, simple manufacturing process, low cost, vertical tensile bearing capacity and stable performance in extremely cold regions due to its specific configuration and materials. The design procedure for the RB-EDC is detailed herein. Subsequently, pseudo-dynamic comparison tests were conducted on both a seismic isolation system specimen and a RC column specimen under frequent and rare earthquake conditions to validate the damping performance of the RB-EDC. The seismic isolation system consists of the RB-EDC and an RC column identical to the RC column specimen. The results indicate that, compared to the RC column specimen, the column in the seismic isolation system specimen significantly reduces crack distribution ranges, rebar strain, concrete strain, and displacement at the column top under seismic actions. The RB-EDC exhibits significant energy dissipation capacity even during frequent earthquakes, demonstrating effective damping performance. However, the residual displacement of the RB-EDC increases with seismic intensity, which may impact the damping performance of the bearing in future potential earthquakes, indicating the need for further redesign to incorporate self-centering capacity.

Experimental investigation and numerical simulation on seismic performance of self-centering bridge bents with energy-dissipation beams

This study explores the creation of self-centering bridge bents with energy-dissipation (ED) beams to enhance seismic resilience. This design combines the concepts of cast-in-place bridge bents with ED components and self-centering rocking piers. The self-centering bridge bent with ED beams integrates cooperative mechanisms, for bearing, stability, energy dissipation, and recoverable capacity. Two types of specimens were designed and constructed: self-centering bridge bents with and without ED beams, referred to as specimens SCB-EDB and SCB, respectively. Quasi-static tests were conducted to thoroughly assess the seismic performance, including lateral force, stiffness, energy dissipation, and self-centering capacity, of these specimens. The results show that both specimens exhibit a distinct flag-shaped hysteresis curve, demonstrating good self-centering capacity. However, the ED beams slightly reduce the self-centering capacity of the bridge bent. Specimen SCB-EDB shows significantly higher lateral force, stiffness, and energy dissipation capacity than specimen SCB. The ED beams also contribute to reducing damage and sliding of the column. Numerical models were established in OpenSees to reproduce the test results of specimens SCB-EDB and SCB. The numerical results closely match the corresponding test results, effectively capturing the hysteresis behavior, skeleton curves, stiffness variations, and energy dissipation capacity. Consequently, both numerical models could accurately replicate the quasi-static test results.

Numerical Investigation on the Hysteretic Performance of Self-Centering Precast Steel–Concrete Hybrid Frame

To improve the construction performance and seismic resilience of precast reinforced-concrete frame structures, an innovative self-centering precast steel–concrete hybrid frame has been proposed and subjected to cyclic loading tests. In this paper, a comprehensive numerical analysis was conducted to further investigate the frame’s hysteretic behavior. Initially, a numerical model was developed using the finite element software OpenSees. Numerical analyses of two frame specimens were conducted, demonstrating good agreement between the numerical and experimental hysteretic characteristics, thus validating the model’s accuracy. Subsequently, based on the numerical simulations, a quantitative comparison of hysteretic performance between a novel frame and a traditional reinforced-concrete frame of the same scale was performed. While the proposed frame exhibited slightly lower initial stiffness and energy dissipation capacity than the traditional frame, it outperformed in terms of load-carrying capacity and self-centering ability. Finally, parametric analyses were carried out to assess the influence of various design parameters on the hysteretic performance, including friction force in the web frictions devices, initial post-tensioned force of the prefabricated steel–concrete hybrid beams, the steel arm length, and the column longitudinal reinforcement ratio. The results showed that increases in these four parameters improved the load-carrying capacity and initial stiffness of the proposed frame. Additionally, an increase in the friction force, steel arm length, or column longitudinal reinforcement ratio enhanced the frame’s energy dissipation capacity, while an increase in the initial post-tensioned force or a decrease in the friction force enhanced the frame’s self-centering capacity.

The probabilistic performance-based seismic assessment of concrete bridge piers with SMASC reinforcing bars: Effect of pulse-like ground motion and vertical load-to-capacity ratio

Concrete bridge piers are critical components of bridge structures and their performance under seismic loading is of utmost importance. Traditional reinforced concrete bridge piers have shown limitations in terms of residual deformations and seismic resilience. This has led researchers to explore alternative reinforcement materials, such as Shape Memory Alloy (SMA) coupled with steel reinforcing bars, which have demonstrated promising attributes like energy dissipation as well as self-centering capacity. This study aims to fill this gap by evaluating the performance of concrete bridge piers with SMA-Steel coupled (SMASC) reinforcing bars under various intensities of vertical gravity loads and the action of pulse-like ground motion components, throughout a probabilistic framework. To this end, a group of bridge piers with different reinforcement types, including pure steel and SMASC are considered. These piers are subjected to 55 near-fault (NF) pulse-like records as well as 32 far-fault (FF) ground motions, throughout the Incremental Dynamic Analysis (IDA). The influence of distinct frequency components is analyzed by decomposing NF records into low-frequency pulses and high-frequency residual components. Also, the role of pulse to the 1st modal period of the piers (Tp/T1) is investigated by evaluating the piers’ response under the action of NF records, which were clustered into four groups. Results were assessed by evaluating the intensity measure and capacity of the studied piers at the desired performance objectives according to the FHWA manual. Moreover, the mean annual frequencies of exceeding performance limit states and the confidence levels of meeting performance objectives are studied. The results of the study indicate that the dominance of the component of NF ground motions depends on factors such as the intensity of gravity loads, ground motion characteristics, and the Tp/T1 ratio. The components of NF records within certain clusters of the Tp/T1 ratio are necessary for accurate response assessment, while FF records can be used for conservative design purposes, depending on the level of ground motion intensity and the intensity of applied gravity load. The SMASC-reinforced piers with specific λ factors (i.e. λ = 0.5 or λ = 1.0) and low intensity of gravity loads lead to a higher (1.6 times higher) mean annual frequency of exceeding a limit state, compared to pure steel rebars. Also, the confidence levels for meeting performance objectives vary depending on the ground motions, but, as gravity load intensity increases, confidence levels decrease, particularly for piers with a λ factor of 0.5.

Theoretical and experimental research on the rocking truss system with post-tensioned rocking connection

The weak story failure often occurs in steel frame structures and the collapse risk of the frames will increase because of concentrated plastic deformation in the soft story. The work presented in this paper aims to avoid the soft story mechanisms and the improve self-centering capacity of steel frames by employing the innovative rocking truss. Compared with the previous rocking system, it is more flexible in application and suitable for retrofit of existing buildings. The theoretical approach to quantifying the stiffness demand of the rocking truss was proposed and presented two critical parameters (equivalent bending stiffness ratio η and the rotation stiffness ratio λ) for the design of the rocking truss. The 1/3 scaled steel frame with rocking truss (SFRT) was tested and theoretical analysis results were validated by test results. The finite element model of SFRT was built following the boundary conditions of the test specimen. The numerical results are consistent with the experimental observations. The nonlinear static and dynamic analysis results of the SFRT were compared with those of the same steel frame (SF) with a bracing system. It was found that the rocking truss can reduce the maximum and residual drifts of the main frame as expected, and the plastic development of the RBS at the beam end in SFRT is less than that in SF with a bracing system. The parametric analysis of the rocking connections with different values of prestressing force was carried out. The results confirm that the rotational stiffness and load-bearing capacity of the rocking connection can be accurately evaluated by the theoretical force-displacement curve. The effect of the equivalent bending stiffness ratio η and the rotation stiffness ratio λ on the lateral deformation pattern of structures was discussed by theoretical analysis, and the design procedure of the rocking truss is recommended to satisfy the demand of uniform inter-story drift and self-centering capacity.

The Use of Externally Bonded Fibre Reinforced Polymer Composites to Enhance the Seismic Resilience of Single Shear Walls: A Nonlinear Time History Assessment

In medium- to high-rise buildings, single shear walls (SSWs) are often used to resist lateral force due to wind and earthquakes. They are designed to dissipate seismic energy mainly through plastic hinge zones at the base. However, they often display large post-earthquake deformations that can give rise to many economic and safety concerns within buildings. Hence, the primary objective of this research study is to minimize residual deformations in existing SSWs located in the Western and Eastern seismic zones of Canada, thereby enhancing their resilience and self-centering capacity. To that end, four SSWs of 20 and 15 stories, located in Vancouver and Montreal, were meticulously designed and detailed per the latest Canadian standards and codes. The study assessed the impact of three innovative strengthening schemes on the seismic response of these SSWs through 2D nonlinear time history (NLTH) analysis. All three strengthening schemes involved the application of Externally Bonded Fiber Reinforced Polymer (EB-FRP) to the shear walls. Accordingly, a total of 208 NLTH analyses were conducted to assess the effectiveness of all strengthening configurations. The findings unveiled that the most efficient technique for reducing residual drift in SSWs involved applying three layers of vertical FRP sheets to the extreme edges of the wall, full FRP wrapping the walls, and full FRP wrapping of the plastic hinge zone. Nevertheless, it is noteworthy that implementing these strengthening schemes may lead to an increase in bending moment and base shear force demands within the walls.

Numerical Assessment of Bidirectional Roller Bearing Isolators under Near-Fault Earthquakes

In this research, a bidirectional seismic isolation device composed of sloped bearing plates and multiple rollers arranged in both orthogonal-in-plane directions is numerically studied. A previous analytical model of a single direction of roller bearing (RB) system is extended to a two-direction RB system. Several experimental tests in a physical building model with and without an RB system are used to validate the numerical model. The model is used to perform the nonlinear response of a four-story multi-column building when subjected to pairs of scaled near-fault earthquake records. The effect of the inclination angle of bearing plates in the range of 1.0° to 4.0°, the sliding friction force, and supplementary damping mechanisms ranging from 0.0 to 0.5 N/kg (i.e. friction force normalized with the structure mass) are also investigated. The results show that the proposed bidirectional RB system is suitable for reducing the seismic response of stiff and flexible multi-column structures. In particular, the RB system reduces the acceleration responses by 5% to 85% in flexible structures and 86% to 96% in stiff structures. Furthermore, bearing plates with an inclination angle greater than or equal to 3.0° have significant benefits in terms of self-centering capacity.

Experimental investigation on seismic behavior of damaged self-centering friction beam-column joints after repair

Self-centering beam-column joints are an effective strategy to improve the seismic resilience of frame structures. Extensive research has been conducted on the seismic performance of newly constructed self-centering joints, involving experiments, theoretical analyses, and simulations. Nevertheless, less attention has been paid to evaluating the seismic resilience of self-centering joints after repair. To address this gap, this paper presents a series of experiments to investigate the mechanical properties of damaged self-centering friction beam-column joints (SCFJ) after repair. Three SCFJs damaged by cyclic loading are repaired using epoxy injection, CFRP wrapping, and replacement concrete. The repaired joints are then subjected to cyclic loading under the same conditions as the original loading. A comprehensive analysis is conducted of the hysteretic curve, skeleton curve, energy dissipation, stiffness degradation, and residual displacement of both the original and repaired SCFJs. The results show that the repaired SCFJs maintain their commendable self-centering capacity. Specifically, the replacement concrete method is the most effective in restoring the initial seismic performance of the SCFJs. The epoxy injection method is the fastest repair method and successfully restore the SCFJ to approximately its original ultimate strength and approximately 85% of its energy dissipation and self-centering capacity. The CFRP wrapping method is able to largely restore the self-centering capacity of the SCFJ to its original level, but with a notable decrease in stiffness.

Seismic performance assessment of RC bridge piers with variable hysteresis performance dampers

A novel variable hysteresis performance damper (VHD)—multi-stage slip friction damper is developed and applied to implement multi-level seismic resistance of structures. Different from the conventional slip friction dampers, which feature only a single type of slip friction surface, this innovative damper incorporates two types: a flat slip surface and a wedge slip surface. The quasi-static cyclic loading tests of the VHD were carried out to investigate its variable hysteresis performance. The test results revealed that the developed damper presented excellent adaptive performance, and its hysteresis behavior changed from a complete rectangle with efficient energy dissipation to a flag-shaped curve with exceptional self-centering capacity as deformation increases. Subsequently, the developed VHD with unique adaptive performance was applied in RC bridge piers (BP) to improve the seismic performance. Nonlinear time history and fragility analysis methods were employed to assess the seismic performance of the RC bridge piers with VHDs (BP-VHD) in deterministic and probabilistic manners, considering maximum and residual deformations as performance indicators. For comparison, seismic responses of RC bridge piers with traditional buckling restrained braces (BRBs) and self-centering energy dissipation braces (SCEBs) were also presented. The analysis and comparison results demonstrate that the developed VHD is as effective as BRB in reducing maximum deformation at small PGAs, meanwhile, it can effectively reduce the residual deformation of the structure to allowable values when the PGA is large. Furthermore, the failure probability of BP-VHDs is lower compared to piers with BRBs and SCEBs, particularly concerning maximum and residual drift ratios as performance indicators. The application of the VHD can effectively achieve the goal of multi-level seismic resistance for RC bridge piers.

A friction-strip hybrid damper with multi-phase energy dissipation mechanism: Cyclic test and numerical verification

By combining the frictional and plastic energy dissipation modules (FEDM and PEDM), a novel multi-phase friction-strip hybrid damper (MFSHD) is proposed in the current study. The theoretical analyses demonstrate that, when applied in a self-centering structure, the MFSHD is able to provide higher strength, secondary stiffness and energy dissipation and maintain the self-centering capacity compared with conventional friction dampers. A series of quasi-static tests was conducted on the MFSHD to evaluate the effects of different parameters on the hysteresis performance of the MFSHD. The results showed that increasing the strip number or the bolt pre-tension force could both improve the mechanical performance of the MFSHD. The MFSHD with sandglass-shaped strips had a better performance than that with I-shaped strips. In the MFSHD with lower slipping displacement, the PEDM was activated earlier and provided higher strength, stiffness and energy dissipation, whereas its low-cycle fatigue life was reduced. The numerical analyses based on the model validated by the test results showed that the self-centering braced frame substructure equipped with the MFSHD exhibited hysteresis behavior in consistency with the theoretical model. The superior performance of the MFSHD compared with conventional friction dampers was verified numerically.

Post-earthquake repairability-based methodology for enhancing steel MRFs

Self-centering beam-to-column connections (SBCs) were widely investigated to enhance conventional steel moment-resisting frame’s (MRF’s) post-earthquake repairability by reducing residual displacements. The peak displacement-targeted design methodology was adopted to develop the design guidelines for enhancing MRFs with the emerging self-centering members, where the desired post-earthquake repairability of the enhanced MRF needs to be achieved with inevitable iterative dynamic analyses. This paper intends to develop a novel post-earthquake repairability-based methodology for enhancing MRFs with SBCs, where residual and peak displacements are both targets. To this end, artificial neural network (ANN) models were developed to estimate the peak and residual displacements of the enhanced MRFs with SBCs under given seismic intensities. Peak and residual displacement-based design (PRBD) procedures were developed based on the proposed post-earthquake repairability-based methodology and established ANN models. Four design cases were designed through the developed PRBD procedure and analyzed. The design and analysis outcomes demonstrate that the improved MRFs can attain the intended post-earthquake repairability and meet the peak and residual displacement objectives without necessitating iterative design and dynamic analyses. This confirms the effectiveness and precision of the proposed post-earthquake repairability-based approach and PRBD procedure. Moreover, the enhanced MRFs with partially self-centering behavior achieved nearly zero residual displacements (lower than 0.2%) under maximum considered earthquakes. This finding shows that the partially self-centering MRF is a more cost-efficient solution for developing seismic resilient MRF than fully self-centering MRF to achieve excellent post-earthquake repairability with a lower requirement of self-centering capacities.

Hybrid self-centering braces with NiTi-SMA U-shaped and frequency-dependent viscoelastic dampers for structural and nonstructural damage control

This study proposes a novel hybrid self-centering brace (HSB) with structural and nonstructural damage-control capabilities for the seismic resilience of building structures. NiTi-based shape memory alloy (SMA) U-shaped dampers and frequency-dependent viscoelastic dampers are included in HSBs to provide self-centering capacity for avoiding structural damage and velocity-proportional damping for nonstructural damage control, respectively. This study includes two major parts, i.e. component-level mechanical behaviour and system-level dynamic response evaluation of HSBs. The working principle and desired nonlinear behaviour of the HSB were first presented. Then, the preliminary design procedures were developed. After validating the efficiency of the modelling of SMA U-shaped and viscoelastic dampers using prior test results, comprehensive 3D finite element model simulations were performed to study the hysteretic responses of HSBs under cyclic loadings, where the influences of loading frequency, loading amplitude and viscoelastic damper’s contribution were considered. Analysis results demonstrated that the designed HSB can attain the desired deformation mechanism and nonlinear hysteretic behaviour during dynamic cyclic loadings. Higher loading frequency and amplitude and more contributions of the viscoelastic damper can introduce higher loading and energy-dissipation capacity. Subsequent dynamic analyses of the single-degree-of-freedom systems were conducted to assess the dynamic performance and advantages of HSBs. Results showed that compared with traditional self-centering systems without velocity-proportional damping, the systems with HSBs can achieve zero residual deformations, lower base shear demands and smaller absolute acceleration responses, confirming the promising potential of HSBs in developing seismic resilient building structures by reducing structural and nonstructural damage.

Numerical Study on Seismic Performance of Rocking Self-Centering (RSC) Bridge Piers Under Bidirectional Excitation

To study the seismic performance of rocking self-centering (RSC) bridge piers, a numerical model of RSC pier is established based on the OpenSees platform. The model is verified by experimental results. The seismic performance of RSC piers is analyzed under quasi-static and seismic loads, respectively, in terms of peak lateral drift, residual deformation, compressive zone height of the cross-section and tendon stress. Far-field, near-field without pulse and near-field pulse-like ground motion records are selected for the time-history analysis. The effects of prestressing tendon reinforcement ratio, energy-dissipating bar ratio and axial load are examined, respectively. The results show that the strength of the RSC pier, the depth of the compressive zone of the cross-section and the self-centering capacity increase with increasing prestressing tendon reinforcement ratio. When the energy-dissipating reinforcement ratio exceeds 1%, the boost of seismic performance of the pier becomes insignificant. The increasing axial load can increase the lateral strength of the pier. However, it could lead to premature yielding of the prestressing tendons.

Experimental Study of a New Self-Centering BRB and Its Application in Seismic Resistance of Frame Structure

In order to enhance the self-centering capacity of steel frame structures after earthquakes and reduce the tubes of traditional double-tube or triple-tube SC-BRB, an innovative single-tube self-centering buckling restrained brace (ST-SC-BRB) is proposed in this paper. Firstly, the structural configuration of the ST-SC-BRB component was described. Then, cyclic tests were conducted on one small-scaled BRB and one ST-SC-BRB with the same core steel plate. The test results indicate that the ST-SC-BRB specimen exhibits an excellent self-centering ability compared to the conventional BRB. However, their energy-dissipation capacities are still determined by the core steel plate. In addition, time–history analyses were conducted to evaluate the seismic performance of steel frame structures with BRBs and ST-SC-BRBs. The results suggest that the ST-SC-BRBs can effectively reduce the residual deformation of steel frame structures after earthquakes and contribute to the self-centering capacity of the steel frame structures. Finally, the influence of design parameters of ST-SC-BRB components on the seismic performance of steel frame structures was discussed. It is confirmed that the initial stiffness of the ST-SC-BRB component significantly influences the seismic response of the structure, while the self-centering ratio of the ST-SC-BRB component is a crucial factor in determining the residual deformations of the structure.

Shaking table test of a controlled rocking reinforced concrete frame with column-end hinge joint

A controlled rocking reinforced concrete frame with column-end hinge joint (CR-RCFC) is proposed, in which the pure hinged joints are adopted, the post-tensioned (PT) tendons are arranged in the columns to provide lateral stiffness and self-centering capacity, and the inter-story metal dampers are utilized to dissipate earthquake energy and control displacement response. Based on the quasi-static cyclic tests of the CR-RCFC, the rotation stiffness of the joint was obtained. Shaking table tests were carried out on the 1/3-scale CR-RCFC and conventional reinforced concrete frame (RCF) test models. The test results are studied in terms of damage observations, dynamic characteristics, peak floor accelerations, peak inter-story drifts, and force changes in the PT tendons. The results indicated that the CR-RCFC can effectively protect concrete members from damage even under rare earthquakes. Meanwhile, the CR-RCFC can significantly reduce the acceleration response compared with the RCF, and the metal dampers can effectively control the displacement response.

Post-earthquake fire resistance of self-centering concrete beam-column joint: An experimental investigation

Fire is an accidental disaster resulting in disastrous consequences for building. Post-earthquake fire is a secondary disaster induced by earthquake, triggering off larger destruction in a higher probability of occurrence. The potential severity of consequences to structures makes fire and post-earthquake fire safety imperative in the design of any new structures. Self-centering concrete joints are introduced as a promoting alternative to traditional reinforced concrete (RC) joints. They always exhibit excellent seismic performance and self-centering capacity, available in high-seismic zone. However, the current lack of experimental data on fire response of self-centering concrete joints means that they remain an open issue in current design codes. In this paper, full-scale quasi-static cyclic test and fire tests were conducted on two self-centering concrete joints connected with bolted angles and posttensioned (PT) tendons. The experiments aimed to explore the performance of self-centering joint in fire situations, and the impact of post-earthquake damages on fire response of self-centering joint. The deformation patterns and thermal responses of self-centering joints including temperature distribution, prestress force of PT tendons, displacements at beam ends and duration were recorded and analyzed. The results show that both self-centering joints exhibited satisfactory fire resistance with endurance over 170 min. Generally, the bolted angles and PT tendons in self-centering concrete joints showed acceptable working performance in fire. The findings unveil the actual response of self-centering concrete joints during the fire and post-earthquake fire conditions, providing experimental data for further numerical simulation and analysis. It can be used to calibrate the design approach for self-centering joints under fire and seismic-induced fire exposure.

Self-centering capacity of RC columns reinforced by martensitic NiTi SMA bars in plastic hinge region

This study aimed to assess self-centering in reinforced concrete (RC) columns incorporating martensitic shape memory alloy (SMA) bars within the plastic hinge region. Three RC columns were prepared: one conventional, the others with SMA bars in the hinge zone. Columns, 400 mm in diameter and 1400 mm in height, with an aspect ratio of 3.5, were used. SMA bars, 400 mm long, were connected to steel rebars with specialized couplers. Through cyclic lateral loading, lateral displacements and corresponding forces were measured. Strain in the SMA bars was also recorded. The RC column with SMA bars displayed a plastic hinge near the couplers, concentrating concrete damage at this location, a departure from the conventional column failure mode. SMA bars remained elastic, while steel rebars yielded within the couplers. The RC column with SMA bars demonstrated exceptional self-centering, recovering about 95% at a 5% drift. However, its energy dissipation capacity was lower than the conventional RC column. The equivalent damping ratio for the RC column with SMA bars stabilized at approximately 3% after a 1.75% drift. This suggests that the remarkable self-centering capacity in the RC column with SMA bars was primarily due to the elastic behavior of the martensitic SMA bars.

Effect of infill walls on progressive collapse behavior of self-centering precast concrete frame

To study the effect of infill walls on the progressive collapse resisting-performance of self-centering precast concrete (PC) frame structures, three 1/2 scaled, two-span and two-story self-centering PC frame specimens with and without infill walls were tested under quasi-static pushdown loading regime. The test results showed that the failure modes of self-centering PC frames were governed by concrete cracking and local spalling at the beam ends under progressive collapse scenario. Compared with self-centering bare frame, the presence of infill walls provided additional load path, thereby reducing the concrete damage at the beam ends to some extent. The full infill walls with lower strength could still increase the initial stiffness and peak resistance of self-centering bare frame to 2.47 times and 1.33 times, while the infill walls with 20% opening ratio could increase to 2.21 times and 1.19 times, respectively. Nevertheless, the infill walls also reduced the self-centering capacity of the structures. Numerical analyses further indicated that the magnitude of prestress force of steel strands between beams and columns, the strength of bed joints as well as the width of infill walls had a great effect on the progressive collapse of self-centering infilled frames. Finally, based on numerical results, a reduction factor formula was proposed to quickly estimate the structural resistance of self-centering infilled frames with different opening ratios.