Self-centering Research Articles

Damage-free self-centering steel columns incorporating SMA bolts and replaceable steel angles

Steel moment-resisting frames (MRFs) are one lateral force-resistant structural system commonly used in high seismicity areas. The current seismic design practice for MRFs expects to develop plastic hinges at the beam ends to dissipate earthquake input energy. Meanwhile, plastic hinges also form almost unavoidably at the column bases of the first story due to the strong-base-weak-column design philosophy. However, concentrated deformation in the predetermined plastic hinges may lead to considerable damage in structural components. The accompanying large residual drifts can substantially compromise post-earthquake reparability and normal functionality. Hence, this paper presents a novel type of self-centering (SC) steel column base incorporating shape memory alloy (SMA) bolts and replaceable steel angles as a damage-free solution. First, the working principle of the column bases is described. Subsequently, the seismic performance of the steel columns is experimentally evaluated by considering the influences of the steel angles and repeated loading scenarios, and the replaceability of steel angles. Results show the novel steel column bases exhibit satisfactory flag-shaped hysteresis loops with excellent SC capability and stable energy dissipation, whereas almost all the damage is concentrated in the steel angles that can be replaced rapidly after the cyclic loading if required. The deformed columns are restored to their upright positions instantaneously with negligible residual deformation after unloading. More importantly, the steel column stays damage-free, and the SMA bolts with prestrain remain tightened. This enables the steel columns to maintain high functionality to withstand immediate aftershocks or future earthquakes, explicitly achieving seismic resilient design.

Damage assessment of self‐centering rocking piers using an input energy‐based damage prediction model coupled with self‐centering index

AbstractThe immediate functionality of bridges following severe earthquakes is vital for uninterrupted rescue operations. Regarding the significance of resiliency in bridges, post‐tensioned (PT) rocking piers with low residual displacements and minimal damages have developed over the past few decades. The rocking mechanism at two ends of the pier avoids bending moments and excessive flexural damage. The self‐centering (SC) capacity in this system is provided through post‐tensioning forces. Concerning optimum seismic design and retrofit purposes, it is essential to predict the actual degree of seismic damage and SC capacity of PT rocking systems after seismic hazards. In this case, a self‐centering index (SI) is proposed to evaluate the SC capacity when piers are subjected to cyclic and seismic loadings. This SI, when used in co‐operation with a viable damage prediction model, predicts whether or not the piers remain reparable under cyclic or seismic loading scenarios. After comparing a number of energy‐based damage indices, all of which consider the cumulative hysteresis energy, with the input energy‐based damage index (IEB‐DI), the latter was calibrated against observed damages under cyclic loading tests. This DI was chosen as the most suitable damage prediction model and was considered to be simply applicable after time history analysis. In this study, the seismic performance of a seismic‐resistant dual system, consisting of three RC bents along with an SC bent, was evaluated using the aforementioned damage limit states and the introduced SI. The damage predictions of the monolithic bridge, as the reference model, were compared with the estimated damage to the dual bridge. The results show that the joint application of the IEB‐DI and the proposed SI in predicting the performance level of SC rocking piers results in a comprehensive damage prediction model.

Shake table tests of steel moment resisting frame with self‐centering SMA‐based isolators

AbstractThis paper investigates a steel moment resisting frame (MRF) with a novel type of self‐centering (SC) base isolators, wherein superelastic shape memory alloy (SMA) U‐shaped dampers (SMAUDs) work as core components. A two‐story steel MRF model equipped with two SMAUD‐based isolators was designed and built in the laboratory, and a series of shake table tests were conducted to examine the dynamic behavior and seismic performance of the frame. Throughout all the tests, no interventions, such as repair or replacement of frame or isolator members, were done. Shake table test results demonstrated that the SMAUD‐based isolators could withstand multiple strong earthquakes with stable SC behavior. The utilization of SMAUD‐based isolators provided effective protection for the frame, enabling it to restore its original position with minimal structural damage. A numerical model of the tested steel MRF with SMAUD‐based isolators was also built. The results obtained from the numerical analyses agreed with those of the shake table tests satisfactorily. A comparative study of the seismic performance between the MRF with SMAUD‐based isolators and the MRF with traditional steel U‐shaped damper‐based isolators was also conducted in the shake table tests. The results showed that SMAUD‐based isolators not only inherit the isolation function of conventional isolators to protect the frame but also possess an SC ability to eliminate residual isolator deformation effectively. Moreover, SMAUD‐based isolators demonstrate remarkable resilience to withstand multiple strong seismic events without any need for repair or replacement.

Experimental investigation on lateral resistance capacity enhancement effect of a self-centering shape factor in self-centering pier systems

In self-centering (SC) pier systems, a rocking interface is typically employed at the bottom of a pier to achieve a gap-opening mechanism. However, compared with the full-section bending state of the bottom section of a ductile pier (DP), the local compressive state of the rocking interface in the SC pier inevitably leads to a significant reduction in the lateral resistance capacity. Although a prestressing tendon (PT) force can improve the lateral resistance capacity, it also induces local damage. Moreover, its enhancement effect is limited, particularly in the case of a column with a high axial compression ratio. Therefore, this study proposes an innovative measure to significantly improve the hysteretic performance of an SC pier without inducing additional damage, which is to raise the location of the rocking interface. First, the SC shape factor ξSC is innovatively defined to quantify the above-mentioned measure, and its working mechanism is investigated in detail in this study. Second, a high-lateral-resistance SC pier system (HLRSCP), which applies the concept of ξSC, is proposed and introduced for its advantages. Third, hysteretic tests of the DP and HLRSCP with high axial compression ratios are performed and analyzed. Finally, the enhancement effect of ξSC on the lateral resistance capacity is parametrically examined using a finite element model, and the feasible region of ξSC is inferred and presented. The results validate the effectiveness and feasibility of the concept of the SC shape factor in improving the hysteretic performance of the SC pier system.

Self-centering concrete-filled steel tubular column-steel beam joint: Experiment and numerical modeling

This paper studied the seismic behavior of a novel self-centering concrete-filled steel tubular column-steel beam (SCSTCSB) joint. The restoring force was provided by the post-tensioned tendons arranged in the CFST columns. Cyclic loading tests were performed on five 1/3 scaled specimens by varying the parameters of steel tendon type, concrete strength (fc), and axial compression ratio (n). The failure modes, hysteresis behavior, stiffness and strength degradation, energy dissipation, post-tensioned tendons response, residual deformation, and strain distribution were studied in detail. The finite element models were established to capture the stress distribution of the joints. In addition, parameter analysis was performed by expanding 17 finite element models. The results show that the ratio of residual deformation to beam rotation angle of the specimens ranged from 0.068 to 0.172. And the proposed joints demonstrated excellent self-centering ability. The self-centering (SC) performance of joints with ordinary steel tendons was better than that of joints with high-strength steel tendons. With the increase of n, the SC performance of the joints intensified at the lower ratio (n from 0.1 to 0.3) and weakened after n = 0.3. The flexural capacity of the joints improved with the increase of axial compression ratio (n), width-thickness ratio (D/t), diameter of steel tendons (d), and assembly part strength (fy,a).

The damage-based inelastic displacement ratio for performance-based design of fully self-centering systems under pulse-like near-fault earthquake ground motions

In this investigation, the damage-based inelastic displacement ratio (IDR) for fully self-centering (SC) systems with flag-shaped hysteresis behavior is determined under pulse-like earthquake ground motions to use in performance-based design theory. Pulsive earthquakes are known as dangerous natural phenomena due to the location of structures in the vicinity of the fault with forward-directivity and high-velocity amplitude features, which expose the system to high risk. Before this, the IDRs were obtained based on constant-ductility and strength reduction factor intensities for designing new and evaluating existing structures with SC behavior. However, the issue could be extended to an energy-based theory using the Park-Ang damage model as a popular index among researchers, with the ability to consider record amplitude, frequency content, and duration. Therefore, the damage-based IDR was determined under 252 pulse-like records with 126 pairs at four damage levels, 30 periods of vibration, four ultimate ductility factors (µu), four stiffness hardening ratios (α), and three dissipative energy factors (βn) by conducting comprehensive nonlinear dynamic analysis. Then, the influence of the mentioned parameters on obtained IDRs is evaluated to propose a robust equation for estimating target displacement in these systems. Statistical results illustrate that the approximate equation based on normalizing the structural period to the predominated period can predict the target displacement compared to achieved ones from direct time-history analysis, where the difference between estimated and mean target displacements is below 15%.

Low temperature effect on cyclic behavior of shape memory alloy U-shaped dampers

Although Nickel-Titanium (NiTi) shape memory alloys (SMAs) have been widely studied as seismic response mitigation devices in civil structures, their temperature sensitivity due to the coupled thermo-mechanical behavior prevents their practical implementation in cold temperature environments. This paper investigated the effects of varying ambient temperatures (particularly low ambient temperature) on the hysteretic behavior and self-centering (SC) ability of shape memory alloy U-shaped dampers (SMAUDs) that were made of NiTi showing superelasticity (SE) at room temperature. Thermo-mechanical properties of SMAUDs were identified through differential scanning calorimetry (DSC) tests. Cyclic loading experiments on SMAUDs were conducted at a wide ambient temperature range from −40 °C to 20 °C. The variations in the hysteretic characteristics of the SMAUDs, including partial superelasticity (SE), strength, stiffness, SC, and energy dissipation capabilities, at different ambient temperatures were investigated. In general, the decreasing ambient temperature leads to the degradation of the SC ability. At ambient temperatures below the phase transformation temperature, the SMAUDs lose the SE but still maintain certain levels of strength and energy dissipation, which is different from common axial-type SMA elements. Meanwhile, the SMAUDs can restore their SC ability and strength after the recovery from low temperatures to room temperature, making them suitable for use in a cold environment.

Seismic evaluation of a self-centering retrofit solution for modular steel structure connections

In this study, a novel plug-in modular steel structure (MSS) connection is proposed, in which the connector, cover plates, and bolts form a complete connecting system. To improve the seismic performance and post-earthquake functional recoverability of the MSS connection, a retrofit solution with diagonal self-centering (SC) haunch braces is introduced, and the self-centering modular steel structure (SC-MSS) connection is developed. Theoretical analysis of the mechanical properties of the MSS and SC-MSS connections are conducted, and the calculation formulas for the initial stiffness and bending bearing capacity are derived. A comparative experimental study of one MSS connection and five SC-MSS connections under cyclic loading was carried out to evaluate their seismic performance, and to explore the influences of the main haunch parameters on the behavior of the SC-MSS connection. The results demonstrate that the plug-in connector, cover plate, and bolts can realize reliable continuity and integrity between modules. The SC haunch braces have good collaborative work with the modules and provide sufficient restoring force, and the damage in all the SC-MSS connections was found to be effectively controlled and delayed as compared with the MSS connection. The MSS connection displays a full shuttle-shaped hysteretic response with adequate plastic development, while the SC-MSS connections successfully exhibit expected flag-shaped hysteretic responses with higher bearing capacity and lower residual displacement. The adjustment of the post-activation stiffness and pre-pressed force of the haunch brace is found to improve the connection performance, and a reasonable selection of the installation scheme could achieve optimal self-centering efficiency. The experimental results also verify the feasibility and correctness of the proposed theoretical formulas and mechanical assumptions.

Seismic behavior of resilient composite steel plate shear wall using experimental investigations

Using composite encased steel plate shear wall (C-SPSW) has been attractively raised for enhancing the lateral seismic performance and increasing the useful floor area. Although, the experimental investigations have proved excellent dynamic behavior of C-SPSWs, structural damage as well as residual displacements are the main disadvantages of C-SPSWs, which are not consistent with low damage design (LDD) approaches. In the current study, the C-SPSWs performance is improved using the self-centering (SC) technique to control the both structural damage and reduce residual displacements as well. Five tests on C-SPSWs including three SC composite encased steel plate shear walls (SC-C-SPSWs) were conducted under gravity and lateral cyclic loads. The SC-C-SPSW consists of C-SPSW equipped with unbonded posttensioned tendons (UPT) to have resilience ability. For this aim, two symmetrical gaps were provided at the ends of the wall, and the UPTs were mounted at the wall ends and crossed into the foundation through the middle of the gaps. Under lateral load, the gap opening allows the elongation of UPTs that induce a high restoring forces, forcing the wall to have rocking movement above the foundation. In comparison with C-SPSWs, the SC-C-SPSWs exhibited low damages, higher shear strength capacity between 28% and 35%, larger ultimate drift capacity and more displacement ductility as 45–136% in average. Furthermore, the SC ability and the UPTs restoring forces effectively reduced the residual drift and the SC moment causes the recovery of the residual drift between 90% and 105%. Moreover, compared to C-SPSWs, the residual lateral strength of SC-C-SPSWs was improved by 30% in average.

Self-Centering Precast Unit as Energy Dissipation Members in Precast Segmental Bridge Columns

This research aims to present a new generation of seismic-resisting systems designed for precast reinforced concrete (RC) bridge piers in modern sustainable cities to withstand moderate to high seismic activity. The proposed system consists of two self-centering (SC) systems operating in parallel to bring together all features of the required resiliency during a seismic action. The first/main system is a hollow core precast segmental bridge column, and the second is composed of an SC precast unit and energy dissipation (ED) steel reinforcements positioned in the main pier segment’s hollow core. To study the performance of the proposed system, a finite element model was first developed to capture the behavior of experimentally tested precast bridge columns. After validation, the created model was systematically studied to investigate the performance of the entire proposed system under cyclic loading. The effects of three parameters related to the ED system were investigated, including the reinforcement ratio, the unbonded length of ED bars, and the SC post-tensioned force ratio. Furthermore, the impact of FRP wrapping on the lower part of the core column of the ED system was also investigated. An analytical model predicting the characteristic points of the lateral response of the proposed system based on the superposition concept is also proposed. The FE results showed that the entire proposed system is a new design-based resilient system with the ability to dissipate energy without compromising the SC capacity of the main resisting system. Compared to the typical precast hollow core segmental column, a 6% reinforcement ratio of the ED unit can cause a 60% increase in lateral resistance and a 220% increase in the ED capacity. The analytical model can successfully be applied in the design of the proposed system to provide customized ED capabilities and controlled lateral resistance.

Self-centering steel beam-to-column connections with novel superelastic SMA angles

This paper proposed a novel type of self-centering (SC) steel beam-to-column connection using superelastic shape memory alloy (SMA) angles and steel angles. Unlike conventional post-tensioned SC connections, the proposed SC connection utilized SMA angles to provide SC ability and moderate energy dissipation, enabling easy installation and replacement. Experimental and numerical studies were conducted to investigate the cyclic behavior of the connection. Two types of steel connections with different configurations were tested: one equipped with SMA angles only and the other with a combination of SMA and steel angles. The cyclic behavior of the SC steel beam-to-column connections was investigated through a series of experiments. A numerical study was also conducted to provide more insight into the mechanical behavior of the connections and the local strain condition of SMA angles. Numerical results were validated with experimental results. Comparative results demonstrated that both connections exhibited desirable flag-shaped hysteresis behavior with SC and energy dissipation. No obvious damage and residual deformation were observed in SMA angles after cyclic loads in both the experiments and numerical simulations, indicating that the SC connection using SMA angles can be reused for successive mainshocks and aftershocks without replacement. Therefore, the proposed SC connection can help achieve the goal of earthquake resilience in structural design.

Modified performance-based plastic design for self-centering structures

The Performance-Based Plastic Design method (PBPD), developed on the energy concept, has been frequently used in technical literature as a performance-based design method for various structures. However, implementing the method for self-centering (SC) structures, which can concentrate damage in replaceable members and reduce residual deformation, encounters difficulties due to selecting an overall energy modification factor regardless of structural geometry, ductility, and energy absorption capacity. In this study, considering the behavior of self-centering structures, the PBPD method is modified to implement any SC structure with a specific energy modification factor. The proposed method was then implemented to design two braced SC structures with different height, cable, and damper configurations. For comparison, the designed structures and similar structures designed by force method under identical conditions were subjected to nonlinear dynamic and pushover analysis employing eleven far-field earthquake records. The results show that the structures designed by the energy method with different heights and configurations exhibit average seismic response close to the target performance response while maintaining cable linearity. While in the force method, the cables did not remain linear in some cases, and the structures were designed with about 20 % deviation of mean response to the target performance. Furthermore, assessing the proposed approach with analytical results in terms of absorbed energy reveals that the accuracy of the proposed method in forecasting the structures' input energy was more than 87 %. The results indicated that the modified energy method is simple, accurate, straightforward, and efficient for the PBPD of SC structures.

Composite CFST column to H-shaped steel beam joint: Experimental and numerical investigation

Conventional CFST column-to-steel beam connection has excellent collapse-resist capacity, good plastic deformation, and high energy dissipation. However, it makes reconstruction challenging after extreme inelastic deformation in a severe earthquake. This paper proposes a self-centering (SC) composite CFST column to H-shaped beam joint (SCCCB joint) using post-tensioned (PT) tendons. The residual deformation of the splicing column can be greatly reduced under the action of pre-tension tendons. Cyclic loading tests were performed on five 1/3 scale test specimens with the main parameter of axial compression ratio (n = 0.10, 0.12, 0.15, and 0.17) and steel tendon types (with or without cutting processing) to investigate the cyclic behaviour and SC performance. The finite element models were established to capture the stress distribution of the joints. Finally, the seismic and SC performance of the joints were studied by the parametrical analysis including five parameters: width-thickness ratio of steel tube (D/t), diameter, number and spacing of steel tendons (d, ns and s), and connecting diaphragm strength (fy,a). The SC performance can be improved with the increase of ns. The bending capacity of the joints increased with the increase of n, D/t, d and fy,a.

Hysteretic model and seismic performance of a self-centering brace equipped with energy absorbing steel plate clusters

The use of self-centering (SC) devices has been recognized as a promising strategy to improve the seismic resilience of structures, owing to their capacities for SC and energy dissipation (ED). This paper presents a comprehensive study on a SC brace (SCB) equipped with energy absorbing steel plate (EASP) clusters. Firstly, the configuration and deformation mode of the SCB were described. Then, a hysteretic model of the SCB was proposed based on the Bouc-Wen model, and the behavior of the SCB was described in detail. The accuracy of the hysteretic model was subsequently verified by experimental results. On the basis of this, the theoretical analysis was carried out to evaluate the effect of the design parameters on the hysteresis performance of the SCB. The results show that the ratio between the activation force of the SC system and the yield force of the ED system (ρ) has a significant impact on the hysteresis performance of the SCB. As the value of ρ increases, the SC capability of the SCB increases, but the ED capacity decreases. Finally, the seismic performance of the steel frame which adopts the SCB was evaluated using nonlinear response history analysis. The results indicate that the SCB with a ρ value of 1.0 can achieve a comparable structural deformation response with a buckling restrained braced (BRB) frame, and the residual drift of the SCB frame is less than 0.2% under ground motions of varying hazard levels.

Experimental and analytical modelling on a novel self-centering viscous damper

Self-centering (SC) supplemental dampers offer a feasible approach to realize low-damage structures. A novel self-centering viscous damper (SCVD) that incorporates an SC part and a viscous damper (VD) part in parallel, and then series with a length adjustable (LA) part. The working mechanism and hysteretic model were both analyzed for the SCVDs. Dynamic reversed sinusoidal displacement inputs were used in experimental proof-of-concept validation studies. Each component was examined separately to describe and distinguish their distinct contributions to the whole device. Individual results in summing are consistent with hybrid device outcomes for the same input. The SCVDs showed excellent self-centering capability with satisfactory energy dissipation. A maximum equivalent viscous damping ratio (EVDR) of 99.37% was observed. A theoretical model and a numerical model were built and examined for the proposed SCVDs. The inevitable gaps from installation have a noticeable effect on the VD part and the SCVD, especially for small strokes. Except for small strokes, comparisons of test findings and analytical models reveal similar hysteretic reactions, for which the coefficients of determination are greater than 0.9, thereby validating the performance of the theoretical and analytical models to simulate the behavior of the tested SCVDs. In comparison to existing SCVDs, the suggested SCVDs have a more controllable SC ability, length adjustability, and energy dissipation capacity based on the demands of the designers. Furthermore, five distinct lateral resisting components were used in nonlinear response history analysis to compare the seismic and resilient performance amongst the moment resisting frame (MRF), buckling restrained brace (BRB), SC, VD and SCVD systems. Finally, the addition of SCVDs and VD parts can both be effective in controlling the maximum and residual story drift ratios on average. Overall, our findings provide innovative, simple implementable choices for developing low-damage structures.

Seismic and resilient assessment on moment resisting frames with novel self-centering viscous dampers

A new type of self-centering viscous dampers (SCVDs) had been developed by the authors to create low-damage structures [1]. Then, the seismic and resilient performance of steel frames equipped with SCVDs were still mysteries waiting for being discovered. So, performance was analyzed among the five systems which were moment resisting, buckling restrained brace (BRB), self-centering (SC), viscous damper (VD), and SCVD frames. The 3- and 6- story frames with the aforementioned systems were subjected to 20 earthquake records of various ground types using nonlinear response history analysis. In comparison to the MRF system, the SCVD system exhibited a significant improvement. The maximum and residual story drift ratios were reduced by 90.27% and 97.78%, respectively. However, there was an increase in the maximum base shears and overturning moments of the SCVD system by 120.65% and 150.31%, respectively. Overall, MRFs equipped with SCVDs or VD parts possess better seismic and resilient performance with higher certainty than the other systems, in special, the total growth rate of the VD system can be reduced by 22.94% comprehensively. Furthermore, addition of energy dissipation capabilities is more effective in decreasing responses with higher certainty than stiffness or self-centering capabilities of the braces.

A sensitivity analysis framework for SMA-based self-centering systems considering uncertainty in hysteretic material parameters

Shape memory alloys (SMAs) are widely utilized as the core component to develop self-centering (SC) structures owing to their excellent super-elasticity. Seismic performance of SMA-based structures is significantly influenced by the hysteretic parameters of the exploited SMAs. Uncertainties in the hysteretic parameters of SMAs could cause variation in seismic performance however have not received sufficient attentions. This paper proposes a sensitivity analysis framework to realistically and efficiently quantify the sensitivity of SMA-based structures to hysteretic model parameters. The experimental data from SMA bars are analyzed through the Markov chain Monte Carlo (MCMC) procedure. The probabilistic distributions of SMA hysteretic parameters are then sampled using the linear moment theory. Polynomial chaos expansions (PCE) based surrogate model is then used to evaluate sensitivity of response to different parametric uncertainties through the Sobol indices. The proposed framework is then applied to a total of 120 single-degree-of-freedom (SDOF) systems to demonstrate its efficacy to generalize observations and findings. The results show that the proposed framework provided more effective and realistic sensitivity analysis of seismic responses of SMA-based SDOF systems to account for uncertainty in the hysteretic model parameters. The Sobol indices also indicate that the sensitivity of different seismic response quantities varies for different hysteretic model parameters of SMAs.

Theoretical investigation on the impact effect in dynamic analysis of self‐centering pier system based on the Hertz contact‐pounding model

AbstractThe self‐centering (SC) pier system exhibits different mechanical behaviors under an earthquake compared with that in quasi‐static experiments, especially the impact effect on the rocking interface. Published theoretical analysis and experiments had indicated that the impact events significantly affected the rocking motion, including extra energy dissipation, greater contact stress, and even more serious damage. To describe the impact mechanism more clearly and obtain the impact responses more directly, this study investigates a dynamic theoretical model considering the impact effect and its influences on the seismic responses and rocking interface. First, a dynamic theoretical model based on the Hertz contact‐pounding model specific to the SC pier system is proposed, and the impact mechanism is described in detail. Subsequently, dynamic motion equations considering the impact effect are derived. The key parameters of the contact‐pounding element (stiffness KHertz and damping CHertz) that significantly affect the impact process are presented. The accuracy of the proposed theoretical model is verified by test data and a finite element model (FEM). Finally, the influences of the key parameters (KHertz and CHertz) on the impact force are analyzed, and the impact effect on the rocking interface is investigated. The results indicate that the impact effect significantly increases the vertical acceleration and contact stress, particularly under near‐fault earthquakes. This may cause unexpected damage on the rocking interface and should be an important consideration in the optimize design of SC pier system.

Experimental and numerical investigations on an assembled self-centering buckling-restrained brace with high post-yield stiffness

In order to facilitate the replacement of damaged components and prevent the weak-story mechanism of frame structure after strong earthquakes, a novel assembled self-centering buckling-restrained brace (ASC-BRB) is proposed in this paper. The proposed bracing system is comprised of the buckling-restrained brace (BRB) system and the self-centering (SC) system. The SC system consists of two sets of steel strands and one group of disc springs stacked in series to achieve the goal of large deformability and post-hardening behavior. The detailed configuration, fundamental working mechanism, and restoring force model of the ASC-BRB are first presented. Different from SC systems with bilinear elastic behavior of existing SC-BRBs, the SC system of ASC-BRB exhibits trilinear elastic behavior due to its special configuration. Then, quasi-static tests are conducted to validate the effectiveness of the proposed ASC-BRB. The experimental results indicate that the ASC-BRB has a flag-shaped hysteretic response with excellent self-centering capability, stable energy dissipation capability, and appreciable deformation capacity with a maximum ductility coefficient of 25.58. More importantly, the specimen can exhibit the anticipated post-hardening behavior. The refined numerical model of ASC-BRB is established and verified by the experimental results, which can effectively analyze the mechanical behavior of the main components of ASC-BRB, making up for the deficiency of the tests. According to the problems discovered in the tests and numerical analyses, an improved configuration of the ASC-BRB is proposed and validated by the numerical simulation of the BRB system before and after improvement. The numerical results indicate that the improved BRB system exhibits more stable hysteretic behavior, and the stress levels of the inner and outer tubes become much lower after replacing 1-shaped cores with steel angle cores.

Enhanced design and experimental investigation of disc spring‐based self‐centering buckling‐restrained braces with a compounded combination mode

AbstractThe disc spring‐based self‐centering energy dissipation (SCED) brace is a high‐capacity resilient structural component, characterized by a flag‐shaped hysteresis curve, which can provide both damping and recentering capacity to a structure. However, the conventional design method for the disc spring‐based SCED brace cannot quantitatively take into account the friction effects induced by combined disc springs, which greatly limits the disc spring size selection and combination mode. To address this issue, the friction effect of the combined springs is quantified using an incremental energy method and then introduced into the existing design method. A fully assembled self‐centering steel buckling‐restrained brace (SC‐SBRB) consisting of an energy dissipation (ED) system and a self‐centering (SC) system is proposed. The SC system employs a combination mode of stacking multi‐section springs in parallel and compounding new and old springs together to provide the desired recentering capacity for the brace; however, it is distinguished by an appreciable ED capacity that is different from the SC devices in previously reported SCED braces. With the use of the energy method for the quantification of the spring friction, the differences between the mechanical properties of a group of old springs in earlier and recent tests were systematically analyzed to check their reliability and serviceability. A series of test procedures were sequentially conducted on a pure BRB brace and a pure SC brace, and then on the full SC‐SBRB. A fatigue test was also performed after the damaged brace was repaired. The experimental results demonstrate that the improved design can provide accurate estimations of the spring friction in the brace design, and that the proposed brace can exhibit a stable and favorable flag‐shaped hysteretic response with negligible residual deformations throughout the loading protocol. The old spring used in the tests was found to have stable and reliable mechanical properties and could be reused in a brace requiring repair after an earthquake.