Buckling-restrained Braces Research Articles

Advancements and Future Prospects of Buckling Restrained Braces for Corrosive-Environments: A Comprehensive Literature Review

The seismic design of structures is crucial for preventing structural collapse and safeguarding human lives. Buckling-restrained braces (BRBs) have emerged as effective seismic protection devices due to their high stiffness, strength, and exceptional energy absorption capabilities. Typically, a conventional BRB consists of a steel core surrounded by concrete-filled steel tubes, with a separation mechanism ensuring axial-only deformation of the core. However, researchers have been increasingly focusing on developing innovative BRB designs with enhanced performance, incorporating different materials and configurations. This paper presents a comprehensive analysis of the development of novel BRBs introduced in the past 15 years. A systematic review approach is adopted, and the selected articles are categorized based on the shapes, materials, and compositions of the BRB components. Although carbon steel has been widely used in numerous studies, its susceptibility to corrosion and its potential impact on the hysteretic behavior of BRBs remain unexplored. Consequently, future research prospects are identified, highlighting the significance of employing anti-corrosive materials in fabricating BRBs to ensure their stable seismic performance under harsh environmental conditions. Investigating novel materials and configurations can lead to the creation of more robust and corrosion-resistant BRBs, thus enhancing the safety and longevity of structures in earthquake-prone areas.

Sensitivity and reliability assessment of buckling restrained braces using machine learning assisted-simulation

Buckling Restrained Braces (BRBs) play an essential role in seismic protection due to their remarkable energy dissipation capacity, ductility, and stiffness. This paper represents the first thorough evaluation of the reliability and uncertainty of BRBs, accounting for various sources of uncertainty and varied conditions, such as different gap sizes, friction coefficients between the encasing and the steel core, and other geometric and mechanical properties of the connecting parts. This paper introduces an innovative application of an integrated probabilistic approach that combined Finite Element (FE) modeling, Artificial Neural Networks (ANN), and Monte Carlo simulation to characterize the seismic behavior of BRBs. Experimental results from literature is used to validate the FE model constructed using ABAQUS. This validated model is then integrated into a Low-rank Tensor Approximation process to yield variance-based sensitivity measures for the considered variables. The most influential variables identified in this process along with the calibrated FE model is utilized to conduct a reliability assessment through an ANN-assisted Monte Carlo simulation. This analysis is conducted to quantify the reliability level of the investigated BRBs as a function of the gap size and establish the resistance factors necessary to maintain the reliability level above prescribed thresholds. It was found that the highest reliability can be achieved at a small gap size equal to half the radius of gyration of the main steel core, requiring a resistance factor of 0.9. For gap sizes higher than this value, a resistance factor ranging between 0.70 and 0.85 is needed.

Buckling-restrained brace with multiple steel bar cores using SHS outer tube

To overcome the limited maximum strength of buckling-restrained braces (BRBs) using single roll-threaded processed core bars, a BRB with multiple steel bar cores was proposed in a recent study. Its mechanical behavior was revealed by experimental studies; however, improvements are required in the structure of the BRB owing to its complexity and heavy weight. This study proposes an improved BRB with multiple steel bar cores in which the dual buckling-restraining member consists of a square hollow section (SHS) outer tube and two sets of circular hollow section (CHS) inner tubes. The outer tube is used to improve the flexural stiffness and solve the weight issues associated with the previous type. Three full-scale specimens were tested to determine their mechanical behaviors, such as the hysteresis behavior and internal force variation of the restraining members. The test results indicate that the proposed BRB can exhibit a stable hysteresis response and satisfactory energy dissipation if it fulfills the requirements of restraining members stipulated in the design method. Furthermore, finite element analysis (FEA) was used to determine the cyclic behavior of the proposed BRB. Based on the analysis results, the inner tube failure mode, core buckling response, and variation in the core strain distribution are presented to complement the observations obtained from the tests.

Shake table tests and numerical studies on buckling-restrained braces as a seismic resilient measure for reinforced concrete twin-column tall bents

Shake table tests and numerical studies on buckling-restrained braces as a seismic resilient measure for reinforced concrete twin-column tall bents

Re-entrant honey comb meta-materials configuration and its application in buckling restrained braces: A numerical study

Evens came up with the term "auxetics" in the 1990s. It is used to describe materials and structures with a negative Poisson's ratio (NPR) that shrink or grow in an unusual way when put under uniaxial compression and tension. These materials have different mechanical properties, such as a high shear bearing capacity, resistance to breaking, ability to absorb energy, and resistance to falling apart. But because auxetics often have holes in them, they are often much less stiff than solid structures. Although these shapes should function well under both static and dynamic loading conditions as energy-absorbing components, the behavior of auxetic metamaterials has been rarely investigated in the field of seismic protection. In this paper, a parametric study was conducted using a metallic damper, such as a buckling restrained brace (BRB) equipped with an auxetic steel core and re-entrant honeycomb cells, with the aim of exploring the performance dissipative of these types of metamaterials. The proposed model of BRB with an auxetic core was modeled and analyzed under cyclic loading using a finite element method. The repetitive re-entrant honeycomb cells are controlled by four parameters: hole ratio (porosity), section weakening rate, concave angle, and angle chamfering radius. Hysteresis behavior and vos mises distribution under large deformation were extracted and discussed. As seen in the results, it was found that the local buckling of the steel core could be improved by the auxetic behavior. The values of 75° angle and 0.5 corner chamfer radius were selected to have the largest effect on the hysteresis curves of BRB model specimens when the axial strain exceeds 1.2%. The dissipative performance of these metamaterials under cyclic tests provides a good basis for further investigations about applying auxetic structures in the field of protective structures.

Model Updating of Nonproportionally Damped Structural Systems Using an Adapted Complex Sum-of-Squares Optimization Algorithm

Various model updating approaches relying on solving nonconvex optimization problems have been developed; however, few of them can reach the global optimum. To obtain the global optimum, the real sum-of-squares optimization algorithm (SOSOA) was proposed to minimize the modal dynamic residuals of proportionally damped structural systems by recasting the nonconvex optimization into a convex optimization. However, this algorithm becomes inefficient for model updating of nonproportionally damped systems with complex-valued eigenvalues and eigvenvectors. This study proposes a model updating approach that exploits and adapts a complex SOSOA to minimize the modal dynamic residuals of nonproportionally damped systems. Numerical considerations unique to using the adapted complex SOSOA to update medium- or large-scale structural models are discussed. Finite-element models of three nonproportionally damped structures—including a base-isolated shear building, a frame building implemented with a tuned mass damper, and a frame building implemented with buckling-restrained braces—are updated to demonstrate that the adapted complex SOSOA finds the global optimum while being orders of magnitude more computationally efficient and far less demanding of computer memory than the real SOSOA.

Theoretical and Numerical Studies of Elastic Buckling and Load Resistance of a Shuttle-Shaped Double-Restrained Buckling-Restrained Brace

A new type of shuttle-shaped double-restrained buckling-restrained brace (SDR-BRB) is proposed, which adopts the form of a shuttle-shaped deformation section similar to its bending moment distribution as the external restraining system. The SDR-BRB has the advantages of superlong size, high load-carrying capacity, and lightweight components, and is suitable for use in large-span spatial structures and bridge structures with an exposed BRB. First, the calculation formula of the elastic buckling load of a pin-ended SDR-BRB is derived based on the equilibrium method, which is verified through the eigenvalue buckling analysis method, and the effects of the main geometric parameters on its elastic buckling behavior are evaluated. The effects of multiple key factors on the load-carrying capacity of the SDR-BRB are then studied by parametric analysis. The results show that the restraining ratio, initial imperfection, and gap have significant effects on the ultimate load-carrying capacity and overall stability of the SDR-BRB, while the effect of the diameter–thickness ratio is relatively small. On this basis, the fitting formula of the critical restraining ratio of the SDR-BRB considering the influences of initial imperfection and gap is proposed and verified by finite element analysis. The research lays a foundation for further research into the elastic–plastic hysteretic behavior and design method of an SDR-BRB.

Evaluation of rocking seismic isolation performance of railway tall piers with different energy dissipation devices

Conventional pier top isolation measures cannot reduce the inertial force produced by railway gravity tall piers. This may damage the pier column and pile foundation during strong earthquakes. As an effective pier bottom seismic isolation structure, rocking piers have broad application prospects in railway tall pier bridges. This paper considers five energy dissipation devices (EDDs) to constrain the bottom of a free rocking pier (F-RP), namely buckling restrained braces (BRBs), yielding steel cables (YSCs), self-centering buckling restrained braces (SC-BRBs), superelastic shape memory alloy wires (SMAs), and viscous dampers (VDs). In particular, an additional “locking” structure is proposed to prevent excessive rocking of the piers and protect the EDDs. Parameter design methods are proposed for damage control and residual deformation control of piers. Nonlinear static and dynamic analyses are performed. The results show that the fixed base piers based on the ductility design suffered severe damage during strong earthquakes. The longitudinal rebar strain ratio is recommended as the damage index for the rocking pier due to large axial force fluctuations. Based on the design method proposed in this paper, the additional EDD constraints make the pier's expected damage level controllable and improve the post-earthquake predictability of the railway pier. BRBs and VDs are unfavorable to pier bottom shear forces. YSCs may produce irrecoverable residual deformation, while BRBs may have significant residual stresses. SC-BRBs and SMAs require no post-earthquake repair. SC-BRBs have more potential for application in rocking piers in high-intensity earthquake areas.

Analysis of the influence on structural seismic performance by the composite reinforcement method

AbstractThis paper proposed three composite strengthening methods for repairing seismic‐damaged RC frames to restore their seismic capacity. Combined with the damage characteristics and failure mode of the frame under the earthquake action, the local strengthening of the column adopts the angle steel and gusset plate, and then the whole frame is strengthened by the inclined brace, the thin‐walled steel plate and the V‐shaped buckling restrained brace (BRB), respectively. Through the cyclic loading test, the main seismic indexes of the strengthened specimen, including hysteresis curve, skeleton curve, ductility, energy dissipation capacity, and stiffness degradation, are studied. The influence of different strengthening methods on the seismic performance of the seismic‐damaged specimens is analyzed. The results show that the seismic performance of strengthened specimens is significantly improved, and the bearing capacity, ductility, and energy dissipation capacity are increased by 2.58–5.57, 1.05–1.24, and 7.67–15.87 times, respectively. The thin‐walled steel plate shear wall and the inclined brace are destroyed at first during loading to effectively delay the premature destruction of the main frame. The composite strengthening method makes the original frame realize the failure mechanism of “strong joint weak member, strong column weak beam” under strong earthquake action. The strengthened specimen satisfies the seismic requirement and has good seismic performance. The seismic performance of the frame strengthened with the V‐shaped BRB is better than that of the other two strengthening methods. Based on the test date, the formula for calculating the shear‐bearing capacity of the beam end is presented.

Development and investigation of a self-centering cable brace with variable slip stiffness for braced frame structure

Extremely rarely occurring earthquake (EROE) level is currently not often considered in most national codes or standards, and the earthquake damage has shown that its consequences are serious. To control the seismic responses of the structures under the EROE level, a novel self-centering cable brace with variable slip stiffness (VSS-SCB) is proposed as the lateral force resisting component of braced frame structure. Firstly, the theoretical analysis of the damper in the VSS-SCB was carried out, it is found that the slope angle, friction coefficient, and compressive stiffness of the disc springs are the main parameters affecting the mechanical behavior of the damper. The combination of strong and weak stacks of disc springs can effectively provide a self-centering damper with adaptive stiffness. Then, pseudo-static tests were carried out on the design specimens of the damper. The test results show that the hysteretic curve of the self-centering cable brace with constant slip stiffness (CSS-SCB) presents a classical flag type, and the residual deformation can be ignored. When the disc spring stacks with different stiffness are combined in series, there are significant strengthened points for the loading and unloading stiffness of the brace. Finally, the displacement-based design method was applied to the design of the braced frame structures with the VSS-SCBs. The dynamic analysis shows that the braced frame structure with the CSS-SCBs has larger displacement response than that with the buckling-restrained braces (BRBs), and the hysteretic curves of the CSS-SCB and VSS-SCB show good self-centering capability. When the deformation of the CSS-SCB and VSS-SCB exceeds the strengthened point, the large strengthened stiffness of VSS-SCB can control the seismic response of the braced frame structure. The seismic fragility curves of the braced frame structures with the BRBs and with the VSS-SCBs are comparable, and are significantly smaller than that with the CSS-SCBs. However, since the BRB is prone to significant residual deformation, the braced frame structure with the VSS-SCBs has more advantages in improving the seismic resilience of the structure.

Buckling-Restrained Bracing System with Ultra-High-Performance Fiber Concrete

Recently, buckling-restrained braces (BRBs) have been widely implemented as seismic load resistance systems in buildings to enhance their response against dynamic vibration. However, during catastrophic earthquakes, the steel core in BRB devices fully yields, which causes the BRB to lose its functionality. While the incorporation of various filler materials, such as new high-performance concretes, has the potential to enhance the performance of buckling-restrained braces (BRBs), there remains a notable gap regarding comprehensive research investigating this aspect. Therefore, this study assessed the effect of implementing ultra-high-performance concrete (UHPFRC) as filler material on BRB behavior. For this purpose, the finite element model for the proposed BRB was developed and hysteresis analysis results under incremental cyclic loads were investigated. Then, the prototype of a BRB with UHPFRC concrete was cast and experimentally tested under cyclic loads by using a dynamic actuator. Based on the testing results, a new design for a BRB device named as rubber buckling-restrained brace (RBRB) was developed, implementing hyperelastic rubber components between the steel core and UHPFRC as an additional load-bearing mechanism to enhance the device vibration dissipation capacity. Subsequently, a finite element model of the newly proposed rubber buckling-restrained brace (RBRB) was developed to assess the device’s performance. The analysis results demonstrate a notable enhancement in load capacity and energy dissipation for the RBRB device compared to conventional BRBs.

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.

Seismic design of buckling-restrained knee-braced frames considering cumulative damage

A buckling-restrained knee-braced frame (BRKBF) is an efficient structural system utilizing short buckling-restrained braces (BRBs) as knee bracing elements. Because of the shorter yielding core length compared to those of conventional BRBs, one of the key parameters concerning the performance of this system is the low cycle fatigue cumulative damage of the BRBs. This paper presents a seismic design method considering the cumulative damage, performance evaluation, and collapse assessment of 3-story, 6-story, and 9-story archetype BRKBFs. An energy-based plastic design method was utilized to design the example frames. The frames were then evaluated by nonlinear static analysis and multiple-stripe analysis (MSA). The results indicated that BRKBs were able to accommodate seismic motions with limited damage. The validity of the design methodology considering cumulative damage was also confirmed.

Study on self-centering mechanism of different yield strength hybrid buckling restrained braces

Conventional buckling-restrained braces (BRBs) exhibit stable compressive and tensile strengths and excellent energy dissipation characteristics. Nevertheless, the low post-yield stiffness limits the capacity of BRBs to control the peak displacement of the structure. This leads to large residual displacements in structures, which increases the probability of collapse under strong earthquakes. Consequently, introducing a reliable system that dissipates seismic energy, and provides an adequate self-centering capability, is necessary. This study has been carried out to investigate the hybrid BRBs response with different yield strengths (DY-HBRB) using numerical analysis. The cyclic responses, residual displacement, energy dissipation, and equivalent damping coefficient of the DY-HBRB models have been assessed. A simplified core-spring finite element model was utilized to model DY-HBRB elements. Moreover, an innovative trilinear kinematic hysteresis (TKH) model is proposed to simulate the cyclic behavior and facilitate the application of DY-HBRBs to seismic designs. The proposed model has been validated with the experimental investigation and numerical analysis results. The results indicate that selecting appropriate combinations of steel cores with different yield strengths in DY-HBRB provides a stable cyclic response with adequate energy dissipation and eliminates a significant part of the residual displacement. In addition, it was confirmed that the proposed TKH model could logically represent the double yield point of the DY-HBRBs with remarkable precision.

Cyclic behavior of ellipse and peanut-shaped perforated buckling-restrained braces

Auxetic (effect of negative Poisson’s ratio) metamaterials have increasingly attracted attention recently. Buckling-restrained braces (BRB) are commonly used as structural components to resist lateral loads and dissipate earthquake input energy. This study introduced the concept of auxetics to develop novel types of BRB. Two forms of perforated auxetic structures, including ellipse and peanut-shaped structures, were used in this study to develop new types of BRB core plates. Both experimental and numerical studies were conducted to evaluate the hysteretic performance of the two newly developed types of perforated BRBs. The test program included two ellipse-shaped BRB and three peanut-shaped BRB specimens. Each specimen had a fracture that occurred at the ligament between neighboring holes. Out-of-plane deformation was insignificant in each specimen. Test results showed that the perforated BRBs had a stable hysteretic response and good energy dissipation capacity. Finite element modeling illustrated that plastic strain was localized at the ligaments between neighboring holes. Parametric studies were also conducted on the effects of two key parameters: the unit cell number and the porosity. With a given dimension of the yielding segment, an increase in the unit cell number increased the BRB load-carrying capacity. With a given unit cell size and number, an increase in the porosity increased the equivalent viscous damping ratio, and decreased the load-carrying capacity and effective Poisson’s ratio. For either ellipse or peanut-shaped structures, the effective Poisson’s ratio may become negative as the porosity larger than 0.4. A negative Poisson’s ratio may be beneficial for BRB energy dissipation capacity. The limitations of the numerical models and future research directions were also discussed in this paper.

A novel buckling-induced planner isotropic auxetic meta-structure and its application in BRB: A numerical study

Recently, anti-tetra-chiral-type bulking-induced auxetic meta-structure (generated by arraying periodic orthogonal elongated holes onto a sheet structure) was proved to exhibit superior aseismic performance. Anti-tetra-chiral-type auxetics, however, present strong anisotropic performance, which may limit their potential applications, as proper structural orientations are required during operations to utilize the beneficial auxetic effect. In analogy with anti-tetra-chiral-type bulking-induced auxetic meta-structure, an anti-tri-chiral-type bulking-induced auxetic meta-structure was therefore proposed by arraying periodic tri-dumbbell-shaped holes onto a sheet structure. Systematic finite element (FE) analyses were then conducted on a unit cell with periodic boundary conditions to elucidate the deformation mechanism and investigate the effective mechanical properties of the proposed auxetic meta-structure. Results show that the proposed design exhibits excellent auxeticity and planner isotropy. A novel auxetic buckling restrained brace (BRB) core brace was then designed based on the proposed auxetic meta-structure. Numerical calculations were then conducted to investigate the aseismic performance of the proposed auxetic BRB core. It is shown that the proposed auxetic BRB core brace demonstrates better energy dissipation capacity compared to a traditional BRB core brace with positive Poisson’s ratio and a recently reported auxetic BRB core brace with orthogonal elliptical holes. Practically, the aseismic performance of the proposed BRB core brace is independent of the orientation of the perforated holes and hence can allow uncertain fairly big manufacturing errors.

Seismic design and performance evaluation of steel braced frames with assembled self-centering buckling-restrained braces

In this study, an assembled self-centering buckling-restrained brace (ASC-BRB) is developed for seismic resilience of structures. The self-centering system of the brace mainly consists of a group of disc springs and two sets of steel strands in series to enhance the deformability and achieve the post-hardening behavior for limiting the rapid displacement development of structures under extreme earthquakes. The theoretical restoring force model is first derived according to the working principle of ASC-BRB and successfully validated by experiments. An empirical ductility demand spectral model of ASC-BRB frames is developed according to the parametric analysis on the seismic responses of the corresponding nonlinear single-degree-of-freedom (SDOF) system. The spectral model considers the influences of all independent hysteretic parameters of ASC-BRB, and the physical parameters of the brace can be determined directly from the complete hysteretic parameters. Then a displacement-based seismic design procedure for designing ASC-BRB frames is proposed. The design results indicate that the designed frames generally need at most one iterative design to meet the target performance. Although the ASC-BRBs are designed with partial self-centering behavior, the frames can still exhibit approving post-earthquake recoverability with negligible residual displacements under strong earthquakes when the values of brace hysteretic parameters are chosen reasonably. When designing ASC-BRB frames, a strength ratio β of 0.25 and a strength ratio of steel strands η2 of 0.2 is recommended for improving the seismic performance and post-earthquake resilience of structures. Compared with the existing SC-BRBs with much higher initial stiffness, the proposed ASC-BRB can control the structural peak floor acceleration more effectively, which is beneficial for non-structural components.

Application of power algorithm optimization for optimal placement of BRB in 3D shear wall frame building structure

This paper examines the optimal placement, optimal numbers, and the optimal shape of Buckling Restrained Braces (BRB) for a 3D shear-wall frame building structure based on linear static analysis utilizing ETABS software. The total amount of BRBs referred to as the number of BRBs are considered as design variables and the objective function to be minimized is the maximum story displacement and inter-story drift. The diagonal shape (D), X-shape (X), V-shape (V), and Inverted V-shape (Inv-V) of BRBs are installed between shear walls simultaneously with initial stiffnesses of 1K0, 2K0, 4K0, and 8K0, respectively. Then, the performance efficiency analysis is carried out to identify the effectiveness of initial stiffness, BRB shapes, and optimal stories. Based on the results of the optimization procedure and efficiency analysis, it is found that the performance of the structure can be improved by optimizing BRB placement within the optimal stories rather than using the maximum amount of BRBs in all stories. The most optimal location to install BRBs is the middle stories and the BRB placement at the upper and lower stories is shown to have minor or no effects on reducing story responses of the structure. Furthermore, the model with Inv-V, V, and X shapes of BRB have almost the same maximum efficiency performance, while the model with diagonal shapes has the lowest performance efficiency. Additionally, the maximum performance of the structure can be achieved by using larger initial stiffness. The proposed method is further validated by comparing the results of ETABS with MATLAB programming. It concludes that the method proposed in this study saves 40% of the total amount of BRBs used in the structure by optimal placement of BRBs within the height of the structure. This method of optimization allows the structural designer to decide the optimal placement, optimal shape, and optimal stiffness of BRBs either by the predetermined performance level of the structure or based on experiences in RC shear wall-frame building structures.

Seismic Retrofit of Pilotis Buildings by Novel Aluminium Buckling-Restrained Braces (Al-BRBs). Application to a Modernist Architecture Building in Lisbon

ABSTRACT The worldwide dissemination of the pilotis multi-storey RC buildings, generally attributed to the architect Le Corbusier, was contemporary with a structural engineering line of thought that advocated a soft first storey as a means of filtering down the seismic inertia forces in the upper storeys. These two architectural and structural international trends, combined with outdated detailing and low-code seismic design, greatly increase the risks of developing a soft storey sidesway mechanism at the first storey, as shown in past earthquake occurrences and other studies. The article explores the possibility of strengthening a representative 1955 pilotis building in Lisbon by the inclusion of novel aluminium buckling-restrained braces (Al-BRBs) at the first soft storey. This should reduce the extreme deformation concentration at that level without fully eliminating it, and thus take advantage of the additional damping provided by the stable hysteretic behaviour of the Al-BRBs. These Al-BRBs have some distinctive features that take advantage of the unique properties of the aluminium alloys, such as the formability (allowing for an extruded casing component) and the possibility of improving the low-cycle fatigue and deformation characteristics of the core component by means of thermal treatments.

Influence of design load determination method for SC-BRBs with trilinear flag-shaped hysteresis behaviour on the seismic performance of braces and structures

Self-centering buckling-restrained braces (SC-BRBs) can effectively reduce the residual deformation and seismic damage of the main structure. Because the first loading curve and subsequent loading curve of SC-BRB trilinear flag-shaped hysteresis behaviour do not coincide, there are two ways to determine the design load of a brace, i.e., the design load is taken as either the bearing force Fy1 at the first stiffness change point of the first loading curve or the bearing force Fy2 at the stiffness change point of the subsequent loading curve. In this study, a numerical analysis method is used to study the differences in the hysteresis performance of braces (i.e., SC-BRB-Fy1 and SC-BRB-Fy2) and the seismic performance of structures (i.e., SCBF-Fy1 and SCBF-Fy2) based on different design load determination methods. The results demonstrate that when the strength ratio β and the first stiffness ratio αc are similar, the hysteresis performance of braces and the seismic performance of structures are basically the same regardless of the method of design load determination. Decreasing β or increasing αc significantly increases the maximum axial force of SC-BRB-Fy1 but has little effect on that of SC-BRB-Fy2. Decreasing β can enhance the energy dissipation capacity of braces, reduce the maximum displacement of structures during earthquakes, and reduce the deformation concentration effect of SCBF-Fy2 but has no obvious influence on the deformation mode of SCBF-Fy1. Increasing αc can improve the energy dissipation capacity of SC-BRB-Fy1 but weaken the energy dissipation capacity of SC-BRB-Fy2, which has the opposite effect on the displacement response of SCBF-Fy1 and SCBF-Fy2.