Buckling-restrained Braces Research Articles

Seismic design and performance evaluation of hybrid braced frames having buckling-restrained braces and self-centering viscous energy-dissipative braces

Hybrid braced frames (HBFs) emerge as an innovative seismic-resilient system, synergizing the strengths of buckling-restrained braces (BRBs) and self-centering viscous energy-dissipative braces (SCVDBs). This novel system has the potential to simultaneously manage three key seismic demand parameters: peak inter-story drift (PID), residual inter-story drift (RID), and peak absolute floor acceleration (PFA). Nevertheless, a dedicated seismic design method for HBFs is yet to be developed. This research proposes a performance-based seismic design (PBSD) method specifically tailored for HBFs. The method's core relies on energy decoupling in the HBFs using a proposed energy distribution factor (η). To validate the proposed design method, sets of 4-, 8-, and 12-story braced frames are designed using varied η. A comprehensive seismic performance evaluation is conducted, utilizing nonlinear static and nonlinear time-history analyses. The findings indicate that the HBFs, designed utilizing different values of η, consistently meet predefined performance objectives. Within the scope of this study, the η value of 0.5 is shown to be optimal, enhancing the structural resilience of HBFs against PIDs and PFAs while exhibiting excellent self-centering performance comparable to the self-centering viscous energy-dissipative braced frame (SCVDF). Additionally, the HBFs demonstrate superior control over PFA compared to pure buckling-restrained braced frame (BRBF) and SCVDF.

Numerical Investigation of the Seismic Performance of an Innovative Type of Buckling-Restrained Brace (BRB)

Previous studies have demonstrated that the inclusion of tire-derived aggregate (TDA) enhances the damping, ductility, and toughness of concrete mixtures. The effectiveness of tire-derived aggregate as a ductile material with a higher damping ratio and lower density in buckling-restrained braces has been examined at California State University’s Structures Laboratory (CSU). Through experimental and theoretical investigations, this study compares the structural application of buckling-restrained braces with TDA and with conventional concrete infill subjected to various ground motions as well as artificial excitations. The evaluations include modeling a full-scale experimental setup equipped with a single-leg BRB utilizing ETABS 2016 and OpenSees 2000 software. The effectiveness of the application is demonstrated through a comparison of accelerations, displacements, stiffness, and damping ratios between TDA and concrete filling. Additionally, a design guideline for TDA-filled buckling-restrained braced frames is provided.

Seismic collapse performance of high-rise mass timber building with buckling-restrained braced frames

The present paper proposes a hybrid building system with the buckling-restrained brace and Glulam frames (BRBGF). For a highly seismic location of Vancouver, Canada, an 18-story building is designed with BRBGF as the lateral load-resisting system for the seismic hazard of NBC 2020. A nonlinear analytical model is developed and validated with the experimental data. Further, 30 pairs of ground motion records are selected to represent the complex seismicity of Southern British Columbia consisting of Shallow Crustal, Subduction Interface, and In-slab faulting mechanisms. The BRBGF system is found to achieve the target of maximum inter-story drift of 2.5% for the 2,475-year return period event. The building also passes the FEMA P695 criteria for acceptable collapse margin for seismic force modification factors of Rd=4 and Ro=1.2. The results from the study indicate the feasibility of high-rise timber buildings in highly seismic regions.

Seismic response and performance prediction of steel buckling-restrained braced frames using machine-learning methods

Nowadays, Buckling-Restrained Brace Frames (BRBFs) have been used as lateral force-resisting systems for low-, to mid-rise buildings. Residual Interstory Drift (RID) of BRBFs plays a key role in deciding to retrofit buildings after seismic excitation; however, existing formulas have limitations and cannot effectively help civil engineers, e.g., FEMA P-58, which is a conservative estimation method. Therefore, there is a need to provide a comprehensive tool for estimating seismic responses of Interstory Drift (ID) and RID with novel approaches to fulfill the shortcomings of existing formulas. The Machine Learning (ML) method is an interdisciplinary approach that makes it possible to solve these types of engineering problems. Therefore, the current study proposes ML algorithms to provide a prediction model for determining the seismic response, seismic performance curve, and seismic failure probability curve of BRBFs. To train ML-based prediction models, Nonlinear Time-History Analysis (NTHA) and Incremental Dynamic Analysis (IDA) were performed on the 2-, to 12-Story BRBFs subjected to 78 far-field ground motions, and 606944 data points were prepared for different prediction purposes. The results indicate that the considered approaches are justified. For instance, the proposed ML methods have the ability to predict the maximum ID, maximum RID and maximum roof ID with the accuracy of even 98.7%, 95.2%, and 93.8%, respectively, for the 4-Story BRBF. Moreover, a general preliminary estimation tool is introduced to provide predictions based on the input parameters considered in the study.

Experimental Study of Newly Developed Hybrid Buckling-Restrained Brace with Different Infill-Layer Geometries under Cyclic Loading

Experimental Study of Newly Developed Hybrid Buckling-Restrained Brace with Different Infill-Layer Geometries under Cyclic Loading

Seismic performance evaluation of a five-story column-and-beam glulam frame with steel-timber buckling restrained braces

This paper summarizes the results of numerical simulation and fragility analysis of a five-story column-and-beam glulam frame with chevron steel-timber buckling restrained braces (BRBs). Key parameters of the rotational behavior of the bolted beam-to-column connections and column base connections were modeled and calibrated using shaking table test results. Prediction methods of the stiffness and capacity of the steel-timber BRBs were proposed and validated with the test results. An FEM model of the glulam frame with steel-timber BRBs was developed to capture the frame seismic response and validated using shaking table test results. The FEM model which considered damping change and damage accumulation achieved good agreement with shaking table test results, with the modelling errors of displacement amplitude for most conditions less than 15 %. Fragility analysis of the frame was conducted based on the validated FEM model. The probability of exceeding the collapse prevention limit state under the VII-rare earthquake excitations was reduced to close to zero when steel-timber BRBs were used. This study demonstrates the potential for using glulam frames with steel-timber BRBs in Chinese VII seismic regions.

NUMERICAL MODELLING OF REINFORCED CONCRETE FRAMES RETROFITTED WITH BUCKLING RESTRAINED BRACE INCORPORATING STEEL AND SUPERELASTIC SHAPE-MEMORY ALLOY CORES

The numerical response of one-storey reinforced concrete frames designed following design standards before the enactment of modern seismic provisions was investigated in this study using the nonlinear finite element method. An unbraced frame and two frames retrofitted with a buckling restrained brace (BRB) incorporating either a stainless steel or chrome molybdenum core bar were modelled. The nonlinear static reverse cyclic loading performance of the frames was assessed. Modifications to the BRB are proposed to mitigate deficiencies identified with the original BRB and steel core bars. The modified BRB incorporating a superelastic shape-memory alloy (SE-SMA) core bar was further modelled. The results illustrate the benefits of implementing SE-SMA as a retrofit strategy to control permanent displacements. The modified BRB with a SE-SMA core exhibited improved lateral strength and displacement capacities relative to the frames retrofitted with steel cores and the control bare frame.

Enhancing seismic performance of buckling-restrained brace frames equipped with innovative bracing systems

Nowadays, to improve the performance of conventional bracing systems, in which, buckling in the pressure loads is the main disadvantage, the buckling-restrained brace (BRB) is introduced as a solution. In this study, the performance of the BRB system was improved with innovative lateral-resisting systems of double-stage yield buckling-restrained brace (DYB), and a combination of DYB improved with shape memory alloy (SMA) materials (DYBSMA). The proposed systems have been verified and implemented in the 2- to 12-story elevation steel buckling-restrained brace frames (BRBFs). To evaluate their effects on the seismic performance, two types of analysis including nonlinear dynamic analysis (NDA) and incremental dynamic analysis (IDA) were performed considering design-based earthquakes (DBE) and maximum considered earthquakes (MCE) levels for far-field ground motions. The results showed that the BRB system in all BRBFs had the highest values of residual drift ratio (RDRMed) demands, while implementing innovative DYBSMA can considerably reduce the values of RDRMed compared to other lateral-resisting systems. In addition, under MCE level, the BRB-DYBSMA system had lower values of the interstory drift ratio (IDRMed) and RDRMed demands (e.g., the IDRMed reduced by 79.67% and 18.5% compared to BRB and DYB systems, respectively), and can be introduced as the best lateral-resisting system. Therefore, the proposed BRB-DYBSMA system can effectively reduce the IDRMed and RDRMed demands, as result, higher performance levels can be achieved, as well as, the collapse probability occurrence over 1 and 50 years impressively decreased.

Energy absorption behaviors of a novel buffer lander-leg with Yoshimura core

In the current soft-landing system, the lander-leg and the buffer are two independent parts which may cause weight problem. The traditional mechanical buffers also have their own shortcomings such as small buffer stroke and being non-reusable. A Novel Buffer Lander-leg with Yoshimura core (NBLY) is proposed in this paper, inspired by the Buckling Restrained Brace (BRB). The design details of NBLY and parameter definitions of the core are presented. The finite element analysis modes have been employed to analyze the nonlinear mechanical behaviors of NBLY subjected to the cyclic loading. NBLY with four different core styles of hexagon, octagon, dodecagon and hexadecagon are analyzed and compared. The restraining ratio and cumulative dissipation energy ratio have been obtained to evaluate the energy absorption properties. The results show that the origami pattern has significant influences on the deformation ductility, plastic energy absorbing and axial load transferring to the core. The NBLY with octagon core has outstanding properties, especially the hysteretic energy dissipation and enhancement of compression capacity. The interaction mechanism between the core and encasing member constrains the deformation extensions and contributes to the frictional energy dissipation of the NBLYs. This paper provides a new conceptual design of buffer lander-leg for soft-landing missions. It can realize the reuse function as a buffer lander-leg with better loading-bearing and energy absorption behaviors.

Cyclic Loading Test of Rectangular Tube-Type Buckling-Restrained Braces with Enhancements to Prevent Local Bulging Failure

In this study, innovative enhancements of rectangular tube-type buckling-restrained braces are proposed to prevent bulging failure on the surface of the outer restrainer and validated experimentally. First, an inner restrainer composed of a bent plate, which increases the stiffness and strength to resist outward force exerted by the steel core subjected to higher-mode buckling, is installed inside the outer restrainer. Second, the unbonding material surrounding the steel core is partially thickened to create additional space to prevent the outward force from being transferred directly along the centerline of the cross-section. Buckling-restrained braces with and without the enhancements are tested via cycling loading to validate the efficiency of the proposed enhancements. Improvements in strength and deformation capacity are evaluated quantitatively. The proposed enhancements increased the compressive strength and cumulative inelastic deformation capacity of the buckling-restrained braces. However, the increased outward force owing to the compression-hardening phenomenon led to bulging failure, where the added inner restrainer terminated. An analytical formula is proposed to estimate the outward-force-resisting capacity of the inner restrainer, which predicted bulging failure adequately.

Design and Cyclic Experiments of a Mass Timber Frame with a Timber Buckling Restrained Brace

Design and Cyclic Experiments of a Mass Timber Frame with a Timber Buckling Restrained Brace

Direct displacement‑based seismic design for a retrofitted RC frame by hinged wall with BRBs at base

A hinged wall (HW) with buckling-restrained braces (BRBs) at the base (HWBB) has been proposed to enhance the seismic performance of a reinforced concrete frame (RCF). In this study, a new direct displacement-based design procedure based on the bottom shear method (DDBDP-BSM) is proposed for low- and multi-rise RCFs with an HWBB (RCF-HWBB). First, the theoretical relationship between the basic period target and displacement target of the RCF-HWBB was deduced based on the DDBDP-BSM and performance targets. Then, a method to determine the HW configuration and BRB sectional area was proposed. Finally, the optimal selection of earthquake intensity at BRB yielding and the applicability of the DDBDP-BSM on a high-rise RCF-HWBB were investigated through a comparison between the design results and the time history analysis results.

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.

Seismic performance of two-story three-bay reinforced concrete frame equipped with K-configured buckling restrained braces

This study presented experimental and numerical investigations into the seismic performance of reinforced concrete (RC) frames equipped with buckling restrained brace (BRB) systems in the central span. The study evaluated the effectiveness of the K-configured BRB system in strengthening the RC frame for engineering construction applications in the seismic region. A 1/3-scaled, three-span, two-story, RC frame was designed in accordance with seismic design requirements and tested under low-reversed lateral cyclic loading. A finite element model of the BRB-equipped RC frame was created using ABAQUS and validated by comparing the numerical and experimental results. The validated model was also modified by removing the BRBs to create the bare RC frame. Seismic behaviors of the bare and RBR-equipped RC frames were numerically examined and compared in terms of failure modes, hysteretic response, ductility, energy dissipation, strength degradation, and stiffness deterioration. The results indicated that the BRB-equipped RC frame achieved a plastic hinge failure mechanism at the beam ends with no severe concrete damage in the supporting columns. Furthermore, the use of the K-shaped BRB in the central span improved the load-carrying capacity by up to 80% and the energy dissipation capacity by up to 50%. Parametric studies were also conducted to investigate the influence of critical design parameters and provide design suggestions for potential improvement in the RC frame's ductility and energy dissipation capacity.

Reliability-based design optimization of post-tensioned self-centering rocking steel frame structures

This paper reports the Reliability-Based Design Optimization (RBDO) of post-tensioned self-centering rocking steel frame structures with buckling-restrained bracing systems. The objective was to investigate the reliability index, optimization of self-centering structures to reach minimum weight using metaheuristic algorithms, and their application in linear and nonlinear reliability problems. For this purpose, three steel structures (10-, 15-, and 20-storey structures) were each evaluated with three steel framing systems (buckling-restrained bracing, post-tensioned self-centering multiple rocking steel frame with buckling-restrained bracing, and post-tensioned self-centering single rocking steel frame with buckling-restrained bracing), making a total of nine models. Subsequently, specific 2D frames of the structural models were numerically simulated using nonlinear dynamic analysis (NDA) in OpenSees software. Optimization was carried out in two stages: with and without considering the uncertainties. Finally, for calculating the failure probability and structural reliability index, Monte-Carlo Simulation (MCS) was employed. Results indicate that, although considering the reliability index leads to heavier structures, structural safety was increased and failure probability was reduced to even lower specified levels. Furthermore, among the incorporated algorithms, the Colliding Bodies Optimization (CBO) and Charged System Search (CSS) algorithms proved to have superior performances in terms of accuracy and converging time. On average, using these two algorithms for cases without uncertainty resulted in maximum weight reductions of 36%, 30%, and 32% for 10-, 15-, and 20-storey structures. In addition, for cases with uncertainty, these two algorithms with reliability index (β) of 2 respectively reduced the weight of 10-, 15-, and 20-storey structures by 21%. Also, it was shown that not considering the uncertainties can increase the failure probability by up to 23%.

Research on high‐performance steel structure with high‐strength steel column, ordinary‐strength steel beam, and low‐yield‐point steel BRB

AbstractIn order to reasonably make full use of the advantages of different steels and then achieve a steel structure with excellent seismic behaviour, the authors proposed novel triple grades hybrid high‐performance steel structures (TGHSSs) comprising high‐strength steel (HSS) columns, ordinary‐strength steel beams, and low‐yield‐point (LYP) steel buckling‐restrained braces (BRBs). The basic concept and expected advantages were introduced. To validate this concept, eight full‐scale single‐bay two‐storey TGHSS specimens were tested under cyclic loads, in which columns are of 460 MPa, 690 MPa, and 890 MPa HSSs, beams are of 345 MPa steel, and BRBs are of 100 MPa, 160 MPa, and 225 MPa LYP steels. Meantime, nine LYP steel BRB specimens were taken out and tested under uniaxial cyclic loads. Based on the experimental study, numerical simulation and parametric analyses on TGHSSs were further conducted, and a performance‐based design method was proposed. Results indicated that the TGHSSs featured a sequential yielding mechanism with excellent seismic performance. Specifically, the LYP steel BRBs yielded at first to dissipate seismic energy. Then, the ordinary‐strength steel beams developed plastic hinges at beam ends. At last, the HSS columns kept almost elastic or presented limited plasticity at column bases. This research proves such a high‐performance structure with a reasonable combination of high, ordinary, and low strength steels, whose advantages can be fully developed.

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.

Probabilistic residual displacement-based design for enhancing seismic resilience of BRBFs using self-centering braces

Buckling-restrained braces (BRBs) can effectively control the structural maximum displacements. However, their full hysteresis tends to cause significant residual drifts after strong earthquakes, resulting in massive economic loss. To improve the resilience of the buckling-restrained braced frames (BRBFs) by reducing the residual drifts, self-centering braces (SCBs) are introduced to BRBFs based on the probabilistic residual displacement-based design (PRDBD) method in this study. Parametric analyses are first carried out on single-degree-of-freedom (SDOF) systems to represent the retrofitted BRBFs subjected to near-fault pulse-like earthquakes, wherein the isotropic strain hardening of BRBs is considered. The probabilistic prediction models for maximum and residual displacement are subsequently developed by employing an artificial neural network (ANN) machine learning algorithm. Subsequently, the PRDBD method is proposed. A benchmark BRBF is retrofitted by SCBs to demonstrate the PRDBD’s effectiveness. System-level nonlinear time-history analyses (THAs) are performed to study the dynamic performance of the enhanced BRBFs. It can be observed from the analysis results that the proposed PRDBD is efficient in controlling residual displacements of the enhanced BRBFs within the prescribed guarantee rate. Moreover, the analysis results confirm that the retrofitted BRBF with partial self-centering behavior can achieve remarkable post-earthquake repairability, as evidenced by residual inter-story drifts below 0.5% with 99% probability subjected to the maximum considered earthquakes.

Hysteretic energy distribution model of CFDST composite frame with metallic dampers using coupled shear-flexural beam model

Novel steel–concrete composite structures have drawn increasingly attention in recent years especially in high-rise buildings owing to its superior structural performance over conventional concrete and steel structures. Moreover, energy dissipation devices such as metallic dampers and buckling-restrained braces (BRB) were necessarily added in this type of structure to resist seismic loads. However, the existing research regarding to the dual system consisting of composite frame and energy dissipation was limited. In this paper, the dual system consisting of concrete-filled double skin steel tubular (CFDST) composite frame and metallic damper was set as the research subject, especially focusing on the analysis of hysteretic energy distribution along the height. The 10- and 20-story dual systems were designed with different parameters revealing the influence of semi-rigid connection and metallic damper. Nonlinear models of structures established by Opensees software were validated by the test results. Afterwards, the energy distributions of all stories were discussed. It demonstrated that the metallic damper could absorb considerable energy under seismic loads while a semi-rigid connection with relatively high moment strength had a detrimental effect on the column. Moreover, the semi-rigid connection in the span without metallic damper in high story exhibited significantly larger rotation than that in the span with metallic damper. Finally, the method to estimate the energy distribution estimation of the dual system was developed, in which the lateral displacement pattern was observed by the coupled shear-flexural beam model to fully consider the flexural deformation of the dual system. An equivalent distribution of the shear and bending stiffness was also proposed considering the effect of the semi-rigid in the span without metallic damper. The predicted results from the model were validated by the analysis results derived from the nonlinear model. The theoretical and analytical results of the paper could activate the application of the dual system and provide a reasonable method to estimate the hysteretic energy distribution of the dual system.

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.