Buckling-restrained Braced Frames Research Articles

Lateral Force Distributions in Braced-Moment Frames

Braced frames intended to resist wind and seismic loads traditionally have been analyzed and designed as trusses with all joints modeled as pins, such that only the braces provide lateral force resistance. However, frames with gusset plate connections create a rigid joint zone between frame beams and columns, effectively resulting in moment frame behavior, particularly at larger drift angles when braces have yielded or buckled. Described herein are the force distributions for buckling-restrained braced frames (BRBF) subjected to story drift angles, where the lateral resistance of the frame comprises both brace and moment frame action.

Substructure-based design method for vertically irregular steel buckling-restrained braced frame structures

Buckling-restrained braces (BRBs) can mitigate the uneven inter-story drifts of vertically irregular steel frame structures during earthquakes, preventing unfavorable seismic forces and failure patterns. However, the structural lateral displacement profile of vertically irregular steel buckling-restrained braced frame structures (VSBFSs) can hardly be predicted; hence, parameter tuning and iterative designing are commonly required in conventional direct displacement-based design (DDBD) methods, which strongly rely on the experience of designers and consumes a considerable amount of time. This study proposes a substructure-based design (SBD) method developed explicitly for VSBFSs. In this method, the substructures of every story of a VSBFS are separated from the entire structure and individually analyzed in the subsequent procedures. The boundary conditions of the substructures are initially simplified as hinges, and an explicit equation of BRB stiffness and inter-story drift for the substructures is established. An iterative calculation procedure is consequently applied to correct the equation by considering the influence of the constraints of adjacent stories. In this manner, the inter-story drifts of all the stories of the entire structure uniformly converge to the predetermined targets, in which the demand of BRBs for each story is also determined. Compared with conventional DDBD methods, the proposed method does not assume the structural lateral displacement profile and is not based on experience, yielding relatively economical and safe design outcomes in a timely manner. The proposed SBD method was first validated by comparing it with existing elastic and elastoplastic design methods through a 15-story VSBFS example. Then, the applicability of the SBD method was further explored through four 6-story VSBFSs with different plan layout reductions and two VSBFSs with heights of 20 stories and 30 stories. Finally, the SBD method was applied to redesign the BRBs of a vertically irregular thermal power plant model (an example of a VSBFS) in a shaking table test.

Hybrid data-driven and physics-based simulation technique for seismic analysis of steel structural systems

This paper proposes 1) a new hybrid analysis technique by integrating a data-driven method with a physics-based technique to perform nonlinear analysis of steel structural systems under seismic loading, 2) two component-based data-driven models (PI-SINDy and DPI-SINDy) for predicting the nonlinear hysteretic response of steel seismic fuses with and without hysteretic degradation. The proposed hybrid data-driven and physics-based simulation (HyDPS) technique offers an efficient approach for seismic analysis of structures and is expected to address the challenges associated with computational cost and modeling uncertainties inherent in physics-based numerical simulations. In this technique, the well-understood components of the structure modeled numerically are combined with the critical components of the structure simulated using one of the data-driven models developed in this study. The proposed data-driven models were trained using experimental and numerical hysteresis data. The results show that these data-driven models can accurately and efficiently predict the nonlinear hysteretic response of steel structural components with and without degradation. Furthermore, the performance of the HyDPS technique powered by the PI-SINDy model is verified in the presence of noise using response history analyses performed on a steel buckling-restrained braced frame.

Near-Fault Response and Loading Protocols of Box Columns in Steel Frames with Self-Centering Braces to Provide Recentering Capability

The main objective of this study was to establish loading protocols for self-centering braced frames (SCBFs) while taking into account the impact of near-fault ground motions. SCBFs are self-centering frames that have lower residual drift than buckling-restrained braced frames (BRBFs) under near-fault earthquakes; thus, SCBFs can better control damage to buildings. Typically, first-story columns are employed to represent the seismic behavior of a structure; therefore, loading protocols were developed for first-story columns in SCBFs under near-fault earthquakes. Nonlinear static and dynamic analyses of SCBFs designed with various periods were conducted for better understanding the seismic performance of SCBFs. Finally, the loading protocols developed for SCBFs were compared with those for BRBFs under the same near-fault motions.

Rotation Capacity of I-Shaped Beams with Concrete Slab in Buckling-Restrained Braced Frames

Rotation Capacity of I-Shaped Beams with Concrete Slab in Buckling-Restrained Braced Frames

External strengthening of RC structures with buckling-restrained braced frames

External strengthening of RC structures with buckling-restrained braced frames

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.

Functional recovery evaluation of hybrid self‐centering piston‐based braced frames

AbstractSevere earthquakes possess formidable destructive potential, leading to substantial damage, widespread disruptions, and tragic loss of life. In response, researchers and policymakers strive to develop innovative solutions to quantify the seismic resilience of structures. This study aims to evaluate the post‐earthquake functional recovery of two types of braced frames: Self‐Centering Piston‐Based Braced Frames (SC‐PBBFs) and Buckling Restrained Braced Frames (BRBFs). The SC‐PBBFs are designed to mitigate structural damage by incorporating Self‐Centering Piston‐Based Bracings (SC‐PBBs) equipped with Shape Memory Alloy (SMA) bars and Friction Springs (FS). A set of building prototypes, representing low‐, mid‐, and high‐rise archetypes in seismic regions, are subjected to comprehensive analyses under 44 far‐field ground motions. This thorough examination incorporates seismic hazards, structural demands, and component damages to quantify the earthquake‐induced losses and repair timelines. The study findings indicate that BRBFs suffer more significant collapse losses than SC‐PBBFs. However, BRBF systems incur lower repair costs, mainly due to limited damage to acceleration‐sensitive non‐structural components. Additionally, the FEMA P‐58/ATC‐138 framework is employed to estimate re‐occupancy, functional recovery, and full repair time, identifying systems and components that exert a significant impact on functional recovery.

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.

Seismic fragility analysis of rocking buckling-resistant braced structures subjected to far-field and near-field ground motions

To address the inadequate seismic performance of traditional buckling-restrained braced frame structures (BRBFS), this study introduces a novel structure, the rocking buckling-restrained braced frame structure (RBRBFS). The RBRBFS achieves effective control of main structure damage and enhances structural energy dissipation and seismic resilience by disconnecting the column feet from the foundation in the BRBFS and using friction energy dissipation devices as rocking column feet. This research aims to quantitatively assess the seismic performance and collapse safety margin of the new RBRBFS under different types of ground motions. To achieve this goal, two eight-story structures, one is traditional BRBFS and the other is RBRBFS, were designed. Incremental Dynamic Analysis (IDA) was employed, accounting for ground motion uncertainty, to conduct a comparative study of the seismic fragility of both structures subjected to near-fault pulse-like and far-field earthquake ground motions. Nonlinear dynamic analysis results indicate that under high-intensity ground motions, the RBRBFS significantly improves structural ductility and effectively controls structural damage. Compared to BRBF structures, the BRBFS exhibit a reduction of 26.5% and 18.3% in damage probability deviation under the two seismic excitations, highlighting their more stable structural response under varying seismic conditions. Furthermore, this novel RBRBFS increases the collapse margin ratio by 25% to 30%, demonstrating its higher seismic collapse resistance capacity

Test of a full-scale two-story steel X-BRBF: Strong-axis instability of buckling restrained brace associated with out-of-plane bending of gusset connections

This paper presents tests and finite element analyses of a two-story, buckling-restrained braced frame (BRBF) with X-bracing configuration, called X-BRBF. The BRB used in this work is composed of a core plate sandwiched by a pair of the restraining member with bolts, called a sandwiched buckling restrained brace (SBRB). The weak-axis of the SBRB core that had a rectangular plate was positioned transverse to the dual-gusset plate connection and in-plane movement of the frame. The objectives of the frame test were to evaluate: (1) the seismic performance of SBRBs with a small width-to-thickness ratio of the core plate (i.e. 3), (2) the effects of free-edge stiffeners on the gusset and BRB stability, and (3) the BRB stability associated with the lateral torsional buckling (LTB) of the beam. The two-story X-BRBF subassembly had two test phases: all gusset connections had free-edge stiffeners in Phase 1 test, and freeedge stiffeners were removed from half of gusset connections in Phase 2 test. The X-BRBF in Phase 1 test exhibited good performance up to a second-floor drift of 1.6%, but in Phase 2 test the second-floor SBRB caused by LTB of the beam showed asymmetric instability about its strong-axis of the core plate at 1.6% second-floor drift. The other SBRB with no LTB of the beam showed one-side instability about its strongaxis at 2% second-floor drift (about 2.5% interstory drift). However, the strength degradation of the X-BRBF subassembly was not observed in the strong-axis instability of SBRBs, indicating an acceptable orientation of BRBs for eliminating a typical weak-axis buckling of BRBs together with out-of-plane bending of gusset plates. The strong-axis instability of SBRBs could be evaluated by using the BRB stability concept together with the measured out-of-plane deformation of gusset plates in Phase 2 test.

Improving the Seismic Resilience of Buckling-Restrained Braced Frames by SMA-Based Hybrid Cores

Improving the Seismic Resilience of Buckling-Restrained Braced Frames by SMA-Based Hybrid Cores

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.

Utilising Artificial Neural Networks for Assessing Seismic Demands of Buckling Restrained Braces Due to Pulse-like Motions

Buckling restrained brace frames (BRBFs) exhibit exceptional lateral stiffness, load-bearing capacity, and energy dissipation properties, rendering them a highly promising choice for regions susceptible to seismic activity. The precise and expeditious prediction of seismic demands on BRBFs is a crucial and challenging task. In this paper, the potential of artificial neural networks (ANNs) to predict the seismic demands of BRBFs is explored. The study presents the characteristics and modelling of prototype BRBFs with different numbers of stories and material properties, utilising the OpenSees software (Version 2.5.0) for numerical simulations. The seismic performance of the BRBFs is evaluated using 91 near-fault pulse-like ground motions, and the maximum inter-storey drift ratio (MIDR) and global drift ratio (GDR) are recorded as a measure of seismic demand. ANNs are then trained to predict the MIDR and GDR of the selected prototypes. The model’s performance is assessed by analysing the residuals and error metrics and then comparing the trend of the results with the real dataset. Feature selection is utilised to decrease the complexity of the problem, with spectral acceleration at the fundamental period (T) of the structure (Sa), peak ground acceleration (PGA), peak ground velocity (PGV), and T being the primary factors impacting seismic demand estimation. The findings demonstrate the effectiveness of the proposed ANN approach in accurately predicting the seismic demands of BRBFs.

Effect of pulse on fragility curves of buckling-restrained braced frames

To investigate the effect of presence of the pulse in earthquake motions on the vulnerability of buckling-restrained braced frames (BRBFs), this technical note uses pulse-like ground motions (original records) and their residual parts obtained by extracting the pulse via wavelet analysis, as input vibrations. Conducting the numerical simulation of 4, 8, 12, and 15-storey BRBFs, their responses to the scaled original and residual motions are recorded using incremental dynamic analysis (IDA). Accordingly, the seismic performance of BRBFs is generally evaluated, and fragility curves are developed at collapse prevention (CP), life safety (LS), and immediate occupancy (IO) performance levels. The results indicate that a maximum difference of about 25%–30% may occur between the fragility curves due to the original and residual parts of ground motions at the maximum considered earthquake (MCE) intensity level for 8, 12, and 15-storey BRBFs, so that the original records lead to a severe damage in comparison with the residual ones. Also, the original records increase the probability by 20% on average compared to the residual records at the LS level for the considered BRBFs.

Performance Evaluation of Structures with Buckling Restrained Braced Frame Under Earthquake Load

Structures with buckling-restrained braced frames (BRBF) resist lateral load, i.e., earthquake, using special bracings that yield under axial tension and compression loads. Following the applicable building code SNI 1726-2019, the design for the BRBF structure has a limitation on the structure height for seismic design category D, which is 48 meters. Three structures are modelled: a 5-story building, a 10-story building, and a 20-story building, to evaluate the height limitation on the code. The initial design of the structures used modal response spectrum analysis (MRSA), then the structures were checked using linear response history analysis (LRHA). Finally, a pushover analysis was conducted to obtain the structural performance level. The study revealed that the structural design for BRBF with MRSA satisfies all requirements of SNI 1726-2019. However, the results of the evaluation of BRBF with LRHA show a structure exceeding the height limit does not meet the requirement for inter-story drift. The pushover analysis showed that the structure’s performance reached the Immediate Occupancy (IO) level. Thus, all structures with BRBF in this study that were designed using MRSA have satisfactory performance under the seismic design load, even though the height limit has been exceeded.

A framework for multi‐element hybrid simulation of steel braced frames using model updating

AbstractThis paper presents a framework for seismic response assessment of steel buckling‐restrained braced frames (BRBFs) by integrating data‐driven techniques into the conventional hybrid simulation to facilitate multi‐element hybrid simulation for structural systems with several potential critical components. The data‐driven brace model incorporates Prandtl‐Ishlinskii hysteresis model into a prediction algorithm to reproduce cyclic nonlinear response of the brace under random earthquake excitations. A two‐storey steel BRBF is selected to illustrate and verify the proposed framework using a set of virtual hybrid simulations. In the BRBF, the first‐storey BRB is virtually simulated, representing the test specimen, while the second‐storey BRB enjoys the data‐driven model trained based on past experimental data. The model parameters are updated in real‐time during hybrid simulation using the data received from the virtual test specimen. The results confirm that the proposed hybrid simulation technique can offer a viable solution to address the shortcomings of conventional seismic hybrid simulation by taking advantage of model updating and multi‐element simulation platforms.

Rotational viscoelastic dampers for steel buckling-restrained braced frames: Concept, validation, and evaluation

Rotational viscoelastic dampers for steel buckling-restrained braced frames: Concept, validation, and evaluation