Buckling-restrained Braces Research Articles

One novel block-type brace connector for retrofitting reinforced concrete frames

Buckling-restrained braces are widely utilized for retrofitting existing reinforced concrete frames. However, conventional plate-type brace connectors and joints often suffer damage from the additional forces exerted by buckling-restrained braces during earthquakes. This paper proposes a novel block-type brace connector to address this issue. The seismic performance of this new connector is evaluated through pseudo-dynamic and quasi-static tests. Pseudo-dynamic test results indicate that the reinforced concrete frame retrofitted with the new connectors demonstrates superior seismic performance compared to the frame without retrofitting. During a rare earthquake, the maximum inter-story drift ratios are 1/308 for the frame with new connectors and 1/84 for the frame without retrofitting. Quasi-static test results show that the new connectors shift the potential plastic hinges of the beam away from the gusset plate region by moving the post-installed anchorage position outward. The gusset plate of the conventional connector buckles at an inter-story drift ratio of 1/30, while that of the new connector avoids buckling due to the restraint from the concrete block. Overall, the new connector can mitigate the adverse effects of the additional forces from buckling-restrained braces and improve the seismic performance of the existing reinforced concrete frames.

Seismic Vulnerability Assessment of the Cliff-Attached Buildings Equipped with Energy Dissipation Devices Under Obliquely Incident Seismic Waves

Cliff-attached structures are structures attached to slopes and connected tightly, which is particularly complex to analyze due to the foundations’ unequal grounding and the lateral stiffness’ irregularity. In rare earthquakes, seismic waves are usually obliquely incident on the foundation at a certain angle. Therefore, it is not appropriate to consider only seismic waves’ vertical incidence, and it is necessary to consider multi-angle oblique incidence. In this paper, based on the theory of viscous-spring artificial boundary and the principle of equivalent nodes at the interface of oblique incidence of ground shaking P-waves, and combined with the dynamic properties related to Buckling-Restrained Brace, the numerical models of slopes and two kinds of cliff-attached structures considering the slope amplification effect and soil-structure interaction are established. The dynamic response of the obliquely incident seismic waves under the action of the cliff-attached vibration reduction structure is studied in depth, and the additional effective damping ratios of the nonlinear energy-dissipated units based on the deformation energy are compared and analyzed. It is shown that under the four oblique incidence angles of incidence (compression waves in the vertical plane) studied in this paper, the seismic dynamic response and damage degree peaked at an angle of incidence of 60°, with a tendency to increase and then decrease with increasing angles of incidence. The ability of an energy-dissipating vibration reduction device to change structural vibration characteristics decreases with an increase in incidence angle. The difference between the total strain energy of the structure in the X-direction (Transverse slope direction) and Y-direction (Down-slope direction) and the total energy dissipation of the dissipative components is obvious, with the X-direction being about 10 times that of the Y-direction.

Performance-Based Design Method of Hinged Wall with Buckling-Restrained Braces at Base Using the Elastic Displacement Spectrum

A performance-based seismic design method using the elastic displacement design spectrum based on equal displacement approximation is proposed for the Hinged Wall with BRBs at Base (HWBB) structural system. HWBB is simplified as an Equivalent Single Degree of Freedom (ESDOF) system. Design flowcharts are given. The proposed design approach aims to limit the lateral displacements to an allowable target displacement. Design examples are presented and target displacements are compared with numerical results. The results indicate that the plastic response of the HWBB structural system is accurately predicted by the elastic displacement spectrum, which verified that the performance-based design method of HWBB is accurate.

Influence of masonry infills on seismic performance of BRB‐retrofitted low‐ductile RC frames

AbstractReinforced concrete (RC) frames with masonry infills represent a prevalent construction typology across the globe, including moderate to high seismic regions. Such structures are often characterized by high seismic vulnerability, and consequently, there is an urgent need for retrofit solutions to effectively improve their seismic performance. Buckling‐restrained braces (BRBs) represent one such solution. They are a type of dissipative device that can be included within the frames of an existing structure to increase its strength, stiffness, and energy dissipation capacity. Although a substantial amount of research has already been performed to understand the effectiveness of BRBs as a retrofit strategy, these studies have often neglected the contribution of masonry infills and the interactions between the infills and the BRBs. While masonry infills are usually overlooked in the analysis and design stage (owing to their brittle nature), past studies indicated that their strength and stiffness may significantly alter the structure's seismic performance, leading to undesirable and unexpected results. This study presents a detailed investigation of the impact of masonry infills on the seismic response and fragility of BRB‐retrofitted RC frames. A three‐story, three‐bay, low‐ductile RC frame has been selected for case study purposes. High‐fidelity finite element models are developed in OpenSees for combinations of infilled and non‐infilled structures—with and without BRBs. Nonlinear static and dynamic analyses are performed to evaluate the seismic response of the different configurations at local and global levels. Successively, cloud analyses are conducted by considering a set of 150 ground motion records to account for the record‐to‐record variability and develop seismic fragility curves. The present study sheds some light on the mutual interaction between the infill panels and BRBs retrofit intervention and highlights the critical aspects that must be considered in the design.

Seismic analysis of bridge with buckling‐restrained brace posttensioned concrete pier

AbstractA two‐span bridge built with a two‐column pier consisting of unbonded posttensioned precast concrete columns and a buckling‐restrained brace (BRB) is analyzed using a three‐dimensional nonlinear numerical model. Seismic damage to the pier is eliminated through rocking of the posttensioned columns and seismic energy dissipation by the BRB. The numerical model is calibrated with experimental results of posttensioned columns and BRB structural elements. Seismic assessment of the bridge pier is performed using the ratio of BRB axial force to base shear as the parameter of interest. Limits for the seismic performance of the bridge pier are established by means of nonlinear static analysis using OpenSees. Bidirectional ground motions are used to perform probabilistic hazard analysis through nonlinear time history simulations. Three damage limit states are defined in this research: the activation point of posttensioning bars, the maximum base shear capacity or onset of concrete spalling, and collapse defined as the state at 20% loss of maximum base shear capacity. The analysis results are formulated into fragility curves for the three damage states as well as the residual drift. The fragility curves could be used for preliminary seismic bridge design. The analysis shows that the BRB dissipates significant seismic energy and the posttensioned concrete columns reduce residual displacements so that the bridge pier can remain functional after severe earthquakes. The fragility approach for designing bridge piers constructed with posttensioned concrete columns and BRB elements is a significant improvement over conventional seismic bridge design and can contribute to functional recovery after severe earthquakes.

Evaluation of blast-induced progressive collapse in steel structures with conventional braces, moment-resisting braces, and buckling-restrained braces using LS-DYNA software

Today, considering the increased cases of terroristic operations, structural design engineers are starting to acknowledge blast-induced loads alongside other design parameters. Since a blast-induced load exhibits a much shorter period than the natural period of the structure, it is unlikely to induce general damages or stimulate the entire structure immediately after the loading, but rather local damages in individual structural elements are the common form of damage. These local damages, however, can set the scene for the gradual failure of the structure. The present study on structures with moment-resisting frames, buckling-restrained braces (BRBs), and conventional steel braces was conducted through an alternative load path (ALP, also known as column elimination) and exact modeling of the blast on the steel frames was undertaken using LS-DYNA software. In this work, the behavior of three five-story steel frames under a blast-induced load of 100 kg TNT equivalent at a distance of 10 m from the structural columns for a period of 100 ms was investigated. Results of analyzing the blast-induced effect on the frames showed that the frame equipped with buckling-restrained braces (BRB) exhibited improved overall peak displacement across the entire frame, peak induced velocity, and peak induced acceleration by 30%, 30%, and 46%, respectively, as compared to other steel frames exposed to blast loads.

Risk Assessment of Overturning of Freestanding Non-Structural Building Contents in Buckling-Restrained Braced Frames

The increasing demand in structural engineering now extends beyond collapse prevention to encompass business continuity planning (BCP). In response, energy dissipation devices have garnered significant attention for building response control. Among these, buckling-restrained braces (BRBs) are particularly favored due to their stable hysteretic behavior and well-established design provisions. However, BCP also necessitates the prevention of furniture overturning—an area that remains quantitatively underexplored in the context of buckling-restrained braced frames (BRBFs). Addressing this gap, this research designs BRBFs using various design criteria and performs incremental dynamic analysis (IDA) with artificially generated seismic waves. The results are compared with previously developed fragility curves for furniture overturning under different BRB design conditions. The findings demonstrate that the fragility of furniture overturning can be mitigated by a natural frequency shift, which alters the threshold of critical peak floor acceleration. These results, combined with hazard curves obtained from various locations across Japan, quantify the mean annual frequency of furniture overturning. The study reveals that increased floor acceleration in stiffer BRBFs can lead to a 3.8-fold higher risk of furniture overturning compared to frames without BRBs. This heightened risk also arises from the greater hazards at shorter natural periods due to stricter response reduction demands. The probabilistic risk analysis, which integrates fragility and hazard assessments, provides deeper insights into the evaluation of BCP.

Development of Novel Buckling-Restrained Steel Braces Enabled by Partial Induction Hardening

Development of Novel Buckling-Restrained Steel Braces Enabled by Partial Induction Hardening

Full-Scale Testing of Two-Tiered Steel Buckling-Restrained Braced Frames

Full-Scale Testing of Two-Tiered Steel Buckling-Restrained Braced Frames

Experimental and numerical study of buckling-restrained braces configured with out-of-plane eccentricity under cyclic loading

Experimental and numerical study of buckling-restrained braces configured with out-of-plane eccentricity under cyclic loading

Seismic Local Buckling Limits for Hollow Structural Section and Built-Up Box Columns

Recently completed research on seismic local buckling limits for steel hollow structural section (HSS) and built-up box columns is featured. These National Center for Research on Earthquake Engineering (NCREE) studies are led by Dr. Chung-Che Chou and Dr. Tung-Yu Wu in the Department of Civil Engineering at National Taiwan University (NTU). Dr. Chou also serves as the NCREE Director. Dr. Chou’s research has focused on seismic testing, analysis, and design for steel and post-tensioned self-centering structures. Some recent work includes studies on hybrid simulation of a full-scale steel moment frame, a post-tensioned self-centering brace, novel prediction models for early earthquake warnings, and earthquake reconnaissance work in eastern Taiwan. Dr. Chou’s numerous accolades include the Awards for Excellent Research and Technology Transfers for his leadership on a research team developing a sandwiched buckling-restrained brace and a self-centering brace. Dr. Wu’s research interests include collapse behavior of cold-formed HSS columns under seismic loading, subwavelength seismic metamaterial structures, crack growth in railway crossings under high wheel-rail impacts, and seismic resilience of steel buildings. In addition to multiple scholarships and fellowships, Dr. Wu’s honors include the Raymond C. Reese Research Prize, awarded by the American Society of Civil Engineers (ASCE) for papers representing notable achievements in research with impact on design. The National Science and Technology Council is supporting this research on seismic local buckling limits for HSS and built-up box columns. Selected highlights from both projects are presented, along with a preview of future research tasks.

Study on the load capacity of prefabricated buckling-restrained braces with ductile steel castings based on singular function

Prefabricated buckling-restrained braces with ductile steel castings were used in the special concentrically braced frames to enable brace yield without buckling and prevent brittle failure of brace joints. This study presents a simplified three-segment calculation model subjected to axial force, based on the failure mode of the bracing system, utilizing singular function to derive formulas for the ultimate capacity of the braces. The accuracy of the computational formula was validated through numerical simulations and experimental findings. The outcomes indicate that the core unit of the brace undergoes third-order buckling deformation under axial force. The ultimate capacity of the braces is observed to increase with the cross-sectional area of the core unit but decrease with the length of the ductile steel castings. The theoretical values of the ultimate bearing capacity of the bracing system closely align with numerical simulations and experimental results, with error margins of 2.9 % to 9.3 % and 3.2 % to 4.6 %, respectively. These findings offer a theoretical foundation for the stability assessment of such brace configurations.

Fatigue Analysis of BRB Weld under Low Period and Large Deformation based on DIC Technology

This paper conducts an in-depth study on the fatigue performance of buckling-restrained braces (BRBs) under low-cycle large deformation conditions. As a device that utilizes the hysteretic energy dissipation of metal yielding, BRBs have been widely used in the design of new structures and the seismic strengthening of existing structures. Its remarkable advantages include stable performance, convenient fabrication, low cost, and excellent hysteretic performance. Applying DIC technology to the fatigue analysis of BRB welds under low-cycle large deformation can achieve full-field measurement of deformation and stress at the weld, providing strong technical support for in-depth study on the fatigue performance of BRB welds.

Seismic assessment of glulam frames with dual-tube self-centering buckling-restrained braces

The development of resilient lateral load-resisting systems is essential for multi-story and high-rise timber buildings in earthquake-prone areas. In this paper, an attempt is made to integrate dual-tube self-centering buckling-restrained braces (DT-SCBRBs) to glulam frames, aiming to improve their structural resilience to earthquakes. To assess the seismic effectiveness of such a DT-SCBRB glulam frame, nonlinear time-history analyses (NLTHAs) were conducted on a series of prototype DT-SCBRB glulam frames with different building heights and design parameters of DT-SCBRBs. The seismic performance of these prototype structures was evaluated in terms of maximum inter-story drift ratios (MaxISDRs), residual inter-story drift ratios (ResISDRs), and inter-story drift uniformity. The results show that the frame with lower post-tensioning-to-yielding ratios of DT-SCBRBs tended to exhibit lower MaxISDRs but could sometimes lead to higher ResISDRs under major earthquakes. Low deformability of tendons could result in tendon fracture under major earthquakes. The ResISDRs of all the prototype frames were lower than 0.5 %, the drift limit for the “Repairable” performance level. Compared to minor and moderate earthquakes, the DT-SCBRB glulam frames deformed more uniformly during major earthquakes. Incremental dynamic analyses (IDAs) were also conducted on these prototype structures, developing a database to quantify performance levels of DT-SCBRB glulam frames. The MaxISDRs of 0.5 %, 0.7 %, and 2.6 % were recommended for immediate occupancy (IO), life safety (LS), and collapse prevention (CP) limit states of DT-SCBRB glulam frames.

Seismic Performance Evaluation of Two- and Three-Story Steel Frames with an Upgraded Hybrid Buckling-Restrained Brace

Seismic Performance Evaluation of Two- and Three-Story Steel Frames with an Upgraded Hybrid Buckling-Restrained Brace

Seismic Performance Assessment of Multitiered Steel Buckling-Restrained Braced Frames Designed to 2010 and 2022 AISC Seismic Provisions

Seismic Performance Assessment of Multitiered Steel Buckling-Restrained Braced Frames Designed to 2010 and 2022 AISC Seismic Provisions

Pseudo-Static Test of Buckling-Restrained Braces Using Friction Energy Consumption

Pseudo-Static Test of Buckling-Restrained Braces Using Friction Energy Consumption

Recovery resilience framework of replaceable AB-BRB for seismic strengthening during the aftershock stage

Earthquakes cause serious damage to structures, and seismic strengthening is an effective solution to improving structural capacity. With the development of prefabricated technology, the assembled buckling-restrained braces (BRBs) have garnered significant attention in structural engineering due to their potentials to enhance seismic resilience and to guarantee recoverability behavior. At this stage, research on the replaceable performance of assembled BRBs is limited in the current body of literature. The specific focus on the replaceability aspect of assembled BRBs, including the ease of replacing individual components or the entire brace system, has not been extensively explored. Meanwhile, research on earthquake resilience during the aftershock stage is relatively limited at present. Despite the recognition of the significant and prolonged impact of aftershocks on communities and infrastructure, there is a paucity of comprehensive studies specifically focusing on the resilience strategies and measures required during this stage. The authors formerly proposed a novel assembled bolt-connected BRB (AB-BRB), and experiments have been conducted to verify its hysteretic and replaceable behaviors. In this paper, the recovery resilience of the proposed replaceable AB-BRB for seismic strengthening is further assessed, especially during the aftershock stage. The replacement realization of AB-BRB in analysis is first introduced. Then the recovery resilience framework for assessment during the aftershock stage is proposed. Finally an implementary example is given to perform the recovery resilience framework, in which two cases and three scenarios are discussed in detail. In general, after using the AB-BRB for seismic strengthening, the recovery time obviously decreases and the resilience index obviously increases when compared with the results in un-strengthened scenario (scenario 3), which demonstrates that the retrofitted system possesses a better resilience recovery capacity. For EEL in case 1, the recovery days are given to be 298.7446 before strengthening (scenario 3), and the results drop to 165.4133 (scenario 1) and 147.0295 (scenario 2) after strengthening. Correspondingly, the resilience index is calculated as 0.5022 before strengthening (scenario 3), and the results increase to 0.7101 (scenario 1) and 0.7411 (scenario 2) after strengthening. Similar conclusions can be given for case 2 and other intensity levels. Meanwhile, after performing the replacement operation of AB-BRB (scenario 2), the seismic performance of the retrofitted system further enhances during the aftershock stage (i.e., less recovery days and larger resilience index). For case 1 and recovery form 1, the resilience index for 1 month is signified as 0.6272, 0.6869 and 0.2066 from scenario 1 to 3, and the resilience index for 3 months is signified as 0.8182, 0.8561 and 0.4965 from scenario 1 to 3. Compared with scenario 1, the recovery ability in scenario 2 is further ensured and the potential risk is further controlled, which demonstrates the importance of replaceable capacity of AB-BRB for resilience improvement especially during the aftershock stage.

Delayed-Action Mechanism of Buckling-Restrained Brace Using Gusset Plates with Multiple Slot Holes

Delayed-Action Mechanism of Buckling-Restrained Brace Using Gusset Plates with Multiple Slot Holes

Effect of loading sequence on the ultra-low-cycle fatigue performance of all-steel BRBs

Buckling-restrained braces (BRBs) are intended to protect the primary structure of buildings by absorbing most earthquake input energy through the plastic deformation of the steel cores. The ultra-low-cycle fatigue performance of BRBs is crucial for their seismic performance as energy dissipators. Despite the plenty of research on the ultra-low-cycle fatigue behavior of steel members, it remains susceptible if arbitrary loading paths have a major effect on the ultra-low-cycle fatigue life or cumulative plastic deformation (CPD) capacity of BRBs. This paper introduces an experimental campaign of nine supposedly identical BRB specimens subjected to three different loading protocols of similar average strain amplitudes. For each loading protocol, the test was repeated for three times to account for possible uncertainty. The results show that the effect of loading protocol is trivial given the similar average strain amplitudes throughout the loading. The Miner's assumption that the loading sequence has no effect on the fatigue life of BRBs is supported by the test results, however, the proper choice of the Coffin-Masson model's parameters is crucial. The skeleton ratio, which is derived from decomposing the hysteresis curve into a skeleton part and a Bauschinger part and has been used to account for the loading path effects, is shown to be insensitive to varied loading protocols by the test results.