Steel Buckling-restrained Braces Research Articles

Comparative Analysis of Concentrically Braced Frames with FeSMA and Steel BRBs Under Long-Duration Earthquakes

ABSTRACT Owing to high fatigue life, the iron-based shape memory alloy (FeSMA) buckling-restrained braces (BRBs) are emerging as a promising candidate against long-duration earthquakes. However, the corresponding analysis cannot be found. Current emphasis is paid on unveiling the seismic response differences between concentrically braced frames (CBFs) with FeSMA and steel BRBs when they are attacked by long-duration earthquakes. To directly assess the effect of earthquake duration, this paper selects a total of 90 pairs of short- and long-duration earthquake records, which are record-to-record spectrally equivalent over a wide range of fundamental periods, for nonlinear time history analysis. A benchmark six-story CBF is selected for demonstration purposes. In the numerical simulation process, the fatigue-induced damage is particularly considered. A preliminary examination is first conducted in the case study, in which a representative pair of short- and long-duration records is selected. In what followed, the statistical results from the ground motion suites are analyzed. This work not only highlights the higher failure risk of steel BRBs than FeSMA BRBs under long-duration earthquakes associated with maximum considered earthquake hazard level, but also confirms the advantages of FeSMA BRBs over steel BRBs in controlling residual deformations.

Effect of Pre-tensioning Force on Behavior of Buckling Restrained Brace (BRB) Supported by Double Pre-tensioning System

The study explores the feasibility of a new all-steel buckling restrained brace (BRB) with the double pre-tensioning system as an alternative to conventional concentrically braced frames by using finite element method (ABAQUS program), And to verify modeling, use U-V1 specimen results and compare them with test results. The restraining element in an all-steel BRB is built from a rectangular plate with a double cross arm and cables, making it easy to fabricate, inspect, and replace after a severe earthquake. Numerical analyses were conducted on four groups: first group of specimens using dynamic loading to achieve the minimum thickness for stable hysteretic behavior and high efficiency for BRB, and three groups of specimens using monotonic loading to achieve the best pre-tensioning forces value in steel 37, 44 and 52 for greater efficient use of all steel BRB. The results showed a 66% improvement in bearing capacity, with the external restraining case thickness reduced to 20 mm, making it lightweight, economical, and easy to maintain. The specimens with a pre-tensioning force of 70 kN, 50 kN and 40 kN providing a 31%, 51% and 73.2 % for steel 37, 44 and 52 respectively over than the design specimen without pre-tensioning system.

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.

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 study on cyclic behaviour of low yield point steel buckling-restrained braces

Low yield point steel is an advanced high-performance material that was deemed to provide reliable cyclic properties based on previous research. This paper presents experimental investigations into low yield point steel buckling-restrained braces (BRBs). Cyclic tests were conducted on nine full-scale specimens made of three grades of low yield point steels in China, including LY100, LY160, and LY225, with the nominal yield strengths of 100 MPa, 160 MPa, and 225 MPa, respectively. The failure modes, hysteresis behaviour, and mechanical indexes were analysed. Results showed that low yield point steel BRBs featured cyclic hardening behaviour with the strain hardening adjustment factor ω of 1.35–2.94, and the LY100 BRB exhibited more significant cyclic hardening (ω = 2.50–2.94) than the other two. Moreover, specimens showed tension–compression asymmetry behaviour with the compression strength adjustment factor β of 1.07–1.51, proving that the maximum compressive loads exceeded 7–51 % of tensile ones. The low yield point steel BRBs could produce stable cyclic behaviour and energy dissipation with the cumulative ductility factor of 491.16–3279.23 upon the acceptance stipulated in American and Chinese codes. Based on the test results, the performance of low yield point steel BRBs was evaluated, and suggestions were proposed for design purposes.

Damage-control design and hybrid tests of a full-scale two-story buckling-restrained braced steel moment frame with sliding gusset connections

Buckling-restrained braces (BRBs) are widely adopted as supplementary energy dissipation devices in steel moment frames (MFs) in Asia to improve the energy dissipation capacity of the whole system. Such systems are referred to as buckling-restrained braced moment frames (BRB-MFs). Nevertheless, adopting BRBs does not guarantee desirable seismic performance of the whole system, as frame action may cause premature fracture or buckling of BRB corner gusset connections, and such frame-to-gusset interaction may limit the ductility of such system. In our previous studies, a sliding corner gusset connection was proposed and proved to be able to substantially reduce the detrimental frame action at the connection level. In this paper, study was extended to (1) damage-control design of BRB-MFs with such connections in pursuit of enhanced system ductility, and (2) experimental evaluation on seismic behavior of BRB-MFs with such connections at the system level. The damage-control design method was first presented and a full-scale two-story BRB-MF designed by such procedure was experimentally studied under four levels of earthquake loading through hybrid tests, followed by a pseudo-static test to examine its failure mode. Test results showed that the sliding gusset connections effectively released the frame action at the system level. By adopting the damage-control design procedure, the test BRB-MF exhibited excellent seismic performance up to an inter-story drift ratio of ± 3 %, and plastic hinges of the MFs developed in the controlled positions without fracture or buckling under four levels of earthquake loading. With the improved ductility of MFs, BRBs achieved their full potential as energy dissipation devices.

Study on numerical seismic performance evaluation of 3D building frame with smart self-centering BRBs system

Structures are generally designed to withstand the applied loads safely. However, in order to secure the stability of structures from earthquakes, which are unpredictable natural disasters, seismic damage reduction technology is required, and various technologies are being developed so far. Recently, to resist seismic loads, new materials are used to reinforce structural members, or technologies to control vibration by applying seismic devices are being developed. In particular, Shape Memory Alloy (SMA), also known as a smart alloy, has a unique re-centering capacity that exhibits a flag-shaped hysteresis curve, so when applied in a structural system, it can provide safer structural performance with higher serviceability. In this study, to prove the structural stability of the SMA buckling restrained brace (BRB) system to which the seismic isolation is applied, a study was conducted to evaluate the seismic performance according to the structural material, type, and device. Response of SMA BRB and base isolation system has been calibrated by following quasi-static and dynamic loading test and substantially matches empirical results. A prototype steel frame has been designed by following standard code which has a single-story basement assumed to be surround by well graded sandy soil. In addition, two different column system has been considered namely as, Hollow Steel Section (HSS) and Concrete Filled Steel Tubes (CFST). For the nonlinear dynamic analysis, two sets of 11 bidirectional artificial earthquakes were considered, and the interstory drift ratio (IDR) and residual interstory drift ratio (RIDR) were considered as main performance evaluation parameters. In moderate ground motion, the performance of the SMA BRB was found to be higher compared to the steel BRB and base isolation system due to its superior self-centering capacity. However, in strong ground motions, periodic damage degrades the performance of the SMA BRB, which was found to be nearly identical to the steel BRB, but still superior to the base isolation system. This performance evaluation study will help to understand design aspects of seismic protection systems for similar types of building frames.

Experimental study on triple grades hybrid high-performance steel structure (TGHSS): Members and joints

The triple grades hybrid high-performance steel structure (TGHSS) is an innovative structural system with excellent seismic behaviour proposed by the authors. The TGHSS comprises high strength steel columns, ordinary strength steel beams, and low yield point steel buckling-restrained braces (BRBs). In full-scale cyclic tests on eight single-bay two-story specimens, strains on surfaces of beams, columns, and joints were extensively monitored, and deformations of BRBs at both stories were recorded. The global responses of TGHSSs were introduced and discussed in the first companion paper. This paper focuses on the local responses of members and joints under real boundary conditions in structures, which is deemed to provide more reasonable performance evaluations than independent tests on extracted specimens. The force analyses of beams, columns, and joints were conducted. The hysteresis behaviour, mechanical indexes, energy dissipation, and end rotation of BRBs were studied. Moreover, the plastic development sequences were obtained and discussed following the above contents. Results showed that the low yield point BRBs could provide reliable cyclic behaviour and energy dissipation with the cumulative ductility factor of 312.03 ∼ 1191.74, meeting the requirement in American and Chinese codes. The ordinary strength steel beams produced plastic hinges with considerable rotations of at least 0.02 rad. The high strength steel columns exhibited limited plasticity, especially the panel zones in beam-to-column joints almost kept elastic. Results revealed that the TGHSS featured a sequential plastic development as expected from BRBs to beams and then to columns. Following the test results, some design suggestions were proposed for TGHSSs.

Seismic performance of knee-braced frames equipped with NiTi BRBs

Knee braces (KBs) are often installed at locations near to the beam-to-column connections in frames. In comparison to concentrical and eccentrical braces, KBs have advantages of occupying less space, less affecting the architectural view, and ease of installing and replacing if necessary. As a comparative analysis, this paper evaluates the seismic performance of knee braced frames (KBFs) equipped with steel or NiTi buckling-restrained braces (BRB). Through machining raw bars into bamboo shape, this paper fabricated two types of KBs and conducted cyclic loading tests on reduced-scale specimens. The testing results show that both KBs have stable cyclic properties under loading reversals. The steel BRB has typical elasto-plastic hysteresis, whereas the NiTi BRB has a flag-shape hysteresis. At the system level, the 3- and 6- story KBFs were first designed by performance-based plastic design (PBPD) method and then subjected to a suite of earthquake records. It indicated that the KBFs equipped with either steel or NiTi BRBs can well meet the prescribed drift target. The major advantage of NiTi BRBs over steel BRBs is that they successfully eliminated residual drift ratios for the protected frames, which means the KBFs with NiTi BRBs have higher seismic resilience.

Development of triple grades hybrid high-performance steel structure (TGHSS): Concept and experiments

To develop an innovative steel structural system with excellent seismic performance, this paper proposed triple grades hybrid high-performance steel structures (TGHSSs), composed of high strength steel columns, ordinary strength steel beams, and low yield point steel buckling-restrained braces (BRBs). The basic concept was introduced, and then eight full-scale specimens were tested under cyclic loads to validate their seismic behaviour. All the specimens were single-bay and two-story, in which seven specimens are TGHSSs, and a benchmark specimen utilised ordinary strength steel columns for comparisons. In TGHSS specimens, columns included three grades of high strength steel (i.e., 460 MPa, 690 MPa, and 890 MPa), beams utilised 345 MPa steel, and BRBs included three grades of low yield point steel (i.e., 100 MPa, 160 MPa, and 225 MPa). Test observations and structural responses were analysed, involving failure modes, hysteresis behaviour, loading resistance, lateral stiffness, deformation responses, and energy dissipation. The results showed that the TGHSS fulfilled a sequential yielding mechanism as expected with satisfactory seismic behaviour. Specifically, the low yield point steel BRBs yielded at first (overall drift ratio 1/820-1/420) to dissipate seismic energy. Then, the ordinary strength steel beams developed plastic hinges at beam ends (approximate overall drift ratio 2%). At last, the high strength steel columns kept almost elastic or only presented limited plasticity at column bases. Results demonstrated that the proposed TGHSS has strong potential to be an alternative structural system in seismic areas and provides feasible solutions for high-performance structures made of steel having multiple strength grades.

Seismic performance analysis of multi-story steel frames equipped with FeSMA BRBs

Buckling-restrained braces (BRBs) have been widely used in seismic prone areas around the world. However, one major problem associated with the steel BRB frames is the excessive residual deformation under strong earthquakes, mainly due to the low post-yield stiffness ratio of the steel BRBs. Recently, the community has fabricated the iron-based shape memory alloy (FeSMA) BRBs, which exhibited full hysteresis with high post-yield stiffness ratios, but the seismic behavior of the FeSMA BRB frames still remains unknown. As such, this paper conducts seismic performance analysis of multi-story steel frames equipped with the FeSMA BRBs, through a comparison with those equipped with conventional steel BRBs. Incremental dynamic analysis (IDA) is further conducted to establish the probability seismic demand models. Based on the IDA data, bivariate fragility analysis is conducted to quantify the probability of exceedance, conditioned on various limitations of the maximum and residual interstory drift ratios. According to current analysis, it indicates that both the maximum interstory drift ratios and the maximum floor accelerations are comparable between these two types of BRB frames. The major advantage of the FeSMA BRBs over the steel BRBs is that the former can better control residual interstory drift ratios.

The effect of design parameters on mechanical performance of all-steel buckling restrained brace with double steel tubes

To explore the effect of design parameters on the mechanical performance of the proposed all-steel buckling-restrained brace (BRB), the finite element software ABAQUS is adopted. The brace consists of an inner round steel tube and an outer square steel tube to restrain its inner core, designed with both the cruciform-section core and the H-section steel core. Quasi-static tests are performed on the all-steel BRB to explore its energy dissipation capacity. The cyclic behavior of the specimen models is evaluated. The validity of the numerical model is verified by comparing the predicted results with the experimental results. Next, the effects of three parameters on the mechanical properties of the brace—the width-thickness ratio of the inner core, the clearance between the inner core and the inner round steel tube c1, and the constraint ratio—are investigated by the validated numerical model. The width-thickness ratio varies from 6 to 20, the gap value ranges from 1 to 7 mm, and the constraint ratio ranges from 0.43 to 1.03. Results show that the hysteresis curves of the two braces are full, with stable hysteretic performance and good energy dissipation capacity, which justifies the construction. Based on the parameters analysis results, the optimum values of the width-thickness ratio, gap, and constraint ratio have been recommended for steel BRBs.

Terminus, Vancouver Island: solving a mass timber challenge in a seismic region

This article describes the design and construction of a five-storey commercial building featuring a novel steel buckling-restrained brace lateral system framed within its mass timber superstructure.

Design of an eccentrically buckling-restrained braced steel frame with web-bolted replaceable links

In this paper, an improved buckling-restrained brace is proposed to replace the traditional brace, and the links of the eccentrically braced steel frames are separated from the beams, forming a new structure system—namely, an eccentrically buckling-restrained braced frame with web-bolted replaceable links. As an independent component, the replaceable link can achieve the goal of confining the inelastic deformation to itself, while being easily replaced after intense earthquakes. Further, the improved buckling-restrained brace acts as a supplementary energy-dissipation member to ensure the energy-dissipation performance of the replaceable link. In this paper, ten web-bolted replaceable-link replacement tests were carried out with 1/3-scale eccentrically buckling-restrained braced steel frames under quasi-static cyclic loading. We analyze the seismic performance of the structure and evaluate the replaceability of the links. The results show that the number and spacing of the stiffeners and the length ratio of the links have a strong influence on the failure mode and energy-dissipation performance of the structure. In addition, we verified the feasibility of repair and replacement through replacement tests, showing that the replaceable link can act as a ‘structural fuse’

Seismic performance of buckling-restrained braced steel frames subjected to earthquake main shock-aftershock sequences

Recently, there are many papers report the development of some new buckling-restrained braced (BRB) frames and the evaluation of its characteristics. At the same time self-centering buckling-restrained braced (SCBRB) frames are considered as new solutions for the increasing of the structural resilience. In this thesis, the seismic performance of structures is analyzed subjected to earthquake main shock-aftershock sequences. There is comparison of two types of the additional BRB elements, and also there is comparison between them and original steel frame to show the effect of using BRB and SCBRB elements. To compare the seismic performance of BRBF and SCBRBF, the same main shock-aftershock sequences were used in this part. Because of the flag-shaped hysteretic curve of the SCBRB elements, big amount of the energy was dissipated during the motion. Compared to steel frame, smaller seismic responses and residual deformation occurred the structure. BRBF and SCBRBF can control the seismic responses effectively due to the energy dissipation of BRB, and SCBRB can also reduce the structural residual deformation. The earthquake aftershock after earthquake main shock can increase the structural damage and enlarge the structural seismic responses.

Numerical Analysis of Steel Buckling-Restrained Braces with Varying Lengths, Gaps, and Stoppers

AbstractThe conventional buckling type of brace members offers lateral stiffness to the structural system; however, such members are likely to yield under tension and buckle under compression when ...

Dynamic response of multi-story buckling-restrained braced steel frames with different β values

The average shear-bearing ratio (β) of buckling restrained brace (BRB) is a key parameter, affecting the seismic performance of buckling restrained braced steel frames (BRBF). In order to determine the dynamic response of multi-story BRBF with different β values, two kinds of structural models are established, one is with the rigid connection of beam-column joints, and the other model has both hinged and rigid joints. The nonlinear time-history analysis of multi-story BRBF structures are carried out by selecting the seismic waves with predominant period close to the first mode period of each research model, and the seismic waves that are significantly different from it. The influence of β on the shear displacement, bending displacement and vibration mode of the structure are revealed: when β ≤ 30%, the story drift of multi-story BRBF structure is mainly shear deformation and the first vibration mode is predominant. When β increases, the bending deformation of the story drift increases. The second vibration mode of the structure is predominant when β ≈ 90%. It is suggested that the equivalent seismic force of multi-story BRBF structure with β > 30% should not be calculated by the base shear force method.

Subassemblage test and gusset rotation response of buckling-restrained braced steel frames

Gusset rotation would cause adverse influence on the buckling-restrained brace (BRB) end zone and even lead to premature buckling of the BRB end zone. However, limited studies to date referred to the gusset rotation response. To evaluate the cyclic behavior and gusset rotation response, five 1/2-scaled buckling-restrained braced frame (BRBF) subassemblages with various gusset connections, i.e., pinned gusset connection, bolted gusset connection, welded gusset connection, pinned-welded gusset connection, and pinned-bolted gusset connection, were conducted under horizontal cyclic loading. The effects of gusset connection type on the failure modes, horizontal initial stiffness, energy dissipation and rotation response of specimens were analyzed in detail. It showed that all specimens performed plump and stable hysteresis behavior. The upper gusset rotation of the specimen with pinned gusset connection was larger than that of bolted gusset connection, followed by welded connection. Meanwhile, the finite element (FE) models were established and validated by test results. Furthermore, the standard FE model of a full-scale one-story one-bay steel moment BRBF with a single diagonal BRB was developed and then extended to a large number of models to investigate the contribution of various parameters on the upper gusset rotation. Finally, the gusset rotational formulae for predicting its response, as the steel moment BRBF reached to either 2.0% or 3.0% drift, were proposed on the basis of the results of the extensive parametric analysis. It could be used to determine the rotation of the BRB end zone, and the flexural moment acting on the BRB end zone and corresponding practical design procedure can be finally derived to avoid the potential premature failure of the BRB end zone.

Seismic Performance Analysis of Buckling-Restrained Braced Steel Frames with Ductile Castings

Buckling-restrained brace (BRB) steel frames with ductile castings are proposed to solve the fracture failure of welded joints between buckling-restrained braces and frames after rare earthquakes. In this paper, quasi-static tests are conducted on two one-story, one-bay steel frames to study their mechanical behaviors, including stress distribution, failure mode, energy dissipation, and skeleton curve, and finite element models are established for verification. Subsequently, 22 models with different parameters of the BRB steel frames with ductile castings are analyzed using ABAQUS. Results indicate that the new frame system has good energy dissipation; it can confine the inelastic deformation of the structure to the ductile castings and BRB. It also satisfies the 1/50 maximum elastic-plastic drift angle set by the Code for Seismic Design of Buildings. The BRB with ductile castings connected to the frames by bolts can relieve the stress distribution in the beam-column region, which can be assembled and replaced after the earthquake.

A new stiffness-strength-relationship-based design approach for global buckling prevention of buckling-restrained braces

This paper proposes a new stiffness-strength-relationship-based design approach that can pinpoint the target design solution for steel buckling-restrained braces (BRB). First, a stiffness–strength requirement interaction curve (the design criterion) with a very simple and easy-to-use form is derived based on a second-order analysis. This interaction curve clearly illustrates the opposing stiffness and strength requirements of the restraining system. Second, based on the geometrical parameters and material properties, a stiffness–strength relationship curve of the BRB restraining system is established. This second relationship curve is expressed by a linear function for a uniform steel BRB. By using the two analytical curves, the point of intersection defines the target design point. A straightforward design procedure for steel BRBs is then developed. A design example of steel BRBs is considered to demonstrate this easy-to-use design procedure for obtaining economical BRB designs. The design is verified and discussed by a rigorous finite element analysis.