Self-centering Brace Research Articles

Experimental evaluation of large-scale dual-core self-centering braces and sandwiched buckling-restrained braces

This paper presents structural characteristics of large-scale dual-core self-centering braces (DC-SCBs) and sandwiched buckling-restrained braces (SBRBs) in a series of cyclic tests. The DC-SCB has a flag-shaped hysteretic response with high axial stiffness and minimal residual deformation, exhibiting a self-centering mechanism. The SBRB as conventional BRBs has much higher energy dissipation capacity than the DC-SCB, but larger residual deformations are expected for structures equipped with SBRBs. The primary objective of the research was to conduct experimental studies that established a direct comparison basis between DC-SCBs and SBRBs designed with similar axial capacity and length. Three SCBs and SBRBs that were about 7.5m long and had maximum axial forces from 1500 to 6000kN were tested to evaluate their cyclic behavior and durability. In general, these tests have shown that the DC-SCB and SBRB exhibit robust cyclic performances with good deformation capacity and durability. The axial elastic and post-elastic stiffnesses of DC-SCB were around two and five times those of SBRB, indicating that the DC-SCB is more effective to resist lateral forces than the SBRB in structures, but the energy dissipation of DC-SCB was around one-third of that of SBRB.

Seismic design and tests of a full-scale one-story one-bay steel frame with a dual-core self-centering brace

Traditional seismic resisting systems in a large earthquake can experience significant damage and residual drifts due to energy dissipation of structural members, which leads to difficult or expensive repairs. A steel dual-core self-centering brace (DC-SCB), which utilizes three steel bracing members, two friction devices, and two sets of tensioning elements that are in a parallel arrangement for doubling its axial deformation, has been proposed and validated to provide both the energy dissipation and self-centering properties to seismic resisting systems. A prototype three-story steel dual-core self-centering braced frame (DC-SCBF) was designed, and its full-scale first-story one-bay DC-SCBF was tested to (1) validate the system response, (2) study force distributions in framing members as damage progresses in the DC-SCB, beam or columns, and (3) investigate the repair and replacement characteristics of the frame. The DC-SCBF subassembly specimen showed beam and column yielding at 1% lateral drift, beam local buckling at 1.5% lateral drift and no damage in the brace at 2% lateral drift; the residual drift that was caused by beam yielding or local buckling was 0.3–0.5% after multiple tests. Nonlinear time history analyses were performed on the prototype braced frame to obtain seismic demands under both design and maximum considerable levels of earthquakes.

High-mode effects on seismic performance of multi-story self-centering braced steel frames

Seismic-resisting, multi-story steel frames with self-centering braces (SCBs) are numerically investigated through pushover and incremental dynamic analyses. The seismic performance of self-centering braced frames (SC-BFs) is systematically compared with that of buckling-restrained braced frames (BRBFs), with emphasis on high-mode effect. The concentration of inter-story drift in the upper part of the buildings is more significant in SC-BFs than in BRBFs as a result of this effect. This high-mode effect strengthens with the increasing intensity of ground motions. Parametric studies indicate that increasing the post-yield stiffness ratio and/or energy dissipation capacity can successfully improve the seismic performance of SC-BFs, particularly in terms of limiting the high-mode effect. SC-BFs with enhanced post-yield stiffness and energy dissipation capacity exhibit relatively uniform inter-story drift ratios and reduced record-to-record variability in seismic performance.

Development of Steel Dual-Core Self-Centering Braces: Quasi-Static Cyclic Tests and Finite Element Analyses

This work presents mechanics, tests, and finite element analyses of a novel steel dual-core self-centering brace (SCB) with flag-shaped re-centering responses. The axial deformation capacity of the brace is doubled with respect to the SCED brace by serial deformations of two sets of parallel tensioning elements when both braces use the same tensioning elements. The mechanics of the brace is first explained; six tensioning elements and four dual-core SCBs are tested to evaluate their cyclic performance. The braces exhibit excellent performance up to a drift of 2% with a maximum axial force around 1,400 kN. The braces also survive 15 low-cycle fatigue tests at a drift of 1.5%. Tensioning elements fail when the braces are overloaded to 2.5–3% drift. Finite element analysis is conducted to further verify hysteretic responses of the dual-core SCB in cyclic tests. A design procedure for the proposed dual-core SCB is also included in the paper.

Comparative Investigation on the Seismic Performance of a Benchmark Steel Frame with Different Bracing Systems

Buckling-restrained braces (BRBs) and self-centering buckling-restrained braces (SC-BRBs) have been verified as novel energy dissipation bracing systems. This paper conducted a comparative investigation on the seismic-resisting performance of a Benchmark steel frame with these two types of bracing systems using the finite element analysis software OpenSEES. The analysis demonstrated that, in the equal-strength design principle, the SC-BRB frame results in weaker energy dissipation, bigger story drifts, and more evenly distributed story drifts along the building height compared to BRB frame. The residual deformations of SC-BRB frame under strong earthquakes are significantly smaller than the pure frame as well as BRB frame, but the maximum axial bracing force and floor accelerations are increased significantly for SC-BRB frame.

Development of a novel self-centering buckling-restrained brace with BFRP composite tendons

Buckling-restrained braces (BRBs) have excellent hysteretic behavior while buckling-restrained braced frames (BRBFs) are susceptible to residual lateral deformations. To address this drawback, a novel self-centering (SC) BRB with Basalt fiber reinforced polymer (BFRP) composite tendons is presented in this work. The configuration and mechanics of proposed BFRP-SC-BRBs are first discussed. Then an 1840-mm-long BFRP-SC-BRB specimen is fabricated and tested to verify its hysteric and self-centering performance. The tested specimen has an expected flag-shaped hysteresis character, showing a distinct self-centering tendency. During the test, the residual deformation of the specimen is only about 0.6 mm. The gap between anchorage plates and welding ends of bracing tubes performs as expected with the maximum opening value 6 mm when brace is in compression. The OpenSEES software is employed to conduct numerical analysis. Experiment results are used to validate the modeling methodology. Then the proposed numerical model is used to evaluate the influence of initial prestress, tendon diameter and core plate thickness on the performance of BFRP-SC-BRBs. Results show that both the increase of initial prestress and tendon diameters can obviously improve the self-centering effect of BFRP-SC-BRBs. With the increase of core plate thickness, the energy dissipation is improved while the residual deformation is generated when the core plate strength exceeds initial prestress force.

Development of cross-anchored dual-core self-centering braces for seismic resistance

The steel dual-core self-centering brace (SCB) is an innovative structural member that provides both energy dissipation and re-centering properties to structures, reducing the residual drift of braced structures in earthquakes. The axial deformation capacity of the brace is doubled by using two inner cores and one outer box and by serial axial deformations of two sets of parallel tensioning elements. The original dual-core SCB that used E-glass fiber tendons or T-700 carbon fiber tendons as tensioning elements exhibited good self-centering and energy dissipation up to an interstory drift of 2.5%. The new cross-anchored dual-core SCB halves the work required to apply the initial post-tensioning forces to tendons. The potential use of high-strength steel tendons as tensioning elements is studied herein, and the effects of the number of cycles on the brace behavior, energy dissipation, and durability of the steel tendon-anchorage system are also examined. First, the mechanics and cyclic behavior of the new brace are explained; a 7950mm-long cross-anchored dual-core SCB is then tested six times. The cross-anchored dual-core SCB exhibits excellent self-centering property up to a drift of 2.5% and a maximum axial load of 1700kN. No damage to the steel tendons, anchors or bracing members is found after three cyclic loading tests with increasing displacement amplitudes and 60 low-cycle fatigue tests. Finite element analysis further confirms the hysteretic responses and mechanics of the cross-anchored dual-core SCB in the cyclic test.

Steel braced frames with dual-core SCBs and sandwiched BRBs: Mechanics, modeling and seismic demands

A new steel dual-core self-centering brace (DC-SCB) is developed to have a flag-shaped re-centering hysteretic response under cyclic loads. Axial deformation capacity of the brace is doubled by serial deformations of two sets of tensioning elements arranged in parallel. In this paper, the mechanics of the new brace is first explained by considering a fabrication error of the member length, followed by testing one DC-SCB to evaluate its cyclic performance. The member length fabrication error, which is even 1/3000 times the brace length, significantly decreases the initial axial stiffness of the brace but does not affect the overall hysteretic behavior. Finite element analysis is conducted on the specimen to verify the mechanics and hysteretic responses observed in the test. Finite element analyses are also performed on other 16 DC-SCBs to evaluate how tensioning element types, initial post-tensioned force, and friction force affect the cyclic performance of the brace. Additionally, three braced frames of varying heights are designed using two bracing members, DC-SCBs and sandwiched buckling-restrained braces (BRBs). Nonlinear time history analyses are conducted on these braced frames to obtain seismic demands under both design and maximum considerable levels of earthquake motions and near-field motions. Self-centering braced frames generally exhibit smaller peak interstory drifts and residual drifts than buckling-restrained braced frames.

Seismic Performance and Application of Sandwiched Buckling-Restrained Braces and Dual-Core Self-Centering Braces

This paper first presents cyclic test results and the application of the proposed sandwiched buckling-restrained brace (BRB). The proposed BRB can be easily disassembled in the field. This provides an opportunity for inspection of the core after a large earthquake. The mechanics and cyclic behavior of a novel steel dual-core self-centering brace (SCB) are then proposed and introduced, followed by the testing of a dual-core SCB in order to evaluate its cyclic performance. Both braces achieve an excellent target lateral drift performance of up to 2.5%, thus satisfying the seismic requirement by the AISC Seismic Provisions 2010.

Low-Damage Earthquake-Resisting Systems Using Sandwiched Buckling-Restrained Braces and Dual-Core Self-Centering Braces

This paper presents a sandwiched buckling-restrained brace (BRB) and a dual-core self-centering brace (SCB) for seismic resistance. The sandwiched BRB has two components: (1) a steel core plate that carries axial forces and (2) two restraining members that sandwich the core plate with A490 bolts. The proposed BRB can be disassembled easily in the field, which not only means that the core plate can be replaced independently of the restraining members but also provides an opportunity for inspection of the core after a large earthquake. Cyclic tests of five sandwiched BRBs and five BRB frames were conducted to verify their good cyclic performances up to a drift of 2.5%. To minimize residual deformations of structural systems under earthquakes, a new steel dual-core self-centering brace (SCB) with flag-shaped hysteretic responses is developed. The axial deformation capacity of the SCB is doubled by serial deformations of two sets of tensioning elements arranged in parallel. The mechanics and cyclic behavior of the brace are first explained; three 5350-mm long dual-core SCBs are tested and modeled to evaluate their cyclic performances. SCBs exhibit excellent performance up to a drift of 2.5% with a maximum axial load of 1300 kN. Test results showed that the application of dual cores in SCBs reduces significant strain demands on tensioning elements and enables self-centering responses to large deformation. Nonlinear time history analyses were conducted on three BRB and SCB frames to obtain seismic demands under both design and maximum considerable levels of earthquake motions. SCB frames generally exhibit smaller peak interstory drifts and residual drifts than BRB frames.

Moving brick houses

Traditional seismic resisting systems in a large earthquake can experience significant damage and residual drifts due to energy dissipation of structural members, which leads to difficult or expensive repairs. A steel dual-core self-centering brace (DC-SCB), which utilizes three steel bracing members, two friction devices, and two sets of tensioning elements that are in a parallel arrangement for doubling its axial deformation, has been proposed and validated to provide both the energy dissipation and self-centering properties to seismic resisting systems. A prototype three-story steel dual-core self-centering braced frame (DC-SCBF) was designed, and its full-scale first-story one-bay DC-SCBF was tested to (1) validate the system response, (2) study force distributions in framing members as damage progresses in the DC-SCB, beam or columns, and (3) investigate the repair and replacement characteristics of the frame. The DC-SCBF subassembly specimen showed beam and column yielding at 1% lateral drift, beam local buckling at 1.5% lateral drift and no damage in the brace at 2% lateral drift; the residual drift that was caused by beam yielding or local buckling was 0.3–0.5% after multiple tests. Nonlinear time history analyses were performed on the prototype braced frame to obtain seismic demands under both design and maximum considerable levels of earthquakes.