Brace Buckling Research Articles

Modified bar-fuse damper in gusset plate detail to improve seismic behavior of bracing system

In this study, a cost-effective and efficient Bar-fuse damper (BFD) modified model is proposed to prevent the buckling and increase the ductility of the concentrically braced frame (CBF) along the longitudinal axis of the diagonal brace to the gusset plate. The step-by-step design of the model is presented in such a way that can dissipate seismic energy by inhibiting the brace buckling. In order to validate the finite element (FE) modeling, the experimental outcomes of a previously tested BFD device and the conventional CBF sample have been compared separately with the FE analysis results using ABAQUS software. To achieve the research goal, the details of combining four different BFD models in connection with the bottom gusset plate are presented and then the behavior of each of the combined systems under cyclic loading is evaluated using finite element modeling. Numerical analysis of various failure modes of the mentioned models showed that model No. 4 has an acceptable performance. One of the features of the proposed modified model is that the axial force is completely eliminated and as a result, the energy-absorbing of the BFD device is obtained only by the flexural plastic hinge formation in its bar-fuse components. Finally, the comparison between the force-displacement diagram of the hybrid system that includes model No. 4 and the results of the conventional CBF shows that this model has an acceptable seismic behavior. In addition, the simplification of the proposed model and its components are easily replaceable upon inelastic energy dissipation. This advantage makes the model known as repairable systems.

Experimental and numerical study of the seismic behavior of cold-formed steel walls with diagonal braces

In this paper, the seismic performance of cold-formed thin-walled steel walls with diagonal braces is studied by means of experiments and finite element analysis. In total, horizontal hysteretic loading tests were carried out on six full-scale cold-formed thin-walled steel walls. The influence of diagonal bracing, the screw spacing, wall panels and vertical loads on the seismic performance of the walls was investigated from the aspects of hysteretic curves, skeleton curves, the lateral stiffness degradation and the energy dissipation capacity. It was found that diagonal bracing could significantly improve the load-bearing capacity, stiffness, and energy dissipation capacity of the walls. However, the lateral resistance increased slightly because of premature buckling of the transverse braces at the connection between the diagonal and transverse braces. In addition, finite element models of the wall specimens were established by ABAQUS software and validated against the experimental data. A preliminary parametric study was also conducted to further examine the influence of essential parameters on the behavior of cold-formed steel walls with diagonal braces.

The Effect of Long Duration Earthquakes on the Overall Seismic Behavior of Steel Structures Designed According to Eurocode 8 Provisions

Premature and simultaneous buckling of several steel braces in steel structures due to the prolonged duration of a seismic motion is one of the issues that must be addressed in the next version of Eurocode 8. In an effort to contribute towards the improvement of the seismic design provisions of Eurocode 8, an evaluation of the overall behavior of some steel building-foundation systems under the action of long duration seismic motions is performed herein by means of nonlinear time-history seismic analyses, taking into account soil–structure interaction (SSI) effects. In particular, the maximum seismic response results—in terms of permanent interstorey drifts, overturning moments and base shears of the steel buildings as well as of the permanent settlement and tilting of their foundations—are computed. It is found that the seismic performance of steel buildings when subjected to long duration seismic motions is: (i) acceptable for the two and five-storey fixed base steel buildings and for the two-storey steel buildings with SSI effects included; (ii) unacceptable for the eight-storey fixed base steel buildings and for the five and eight-storey steel buildings with SSI effects included. In all cases of steel buildings with SSI effects included, the seismic performance of the mat foundation, as expressed by the computed values of residual settlement and tilting, is always acceptable.

Effect of steel braces buckling on inelastic torsion and design prevention of steel braced concrete frame structure

The influence of steel brace buckling on inelastic torsion of steel braced concrete frame structure is studied. On the background of a project, the shaking table test results of two structural models with ordinary steel brace (BRC) and buckling-restrained brace (BRB) are compared, and the inelastic torsion and sudden increase caused by steel brace buckling is confirmed. Finite element analysis models with BRC, BRB and floor load eccentricity are established, in which the restoring force model of steel brace considered the asymmetry of tensile and compressive bearing capacity, and the concrete beam and column members considered M3 and PMM hinge respectively to study the process and characteristics of the influence of BRC buckling on the nonlinear torsion of the structure. The mechanism of inelastic torsion of steel braced concrete frame structure (F-BRC) induced by BRC buckling is studied, and the principle that the dynamic BRC buckling makes the structure acquire inertial force as well as inertial torsion moment is found out. It is more reasonable to explain the inelastic torsional process and the mechanical characteristics of the structure by this principle than by the theory of strength eccentricity and stiffness eccentricity. Finally, based on the principle, six numerical examples with different brace schemes under the excitation of eight earthquake waves are calculated, and the changing rules of the torsional moment are studied. Some design limitation suggestions are put forward.

Performance of concrete-filled steel tube truss girders strength by adding reinforcement

Concrete filled steel tube (CFST) truss girder usually consists of CFST chords and hollow braces. The performance of steel tube truss girders filled with self-compacting concrete was investigated in this study. A total of eight CFST truss girders (Warren-vertical truss) specimens were tested. The main parameters were the concrete compressive strength and adding a reinforced bar in the concrete core of the bottom chord. Two of specimens without reinforcement were suggested as reference specimens. This study shows the load-deflection curves at the midspan, overall deflections, ultimate loads, flexural strength and failure modes of the tested specimens. The Proposed design equation found in the literature was used to predict the flexural strength of CFST trusses. The failure mode includes: weld fracture and shredding around joints and local buckling of the diagonal braces. Results show that the increase of concrete compressive strength caused a slight increase of the CFST truss strength by about (2.8%-10.34%), also the results showed that the best addition to the core concrete of the bottom chord was the circular steel tube compared with the addition of the steel bars.

Nonlinear behaviour of fully grouted CHS X joints and associated representation for overall frame analysis

Abstract The nonlinear behaviour of fully grouted (FG) circular hollow section (CHS) X joints and the associated representation for overall frame analysis are investigated in this study. Infilled grout always causes brace buckling of FG X joints under brace compression and leads to punching shear failure of the FG X joints under brace tension. The former is considered as a rigid-joint connection, and only the latter is covered in the current research scope. Joint representation includes the load–deformation formulation and ultimate-strength equation. The load–deformation formulation is developed as a linear function in the elastic stage and a parabolic function in the nonlinear plastic stage. The ultimate-strength equation is based on the fracture study of a series of FG X joints with a broad range of geometric sizes. The fracture study develops a fracture locus of steel S355 and incorporates the fracture locus into the Johnson–Cook model for fracture simulation. A simple ultimate-strength equation is derived based on a straightforward relationship discovered between the nondimensional ultimate resistance and geometric parameters β and γ . The available test data successfully validate both the load–deformation formulation and ultimate-strength equation.

Compact Hybrid Simulation System: Validation and Applications for Braced Frames Seismic Testing

ABSTRACT Hybrid Simulation (HS) is a well-established testing method that combines both experimental and analytical components to evaluate the performance of structures under extreme events, commonly earthquakes. While several configurations and systems are available around the world to conduct HS, one goal of this paper is to document the development and verification of a compact HS setup at the University of Nevada, Reno to be used for tackling new research problems and educational purposes. A new substructured HS approach is proposed for seismic testing of concentric-braced frames (CBFs) with focus on capturing brace buckling and low-cycle fatigue induced-rupture. The paper presents the capabilities and verification methods for the developed system for slow and real-time HS testing with two different alternatives for the computational substructures: Simulink and OpenSEES along with OpenFresco. Two new applications were pursued to demonstrate HS testing of CBFs. The first used cyclic loading and HS under earthquake loading to capture brace buckling and failure to compare damage accumulation and brace fatigue life through rupture. The second application used HS testing to investigate the effect of earthquake duration on seismic performance of CBFs. The two applications demonstrate that the proposed HS approach can be potentially used to accurately capture CBFs seismic behavior and provide new datasets for modeling brace buckling and rupture under realistic earthquake loading. The paper also provides a brief discussion on the potential use of the compact HS setup for developing teaching modules.

Seismic performance analysis of steel-brace RC frame using topology optimization

Seismic performance analysis of steel-brace reinforced concrete (RC) frame using topology optimization in highly seismic region was discussed in this research. Topology optimization based on truss-like material model was used, which was to minimum volume in full-stress method. Optimized bracing systems of low-rise, mid-rise and high-rise RC frames were established, and optimized bracing systems of substructure were also gained under different constraint conditions. Thereafter, different structure models based on optimized bracing systems were proposed and applied. Last, structural strength, structural stiffness, structural ductility, collapse resistant capacity, collapse probability and demolition probability were studied. Moreover, the brace buckling was discussed. The results show that bracing system of RC frame could be derived using topology optimization, and bracing system based on truss-like model could help to resolve numerical instabilities. Bracing system of topology optimization was more effective to enhance structural stiffness and strength, especially in mid-rise and high-rise frames. Moreover, bracing system of topology optimization contributes to increase collapse resistant capacity, as well as reduces collapse probability and accumulated demolition probability. However, brace buckling might weaken beneficial effects.

Steel Structures Research Update:Seismic Performance and Design of Steel Panel Dampers for Steel Moment Frames

Ongoing work on the seismic performance and design of steel panel dampers for steel moment frames is highlighted. Dr. Keh-Chyuan Tsai, professor in the Department of Civil Engineering at National Taiwan University, leads the team from National Taiwan University and the National Center for Research on Earthquake Engineering (NCREE) in Taipei. In 2018, At NCREE, one recent collaboration with the University of Washington included cyclic tests of a three-story chevron special concentrically braced frame (SCBF). Current seismic design provisions require large beam sizes to resist the unbalanced forces from the chevron braces after brace buckling. The research has explored options for alternative ductile mechanisms and reduced beam sizes. Steel research at NCREE has also included studies on steel beam-to-box-column moment connections and electro-slag-welded (ESW) joints in those connections. Meanwhile, research into premature fracture of ESW diaphragm-to-column joints in beam-to-box-column connections has revealed sensitivity to eccentricity in loading between the beam flange and the diaphragm. Further, a micromechanical-based stress-modified critical stress (SMCS) model has been developed and shown to be capable of predicting the crack initiation of the diaphragm-to-column ESW joint (Li et al., 2018).

Ultra-Low Cycle Fatigue Fracture Life of a Type of Buckling Restrained Brace

Buckling restrained braced frames (BRBFs) are considered as popular seismic-resistant structural systems. A BRB sustains large plastic deformations without brace buckling. The core of a buckling restrained brace is prone to fatigue fracture under cyclic loading. The earthquake induced fracture type of the core plate in a buckling restrained brace can be categorized as ultra-low cycle fatigue fracture. This paper investigates the ultra-low cycle fatigue fracture life of a type of composite buckling restrained brace previously tested. The newly developed cyclic void growth model was adopted to theoretically predict the fracture and crack initiation in the core. In addition, the Coffin-Manson fatigue damage model was applied to estimate the fracture life of the brace. A FEM model of the BRB developed in ABAQUS was used to evaluate the fatigue life. The analysis results showed that the cyclic void growth model is capable to nearly predict the fracture life of the core in buckling restrained brace.

Seismic Behavior of Symmetric and Asymmetric Steel Structures with Rigid and Semirigid Diaphragms

AbstractThe torsional behavior of braced frames can be significantly influenced by the sequence of brace buckling, hinge development in beams or columns, and in-plane deformation of the diaphragm, ...

Seismic-resistant self-centering rocking core system with buckling restrained columns

Conventional concentrically braced frame (CBF) systems have limited drift capacity prior to brace buckling, and related damage leads to deterioration in strength and stiffness. CBFs are also susceptible to soft-story failure. A pin-supported self-centering rocking core system with buckling-restrained columns (SCRC-BRC) is being developed to provide significant drift capacity while limiting damage due to residual drift and soft-story mechanisms.The SCRC-BRC system consists of beams, columns, and braces branching off a central column, with buckling restrained columns (BRCs) incorporated into the system at the first story external column positions. The BRCs and friction generated at lateral-load bearings at each floor level are used to dissipate energy to reduce the overall seismic response of the SCRC-BRC system. Vertically-aligned post-tensioning bars provide additional overturning moment resistance and aid in self-centering the system to eliminate residual drift. The pin support condition at the base of the central column and the lateral stiffness of the system enable it to exhibit a nearly uniform inter-story drift distribution.In this study, the suite of 44 DBE-level ground motions used in FEMA P695 is numerically applied to several SCRC- BRCs to demonstrate the seismic performance of the system. The results show that the SCRC-BRC system has a nearly uniform inter-story drift response, high ductility, and a high energy dissipation capacity, and is an effective seismic-resistant system.

Probabilistic seismic performance assessment of ribbed bracing systems

This article evaluates the seismic performance of structures equipped with a ribbed bracing system (RBS). RBS uses ribbed faces that freely slide under compression, however, interlock under tensile forces. Two RBS mechanisms; Completely-closed RBS (CC-RBS) and Improved-centering RBS (IC-RBS), were proposed and successfully tested for eliminating compressive buckling of braces. CC-RBS and IC-RBS provide high energy dissipation capacity and small residual story drifts, respectively. Here, these mechanisms were employed for design and modeling of three structures with varying heights. The models were then subjected to incremental dynamic analysis (IDA), and their seismic performance was probabilistically evaluated at different levels of intensity. Based on the results, in the low to moderate lateral deformations, structural performance benefitted more from the energy dissipation capacity provided by CC-RBS. Nevertheless, CC-RBS demands were increased due to the accumulation of plastic deformations by surpassing height-dependent deformation thresholds. The governing thresholds were also observed to decrease with increasing buildings height as a result of the elevated significance of p-delta effects in tall structures.

Experimental and numerical studies on ribbed bracing system

SummaryRibbed bracing system (RBS) is an innovative structural system designed to eliminate the buckling of braces and enhance the behavior of structures under seismic loads. In this study, a collaborative performance of 2 RBS devices bracing a frame was assessed numerically and experimentally. In the numerical phase, the collaboration of ribbed braces at various stages of reversal loading was elaborated mathematically and was used for representing the system using finite element modeling. In the next phase, the numerically observed behavior was validated experimentally by conducting cyclic quasistatic tests of the proposed configurations. Two alternative RBS configurations—called completely closed (CC) and improved centering (IC)—were considered in this regard. Various characteristics of CC‐ and IC‐RBS configurations were evaluated using validated methods, after which they were compared against configurations of concentrically braced frames and buckling‐restrained braces. The stiffness and the energy absorption capacity of CC‐RBS configuration were shown to exceed all the considered bracing types. IC‐RBS, on the other hand, showed the lowest residual drift. The CC‐RBS configuration was also shown to have excellent performance under moderate loadings experienced under service level.

Experimental study on seismic behavior of full-scale fully prefabricated steel frame: Global response and composite action

To investigate the seismic behavior of a fully prefabricated steel frame with new type construction process, to provide a unique set of data on frame test, and to lay the foundation for follow-up research, a full-scale test was performed under cyclic loads. This frame was composed of box cold-formed columns, hot-rolled I-section beams, end-plate joints, rod flexible braces, and prefabricated concrete slabs. A recently proposed type of bolted end-plate joint and a new proposed construction method were used in this test. Because limited concrete casting and field welding were involved during the structural assembly process, construction efficiency was improved. The design details of the test specimen, the test setup, the loading protocol, the construction process, and the measurement arrangement are introduced. Test observations of braces, beams, joints, columns, and slab behavior are described in detail. Hysteresis behavior of the frame is discussed, including hysteresis curves, backbone curves, overall deformation and energy dissipation behavior. The composite action of the prefabricated slabs under cyclic loads is also studied. The results indicate that the specimen exhibited satisfactory cyclic behavior, horizontal load-carrying capacity and ductility performance, with no obvious degradation in strength was observed even at the large overall drift ratio of 7.69%. Plastic hinges formed at beam-ends and column bases. The frame’s lateral stiffness in the initial position degraded significantly following brace buckling, however, no soft-story mechanisms were developed.

Seismic Behavior of Chevron Concentrically Braced Frames with Weak Beam

Concentrically braced frames provide ductility and imparted seismic energy dissipation through yielding of tension braces and buckling of compression braces. In braced frames with chevron configuration, difference of actions in tension and buckled brace results in considerable unbalanced force at brace-beam intersection, which is addressed in modern seismic design provisions. In this paper, effect of flexural capacity of beam to carry this unbalanced force and consequently seismic behavior of braced frame is investigated by finite element analysis. Two-story and four-story chevron braced frames were modeled in ABAQUS software and studied by means of nonlinear cyclic pushover and nonlinear response history analysis methods. Results showed that inadequate flexural strength of the beams reduce lateral stiffness and strength of braced frame significantly as lateral drift increases; therefore, concentration of lateral deformation in one story may cause formation of soft and weak story. Furthermore, seismic behavior of chevron braced frame and two-story X braced frames were compared.

Proposed Relationship for Proper Shear Strength of Elliptical Damper Based on Its Geometrical Parameters

Vertical link beam as a practical yielding damper is a kind of passive control device which dissipates seismic energy and thus reduces the rate of damage to structures through in-plane shear deformations. Proper stiffness, ductility and significant energy dissipation of these dampers together with their practical advantages justify their widespread experimental and numerical research. In this paper, a total of 42 elliptical dampers (vertical link beams with elliptical cross sections) in various lengths and thicknesses are modeled using the ABAQUS finite element software and finally a design relationship for this damper is presented based on the above mentioned geometrical parameters using pushover analysis. The accuracy of the proposed relationship is studied by applying various layouts of designed dampers on two types of chevron bracings to improve their performance and obtain proper energy dissipation without brace buckling. The equivalent viscous damping ratios of 32–33% obtained for elliptical dampers indicate high increase in energy dissipation capability.

Analytical Investigation on Seismic Behavior of Inverted V-braced Frames

An inverted V-braced frame is one of the most widely used CBFs (Concentrically Braced Frames) owing to many advantages in constructional design. The seismic behaviors of inverted V-braced frames is that brace buckling occurs due to strong motion generation, and that in turn vertical unbalanced force is created between tension brace and compression brace, resulting in an additional load onto beams. Thus, members of beams should be designed to have enough strength to ensure plastic hinge is not created. In this study, a series of finite element analysis was conducted to evaluate the earthquake-resistant performances of the methods to design the clearance distance of gusset plates in inverted V-braced frames, and to evaluate vertical unbalanced force depending on the cross-section size of beams. It was found that the results of the equation of vertical unbalanced force in the current standards were more conservative than the load generated through the real analysis model. In addition, the model of designing elliptical clearance distance showed higher earthquake-resistant performances than that of designing linear clearance distance, which requires the reconsideration and improvement of the current practices of calculating vertical unbalanced force and setting clearance distance.

Cyclic Performance of Braces with Different Support Connections in Special Concentrically Braced Frames

Gusset plate connections between the steel braces and the supporting frame members play an important role in the performance of special concentrically braced frames (SCBFs) under earthquake loading conditions. Extensive studies have been conducted on SCBFs in which the gusset plate connections are designed to ensure the out-of-plane buckling of steel braces. However, research on the cyclic behavior of gusset plate connections allowing the in-plane buckling of braces is very limited. An experimental investigation has been carried out in this study to investigate the cyclic performance of the in-plane buckling of gusset-brace assemblies. Tests showed that the gusset plate connections detailed for in-plane buckling of braces provided performance at par with those detailed for the out-of-plane deformation arrangement. A numerical comparative study on three types of connection arrangements has also been conducted, namely, a) out-of-plane buckling of braces using gusset plates, b) in-plane buckling of braces using knife plates, and c) direct connection of braces without using any gusset plates. Braces made of hollow steel sections having constant slenderness ratio and width-to-thickness ratio are used in all the numerical models. The main parameters compared are the energy dissipation capacity, displacement ductility, patterns of failure, and the sequence of yielding in the components. Both test and analysis results are used to quantify the performances of gusset plate connections in order to achieve an efficient and reliable concentrically braced frame systems.

Seismic Design of Gusset Plate Connections in Concentrically Braced Frames

In concentrically braced frames (CBF), gusset plates as the connected members are subjected to forces not only from brace but also from frame action. When the braced frame is deformed, the beam-column connection will deform, and the deformation of beam-column connection either “open” or “close” as the brace under “compression” or “tension”. Therefore, the design of gusset plate should consider the effect of such frame action, in addition of the brace axial load. Six finite element models were developed using ABAQUS to investigate the force distribution of gusset plate under the two actions. It is noted that force in gusset plate can be divided into two parts and frame action is so small that can be neglected during brace buckling.