• Proceedings of the Korea Concrete Institute Conference
• /
• 2010.05a
• /
• pp.137-138
• /
• 2010

This paper presents new seismic control system that utilize toggle brace to amplify the displacement of damper. A full scale steel moment frame was constructed for the purpose of testing the energy dissipation system with double toggle brace.

• Journal of the Earthquake Engineering Society of Korea
• /
• v.21 no.3
• /
• pp.145-152
• /
• 2017

The objective of this study is to propose a simple and accurate analytical model for HSS braces. For this purpose, a physical theory model is adopted. Rectangular hollow section steel (HSS) braces are considered in this study. To accurately simulate the cyclic behavior of braces using the physical theory model, empirical equations calculating constituent parameters are implemented on the analytical model, which were proposed in the companion paper. The constituent parameters are cyclic brace growth, cyclic buckling load, and the incidence of local buckling and fracture. The analytical model proposed in this study was verified by comparing actual and simulated cyclic curves of brace specimens. It is observed that the proposed model accurately simulates the cyclic behavior of the braces throughout whole response range.

• Earthquakes and Structures
• /
• v.12 no.4
• /
• pp.449-455
• /
• 2017

Using X-braced frames in steel structures is a current procedure to achieve good strength against lateral loads. Study on mid-connections of X-braces and their effects on frame behavior is a subject whose importance has been more or less disregarded by researchers. Experimentally inspecting models involves considerable expense and time; however, computer models can be more suitable substitutes. In this research, a numerical model of X-braced frame has been analyzed using finite element software. The results of pushover analysis of this frame are compared with those of the experimental test. With the help of computer model, the effects of different mid-connection details on ductility and lateral strength of the frame are inspected. Also performances of bolted and welded connections are compared. Taking into account ductility and strength, this study suggests details of a decent pattern for the mid-connection.

• Journal of the Korea Concrete Institute
• /
• v.25 no.6
• /
• pp.667-674
• /
• 2013

Improving the earthquake resistance of buildings through seismic retrofitting using steel braces can result in brittle failure at the connection between the brace and the building, as well as buckling failure of the braces. This paper proposes a new seismic retrofit methodology combined with glass fiber sheet (GFS) and non-compression X-brace system using carbon fiber (CFXB) for reinforced concrete buildings damaged in earthquakes. The GFS is used to improve the ductility of columns damaged in earthquake. The CFXB consists of carbon fiber bracing and anchors, to replace the conventional steel bracing and bolt connection. This paper reports the seismic resistance of a reinforced concrete frame strengthened using the GFS-CFXB system. Cyclic loading tests were carried out, and the hysteresis of the lateral load-drift relations as well as ductility capacities were investigated. Carbon fiber is less rigid than the conventional materials used for seismic retrofitting, resulting in some significant advantages: the strength of the structure increased markedly with the use of CF X-bracing, and no buckling failure of the bracing was observed.

• Journal of Korean Society of Steel Construction
• /
• v.21 no.3
• /
• pp.257-266
• /
• 2009

The results of the analysis of the structural behavior of diagrid nodes that were subjected to cyclic loads such as wind and earthquakes was not fully understood due to difficulties in considering the welding type. In this study, diagrid nodes were tested to determine their behavior when they are subjected to seismic or wind loads. Five specimens were designed and fabricated. The corresponding test parameters were the welding type for each point and the length of the overlap of the side stiffener and the brace web. Tensile force was applied to one diagrid brace member, and compression force was applied to the other diagrid brace member. Cyclic loading was applied until the failure. The test showed that failures are due to axial stress from axial force and the additional bending moment of the two combined axial forces that have different directions. Tensile failure was observed from the tensile force, and local buckling was observed from the compressive force at the flange of the brace member. In addition, the welding type and the length overlap affected the initial stiffness, the yielding stress, and the energy absorption of the diagrid node.

• Earthquakes and Structures
• /
• v.23 no.2
• /
• pp.139-150
• /
• 2022

In most self-center braces, decreasing residual deformation is possible only by increasing pretension force, which results in lower energy dissipation capacity. On the other hand, increasing energy dissipation capacity means higher values of residual deformation. The goal of this research was to find the best design for a self-centering buckling restrained brace (SC-BRB) system by balancing self-centering capability and energy dissipation. Three, six, and nine-story structures were investigated using OpenSees software and the TCL programming language to achieve this goal. For each height, 62 different SC-BRBs were considered using different values for the pretension force of cables, the area of the buckling restrained brace (BRB) core plate, and the yield stress of the core plate. The residual deformation and dissipated energy of all the models were calculated using nonlinear analyses after cyclic loading was applied. The optimum design for each height was determined among all the models and was compared to the structure equipped with the usual BRB. The residual deformation of the framed buildings was significantly reduced, according to the findings. Also the reduction of the energy dissipation was acceptable. The optimum design of SC-BRB in 6-story building has the most reduction percent in residual deformation, it can reduce residual deformation of building 83% while causing only a 57% of reduction in dissipated energy. The greatest reduction in residual deformation versus dissipated energy reduction was for the optimum SC-BRB design of 9-story building, results indicated that it can reduce residual deformation of building 69% while causing only a 42% of reduction in dissipated energy.

• Steel and Composite Structures
• /
• v.45 no.1
• /
• pp.83-100
• /
• 2022

Timber is one of the few natural, renewable building materials and glulam is a type of engineering wood product. In the present work, timber-based braces are applied for retrofitting midrise Special Moment Resisting Frame (SMRF) using two types of timber base braces (Timber base glulam, and hybrid Timber-Steel-BRB) as alternatives for retrofitting by traditional steel bracings. The improving effects of adding the bracings to the SMRF on seismic characteristics of the frame are evaluated using load-bearing capacity, energy dissipation, and story drifts of the frame. For evaluating the retrofitting effects on the seismic performance of SMRF, a five-story SMRF is considered unretofitted and retrofitted with steel-hollow structural section (HSS) brace, Glued Laminated Timber (Glulam) brace, and hybrid Timber-Steel BRB. Using OpenSees structural analyzer, the performance are investigated under pushover, cyclic, and incremental loading. Results showed that steel-HSS, timber base Glulam, and hybrid timber-steel BRB braces have more significant roles in energy dissipation, increasing stiffness, changing capacity curves, reducing inter-story drifts, and reducing the weight of the frames, compared by steel bracing. Results showed that Hybrid BRB counteract the negative post-yield stiffness, so their use is more beneficial on buildings where P-Delta effects are more critical. It is found that the repair costs of the buildings with hybrid BRB will be less due to lower residual drifts. As a result, timber steel-BRB has the best energy dissipation and seismic performance due to symmetrical and stable hysteresis curves of buckling restrained braces that can experience the same capacities in tension and compression.

• Structural Engineering and Mechanics
• /
• v.60 no.3
• /
• pp.471-488
• /
• 2016

This study predicts the strength of rotary brace damper by analyzing a new set of probabilistic models using the usual method of multiple linear regressions (MLR) and advanced machine-learning methods of multivariate adaptive regression splines (MARS), Rotary brace damper can be easily assembled with high energy-dissipation capability. To investigate the behavior of this damper in structures, a steel frame is modeled with this device subjected to monotonic and cyclic loading. Several response parameters are considered, and the performance of damper in reducing each response is evaluated. MLR and MARS methods were used to predict the strength of this damper. Displacement was determined to be the most effective parameter of damper strength, whereas the thickness did not exhibit any effect. Adding thickness parameter as inputs to MARS and MLR models did not increase the accuracies of the models in predicting the strength of this damper. The MARS model with a root mean square error (RMSE) of 0.127 and mean absolute error (MAE) of 0.090 performed better than the MLR model with an RMSE of 0.221 and MAE of 0.181.

• Steel and Composite Structures
• /
• v.21 no.5
• /
• pp.1017-1029
• /
• 2016

When a welded circular hollow section (CHS) tubular joint is subjected to brace axial loading, failure position is located usually at the weld toe on the chord surface due to the weak flexural stiffness of the thin-walled chord. The failure mode is local yielding or buckling in most cases for a tubular joint subjected to axial load at the brace end. Especially when a cyclic axial load is applied, fracture failure at the weld toe may occur because both high stress concentration and welding residual stress along the brace/chord intersection cause the material in this region to become brittle. To improve the ductility as well as to increase the static strength, a tubular joint can be reinforced by increasing the chord thickness locally near the brace/chord intersection. Both experimental investigation and finite element analysis have been carried out to study the hysteretic behaviour of the reinforced tubular joint. In the experimental study, the hysteretic performance of two full-scale circular tubular T-joints subjected to cyclic load in the axial direction of the brace was investigated. The two specimens include a reinforced specimen by increasing the wall thickness of the chord locally at the brace/chord intersection and a corresponding un-reinforced specimen. The hysteretic loops are obtained from the measured load-displacement curves. Based on the hysteretic curves, it is found that the reinforced specimen is more ductile than the un-reinforced one because no fracture failure is observed after experiencing similar loading cycles. The area enclosed by the hysteretic curves of the reinforced specimen is much bigger, which shows that more energy can be dissipated by the reinforced specimen to indicate the advantage of the reinforcing method in resisting seismic action. Additionally, finite element analysis is carried out to study the effect of the thickness and the length of the reinforced chord segment on the hysteretic behaviour of CHS tubular T-joints. The optimized reinforcing method is recommended for design purposes.

• Journal of Korean Society of Steel Construction
• /
• v.21 no.1
• /
• pp.71-81
• /
• 2009

In this study, the seismic performance of the Buckling Restrained Knee Bracing (BRKB) system was evaluated through a pin-connected one-bay, one-story frame. The BRKB system developed in this study was composed of a steel plate as a load-resisting core member and two channel sections to restrain local and global buckling of the core plate. The main purpose of the BRKB system is to restrengthen/rehabilitate old low- and mid-rise RC buildings, which, it is assumed, were designed with non-seismic designs and details. The main variables for the test specimens were the size of the core plates and the stiffeners, and the condition of the end plates. The test results showed that the size of the core plate, which was the main element of the load-resisting member, was the most important parameter in achieving a ductile behavior under tension as well as compression until the maximum displacement exceeds twice the design drift limit.