• Steel and Composite Structures
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• v.19 no.4
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• pp.917-937
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• 2015

During a seismic event, a considerable amount of energy is input into a structure. The law of energy conservation imposes the restriction that energy must either be absorbed or dissipated by the structure. Recent earthquakes have shown that the use of concentric bracing system with their low ductility and low energy dissipation capacity, causes permanent damage to structures during intense earthquakes. Hence, engineers are looking at bracing system with higher ductility, such as chevron and eccentric braces. However, braced frame would not be easily repaired if serious damage has occured during a strong earthquake. In order to solve this problem, a new bracing system an off-centre bracing system with higher ductility and higher energy dissipation capacity, is considered. In this paper, some numerical studies have been performed using ANSYS software on a frame with off-centre bracing system with optimum eccentricity and circular element created, called OBS_C_O model. In addition, other steel frame with diagonal bracing system and the same circular element is created, called DBS_C model. Furthermore, linear and nonlinear behavior of these steel frames are compared in order to introduce a new way of optimum performance for these dissipating elements. The obtained results revealed that using a ductile element or circular dissipater for increasing the ductility of off-centre bracing system and centric bracing system is useful. Finally, higher ductility and more energy dissipation led to more appropriate behavior in the OBS_C_O model compared to DBS_C model.

• Journal of the Earthquake Engineering Society of Korea
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• v.20 no.7_spc
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• pp.553-560
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• 2016

After an earthquake occurred in the Gyeongju, 2016, many low-story buildings have been questioned in terms of the seismic performance since mostly they have been exempted from the seismic design requirement since 1988. In this study, a 3-story moment resisting frame (MRF) building was analyzed and evaluated the seismic performance. Due to the insufficient seismic performance required for the seismic performance levels, three different seismic retrofit schemes were proposed and their seismic performances were re-evaluated. While steel brace and open shear wall retrofit systems mainly focused on the strength retrofit, the VES damper retrofit system is mainly to enhance the energy dissipation capacity of the system and resultes in the increased ductility. The original building and 3 retrofitted buildings were evaluated using the nonlinear static and nonlinear dynamic analyses and suggestions were proposed. Through the analysis of nonlinear time history and push-over using MIDAS/Gen program, damages of the building in terms of top story and average story drift and effect of reinforcement were analyzed.

• Steel and Composite Structures
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• v.37 no.5
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• pp.571-587
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• 2020

In this article the seismic demand and performance of two recent braced steel frames named steel moment frames with the elliptic bracing (ELBRFs) are assessed through a laboratory program and numerical analyses of FEM. Here, one of the specimens is without connecting bracket from the corner of the frame to the elliptic brace (ELBRF-E), while the other is with the connecting brackets (ELBRF-B). In both the elliptic braced moment resisting frames (ELBRFs), in addition to not having any opening space problem in the bracing systems when installed in the surrounding frames, they improve structure's behavior. The experimental test is run on ½ scale single-story single-bay ELBRF specimens under cyclic quasi-static loading and compared with X-bracing and SMRF systems in one story base model. This system is of appropriate stiffness and a high ductility, with an increased response modification factor. Moreover, its energy dissipation is high. In the ELBRF bracing systems, there exists a great interval between relative deformation at the yield point and maximum relative deformation after entering the plastic region. In other words, the distance from the first plastic hinge to the collapse of the structure is fairly large. The experimental outcomes here, are in good agreement with the theoretical predictions.

• Journal of Korean Association for Spatial Structures
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• v.22 no.4
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• pp.39-48
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• 2022

The energy dissipation of inverted V-type eccentric steel braced frames can be achieved through the yielding of a slit link, through yielding of a number of strips between slits when the frame is subjected to inelastic cyclic deformation. On the other hand, the development of seismic resistance system without residual deformation is obtained by applying the superelasdtic shape memory alloy (SMA) material into the brace and link elements. This paper presents results from a systematic three-dimensional nonlinear finite element analysis on the structural behavior of the eccentric bracing systems subjected to cyclic loadings. A wide scope of structural behaviors explains the horizontal stiffness, hysteretic behaviors, and failure modes of the recentering eccentric bracing system. The accurate results presented here serve as benchmark data for comparison with results obtained using modern experimental testing and alternative theoretical approaches.

• Steel and Composite Structures
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• v.11 no.2
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• pp.93-114
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• 2011

Flange and web local buckling in beam plastic hinge regions of steel moment frames can prevent beam-column connections from achieving adequate plastic rotations under earthquake-induced forces. This threat is especially valid for existing steel moment frame buildings with beams that lack adequate flange/web slenderness ratios. As the use of fiber reinforced polymers (FRP) have increased in strengthening and repair of steel members in recent years, using FRPs in stabilizing local instabilities have also attracted attention. Previous computational studies have shown that longitudinally oriented glass FRP (GFRP) strips may serve to moderately brace beam flanges against the occurrence of local buckling during plastic hinging. An experimental study was conducted at Izmir Institute of Technology investigating the effects of GFRP reinforcement on local buckling behavior of existing steel I-beams with flange slenderness ratios (FSR) exceeding the slenderness limits set forth in current seismic design specifications and modified by a bottom flange triangular welded haunch. Four European HE400AA steel beams with a depth/width ratio of 1.26 and FSR of 11.4 were cyclically loaded up to 4% rotation in a cantilever beam test set-up. Both bare beams and beams with GFRP sheets were tested in order to investigate the contribution of GFRP sheets in mitigating local flange buckling. Different configurations of GFRP sheets were considered. The tests have shown that GFRP reinforcement can moderately mitigate inelastic flange local buckling.

• Journal of Korean Association for Spatial Structures
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• v.19 no.4
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• pp.45-52
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• 2019

The purpose of the paper is to introduce a system that reduces the occurrence of weak-story in the event of earthquake. Weak-story concentrates deformation on the story and causes all member to collapse before the capacity of all member is reached. This paper introduces Strong-Back system (SB) to protect weak story. SB is a hybrid of zipper frame, tied eccentrically braced frame, and elastic truss system and it is divided into elastic and inelastic areas. Elastic areas prevent the generation of weak story by distributing energy, and inelastic areas dissipate energy through buckling or yielding. In this paper, the seismic performance is evaluated by comparing the four type braced frame with SB through push-over analysis. The four criteria are compared from the base shear, the ductility capacity, the column failure order, and the quantity of brace. As a result, SB proved to have sufficient performance to protect the weak-story.

• Steel and Composite Structures
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• v.34 no.4
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• pp.561-580
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• 2020

Buckling restrained braces (BRBs) were developed as an enhanced alternative to conventional braces by restraining their global buckling, thus allowing development of a stable quasi-symmetric hysteretic response. A wider adoption of buckling restrained braced frames is precluded due to proprietary character of most BRBs and the code requirement for experimental qualification. To overcome these problems, BRBs with capacities corresponding to typical steel multi-storey buildings in Romania were developed and experimentally tested in view of prequalification. In the second part of this paper, a complex nonlinear numerical model for the tested BRBs was developed in the finite element environment Abaqus. The calibration of the numerical model was performed at both component (material models: steel, concrete, unbonding material) and member levels (loading, geometrical imperfections). Geometrically and materially nonlinear analyses including imperfections were performed on buckling restrained braces models under cyclic loading. The calibrated models were further used to perform a parametric study aiming at assessing the influence of the strength of the buckling restraining mechanism, concrete class of the infill material, mechanical properties of steel used for the core, self-weight loading, and frame effect on the cyclic response of buckling restrained braces.

• Structural Engineering and Mechanics
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• v.89 no.3
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• pp.239-252
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• 2024

Steel plate shear walls (SPSWs) are classified as lateral load-resisting systems. The feasibility of openings in the steel plate is a characteristic of SPSWs. The use of openings in SPSWs can lower the load capacity, stiffness, and energy dissipation. This study proposes a novel form of SPSWs that provides convenient access through openings by combining steel plates and eccentrically braced frames (EBFs). The proposed system also avoids a substantial reduction in the strength and stiffness. Hence, various geometric forms were analyzed through two different structural approaches. Groups 1, 2, and 3 included a steel EBF with a steel plate between the column and EBF in order to improve system performance. In Group 4, the proposed system was evaluated within an SPSW with openings and an EBF on the opening edge. To evaluate the performance of the proposed systems, the nonlinear finite element method (NL-FEM) was employed under cyclic loading. The hysteresis (load-drift) curve, stress contour, stiffness, and damping were evaluated as the structural outputs. The numerical models indicated that local buckling within the middle plate-EBF connection prevented a diagonal tension field. Moreover, in group 4, the EBF and stiffeners on the opening edge enhanced the structural response by approximately 7.5% in comparison with the base SPSW system.

• Journal of the Earthquake Engineering Society of Korea
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• v.16 no.6
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• pp.1-12
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• 2012

The researches related to active control systems utilizing superelastic shape memory alloys (SMA) have been recently conducted to reduce critical damage due to lateral deformation after severe earthquakes. Although Superelastic SMAs undergo considerable inelastic deformation, they can return to original conditions without heat treatment only after stress removal. We can expect the mitigation of residual deformation owing to inherent recentering characteristics when these smart materials are installed at the part where large deformation is likely to occur. Therefore, the primary purpose of this research is to develop concentrically braced frames (CBFs) with superelastic SMA bracing systems and to evaluate the seismic performance of such frame structures. In order to investigate the inter-story drift response of CBF structures, 3- and 6-story buildings were design according to current design specifications, and then nonlinear time-history analyses were performed on numerical 2D frame models. Based on the numerical analysis results, it can be comparatively verified that the CBFs with superelastic SMA bracing systems have more structural advantages in terms of energy dissipation and recentering behavior than those with conventional steel bracing systems.

• Journal of Korean Society of Steel Construction
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• v.22 no.3
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• pp.261-269
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• 2010

It is now possible to design buildings in various forms using a diagrid structural system, which is the one of the most useful structural systems. It is difficult to design and construct the connections, however, and the bucklings in braces weaken the seismic performance of structures. In this study, the initial stiffness, ductility, and energy-dissipated capacity of a diagrid and a diagrid BRB were evaluated via frame tests. The results of the cycling load tests showed that the diagrid BRB had better initial stiffness and ductility, and dissipated extra energy after the BRBs were yielded.