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

• Journal of Korean Society of Steel Construction
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• v.22 no.1
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• pp.1-12
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• 2010

According to the capacity design concept which forms the basis of the current steel seismic codes, the braces in concentrically braced frames (CBFs) should dissipate seismic energy through cyclic tension yielding and cyclic compression buckling while the beams and the columns should remain elastic. Brace buckling in inverted V-braced frames induces unbalanced vertical forces which, in turn, impose the additional beam moments and column axial forces. However, due to difficulty in predicting the location of buckling stories, the most conservative approach implied in the design code is to estimate the column axial forces by adding all the unbalanced vertical forces in the upper stories. One alternative approach, less conservative and recommended by the current code, is to estimate the column axial forces based on the amplified seismic load expected at the mechanism-level response. Both are either too conservative or lacking technical foundation. In this paper, three combination rules for a rational estimation of the column axial forces were proposed. The idea central to the three methods is to detect the stories of high buckling potential based on pushover analysis and dynamic behavior. The unbalanced vertical forces in the stories detected as high buckling potential are summed in a linear manner while those in other stories are combined by following the SRSS(square root of sum of squares) rule. The accuracy and design advantage of the three methods were validated by comparing extensive inelastic dynamic analysis results. The mode-shape based method(MSBM), which is both simple and accurate, is recommended as the method of choice for practicing engineers among the three.

• Proceedings of the Earthquake Engineering Society of Korea Conference
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• 2000.04a
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• pp.267-274
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• 2000

Current seismic design codes for building structures are based on the method which can provide enough capacity to satisfy objected performance level and exactly evaluate the seismic performance of buildings. The capacity spectrum method using the nonlinear static(pushover) analysis is becoming a popular tool for evaluating the seismic performance of existing and new building structures. By means of a graphical procedure capacity spectrum method esimates the performance level of structure by comparing the capacity of structure with the demand of earthquake ground motion on the structure. In the method the relation between base shear estimated by a nonlinear static analysis and horizontal displacement is used. Capacity spectrum is usually expressed as what represent the responses of the equivalent single degree of freedom (ESDOF) system for the building structures. However there are some problems in converting procedures into ESDOF system which include not considering the effect of higher modes of structures. The objective of this paper is to compare and verify existing methods and suggest the modified capacity spectrum for seismic performance evaluation of building structures.

• Proceedings of the Earthquake Engineering Society of Korea Conference
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• 2000.10a
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• pp.304-313
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• 2000

This study presents the behavior of traditional wood structures of national heritage under earthquake loadings. A series of experimental program for four wood frames was performed to investigate characteristics of initial stiffness, behavior after ultimate loads, and hysteretic behaviors. The frames consisted of columns with a lintel by special joint and a bare frame was infilled by a mud wall. A pushover est was aimed to estimate the range of ultimate rotation of connection as a pilot test for cyclic load tests. One of frames infilled by a mud wall showed a larger stiffness than those of bare frames due to a strut action in the diagonal direction. However, the post yielding stiffness of the infilled frame was not increased.

• Earthquakes and Structures
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• v.1 no.1
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• pp.129-146
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• 2010

This paper proposes an approximate procedure to estimate seismic displacement capacity - defined as yield displacement times the displacement ductility - of piles in marine oil terminals. It is shown that the displacement ductility of piles is relatively insensitive to most of the pile parameters within ranges typically applicable to most piles in marine oil terminals. Based on parametric studies, lower bound values of the displacement ductility of two types of piles commonly used in marine oil terminals - reinforced-concrete and hollow-steel - with either pin connection or full-moment-connection to the deck for two seismic design levels - Level 1 or Level 2 - and for two locations of the hinging in the pile - near the deck or below the ground - are proposed. The lower bound values of the displacement ductility are determined such that the material strain limits specified in the Marine Oil Terminal Engineering and Maintenance Standard (MOTEMS) are satisfied at each design level. The simplified procedure presented in this paper is intended to be used for preliminary design of piles or as a check on the results from the detailed nonlinear static pushover analysis procedure, with material strain control, specified in the MOTEMS.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 2005.04a
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• pp.97-104
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• 2005

The seismic behavior of framed structure with Chevron-type bucking restrained braces were investigated and their behavior factors were evaluated following the procedure proposed in ATC-19 & ATC-34. Two types of structures, building frame systems and dual systems, with 4, 8, 12, and 16 stories were designed per the IBC 2000, the AISC LRFD and the AISC/SEAOC Recommended Provisions for BRBF. Nonlinear static pushover analyses were carried out to observe the plastic hinge formation and to identify the loads and the displacements at the yield and the ultimate states. Time history analyses were also carried out to compute the permanent displacement md the dissipated hysteretic energy. According to the analysis results, the response modification factors of model structures fumed out to be larger than what is proposed in the provision in low story structures, and a little smaller in medium-story structures. The dual systems, even though designed with smaller seismic load, showed superior static and dynamic performances.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 2009.04a
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• pp.200-204
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• 2009

구조물의 건전도를 평가하기 위하여 계측된 데이터로부터 구조물의 동특성 변화를 분석하여 손상정도를 추정하는 방법이 많이 사용되고 있다. 최근, 다점 측정된 가속도 데이터로부터 구조물의 고유진동수 및 모드형상을 추출하고 이를 초기값과 비교하여 손상탐지를 실시함으로써 손상위치 및 손상정도를 추정하는 기법이 활발히 연구되고 있다. 그러나 이러한 방법을 실제 적용하기 위해서는 계측시스템 구축에 많은 비용이 소요되며, 손상탐지를 위한 해석과정이 복잡하기 때문에 실시간에 가깝게 유용한 정보를 거주자에게 제공하는데 한계가 있다. 따라서 본 연구에서는 실용적인 계측유지관리 시스템을 구축할 수 있도록 구조물의 손상도에 따른 동적특성의 변화를 사전에 예측하여 실제 계측된 동적특성에 대한 관리 한계치를 제공하는 방안을 제시하고자 한다.

• Earthquakes and Structures
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• v.8 no.2
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• pp.401-422
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• 2015

This paper evaluates the effectiveness of three nonlinear static methods for the prediction of the dynamic response of in-plan irregular buildings. The methods considered are the method suggested in Eurocode 8, a method previously proposed by some of the authors and based on corrective eccentricities and a new method in which two pushover analyses are considered, one with lateral forces applied to the centres of mass of the floors and the other with only translational response. The numerical analyses are carried out on a set of refined models of reinforced concrete framed buildings. The response predicted by the nonlinear static analyses is compared to that provided by nonlinear dynamic analyses. The effectiveness of the nonlinear static methods is evaluated in terms of absolute and interstorey displacements.

• Proceedings of the Korea Concrete Institute Conference
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• 1998.10a
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• pp.535-540
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• 1998

Nowadays, the pushover analysis technique is becoming a very useful tool for the prediction of inelastic behavior of structures in the seismic evaluation of existing buildings in the worldwide. However, the reliability of this analysis method has not been fully checked by the test results. The objective of this study is to verify the correlation between the experimental and analytical response of a high-rise nonseismic reinforced concrete frame using DRAIN-2DX program and the test results performed previously. This study concludes that the overall responses such as story-shear versus story-drift can be predicted with quite high reliability while the local deformations such as plastic rotations in the ends of critical members can not be described reasonably.

• Proceedings of the Korea Concrete Institute Conference
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• 1999.10a
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• pp.487-490
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• 1999

Nowadays, the pushover analysis technique is becoming a very useful tool for the prediction of inelastic behavior of structures in the seismic evaluation of existing buildings in the world. However, the reliability of this analysis method has not been fully checked by the test results. The objective of this study is to verify the correlation between the analytical and experimental response of a high-rise masonry infilled reinforced concrete frame using DRAIN-2DX program and the test results performed previously. This study concludes that the strength and stiffness of members can be predicted with quite high reliability while the ductility capacity of members can not be described reasonably.