• Journal of the Earthquake Engineering Society of Korea
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• v.9 no.5 s.45
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• pp.75-86
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• 2005

In performance-based design methods, it is clear that the evaluation of the nonlinear response is required. Analysis methods available to the design engineer today are nonlinear time history analyses, or monotonic static nonlinear analyses, or equivalent static analyses with simulated inelastic influences. The nonlinear time analysis is the most accurate method in computing the nonlinear response of structures, but it is time-consuming and necessitate more efforts. Some codes proposed the capacity spectrum method based on the nonlinear static analysis to determine earthquake-induced demand. The nonlinear direct spectrum method is proposed and studied to evaluate nonlinear response of structures, without iterative computations, given by the structural linear vibration period and yield strength from pushover analysis. The purpose of this paper is to compare the accuracy and the reliability of approximate nonlinear methods with respect to shear buildings and various earthquakes. The conclusions of this study are summarized as follows: 1) Linear capacity spectrum method may fail to find a convergent answer or make a divergence. Even if a convergent answer is found, it has a large error in some cases and the error varies greatly depending on earthquakes. 2) Although nonlinear capacity spectrum method need much less calculation than capacity spectrum method and find an answer in any case, it may be difficult to obtain an accurate answer and generally large error occurs. 3) The nonlinear direct spectrum method is thought to have good applicability because it produce relatively correct answer than other methods directly from pushover curves and nonlinear response spectrums without additional and iterative calculations.

• Journal of the Earthquake Engineering Society of Korea
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• v.5 no.2
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• pp.103-111
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• 2001

본 연구에서는 능력스펙트럼법을 이용하여 성능목표를 만족하기 위하여 필요한 점성 감쇠기？ 양을 간단하고 직접적인 방법으로 산정하는 방법에 관하여 연구하였다. 먼저 능력스펙트럼법을 이용하여 구조물의 비탄성 응답을 구하고 구조물의응답과 목표변위의 차이를 이용하여 필요한 유효감쇠비를 구하였다. 그리고 이러한 유효감쇠비를 이용하여 필요한 점성감쇠기의 양을 선정하였다. 본 연구에서 제안한 방법의 타당성을 검증하기 위해 10층의 철골조 건물에 세 가지 유형의 층지진하중을 가하고 제안된 절차에 따라 필요한 감쇠기의 양을 구하였다. 해석결과에 따르면 제안된 방법에 의하여 설계된 점성 감쇠기를 해석 모델에 설치하고 시간이력 해석을 수행한 결과 최대응답은 목표변위와 잘 일치함을 발견하였다.

• Journal of the Earthquake Engineering Society of Korea
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• v.5 no.1
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• pp.45-52
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• 2001

에너지 소산장치가 설치된 건무의 비선형 시간이력해석은 복잡하고 많은 시간이 소모된다. 본 연구에서는 비선형 정적해석법인 능력 스펙트럼을 이용하여 구조물의 주어긴 거동 한계를 만족할 수 있는 감쇠기의 양을 산정하는 방법에 관하여 연구하였다. 먼저 능력스펙트럼법을 이용하여 건물의 비선형 정적응답을 구하고 건물의 응답과 목표변위의 차이를 이용하여 유효감쇠비를 구하고 이러한 유효 감쇠비를 이용하여 필용한 점성 감쇠기의 양을 구하였다. 본 연구에서는 단자 유도계에서 건물의 주기, 요구되는 탄성강도에 대한 항복강도의 비, 항복 후 강성비 등을 변수로 하여 연구를 수행하였다. 제안된 방법에 따라 설계된 점성 감쇠기를 설치한 예제 구조물의 시간이력 해석에 의한 최대 응답은 설계의 초기단계에서 사용한 목표변위와 잘 일치하였다.

• Journal of the Earthquake Engineering Society of Korea
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• v.12 no.2
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• pp.69-80
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• 2008

In this study, improved capacity spectrum method (CSM) is proposed. The method can account for higher mode contribution to the seismic response of MDOF systems. The CSM has been conveniently used for determining maximum roof displacement using both demand spectrum and capacity curve of equivalent SDOF system. Unlike the conventional CSM, the maximum roof displacement is determined without iteration using inelastic displacement ratio and R factor calculated from demand spectrum and capacity curve. Three moment resisting steel frames of 3-, 9- and 20-stories are considered to test the accuracy of the proposed method. Nonlinear response history analysis (NL-RHA) for three frames is also conducted, which is considered as an exact solution. SAC LA 10/50 and 2/50 sets of ground motions are used. Moreover, this study estimates maximum story drift ratios (IDR) using ATC-40 CSM and N2-method and compared with those from the proposed method and NL-RHA. It shows that the proposed CSM estimates the maximum IDR accurately better than the previous methods.

• Journal of the Earthquake Engineering Society of Korea
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• v.6 no.4
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• pp.65-73
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• 2002

It has been recognized that the damage control must become a more explicit design consideration. In an effort to develop design methods based on performance it is clear that the evaluation of the nonlinear response is required. The methods available to the design engineer today are nonlinear time history analyses, monotonic static nonlinear analyses, or equivalent static analyses with simulated nonlinear influences. Some building codes propose the capacity spectrum method based on the nonlinear static analysis(pushover analysis) to determine the earthquake-induced demand given by the structure pushover curve. These procedures are conceptually simple but iterative and time consuming with some errors. This paper presents a nonlinear direct spectrum method(NDSM) to evaluate seismic performance of structures, without iterative computations, given by the structural initial elastic period and yield strength from the pushover analysis, especially for MDF(multi degree of freedom) systems. The purpose of this paper is to investigate the accuracy and confidence of this method from a point of view of various earthquakes and unloading stiffness degradation parameters. The conclusions of this study are as follows; 1) NDSM is considered as practical method because the peak deformations of nonlinear system of MDF by NDSM are almost equal to the results of nonlinear time history analysis(NTHA) for various ground motions. 2) When the results of NDSM are compared with those of NTHA. mean of errors is the smallest in case of post-yielding stiffness factor 0.1, static force by MAD(modal adaptive distribution) and unloading stiffness degradation factor 0.2~0.3.

• Journal of the Earthquake Engineering Society of Korea
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• v.8 no.2
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• pp.35-44
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• 2004

In the capacity spectrum method(CSM) using a linear response spectrum, the peak response of an inelastic system under a given earthquake load is estimated transforming the system into the equivalent elastic one. The CSM for estimating the peak inelastic response is evaluated in this paper. The equivalent period and damping ratio are calculated using the ATC-40, G lkan, Kowalsky, and Iwan methods, and the performance points are obtained according to the procedure B of ATC-40. Analysis results indicate that the ATC-40 method generally underestimates the peak response resulting in the unsafe design, while the G lkan and Kowalsky methods overestimate the responses. The Iwan method produces the values between those by the ATC-40 method and the G lkan and Kowalsky methods, and estimates the responses relatively closer to the exact ones. Further, it is found that the Kowalsky method gives the negative equivalent damping ratios depending on the hardening ratios, and thereby can not be used to estimate the responses in some cases.

• Journal of the Earthquake Engineering Society of Korea
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• v.7 no.6
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• pp.109-117
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• 2003

Traditional nonlinear static and dynamic analyses do not accurately estimate the energy dissipation capacity of reinforced concrete structure. Recently, simple equations which can accurately calculate the energy dissipation capacity of flexure-dominated RC members, were developed in the companion study. In the present study, nonlinear static and dynamic analytical methods improved using the energy-evaluation method were developed. For nonlinear static analysis, the Capacity Spectrum Method was improved by using the energy-spectrum curve newly developed. For nonlinear dynamic analysis, a simplified energy-based cyclic model of reinforced concrete member was developed. Unlike the existing cyclic models which are the stiffness-based models, the proposed cyclic model can accurately estimate the energy dissipating during complete load-cycles. The procedure of the proposed methods was established and the computer program incorporating the analytical method was developed. The proposed analytical methods can estimate accurately the energy dissipation capacity varying with the design parameters such as shape of cross-section, reinforcement ratio and arrangement, and can address the effect of the energy dissipation capacity on the structural performance under earthquake load.

• Computational Structural Engineering
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• v.12 no.4
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• pp.31-35
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• 1999

• Journal of the Earthquake Engineering Society of Korea
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• v.6 no.2
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• pp.1-7
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• 2002

A procedure for determination of performance point was developed based on the concept of the direct displacement-based design method. Using the proposed procedure, parametric study has been performed for various natural periods of the structure, yield strength, and the stiffness after the first yield. The proposed method was also applied to a 10-story steel frame, and the results were compared to those from the capacity spectrum method and the time history analysis. It was found from the comparison that there were good agreement between the results.

• 건축구조
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• v.13 no.1
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• pp.46-58
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• 2006

구조동력학 이론에 기초하여 내진설계 기술이 개발되었다. 그러므로 건축물의 내진설계를 근본적으로 이해하기 위해서는 구조동력학의 여러 가지 이론들을 먼저 알고 이들이 내진설계에 어떻게 적용이 되는지를 알아야 한다. 이 글은 구조기술자 여러분이 건축물의 내진설계를 이해하는데 도움이 될 수 있도록 하기 위하여 다음과 같이 3부로연재될예정이다. 제1부: 응답스펙트럼과구조물의동적해석 제2부: 등가정적해석법과반응수정계수의배경 제3부: 능력스펙트럼법에의한비탄성해석 제1부에서는 단자유도 구조물의 지진해석을 통하여 응답스펙트럼을 작성하는 원리와 이를 이용하여 간편하게 지진해석을 수행하는 방법을 소개하고 응답스펙트럼에 근거하여 설계응답스펙트럼을 작성하는 방법과 다자유도 구조물의 지진응답을 알아내기 위한 응답 스펙트럼 해석법에 관하여 소개한다. 제2부에서는 구조동력학 이론에 근거하여 등가정적해석법이 유도된 근거와 반응수정계수를 사용하게 되는 배경을 소개하여 구조기술자들이내진설계에좀더확실한이해를할수있도록할것이다. 마지막으로 제3부에서는 비탄성해석을 좀 더 쉽게 하기 위하여 사용되는 능력스펙트럼법의 배경과 이를 이용하여 건축물의 성능점을 찾는 방법과 구조물의 비탄성 지진응답을 평가하는 방법에 대하여 소개함으로써 성능에 기초한 내진설계를 위한 기초 이론을 확실히 이해할수있도록할것이다. 구조동력학에 관한 내용을 여기에 상세히 소개하자면 엄청난 분량이 될 것이므로 여기서는 이 글을 읽는 구조기술자들이 구조동력학에 관한 기초적인 내용을 이해하고 있는 것으로 가정하기로 한다. 그러므로 구조동력학에 대한 기초적 이론을 확실히 이해하고 있지 못한분들은이글을읽기전에먼저구조동력학에관한알기쉬운서적을 먼저 읽도록 추천한다.