Earticle

최근 우리나라와 인접한 일본(2011년 3월, 규모 9.0)과 중국(2008년 5월, 규모 8.0)에 발생한 대지진의 영향으로 우리나라 또한 대규모 지진 발생 가능성에 대한 우려가 커져가고 있다. 따라서 우리나라에서도 경제적이면서도 안전한 성능기반 내진설계가 이루어져야 하며 이를 위해서는 비선형 응답산정이 필수적이다. 구조물의 비선형 응답을 가장 정확하게 산출할 수 있는 해석법은 비선형 동적해석법 (Nonlinear Dynamic Analysis; NDA)이나, 많은 시간과 노력을 필요로 한다. 이에 따라 다자유도계 구조물(Multi Degree of Freedom; MDF)의 비선형 정적해석(pushover)과 등가단자유도계(Equivalent Single Degree of Freedom; ESDF)의 비선형 동적응답을 고려하여 구조물의 비선형 최대응답을 정확성과 실용성의 측면에서 보다 간편하게 산정하는 약산적인 방법들이 연구되고 있다. 이러한 약산법들로서 능력스펙트럼법(Capacity Spectrum Method; CSM)과 비선형 직접스펙트럼법(Nonlinear Direct Spectrum Method; NDS) 등이 기존에 제시된바 있다. 그 중에서 CSM는 반복과정이 요구되며 해가 수렴하지 않거나 수렴하여도 오차가 크게 발생하는 경우가 있으며, NDS는 ESDF의 항복강성비와 진동주기에 대한 비선형 가속도 스펙트럼이 존재하지 않는 범위에서는 연성계수를 구할 수 없는 등의 취약점이 있다. 따라서 본 연구에서는 위와 같은 약산법들의 문제점을 개선하기 위하여, 비선형 연성 스펙트럼으로부터 연성계수를 직접 구하여 구조물의 비선형 최대응답을 약산적으로 산정하는 비선형 연성계수법(Nonlinear Ductility Factor Method; NDF)을 제시하고 신뢰성을 검토하기로 한다.

Many researchers in earthquake engineering have recently argued that Korea is not safe from possible earthquakes around the Korean Peninsula. Therefore they are studying regarding performance-based seismic design which could estimate behavior of structure like real structure and reflect the performance for minimizing damage of the earthquakes and estimate. Accordingly, estimating nonlinear response of structures become very important tasks. The most accurate method for computing nonlinear behavior of structure is nonlinear dynamic analysis, but it is time-consuming and necessitate more efforts. So, approximate nonlinear methods have been studied to conveniently estimate nonlinear response of structure with sufficient accuracy and practicality. Nonlinear ductility factor method is proposed here to estimate nonlinear response of structure and to improve existing approximate methods. It is possible to find ductility factor directly from nonlinear ductility spectrum. In this study, it is to estimate nonlinear response of structure under earthquake load by nonlinear dynamic analysis, nonlinear ductility factor method and nonlinear direct spectrum method. And it is to look over reliability of nonlinear ductility factor method compared with other exact and approximate methods.

It has been recognized that 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 inelastic response is required. The 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. Some codes proposed the capacity spectrum method based on the nonlinear static(pushover) analysis to determine earthquake-induced demand given the structure pushover curve. This procedure is conceptually simple but iterative and time consuming with some errors. This paper presents a nonlinear direct spectrum method to evaluate seismic Performance of structure, without iterative computations, given the structural initial elastic period and yield strength from the pushover analysis, especially for multi degree of freedom structures. The purpose of this paper is to investigate accuracy and confidence of this method from a point of view of various earthquakes and unloading stiffness degradation parameters.

Most structures are expected deform nonlinear and inelastic behavior when subjected to strong ground motion. Nonlinear time history analysis(NTHA) is the most rigorous procedure to compute seismic performance in the various inelastic analysis methods. But nonlinear analysis procedures necessitate more reliable and practical tools for predicting seismic behavior of structures. Some building codes propose the capacity spectrum method. This method is the concept of an equivalent linear system, wherein a linear system having reduced stiffness and increased damping is used to estimate the response of the nonlinear system. This procedure are conceptually simple, but the iterative procedure is time-consuming and may sometimes lead to no solution or multiple solutions. 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 mixed building structure.

Most structures are expected to deform beyond the limit of linearly elastic behavior when subjected to strong ground motion. Seismic evaluation of structure requires an estimation of the structural performance in terms of displacement demand imposed by earthquakes on the structure. Nonlinear response history analysis(NRHA) is the most rigorous procedure to compute seismic performance among various inelastic analysis methods. But nonlinear analysis procedures necessitate more practical and reliable tools for predicting seismic behavior of structures. 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) system. The purpose of this paper is to investigate the accuracy and reliability of this method from a point of view of various earthquakes and structure parameters.