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      • Buckling Enhancement of Column Strips with Piezoelectric Layer

        Wang, Quan,Wang, Dajun Computational Structural Engineering Institute of 2003 Computational structural engineering Vol.3 No.1

        This paper discusses the enhancement of the buckling capacity of column strips by use of piezoelectric layer. The analytical model for obtaining the buckling capacity of the piezoelectric coupled column with general boundary conditions modelled with different types of springs applied at the ends of the column is derived the first time. Based on this proposed model, the buckling capacity of the column strips can be accurately predicted by solving an eigenvalue problem. The computational results show the great potential of the piezoelectric materials in enhancing the buckling capacity of the column strips. The optimal locations of the piezoelectric layer for higher buckling capacity are also obtained for the columns with. standard pinned-pinned, fixed-free, and fixed-pinned structures. In addition, the buckling capacity and the increase of buckling capacity are discussed for those columns with the general boundaries as well. This research may provide a benchmark for the buckling analysis of the piezoelectric coupled strips.

      • Topology Optimization of Continuum Structures Using a Nodal Volume Fraction Method

        Lee, Jin-Sik,Lim, O-Kaung Computational Structural Engineering Institute of 2001 Computational structural engineering Vol.1 No.1

        The general topology optimization can be considered as optimal material distribution. Such an approach can be unstable, unless composite materials are introduced. In this research, a nodal volume fraction method is used to obtain the optimum topology of continuum structures. This method is conducted from a composite material model composed of isotropic matter and spherical void. Because the appearance of the chessboard patterns makes the interpretation of the optimal material layout very difficult, this method contains a chessboard prevention strategy. In this research, several topology optimization problems are presented to demonstrate the validity of the present method and the recursive quadratic programming algorithm is used to solve the topology optimization problems.

      • Sensitivity Property of Generalized CMAC Neural Network

        Kim, Dong-Hyawn,Lee, In-Won Computational Structural Engineering Institute of 2003 Computational structural engineering Vol.3 No.1

        Generalized CMAC (GCMAC) is a type of neural network known to be fast in learning. The network may be useful in structural engineering applications such as the identification and the control of structures. The derivatives of a trained GCMAC is relatively poor in accuracy. Therefore to improve the accuracy, a new algorithm is proposed. If GCMAC is directly differentiated, the accuracy of the derivative is not satisfactory. This is due to the quantization of input space and the shape of basis function used. Using the periodicity of the predicted output by GCMAC, the derivative can be improved to the extent of having almost no error. Numerical examples are considered to show the accuracy of the proposed algorithm.

      • KCI등재

        MCMC Approach for Parameter Estimation in the Structural Analysis and Prognosis

        An, Da-Wn,Gang, Jin-Hyuk,Choi, Joo-Ho Computational Structural Engineering Institute of 2010 한국전산구조공학회논문집 Vol.23 No.6

        Estimation of uncertain parameters is required in many engineering problems which involve probabilistic structural analysis as well as prognosis of existing structures. In this case, Bayesian framework is often employed, which is to represent the uncertainty of parameters in terms of probability distributions conditional on the provided data. The resulting form of distribution, however, is not amenable to the practical application due to its complex nature making the standard probability functions useless. In this study, Markov chain Monte Carlo (MCMC) method is proposed to overcome this difficulty, which is a modern computational technique for the efficient and straightforward estimation of parameters. Three case studies that implement the estimation are presented to illustrate the concept. The first one is an inverse estimation, in which the unknown input parameters are inversely estimated based on a finite number of measured response data. The next one is a metamodel uncertainty problem that arises when the original response function is approximated by a metamodel using a finite set of response values. The last one is a prognostics problem, in which the unknown parameters of the degradation model are estimated based on the monitored data.

      • System Identification and Damage Estimation via Substructural Approach

        Tee, K.-F.,Koh, C.-G.,Quek, S.-T. Computational Structural Engineering Institute of 2003 Computational structural engineering Vol.3 No.1

        For system identification of large structures, it is not practical to identify the entire structure due to the prohibitive computational time and difficulty in numerical convergence. This paper explores the possibility of performing system identification at substructure level, taking advantage of reduction in both the number of unknowns and the number of degrees of freedom involved. Another advantage is that different portions (substructures) of a structural system can be identified independently and even concurrently with parallel computing. Two substructural identification methods are formulated on the basis whether substructural approach is used to obtain first-order or second-order model. For substructural first-order model, identification at the substructure level will be performed by means of the Observer/Kalman filter Identification (OKID) and the Eigensystem Realization Algorithm (ERA) whereas identification at the global level will be performed to obtain second-order model in order to evaluate the system's stiffness and mass parameters. In the case of substructural second-order model, identification will be performed at the substructure level throughout the identification process. The efficiency of the proposed technique is shown by numerical examples for multi-storey shear buildings subjected to random forces, taking into consideration the effects of noisy measurement data. The results indicate that both the proposed methods are effective and efficient for damage identification of large structures.

      • Using System Reliability to Evaluate and Maintain Structural Systems

        Estes, Allen C.,Frangopol, Dan M. Computational Structural Engineering Institute of 2001 Computational structural engineering Vol.1 No.1

        A reliability approach to evaluate structural performance has gained increased acceptability and usage over the past two decades. Most reliability analyses are based on the reliability of an individual component without examining the entire structural system. These analyses often result in either unnecessary repairs or unsafe structures. This study uses examples of series, parallel, and series-parallel models of structural systems to illustrate how the component reliabilities affect the reliability of the entire system. The component-system reliability interaction can be used to develop optimum lifetime inspection and repair strategies for structural systems. These examples demonstrate that such strategies must be based on the reliability of the entire structural system. They also demonstrate that the location of an individual component in the system has a profound effect on the acceptable reliability of that component. Furthermore, when a structure is deteriorating over time, the reliability importance of various components is a1so changing with time. For this reason, the most critical component in the early life of the structure may not tie the most critical later.

      • KCI등재

        Data Model for Hybrid Structural Experiments

        이창호,토마스 마룰로,리차드 소스,Lee, Chang-Ho,Marullo, Thomas,Sause, Richard Computational Structural Engineering Institute of 2009 한국전산구조공학회논문집 Vol.22 No.5

        The hybrid approach for structural experiments decomposes a structure into independent substructures that can be tested or simulated. The results from the decomposed substructures are combined to predict the behaviors of the entires structure. The hybrid approach is especially useful for the hybrid pseudo-dynamic tests that overcome the limitations of size of a test structure present in a shaking table test. The development of a computer system for the hybrid experiment requires a data model that formally organizes the information involved in the hybrid experiments. This paper provides the data model for representing the information involved in the hybrid experiments, by modifying the classes and attributes for the hybrid experiments in the Lehigh Model that is one of the data models for structural experiments. The data model for the hybrid experiments includes the classes for the physical substructures being tested and the analytical substructures being analyzed, and the simulation coordinator managing the overall experiments. Some objects for classes are implemented as an example to show the links among the classes. The data model presented in this paper can be applied for developing a computer system that helps structural engineers and researchers store, share, and access the information for the hybrid experiments. 하이브리드 구조실험에서는 구조물을 여러 개의 부분구조물로 나누어서 실험과 해석을 하고 이의 결과를 합쳐서 전체적인 구조물의 거동을 파악한다. 이러한 방법은 진동대 실험과 비교하여 구조물의 크기제한의 영향을 받지 않는 유사동적 실험에 효과적이다. 하이브리드 구조실험과정에서 발생된 데이터와 관련 정보를 저장하고 검색할 수 있는 컴퓨터시스템을 만들기 위해서는 하이브리드 구조실험과 관련된 정보를 체계화시켜서 구성하는 작업이 선행되어야 한다. 본 논문은 하이브리드 구조실험에 관련된 정보를 표현하는 데이터 모델을 제시하고 있는데, 이 데이터 모델은 포괄적인 구조실험 정보를 표현하는 데이터 모델의 하나인 리하이 모델에서 하이브리드 실험부분을 개선한 것이다. 하이브리드 구조실험에서의 부분구조물들을 표현하기 위하여 실험모델 클래스와 해석모델 클래스를 정의하였고, 이러한 클래스들의 정보교환을 조정하는 클래스를 정의하였으며, 제한된 범위의 시스템을 구현하여 객체들 간의 연결 상태를 파악할 수 있도록 하였다. 본 논문에서 기술한 데이터 모델은 구조실험자와 연구자들이 사용할 수 있는 하이브리드 구조실험 정보를 저장하는 컴퓨터 시스템을 개발하는데 적용할 수 있을 것으로 사료된다.

      • KCI등재

        Effects of the Recorded Earthquake Data on the Seismic Fragilities of Korean Nuclear Power Plant Structures

        조양희,조성국,Joe, Yang-Hee,Cho, Sung-Gook Computational Structural Engineering Institute of 2003 한국전산구조공학회논문집 Vol.16 No.3

        지진취약도분석 기술은 원자력발전소의 구조물 및 기기의 실제 내진성능을 평가하기 위하여 이용된다. 이 논문에서는 원자력 발전소를 구성하는 구조물들의 지진취약도를 평가하는 개선된 기법에 대하여 요약하였다. 또한, 최근 몇 년간 한반도에서 발생된 소규모 기록지진의 응답스펙트럼에 대한 공학적 특성을 평가하고, 이러한 기록지진의 응답스펙트럼을 부지의 실제 지반운동으로 사용할 경우, 지진취약도 분석에 미치는 영향을 검토하였다. 몇가지 예제 구조물에 대한 지진취약도분석을 통하여 기록지진의 특성이 한국형 원자력발전소의 내진성능에 미치는 영향을 정량적으로 평가하였다. 평가결과, 현재까지 부지의 실제 지반운동으로 사용되어 오던 Newmark 스펙트럼은 국내 시설물의 내진성능을 과대평가 할 수 있음을 보여주었다. Seismic fragility analysis (SFA) has been utilized to evaluate the actual seismic capacity of structure and equipment in nuclear power plants (NPP). This paper briefly introduces an improved method for evaluating seismic fragilities of components of NPP's in Korea. Engineering characteristics of small magnitude earthquake spectra recorded in the Korean peninsula during the last several years are also discussed in this paper. Some significant differences between the Newmark's spectra and the recorded spectra as a site-dependent spectra are assessed. Several comparative SFA's have been performed to evaluate the effects of the recorded earthquakes on the seismic capacities of Korean NPP structures. The results showed that SFA using the Newmark's spectra might over estimate the actual seismic capacities of Korean facilities.

      • KCI등재

        Three Dimensional Responses of Middle Rise Steel Building under Blast Loads

        황영서,이완수,Hwang, Young-Seo,Lee, Wan-Soo Computational Structural Engineering Institute of 2011 한국전산구조공학회논문집 Vol.24 No.6

        최근 들어 여러 테러에 의한 폭발사건에서 유발된 위험상황에서 보듯이 폭발에 의한 인명피해나 시설물의 손상은 우리가 고려하는 재해수준을 넘는 비참한 결과를 항상 수반한다. 하지만 폭발에 대한 구조물의 설계는 그 연구나 대책이 상당히 미비한 실정이다. 이에 미국건물설계기준(UBC94)을 바탕으로 내진설계(Welded Moment Resistant Frame)된 10층 건물의 폭발에 대한 해석적 모델을 제공하고자 한다. 현재 폭발하중의 정량적인 결과는 미국 육군(U.S.Department of Army)에서 개발된 경험적 방법에 기반을 둔 프로그램을 통해 폭간거리에 따른 하중의 크기와 분포를 알 수 있다. 본 연구에 사용된 폭원의 성격은 반구형 표면 폭발(Hemispherical Surface Burst)의 경우를 사용하였으며, 또한 선형 및 비선형 시간 이력해석을 통해 건물의 변위, 상대변위, 요구/수행비 및 비선형 거동에 대한 해석적 결과를 제공하였다. 또한 현재 사용되고 있는 내진기준(FEMA356)에 적용하여 소성힌지의 거동을 통해 폭발에 대한 건물의 성능수준을 예상하였다. It has been suggested that buildings designed for strong ground motions will also have improved resistance to air blast loads. As an initial attempt to quantify this behavior, the responses of a ten story steel building, designed for the 1994 building code, with lateral resistance provided by perimeter moment frames, is considered. An analytical model of the building is developed and the magnitude and distribution of blast loads on the structure are estimated using available computer software that is based on empirical methods. To obtain the relationship between pressure, time duration, and standoff distance, these programs are used to obtain an accurate model of the air blast loading. A hemispherical surface burst for various explosive weights and standoff distances is considered for generating the air blast loading and determining the structural response. Linear and nonlinear analyses are conducted for these loadings. Air blast demands on the structure are compared to current seismic guidelines. These studies present the displacement responses, story drifts, demand/capacity ratio and inelastic demands for this structure.

      • KCI등재

        Simulation of Dynamic Crack Propagation in Uni-Directional and Cross-Ply Fiber-Reinforced Composites

        황찬규,Hwang, Chan-Gyu Computational Structural Engineering Institute of 2008 한국전산구조공학회논문집 Vol.21 No.4

        이 논문에서는 단일방향 및 크로스-플라이 섬유강화 복합재에서의 동적 균열 전파를 모사하기 위해 특별히 고안된 스펙트랄 방법의 정식화와 수치적 구현 방법에 대해 제시한다. 이 방법은 균열면에서 작용하는 힘과 변위 사이의 스펙트랄 관계식에 기초하고 있고, 재료는 횡등방성 고체로 가정된다. 본 논문에서 제안된 방법에 의해 섬유보강 복합재에서 전파하는 균열문제가 대해 검토 해석되며, 실험 및 문헌에 나와 있는 결과와 비교된다. 이 방법은 FRP 보강 철근 콘크리트 구조물에서의 균열해석문제에 직접 적용이 가능하다. This paper presents the formulation and numerical implementation of a spectral scheme specially developed to simulate dynamic fracture events in unidirectional and cross-ply fiber-reinforced composites. The formulation is based on the spectral representation of the transversely isotropic elastodynamic relations between the traction stresses along the fracture plane and the resulting displacements. Example problem of dynamically propagating cracks in fiber-reinforced composites is investigated and compared with reference solutions available in the literature and/or experimental observations. This scheme can be directly applicable to the interfacial fracture analysis in the FRP reinforced concrete structures.

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