• 한국구조물진단유지관리공학회 논문집
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• 제6권2호
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• pp.157-165
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• 2002

Nonlinear analysis of the reinforced concrete beam subjected to torsion is presented. Seventeen equations involving seventeen variables are derived from the equilibrium equation, compatibility equation, and the material constitutive laws to solve the torsion problem. Newton method was used to solve the nonlinear simultaneous equations and efficient algorithms are proposed. Present model covers the behavior of reinforced concrete beam under pure torsion from service load range to ultimate stage. Tensile resistance of concrete after cracking is appropriately considered. The softened concrete truss model and the average stress-strain relations of concrete and steel are used. To verify the validity of present model, the nominal torsional moment strengths according to ACI-99 code and the ultimate torsional moment by present model are compared to experimental torsional strengths of 55 test specimens found in literature. The ultimate torsional moment strengths by the present model show good results.

• 한국전산구조공학회논문집
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• 제23권6호
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• pp.659-665
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• 2010

The finite element method(FEM) is proven to be an effective approximate method of structural analysis if proper element types and meshes are chosen, and recently, the method is often applied to solve complex dynamic and nonlinear problems. A properly chosen element type and mesh yields reliable results for dynamic finite element structural analysis. However, dynamic behavior of a structure may include unpredictably large strains in some parts of the structure, and using the initial mesh throughout the duration of a dynamic analysis may include some elements to go through strains beyond the elements' reliable limits. Thus, the finite element mesh for a dynamic analysis must be dynamically adaptive, and considering the rapid process of analysis in real time, the dynamically adaptive finite element mesh generating schemes must be computationally efficient. In this paper, a computationally efficient dynamically adaptive finite element mesh generation scheme for dynamic analyses of structures is described. The concept of representative strain value is used for error estimates and the refinements of meshes use combinations of the h-method(node movement) and the r-method(element division). The shape coefficient for element mesh is used to correct overly distorted elements. The validity of the scheme is shown through a cantilever beam example under a concentrated load with varying values. The example shows reasonable accuracy and efficient computing time. Furthermore, the study shows the potential for the scheme's effective use in complex structural dynamic problems such as those under seismic or erratic wind loads.

• 한국구조물진단유지관리공학회 논문집
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• 제13권2호통권54호
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• pp.215-222
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• 2009

콘크리트 공시편의 외부보강을 위해서 강판과 FRP 자켓을 이용하였다. 기존의 강판 또는 FRP 자켓 보강기법은 보강재와 콘크리트 사이에 접착제를 이용하여 시공하므로 콘크리트와 보강재가 합성거동 하게 된다. 그러나 본 연구에서 사용한 강판 보강기법은 외부압착에 의한 기법으로 강판과 콘크리트가 합성거동을 하지 않는다. 본 연구에서는 비합성거동과 합성거동을 하는 보강된 콘크리트 시편의 압축 변형률의 측정과 이를 보정하는 기법을 제시하였다. 비합성거동의 강판보강 콘크리트 시편의 압축변형률 측정은 강판의 표면에서 변형률을 측정하여 표시할 수 없으며, 시편에 설치하여 측정하는 compressometer를 사용할 수도 없었다. 따라서 시편의 상하단에 두꺼운 판을 설치하여 두 판사이의 변형을 측정한 후. 이를 압축변형률로 변환하였다. 합성 거동을 하는 FRP 보강의 경우는 FRP 튜브 표면에서 측정되는 수직방향의 변형률을 콘크리트의 압축변형률로 사용이 가능하다. 그러나 튜브 표면의 수직변형률은 시편의 부풀음에 의한 인장변형률이 포함되어 있기 때문에 콘크리트의 압축변형률을 추정하기 위해서는 이를 보정하여야 한다. 보정된 압축변형률은 콘크리트 내부에서 측정한 변형률과 기존의 콘크리트 연속체 모델과 비교하였을 때, 만족한 결과를 보였다. 보정 전의 응력-변형률 곡선은 콘크리트의 연성거동 및 에너지 소산능력을 보정 전에 비해 낮게 평가할 위험성이 있다.

• Structural Engineering and Mechanics
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• 제53권2호
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• pp.205-226
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• 2015

Finite element method (FEM) is an effective quantitative method to solve complex engineering problems. The basic idea of FEM for a complex problem is to be able to find a solution by reducing the problem made simple. If mathematical tools are inadequate to obtain precise result, even approximate result, FEM is the only method that can be used for structural analyses. In FEM, the domain is divided into a large number of simple, small and interconnected sub-regions called finite elements. FEM has been used commonly for linear and nonlinear analyses of different types of structures to give us accurate results of plane stress and plane strain problems in civil engineering area. In this paper, FEM is used to investigate stress analysis of a shear wall which is subjected to concentrated loads and fundamental principles of stress analysis of the shear wall are presented by using matrix displacement method in this paper. This study is consisting of two parts. In the first part, the shear wall is discretized with constant strain triangular finite elements and stiffness matrix and load vector which is attained from external effects are calculated for each of finite elements using matrix displacement method. As to second part of the study, finite element analysis of the shear wall is made by ANSYS software program. Results obtained in the second part are presented with tables and graphics, also results of each part is compared with each other, so the performance of the matrix displacement method is demonstrated. The solutions obtained by using the proposed method show excellent agreements with the results of ANSYS. The results show that this method is effective and preferable for the stress analysis of shell structures. Further studies should be carried out to be able to prove the efficiency of the matrix displacement method on the solution of plane stress problems using different types of structures.

• 대한기계학회논문집A
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• 제35권9호
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• pp.1041-1050
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• 2011

미크론 단위의 크기를 갖는 구조물의 소성변형에서 나타나는 길이 효과를 고려하여 유한요소 해석을 하기 위하여 변형률 구배 소성이론을 이용하는 탄소성 유한요소 모델링 및 해석법을 제안하였다. 기존의 연구에서 주로 고차, 고자유도 및 혼합요소, 초 요소 등을 필요로 하였던 것에 비하여 본 논문에서는 이들을 배제하는 변위법 저차 평면 요소 및 삼차원 요소를 도입하였다. 이는 비선형 증분 해석의 프레임워크에서 계산된 소성 변형률의 절점 평균값으로 보간하여 적분점에서의 변형률 구배를 구하고 테일러 전위 모델에 의한 변형률 경화 구성방정식을 적용하므로서 가능하였다. 제안된 방법론은 선형 삼각 및 사각요소, 선형 사면체, 육면체 요소에 대해 적용되었으며 마이크로 굽힘, 마이크로 비틀림, 마이크로 기공과 같은 대표적인 길이 스케일 문제를 통하여 수치적으로 검증하였다. 본 논문에서 제안한 방법은 계산이 매우 쉬우면서도 실험값들과 비교해 볼 때, 변형률 구배 소성이론 즉, 길이 효과를 잘 나타내어 주었다.

• Structural Engineering and Mechanics
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• 제66권6호
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• pp.693-701
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• 2018

This paper develops a nonlocal strain gradient plate model for vibration analysis of graphene sheets under thermal environments. For more accurate analysis of graphene sheets, the proposed theory contains two scale parameters related to the nonlocal and strain gradient effects. Graphene sheet is modeled via a two-variable shear deformation plate theory needless of shear correction factors. Governing equations of a nonlocal strain gradient graphene sheet on elastic substrate are derived via Hamilton's principle. Differential quadrature method (DQM) is implemented to solve the governing equations for different boundary conditions. Effects of different factors such as temperature rise, nonlocal parameter, length scale parameter, elastic foundation and aspect ratio on vibration characteristics a graphene sheets are studied. It is seen that vibration frequencies and critical buckling temperatures become larger and smaller with increase of strain gradient and nonlocal parameter, respectively.

• 한국지반공학회:학술대회논문집
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• 한국지반공학회 1991년도 추계학술발표회 논문집 지반공학에서의 컴퓨터 활용 COMPUTER UTILIZATION IN GEOTECHNICAL ENGINEERING
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• pp.216-232
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• 1991

This Finite Element Program(TAFEM) has been developed to be able to carry out the structural analsis of tunnel section and simulate the surrounding ground behaviour due to New Austrian Tunnelling Method, of which main support is the surrounding ground, itself. The Elasto-plastic theory has been applied. The used finite elements are 8-noded isoparametric element(rock & shotcrete), 2 or 3-noded rod element(rock bolt) and infinite boundary element. The load incremental method and tangential stiffness method has been used. Associated flow rule was applied to plastic flow and yield criteria inclued not only Mohr-Coulomb but also Drucker-Prager. In this paper, Drucker-Prager yield criterion has been used. The relationship between plastic strain and stress is based on the incremental strain concept and stress-strain equation on the basis of the stress path of each gauss point has been adopted. It may be rational that rock is considered to be no-tension material, so that no-tension analysis has been adopted in accordance with the brittle fracture constitutive equation.

• Structural Engineering and Mechanics
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• 제19권6호
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• pp.603-618
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• 2005

The split Hopkinson pressure bar (SHPB) technique is widely used to characterize the dynamic mechanical response of engineering materials at high strain rates. In this paper, attendant problems associated with testing 70 mm diameter concrete specimens are considered, analysed and resolved. An adaptation of a conventional solid circular striker bar, as a means of achieving reliable and repeatable SHPB tests, is then proposed. In the analysis, a pseudo one-dimensional model is used to analyse wave propagation in a non-uniform striker bar. The stress history of the incident wave is then obtained by using the finite difference method. Comparison was made between incident waves determined from the simplified model, finite element solution and experimental data. The results show that the simplified method is adequate for designing striker bar shapes to overcome difficulties commonly encountered in SHPB tests. Using two specifically designed striker bars, tests were conducted on 70 mm diameter steel fibre reinforced concrete specimens. The results are presented in the paper.

• 한국전산구조공학회논문집
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• 제16권3호
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• pp.333-342
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• 2003

본 논문의 목적은 빔 구조물에서 발생할 수 있는 손상의 위치를 탐색하고, 그 손상의 정도를 추정할 수 있는 알고리즘을 제안하는 것이다. 제안된 방법은 구조물의 모달 변형에너지의 차이를 이용한다. 구조물 내 발생한 국부적인 손상의 위치를 파악하고 그에 상응하는 손상도를 추정할 수 있는 손상지수를 손상 전과 손상 후 구조물의 모드형상에서 얻을 수 있는 모달 변위로 표현하였고 그 관계식을 정립하였다. 구조물 내 손상의 위치를 결정하는 방법은 기 개발된 손상 지표를 적용하였다. 제안된 방법의 우수성과 효용성은 수치적으로 손상을 모사한 빔 구조물을 이용하여 입증하였다.

• 전산구조공학
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• 제10권3호
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• pp.185-193
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• 1997

탄성 선형 경화 재료로 구성된 복합 구조물의 자유 경계면에서 나타나는 응력 특이도를 평면 변형률 상태에서 계산하였다. 자유 표면력 경계조건과 계면 연속조건을 만족해야하는 지배 탄성 방정식은 2점 경계치문제로 정의되며, 일반 고유치 문제의 해인 고유치가 응력 특이도가 될 것이다. 자유경계면 근처에서 응력 성분을 r/sup s-1/에 비례한다고 가정하여 특정한 s(고유치)를 구하는 고유치 문제를 뉴톤향상법과 사격법을 사용하여 수치적으로 해를 구하였다.