• Structural Engineering and Mechanics
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• 제59권6호
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• pp.973-992
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• 2016

A direct and relatively simple method for controlling nodal displacements and/or internal bar forces has been developed for prestressable structural assemblies including complex elements ("macro-elements", e.g., the pantographic element), involving Matrix Condensation, in which structural matrices being built up from matrices of elementary elements. The method is aimed at static shape control of geometrically sensitive structures. The paper discusses identification of the most effective bars for actuation, without incurring violation in bar forces, and also with objective of minimal number of actuators or minimum actuation. The advantages of the method is that the changes for both force and displacement regimes are within a single formulation. The method can also be used for adjustment of bar forces to either reduce instances of high forces or increase low forces (e.g., in a cable nearing slack).

• Earthquakes and Structures
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• 제13권3호
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• pp.241-253
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• 2017

In this paper, dynamic response of the horizontal nanofiber reinforced polymer (NFRP) strengthened concrete beam subjected to seismic ground excitation is investigated. The concrete beam is modeled using hyperbolic shear deformation beam theory (HSDBT) and the mathematical formulation is applied to determine the governing equations of the structure. Distribution type and agglomeration effects of carbon nanofibers are considered by Mori-Tanaka model. Using the nonlinear strain-displacement relations, stress-strain relations and Hamilton's principle (virtual work method), the governing equations are derived. To obtain the dynamic response of the structure, harmonic differential quadrature method (HDQM) along with Newmark method is applied. The aim of this study is to investigate the effect of NFRP layer, geometrical parameters of beam, volume fraction and agglomeration of nanofibers and boundary conditions on the dynamic response of the structure. The results indicated that applied NFRP layer decreases the maximum dynamic displacement of the structure up to 91 percent. In addition, using nanofibers as reinforcement leads a 35 percent reduction in the maximum dynamic displacement of the structure.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2011년도 추계학술대회 논문집
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• pp.572-577
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• 2011

A disc spring consists of a conical disc. A load-displacement formula was newly developed in the form of energy method to consider both rigid and friction. The cross section of the disc spring has identical slope angles at the bottom of conical. To solve such a problem, an energy method calculation is proposed. To achieve the goal of this study, the proposed calculation is extended to a disc spring with friction. A firm basis background study based on Almen's work is presented in developing a new numerical approach to predict the available formulation for a disc spring with friction.

• 한국농공학회지
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• 제43권4호
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• pp.89-96
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• 2001

In this study non-linear finite element analysis of dynamic response of steel arch under partially distributed dynamic load was discussed. Material and geometric non-linearities were included in finite element formulation and steel behavior was modeled with Von Mises yield criteria. Either radial or vertical dynamic load was dealt in numerical examples. Normal arch and arch with maximum shape imperfection of L/11,000 were studied. The analysis results showed that maximum displacement at the center of arch was occurred when 70% of arch span was loaded. The maximum displacement at a quarter of arch span was occurred when 50% of arch span was loaded and the displacement was larger than that of center of arch. Ratio of arch rise to arch span within 0.2∼-.3 seems to be appropriate for arch under radial or vertical load.

• Structural Engineering and Mechanics
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• 제13권5호
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• pp.491-504
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• 2002

Recently we formulated a 2D hybrid stress element from the 3D Hellinger-Reissner principle for the analysis of thick bodies that are symmetric to the thickness direction. Polynomials have typically been used for all the displacement and stress fields. Although the element predicted the dominant stress and all displacement fields accurately, its prediction of the out-of-plane shear stresses was affected by the very high order terms used in the polynomials. This paper describes an improved formulation of the 2D element using Fourier series expansion for the out-of-plane displacement and stress fields. Numerical results illustrate that its predictions have markedly improved.

• 터널과지하공간
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• 제10권2호
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• pp.173-179
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• 2000

절리면의 전단거동에서 나타나는 응력 및 변위의 비선형 특성을 탄소성해석에 의해 모사하는 경우 소성유동법칙이 해석결과에 미치는 영향을 검토하였다. Plesha의 절리구성모델을 적용하여 일정수직응력조건과 일정수직변위조건에서 수치직접전단시험을 실시하였다. 연상유동법칙을 적용하면 과도한 수직팽창이 예측되는 반면에 비연상유동법칙을 적용한 해석은 실제 절리거동을 잘 모사하고 있음을 보였다. 비연상유동법칙의 적용으로 강성행렬이 비대칭이 피는 단점을 보완하기 위해 비연상유동법칙을 적용하는 경우라도 요소의 접선강성행렬을 대칭화시키는 수치해석 기법이 제안되었다. 본래의 절리면과 동일한 소성변형을 일으키지만 연상유동법칙을 따르는 등가의 절리면을 가정함으로써 대칭인 탄소성행렬을 유도하였다. 일정수직음력조건에서 수티 직접전단시험을 실시하여 제안된 강성행렬 대칭화 기법의 유효성을 검증하였다.

• 전산구조공학
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• 제3권3호
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• pp.113-123
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• 1990

본 연구에서는 개선된 degenerated 쉘 유한요소의 탄소성 및 기하학적 비선형 해석에의 적용성을 고찰하였다. 본 연구의 개선된 degenerated 쉘요소는 shear locking 해결에 우수한 결과를 보인 가정된 전단변형도를 대치사용하고, membrance locking 현상을 제거하기위해 평면내 변형도의 구성시 감차적분을 행하며, 쉘요소 자체의 거동을 보완하기위해 비적합변위형을 선택적으로 추가하였다. 본 요소는 shear/membrance locking이 발생하지 않으며, 전달가능한 거짓 영에너지모드도 나타나지않는다. 소성변형 정형화에서는 적층모델을 사용하며, 재료는 von Mises항복조건을 따른다고 가정한다. 유한변형을 고려한 기하학적 비선형 방정식을 total lagrangian수식화를 사용하여 정형화 하였고, 비선형 방정식은 하중제어 및 변위제어법을 사용한 Newton-Raphson 반복법으로 반복 계산한다. 여러 예제해석을 통하여 본 개선된 degenerated 쉘 유한요소의 정확도를 고찰하였다.

• 대한토목학회논문집
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• 제12권4_1호
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• pp.67-76
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• 1992

축대칭(軸對稱) 선형강성(線形彈性) 응력해석을 위해 p-version 유한요소법에 기초한 계층적(階層的) 정식화 과정이 제안되었다. 이 방식은 적분형 르장드르 다항식을 사용하여 절점좌표값을 갖지 않는 절점을 추가하여 형상함수의 조합형태로 변위함수(變位)를 근사시키는 방법이다. 형상함수(形狀函數)가 계층적 성질을 갖기 때문에 강성도(剛性度)행렬과 하중벡터도 계층적이 된다. 본 연구에서 제안된 요소(要所)의 장점(長點)은 다음과 같다. 첫째, 개선된 수치연산의 효율성이며 둘째, 요소간에 서로 다른 차수(次數)의 형상함수를 사용할 수 있고 셋째, p-세분화를 할 때 저차(低次)일 때 계산된 값을 그대로 사용할 수 있다. 수치예제를 통해 제안된 요소의 정확도(正確度), 효율성(效率性), 모델링의 간편성(簡便性), 적용성(適用性) 및 변위와 응력 그리고 에너지 Norm등을 사용하여 그 우월성을 입증하고 있다. 몇 가지 예제의 해석결과는 이미 발표된 논문과 아울러 해석적 방법에 의한 결과와 비교되었다.

• 한국전산구조공학회논문집
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• 제13권2호
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• pp.197-208
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• 2000

최 등/sup 1)/은 total lagrangian formulation에 근거한 증분 평형방정식을 적용하고, 강도행렬 산정시 회전각의 2차항을 포함시켜 기하학적 비선형 해석시 해의 수렴성을 향상시켰다. 또한 등매개 쉘 유한요소의 단점인 전단구속 현상과 제로 에너지 모드가 발생하는 문제를 극복하기 위하여 가정 변형률장을 적용하여 보강된 판 및 쉘 구조의 비선형 해석법을 개발하였다. 본 연구에서는 잔류응력을 고려한 쉘구조의 극한강도 해석을 수행하기 위하여, 대변형거동과 함께 소성붕괴거동을 추적할 수 있는 알고리즘을 제시한다. 잔류응력을 고려한 증분평형방정식에 return mapping algorithm을 이용한 탄소성 해석법을 결합시켜서 보강된 판 및 쉘구조의 극한거동을 파악한다. 수치해석 예제를 통하여 본 연구에서 제시된 유한요소 및 비선형 해석 알고리즘에 대한 효율성 및 적용성을 확인하였다.

• Steel and Composite Structures
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• 제52권3호
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• pp.273-291
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• 2024

This paper presents a three-dimensional displacement-based formulation to investigate the free vibration of functionally graded nanoplates resting on a Winkler-Pasternak foundation based on the nonlocal elasticity theory. The material properties of the FG nanoplate are considered to vary continuously through the thickness of the nanoplate according to the power-law distribution model. A general three-dimensional displacement field is considered for the plate, which takes into account the out-of-plane strains of the plate as well as the in-plane strains. Unlike the shear deformation theories, in the present formulation, no predetermined form for the distribution of displacements and transverse strains is considered. The equations of motion for functionally graded nanoplate are derived based on Hamilton's principle. The solution is obtained for simply-supported nanoplate, and the predicted results for natural frequencies are compared with the predictions of shear deformation theories which are available in the literature. The predictions of the present theory are discussed in detail to investigate the effects of power-law index, length-to-thickness ratio, mode numbers and the elastic foundation on the dynamic behavior of the functionally graded nanoplate. The present study presents a three-dimensional solution that is able to determine more accurate results in predicting of the natural frequencies of flexural and thickness modes of nanoplates. The effects of parameters that play a key role in the analysis and mechanical design of functionally graded nanoplates are investigated.