• 한국정밀공학회지
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• 제34권4호
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• pp.259-264
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• 2017

Spectrally resolved interferometry (SRI) is an attractive technique to measure absolute distances without any moving components. In the spectral interferogram obtained by a spectrometer, the optical path difference (OPD) can simply be extracted from the linear slope of the spectral phase. However, SRI has a fundamental measuring range limitation due to maximum and minimum measurable distances. In addition, SRI cannot distinguish the OPD direction because the spectral interferogram is in the form of a natural sinusoidal function. In this investigation, we describe a direction determining SRI and propose the optimal conditions for determining OPD direction. Spectral phase nonlinearity, caused by a dispersive material, effects OPD direction but deteriorates spectral interferogram visibility. In the experiment, various phase nonlinearities were measured by adjusting the dispersive material (BK7) thickness. We observed the interferogram visibility and the possibility of direction determination. Based on the experimental results, the optimal dispersion conditions are provided to distinguish OPD directions of SRI.

• Structural Engineering and Mechanics
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• 제29권3호
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• pp.259-278
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• 2008

This paper presents a nonlinear finite element procedure accounting for the effects of geometric as well as material nonlinearities for reinforced concrete bridge piers supported by laminated rubber bearings. Reinforced concrete bridge piers supported by laminated rubber bearings and carrying a cyclic load were analyzed by using a special purpose, nonlinear finite element program, RCAHEST. For reinforced concrete, the proposed robust nonlinear material model captures the salient response characteristics of the bridge piers under cyclic loading conditions and addresses with the influence of geometric nonlinearity on post-peak response of the bridge piers by transformations between local and global systems. Seismic isolator element to predict the behaviors of laminated rubber bearings is also developed. The seismic performance of reinforced concrete bridge piers supported by laminated rubber bearings is assessed analytically. The results show good correlation between the experimental findings and numerical predictions, and demonstrate the reliability and robustness of the proposed analytical model. Additionally, the studies and discussions presented in this investigation provide an insight into the key behavioral aspects of reinforced concrete bridge piers supported by laminated rubber bearings.

• 한국전산구조공학회논문집
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• 제15권3호
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• pp.491-499
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• 2002

직교이방성 적층평판해석을 위해 퇴화 쉘요소에 기초를 둔 p-version 유한요소법이 제안되었다. 이 모델의 비선형 정식화과정에서 기하비선형의 경우 von Karman의 대변형-소변형률 가정을 설명하기 위해 Total Lagrangian 방법이 채택되었으며, 재료비선형의 경우 Huber-Mises의 항복기준과 변형률경화 항복함수에 근거를 둔 Prandtl-Reuss 유동법칙이 사용되었다. 재료모델은 이방성을 표현하는 매개변수에 의해 이방겅재료를 고려할 수 있도록 하였다. 적층평판이론으로는 전단변형 효과를 고려할 수 있는 등가단출이론(ESL Theory)에 기초를 두었기 때문에 두 적층간 계면에서의 전단변형률은 연속이라는 조건을 갖게된다 적분형 르장드르 다항식이 형상함수로 사용되었으며 형상함수의 차수는 1차에서 10차까지 변화시킬 수 있다. 또한, Causs-Lobatto 수치적될법을 사용하기 때문에 기존의 가우스 적분점에서 계산되던 응력값은 이 적분법의 적분점이 절점에 위치하므로 절점에서 바로 응력값이 산출되도록 하였다 극한하중 수렴성, 비선형 효과, 소성역의 형상 등의 비교관점을 통해 p-version 유한요소 모델의 적정성을 보이고자 하였다.

• Steel and Composite Structures
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• 제22권2호
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• pp.429-448
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• 2016

This paper presents a finite element (FE) model for predicting the behaviour of steel column-column connections under axial compression and tension. A robustness approach is utilised for the design of steel column-column connections. The FE models take into account for the effects of initial geometric imperfections, material nonlinearities and geometric nonlinearities. The accuracy of the FE models is examined by comparing the predicted results with independent experimental results. It is demonstrated that the FE models accurately predict the ultimate axial strengths and load-deflection curves for steel column-column connections. A parametric study is carried out to investigate the effects of slenderness ratio, contact surface imperfection, thickness of cover-plates, end-plate thickness and bolt position. The buckling strengths of steel column-column connections with contact surface imperfections are compared with design strengths obtained from Australian Standards AS4100 (1998) and Eurocode 3 (2005). It is found that the column connections with maximum allowable imperfections satisfy the design requirements. Furthermore, the steel column-column connections analysed in this paper can be dismantled and reused safely under typical service loads which are usually less than 40% of ultimate axial strengths. The results indicate that steel column-column connections can be demounted at 50% of the ultimate axial load which is greater than typical service load.

• 대한기계학회논문집
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• 제16권4호
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• pp.621-629
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• 1992

본 연구에서는 Kelvin의 기본해와 초기응력 증분에 의해 정식화된 경계적분방 정식을 이용하여 점차적으로 외력을 증가시켰을 때, 선형등방경화재에 국부적으로 생 기는 항복영역과 항복하중, 탄소성 응력해석등을 재료비선형문제로 해석하였다. 이 때 초기응력 증분을 결정함에 있어서 종래에는 등가 소성변형률을 수렴판정으로 해석 하였지만, 이는 구분적인 선형 경화재와 온도 의존성 문제에는 적당하지 않으므로 암 기용일등은 등가응력과 응력-변형률 선도를 이용하여 수렴판정을 하였다. 그러나 이 방법은 소성역에서의 기울기가 변화하는 곳에서는 피할 수 없는 오차가 존재한다. 따라서 여기에서는 계산된 초기응력 증분에 의한 초기 탄성변형률에너지 증분과 응력 -변형률선도로 부터 구해지는 초기 탄성변형률에너지 증분을 이용한 수렴판정으로 초 기응력증분을 결정하였다. 또한, 내부영역적분을 일부 해석적인 적분과 수치적분을 병행한 경우와 전부 수치적분방법으로 내압을 받는 실린더와 단순 인장하중이 작용하 는 양편 Ⅴ형 노치를 갖는 박판의 경우에 적용하여 해석하였으며, 그 결과를 유한요소 법 프로그램인 NISA(numerically integrated elements for system analysis)로 구한 결과치와 비교, 고찰하였다.

• 한국전산구조공학회논문집
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• 제18권4호통권70호
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• pp.395-404
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• 2005

본 논문에서는 동적하중 재하 시 공간 강뼈대 구조물의 비선형 시간이력 해석에 대한 간편하고 효율적인 수치해석 기법을 제시하였다. 뼈대의 강성행렬에 안정함수를 적용함으로서 기하학적 비선형성 즉 P-$\delta$ 및 P-$\Delta$ 효과를 고려하였다. 접선계수 개념 및 New Orbison 완전 소성면에 기초한 연화소성힌지를 적용하여 축방항력에 의한 부재의 점진적 항복 및 휨에 의한 부재의 부분 소성화를 고려하였다. 증분형태로 정식화된 뼈대 구조의 동적평형방정식의 해를 수치적으로 구하기 위하여 적분형태의 평균가속도법을 사용하여 컴퓨터 프로그램을 개발하였다. 검증 예제에 대하여 보요소 모델을 사용한 ABAQUS 및 개발된 프로그램에 의한 해석결과를 비교함으로서 개발된 프로그램의 정밀도와 해석시간에 대한 효율성을 입증하였다.

• 한국철도학회:학술대회논문집
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• 한국철도학회 2011년도 춘계학술대회 논문집
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• pp.1242-1247
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• 2011

This study investigates vertical vibration control method for railway structure by using vertical vibration control device. The device consists of high stiffness polyurethane spring and friction damper recognized by National Center for Earthquake Engineering Research of USA for durability. To confirm the capacity of vertical vibration control, at first, behavior equation is established by considering correlation among the components. Then, hysteresis curve is drawed from behavior equation. By considering both dynamic behaviors and material nonlinearities, more reasonable behavior of the device can be simulated. After that, the Validity of the vibration control trend is proved by FEM(Finite Element Method).

• Structural Engineering and Mechanics
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• 제2권4호
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• pp.313-326
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• 1994

Some structures under the action of some specific loads can be treated as consisting of rigid and deformable parts. The paper presents a way to include rigid elements into a finite element model accounting for geometrical and material nonlinearities. Lagrange multipliers technique is used to derive equations of motion for the coupled deformable-rigid system. Solution algorithm based on the elimination of the Lagrangian multipliers and dependent kinematic unknowns at the element level is described. A follow-up paper(Rojek and Kleiber 1993) complements the discussion by giving details of the computer implementation and presenting some realistic test examples.

• Structural Engineering and Mechanics
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• 제20권6호
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• pp.609-630
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• 2005

A reliability analysis method is proposed in this paper through a combination of the advantages of the response surface method (RSM), finite element method (FEM), first order reliability method (FORM) and the importance sampling updating method. The accuracy and efficiency of the method is demonstrated through several numerical examples. Then the method is used to estimate the serviceability reliability of cable-stayed bridges. Effects of geometric nonlinearity, randomness in loading, material, and geometry are considered. The example cable-stayed bridge is the Second Nanjing Bridge with a main span length of 628 m built in China. The results show that the cable sag that is part of the geometric nonlinearities of cable-stayed bridges has a major effect on the reliability of cable-stayed bridge. Finally, the most influential random variables on the reliability of cable-stayed bridges are identified by using a sensitivity analysis.

• Structural Engineering and Mechanics
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• 제30권6호
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• pp.763-785
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• 2008

In this study, a flexibility-based finite element method considering geometric and material nonlinearities is developed for analyzing steel-concrete frame structures. The stability functions obtained from the exact buckling solution of the beam-column subjected to end moments are used to accurately capture the second-order effects. The proposed method uses the force interpolation functions, including a moment magnification due to the axial force and lateral displacement. Thus, only one element per a physical member can account for the interaction between the bending moment and the axial force in a rational way. The proposed method applies the Newton method based on the load control and uses the secant stiffness method, which is computationally both efficient and stable. According to the evaluation result of this study, the proposed method consistently well predicts the nonlinear inelastic behavior of steel-concrete composite frames and gives good efficiency.