• 콘크리트학회지
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• 제7권1호
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• pp.145-155
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• 1995

본 논문에서는 단조증가하중을 받는 철근콘크리트 보의 비선형거동, 즉, 탄성, 비탄서의 극한영역에 이르기까지의 모든 하중이력에 대한 응력-변형도 관계와 균열의 진행 및 철근과 콘크리트의 응력과 변형도 등을 정확히 해석할 수 있는 해석법의 제시를 목적으로 한다. 이러한 목적을 위하여 철근콘크리트의 재료적 비선형성으로 균열발생후 이장, 압축 및 전단모델과 철근에 대한 모델을 각각 조합하여 고려하였다. 콘크리트의 해석모델로서 분산균열모델을 사용하였고, 철근에 대해서는 등가의 분산분포된 요소와 철근의 정확한 거동과 위치를 확보하기 위해 별도의 축력만을 받는 봉요소로 모델화하여 사용하였다. 본 논문에서 제안한 해석법의 타당성을 검증하기 위해 몇 개의 실험치를 해석치와 비교, 검토한 결과, 본 논문의 해석법이 3.5-15(%)의 오차를 보이며, 정확함을 알 수 있었다.

• Steel and Composite Structures
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• 제7권4호
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• pp.279-301
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• 2007

When coupling beams are proportioned appropriately in coupled core wall (CCW) systems, the input energy from ground motions is dissipated primarily through inelastic deformations in plastic hinge regions at the ends of the coupling beams. It is desirable that the plastic hinges form at the beam ends while the base wall piers remain elastic. The strength and stiffness of the coupling beams are, therefore, crucial if the desired global behavior of the CCW system is to be achieved. This paper presents the results of nonlinear response history analysis of two 20-story CCW buildings. Both buildings have the same geometric dimensions, and the components of the buildings are designed based on the equivalent lateral force procedure. However, one building is fitted with steel coupling beams while the other is fitted with diagonally reinforced concrete coupling beams. The force-deflection relationships of both beams are based on experimental data, while the moment-curvature and axial load-moment relationships of the wall piers are analytically generated from cross-sectional fiber analyses. Using the aforementioned beam and wall properties, nonlinear response history analyses are performed. Superiority of the steel coupling beams is demonstrated through detailed evaluations of local and global responses computed for a number of recorded and artificially generated ground motions.

• Advanced Composite Materials
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• 제18권1호
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• pp.21-42
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• 2009

The vibration characteristics of post-buckled laminated composite doubly curved shells are investigated. The finite element method is used for the analysis of post-buckling and free vibration of post-buckled laminated shells. The geometric non-linear finite element model includes the general non-linear terms in the strain-displacement relationships. The shell geometry used in the present formulation is derived using an orthogonal curvilinear coordinate system. Based on the principle of virtual work the non-linear finite element equations are derived. Arc-length method is implemented to capture the load-displacement equilibrium curve. The vibration characteristics of post-buckled shell are performed using tangent stiffness obtained from the converged deflection. The code is first validated and then employed to generate numerical results. Parametric studies are performed to analyze the snapping and vibration characteristics. The relationship between loads and fundamental frequencies and between loads and the corresponding displacements are determined for various parameters such as thickness ratio and shallowness.

• 전산구조공학
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• 제4권3호
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• pp.99-106
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• 1991

강섬유 보강 콘크리트(SFRC)의 휨 거동은 재료의 인장 및 압축 응력-변형도에 의존하며 이때 이들은 휨응력시 작용하는 strain gradient의 영향을 받게 된다. SFRC의 경우, 휨 실험은 직인장 실험과 비교하여 볼 때 상대적으로 간편하며 또한 다수의 실험결과가 확보되어 있다. 따라서 이들 휨 실험 결과로부터 SFRC의 기본적 재료 성질인 인장응력-변형도를 유출하는 것은 중요하다고 하겠다. 본 연구의 목적을 위하여 휨 실험 data를 해석하기 위한 "System Identification"방법론이 사용되었으며 그 결과 휨 응력하에서의 SFRC의 인장거동을 설명하는 주요 변수들이 고찰되었다.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 1996년도 가을 학술발표회 논문집
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• pp.328-334
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• 1996

This report is the results of an experimental study on the relative effectiveness of different types of steel fiber in concrete. The fibers considered in the study were straight-indent and hooked-collated with aspect ratios of about 50~100. A fiber volume of 0~2 percent was used throughout this investigation. The fresh fibrous mixes were characterized by the slump and vebe-time, and the hardened materials by their compressive and flexural load-deflection relationships. Hooked fibers were found to be more effective than straight ones in improving the strength and energy absorption of concrete.

• 한국안전학회지
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• 제8권1호
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• pp.47-53
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• 1993

Residual Deformation Analysis(RDA) is a new method for ratings of the continuous bridges. The RDA makes it possible to expand the inelastic steel girder bridge design method set forth in the American Association of State Highway Officals'(AASHTO) Guide Specifications for Alternate Load Factor Design Procedures for Steel Beam Bridges Using Braced Compact Sections(1986) into an inelastic rating method. It is a method to assess the residual moments and deformations that are set up in a beam that has been loaded into the post-elastic range This method combines classical elastic conjugate beam theory with linear moment-rotation relationships for midspan inelastic positive moment. The limit state is inelastic serviceability limit. which is defined as the ratio of the span to midspan inelastic deflection(C=L/D).

• Structural Engineering and Mechanics
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• 제59권3호
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• pp.431-454
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• 2016

In this paper, the nonlinear static and free vibration analysis of Euler-Bernoulli composite beam model reinforced by functionally graded single-walled carbon nanotubes (FG-SWCNTs) with initial geometrical imperfection under uniformly distributed load using finite element method (FEM) is investigated. The governing equations of equilibrium are derived by the Hamilton's principle and von Karman type nonlinear strain-displacement relationships are employed. Also the influences of various loadings, amplitude of the waviness, UD, USFG, and SFG distributions of carbon nanotube (CNT) and different boundary conditions on the dimensionless transverse displacements and nonlinear frequency ratio are presented. It is seen that with increasing load, the displacement of USFG beam under force loads is more than for the other states. Moreover it can be seen that the nonlinear to linear natural frequency ratio decreases with increasing aspect ratio (h/L) for UD, USFG and SFG beam. Also, it is shown that at the specified value of (h/L), the natural frequency ratio increases with the increasing the values amplitude of waviness while the dimensionless nonlinear to linear maximum deflection decreases. Moreover, with considering the amplitude of waviness, the stiffness of Euler-Bernoulli beam model reinforced by FG-CNT increases. It is concluded that the R parameter increases with increasing of volume fraction while the rate of this parameter decreases. Thus one can be obtained the optimum value of FG-CNT volume fraction to prevent from resonance phenomenon.

• 대한기계학회논문집A
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• 제33권9호
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• pp.859-869
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• 2009

물성치와 하중-변위곡선을 일대일 대응 시킬 수 있는 함수를 생성함으로써, 미지 재료에 대한 압입시험 데이터로부터 바로 재료물성을 찾는 압입물성평가 기법을 제시했다. 원뿔형 압입 유한요소해석으로 압입자 중심각이 압입 하중-변위 곡선에 주는 영향을 살펴 보았다. 이로부터 한 압입자 중심각에 대해 같은 Kick's law 계수 C를 갖는 두 재료들이 압입자 중심각이 변하면 서로 다른 C 값들을 가짐을 확인했다. 이어 영률, 항복강도, 변형경화지수와 하중-변위곡선 사이의 상관관계들을 분석하고, 항복변형률이 변형경화 지수와 더불어 중요한 변수임을 확인했다. 이 두 특성들을 바탕으로 이중원뿔형 압입 물성평가 수식들을 작성했다. 1회 압입 후 재료의 영률을 평가하고, 두 압입자를 이용해 얻은 하중-변위 곡선들로부터 곡률계수들을 구해 항복변형률과 변형경화 지수를 구했다. 제시된 물성평가법은 압입 하중-변위곡선들로부터, 압입자 물성과 선단반경에 상관없이, 평균오차 2% 내에서 재료 물성값들을 준다.

• Steel and Composite Structures
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• 제25권4호
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• pp.457-472
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• 2017

The objective of this paper is to investigate the flexural behavior of concrete-filled round-ended steel tubes (CFRTs) under bending. Beam specimens were tested to investigate the mechanical behavior of the CFRTs, including four CFTs with different concrete strengths and steel ratios, and three CFRTs with varied aspect ratios. The load vs. deflection relationships and the failure modes for CFRTs were analyzed in detail. The composite action between the core concrete and steel tube was also discussed and examined based on the experimental results. In addition, ABAQUS program was used to develop the full-scale finite element model and analyze the effect of different parameters on the moment vs. curvature curves of the CFRTs bending about the major and minor axis, respectively. Furthermore, design formulas were proposed to estimate the ultimate moment and the flexural stiffness of the CFRTs, and the simplified theoretical model of the moment vs. curvature curves was also developed. The predicted results showed satisfactory agreement with the experimental and FE results. Finally, the differences of the experimental, FE and predicted results using the existing codes were illustrated.

• Computers and Concrete
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• 제15권3호
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• pp.411-436
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• 2015

In this work, a comprehensive approach to model the structural behaviour of Reinforced Concrete (RC) beams subjected to reinforcement corrosion is proposed. The coupled environmental - mechanical damage model developed by some of the authors is enhanced for considering the main effects of corrosion on concrete, on composite interaction between reinforcement bars and concrete and on steel reinforcement. This approach is adopted for reproducing a set of experimental tests on RC beams with different corrosion degrees. After the simulation of the sound beams, the main parameters involved in the relationships characterizing the effects of corrosion are calibrated and tested, referring to one degraded beam. Then, in order to validate the proposed approach and to assess its ability to predict the structural response of deteriorated elements, several corroded beams are analyzed. The numerical results show a good agreement with the experimental ones: in particular, the proposed model properly predicts the structural response in terms of both failure mode and load-deflection curves, with increasing corrosion level.