• Structural Engineering and Mechanics
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• 제61권4호
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• pp.463-473
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• 2017

Reinforced concrete is a complex material to be modeled in finite element domain. A proper material model is necessary to represent the nonlinear behaviour accurately. Though the nonlinear analysis of RC structures evolved long back, still an accurate and reliable model to predict the realistic behaviour of components are limited. It is observed from literature that there are three well-known models to represent the nonlinear behaviour of concrete. These models include Chu model (1985), Hsu model (1994) and Saenz model (1964).A new stress-strain model based on Weibull distribution has been proposed in the present study. The objective of the present study is to analyze a reinforced concrete beam under flexural loading by employing all the models. Nonlinear behaviour of concrete is considered in terms of stress vs. strain, damage parameter, tension stiffening behaviour etc. The ductility of the RC beams is computed by using deflection based and energy based concepts. Both deflection ductility and energy based ductility is compared and energy based concept is found to be in good correlation with the experiments conducted. The behavior of RC beam predicted using ABAQUS has been compared with the corresponding experimental observations. Comparison between numerical and experimental results confirms that these four constitutive models are reliable in predicting the behaviour of RC structures and any of the models can be employed for analysis.

• Structural Engineering and Mechanics
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• 제64권4호
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• pp.437-447
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• 2017

Explicit expressions for rapid prediction of inelastic design quantities (considering cracking of concrete) from corresponding elastic quantities, are presented for multi-storey composite frames (with steel columns and steel-concrete composite beams) subjected to service load. These expressions have been developed from weights and biases of the trained neural networks considering concrete stress, relative stiffness of beams and columns including effects of cracking in the floors below and above. Large amount of data sets required for training of neural networks have been generated using an analytical-numerical procedure developed by the authors. The neural networks have been developed for moments and deflections, for first floor, intermediate floors (second floor to ante-penultimate floor), penultimate floor and topmost floor. In the case of moments, expressions have been proposed for exterior end of exterior beam, interior end of exterior beam and both interior ends of interior beams, for each type of floor with a total of twelve expressions. Similarly, in the case of deflections, expressions have been proposed for exterior beam and interior beam of each type of floor with a total of eight expressions. The proposed expressions have been verified by comparison of the results with those obtained from the analytical-numerical procedure. This methodology helps to obtain the inelastic design quantities from the elastic quantities with simple calculations and thus would be very useful in preliminary design.

• Structural Engineering and Mechanics
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• 제58권5호
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• pp.799-823
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• 2016

A finite element model for the non-linear dynamic analysis of a reinforced concrete (RC) containment shell of a nuclear power plant subjected to extreme loads such as impact and earthquake is presented in this work. The impact is modeled by using an uncoupled approach in which a load function is applied at the impact zone. The earthquake load is modeled by prescribing ground accelerations at the base of the structure. The nuclear containment is discretized spatially by using 20-node brick finite elements. The concrete in compression is modeled by using a modified $Dr{\ddot{u}}cker$-Prager elasto-plastic constitutive law where strain rate effects are considered. Cracking of concrete is modeled by using a smeared cracking approach where the tension-stiffening effect is included via a strain-softening rule. A model based on fracture mechanics, using the concept of constant fracture energy release, is used to relate the strain softening effect to the element size in order to guaranty mesh independency in the numerical prediction. The reinforcing bars are represented by incorporated membrane elements with a von Mises elasto-plastic law. Two benchmarks are used to verify the numerical implementation of the present model. Results are presented graphically in terms of displacement histories and cracking patterns. Finally, the influence of the shear transfer model used for cracked concrete as well as the effect due to a base slab incorporation in the numerical modeling are analyzed.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2004년도 추계 학술발표회 제16권2호
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• pp.49-52
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• 2004

In this studies, Dapped End Beams(DEB) having disturbed regions were designed by using strut tie model, and the main purpose of this paper is that whether T-headed bars and Steel fibers will be present or not. The ability of DEB with T-headed bars have a superior performance rather than others, such as improved ductility, larger energy adsorption and enhanced post-peak load carrying capability. The capacity of DEB with steel fibers also show increase of ductility, shear strength, fatigue strength and crack. Each DEB with both headed bars and steel fibers, headed bars, and steel fibers as a substitute reinforced steel in the disturbed regions and a DEB with only stirrup and tie reinforced steel were comparable. In contrast, the headed bar stirrups, the tie headed bars and the reinforced steel fibers did not lose their anchorage and hence were able to develop strain hardening and also served to delay buckling of the flexural compression steel. Excellent load-deflection predictions were obtained by increasing the tension stiffening effect to account for high load effects.

• Structural Engineering and Mechanics
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• 제50권5호
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• pp.617-633
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• 2014

Because the elevated temperature degrades the mechanical properties of materials used in containments, the global behavior of containments subjected to the internal pressure under high temperature is remarkably different from that subjected to the internal pressure only. This paper concentrates on the nonlinear finite element analyses of the nuclear power plant containment structures, and the importance for the consideration of the elevated temperature effect has been emphasized because severe accident usually accompanies internal high pressure together with a high temperature increase. In addition to the consideration of nonlinear effects in the containment structure such as the tension stiffening and bond-slip effects, the change in material properties under elevated temperature is also taken into account. This paper, accordingly, focuses on the three-dimensional nonlinear analyses with thermal effects. Upon the comparison of experiment data with numerical results for the SNL 1/4 PCCV tested by internal pressure only, three-dimensional analyses for the same structure have been performed by considering internal pressure and temperature loadings designed for two kinds of severe accidents of Saturated Station Condition (SSC) and Station Black-out Scenario (SBO). Through the difference in the structural behavior of containment structures according to the addition of temperature loading, the importance of elevated temperature effect on the ultimate resisting capacity of PCCV has been emphasized.

• Structural Engineering and Mechanics
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• 제83권2호
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• pp.179-193
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• 2022

The shear behaviour of reinforced concrete members has been studied over the past decades by various researchers, and it can be simulated by analysing shear panel elements which has been regarded as a basic element of reinforced concrete members subjected to in-plane biaxial stresses. Despite various experimental studies on shear panel element which have been conducted so far, there are still a lot of uncertainties related to what influencing factors govern the shear behaviour and affect failure mechanism in reinforced concrete members. To identify the uncertainties, a finite element analysis can be used, which enables to investigate the impact of specific variables such as the reinforcement ratio, the shear retention factor, and the material characteristics including aggregate interlock, tension stiffening, compressive softening, and shear behaviour at the crack surface. In this study, a non-linear probabilistic analysis was conducted on reinforced concrete panels using a finite element method optimized for reinforced concrete members and advanced sampling techniques so that probabilistic analysis can be performed effectively. Consequently, this study figures out what analysis methodology and input parameters have the most influence on shear behaviour of reinforced concrete panels.

• 한국강구조학회 논문집
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• 제16권6호통권73호
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• pp.769-780
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• 2004

본 논문의 목적은 인장용 연결 플레이트를 갖는 냉간성형 각형강관 갭 N형 접합부의 실험연구를 통하여 접합부 거동을 평가하는데 있다. 실험을 위한 주요 변수로는 주관의 폭두께비, 주관에 대한 지관의 폭의 비, 편심비, 압축지관 형상, 지관의 각도, 주관 상부 플랜지면 보강 등이 있다. 이와 같은 변수들로 구성된 갭 N형 접합부에 대한 내력 및 파괴모드 등에 대하여 실험을 통해 고찰하고자 한다. 실험결과, 갭 N형 접합부는 폭비에 관계없이 접합부의 인장측 변위가 선행하여 접합부의 내력이 결정되었으며, 접합부 파괴는 접합된 주관면의 찢어짐 파괴모드로 결정되었다. 인장 및 압축측 폭비(${\beta}$)가 클수록 주관 폭두께비가 작을수록 접합부의 항복하중 및 최대하중은 선형으로 상승하는 것으로 나타났다. 주관의 폭두께비($2{\gamma}$)가 작을수록 접합부의 내력비교 곡선은 급격히 상승함을 알 수 있다. 인장용 연결 플레이트를 갖는 갭 N형 접합부에 대하여 변수에 따른 접합부의 하중, 초기강성, 연성능력 및 파괴모드 변화 등에 대한 결과에 대해서도 정리하여 나타내었다.

• 콘크리트학회논문집
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• 제16권6호
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• pp.785-794
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• 2004

이 논문은 휨과 전단이 동시에 작용하고 있는 철근콘크리트 보에서 전단은 휨모멘트의 변화율(V=dM/dx)이라는 기본 관계식에 근거한 새로운 트러스모델링기법을 제안하는 것이다. 이 새로운 모델의 핵심은 보의 경간에서 내부 모멘트 팔길이의 변화를 고려함으로써, 보의 전단 저항 메커니즘을 아치작용과 보작용이라는 두 기본 성분의 합으로 표현할 수 있게 한 것이다. 이두 작용에 의한 전단 저항 구성비는 상호 변형 적합조건을 적용하여 계산하였는데, 이 때 수정압축장이론과 CEB/FIP MC-90의 인장강화효과 공식을 이용하였다. 이렇게 함으로써 전단과 모멘트 관계식 V=dM/dx을 수치적으로 복제할 수 있는 새로운 트러스모델을 결정하였다.

• 대한토목학회논문집
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• 제3권4호
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• pp.1-10
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• 1983

평면내력(平面內力)을 받는 철근(鐵筋)콘크리트슬래브, 판(板) 및 쉘 등(等)의 벽부재(壁部材)의 정확한 변형해석(變形解析)을 위하여 균열의 마찰일팽창거동(摩擦一膨脹擧動), 인장증강효과(引張增剛効果) 및 철근의 연결작용(連結作用)을 고려한 실제적인 해석모델을 수립하였다. 본 연구의 이론(理論)에 입각한 전산(電算)프로그램을 작성(作成)하여 포괄적인 변형해석이 수행되었으며, 새로운 개념의 마찰평형설계(摩擦平衡設計)와 종래(從來)의 무마찰평형설계(無摩擦平衡設計)에 입각한 철근설계에 대하여 각각 균열폭을 계산하여 비교하였다. 마찰설계개념에 의해 철근을 설계했을 경우 종래의 무마찰설계보다 변형량이 상당히 감소됨을 발견하였다. 또한, 철근직경과 균열간격이 균열폭에 미치는 영향을 연구(硏究)하였다. 본(本) 연구(硏究)에서 개발된 해석모델로 철근콘크리트부재(部材)의 좀 더 실제적이고 정확한 변형해석(變形解析)을 할 수 있게 되었다.

• 콘크리트학회지
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• 제8권3호
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• pp.187-195
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• 1996

콘크리트 구조요소의 비선형거동을 예측하기 위하여 압축응력장 이론의 기본개념인 압축강도 연화 현상, 거시적 및 회전균열 모델을 고려한 유한요소해석이 제시되었다. 수치해석상의 효율성 및 최대하중 이후의 거동에 주안점을 두어 초기재료 강성을 채택한 변위증분법 논리 및 빠른 수렴을 위한 Over-Relaxation 방법이 Isoparametric계의 8-Node 요소에 포함.유도되었다. 상기에 근거하여 제작된 비선형 프로그램, NASCOM은 다조하중을 지지하는콘크리트 구조요소의 내력, 변형특성, 균열 분포 상황 및 보강근의 항복 분포를 예측하는데 사용할 수 있다. NASCOM의 성능을 검토하기 위하여 이러한 목적에 빈번히 사용되는 Bhide의 패널(PB21) 및 Leonhardt의 춤이 큰보에 대한 해석이 실시되었다. 패널에 대한 해석결과는 대체로 변형이력 및 강도가 강한 거동을 나타내는 반면에, 춤이 큰보에 대해서는 변형이력이 유연한 거동을 나타내고있어, 향후 보다 정확한 결과를 예측하기 위해서는 콘크리트의 인강강화 및 압축강도 연화현상에 대하여 좀더 향상된 재료모델의 고려가 필요한 것으로 판단되었다.