• Magazine of the Korea Concrete Institute
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• 제9권5호
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• pp.115-125
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• 1997

콘크리트의 변형률국소화는 콘크리트의연화거동에 수반되어 변형이 국부적으로 집중되는 현상이다. 본 연구의 목적은 인장과 압축하중상태에서 콘크리트 부재에 발생하는 콘크리트 변형률 국소화 거동을 해석적으로 재현할 수 있는 통일된 모형을 제안하는 것이다. 본 논문에서는 인장과 압축에 대하여 변형률국소화가 일어나는 콘크리트 부재를 변형률 연화가 일어나는 국소화영역과 탄성제하가 발생하는 비국소화영역으로 구분하여 모델링하는 통일된 모형을 제안하였다. 또한 제안된 모형에서 미시역학적 평균화기법을 이용해 평균등가탄성계수와 수정된 평균등가탄성계수를 구하여 시편의 크기와 국소화영역의 크기에 따는 해석을 수행하였으며 기존의 실험값과 비교하였다. 연구결과, 본 연구에서의 변형률국소화모형이 크기효과를 포함한 콘크리트의 변형률국소화거동 해석에 타당하게 적용될 수 있음을 보여주었다.

• Computational Structural Engineering
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• 제10권3호
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• pp.241-250
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• 1997

The strain localization of concrete is a phenomenon such that the deformation of concrete is localized in finite region along with softening behavior. The objective of this paper is to develop a plasticity and damage algorithm for the finite element analysis of the strain-localization in concrete. In this paper, concrete member under strain localization is modeled with localized zone and non-localized zone. For modeling of the localized zone in concrete under strain localization, a general Drucker-Prager failure criterion by which the nonlinear strain softening behavior of concrete after peak-stress can be considered is introduced in a thermodynamic formulation of the classical plasticity model. The return-mapping algorithm is used for the integration of the elasto-plastic rate equation and the consistent tangent modulus is also derived. For the modeling of non-localized zone in concrete under strain localization, a consistent nonlinear elastic-damage algorithm is developed by modifying the free energy in thermodynamics. Using finite element program implemented with the developed algorithm, strain localization behaviors for concrete specimens under compression are simulated.

• Computational Structural Engineering
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• 제17권2호
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• pp.20-23
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• 2004

공학적 응력-변형률 곡선에서 재료의 파괴직전에 흔히 나타나는 변형률연화 (strain softening) 현상은 국부의 집중소성변형 현상과 밀접한 관계가 있다 그러나 변형률연화는 음수의 기울기를 가지는 응력-변형률 곡선을 의미하며, 이 모델은 유한요소해석의 결과가 그 요소의 크기에 따라 수렴점이 달라지는 근본적인 문제를 가진다. 따라서 1980년대 이후 많은 학자들이 이 현상의 적절한 모델을 찾기 위한 노력을 기울여왔다. (중략)

• Journal of the Korea institute for structural maintenance and inspection
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• 제23권1호
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• pp.54-62
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• 2019

In this paper, a stress-strain model for high-strength confined concrete is proposed using compressive fracture energy. In the compression test performed by author in Reference [6], an acrylic bar with strain gauges was embedded in the center of the specimen to measure the local strain distribution. It was found from the test that the local strain measurement by this acrylic rod is very effective. The local fracture zone length was defined based on the local strain distribution measured by the acrylic rod. Specifically, it was defined as the length where the local strain increases more than twice of the strain corresponding to maximum stress. In addition, the stress-strain relationship of confined concrete with compressive fracture energy is proposed on the assumption that the amount of energy absorbed by the compressive members subjected to the given lateral confining pressure is constant regardless of the aspect ratio and size. The proposed model predicts even results from other researchers accurately.

• Journal of Korean Society of Steel Construction
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• 제14권5호통권60호
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• pp.613-625
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• 2002

This paper aimed to investigate the damage process of steel parts experiencing failure under strong repeated loading. Likewise, a damage index using various factors related to the damage was proposed. An analysis method for evaluating the damage state was also developed. The damage assessment method focused on the local strain history at the cross-section of the heaviest concentration of deformation. Cantilever-type steel parts were analyzed under uniaxial load combined with a constant axial load, considering horizontal displacement history, Loading patterns and steel types were considered as the main parameters in analyzing the models. The effects of the parameters on the failure modes, deformation capacity, and damage process as seen from the analysis results were also discussed. Each failure process was compared as steel types. In addition, the failure of steel parts under strong repeated loading was determined according to loading. Results revealed that the state of the failure is closely related to the local plastic strain.

• Journal of Korean Society of Steel Construction
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• 제15권4호통권65호
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• pp.369-378
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• 2003

This study proposed a damage index for steel members and examined a process where steel square tubular columns under cycle loading failed to meet the damage index. A nonlinear analysis was carried out and a damage process analyzed using a finite element program. Material properties and strain characteristics were obtained from material testing. The effect on the damage of members was analyzed according to varying kinds of steels and conditions of loading based on material testing results. According to strain characteristics and cumulative plastic strain of each variable, the effect of conditions of loading and kinds of steels on the damage could be estimated quantitatively.

• Magazine of the Korea Concrete Institute
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• 제8권2호
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• pp.129-138
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• 1996

Localization of concrete is a phenomenon such that the deformation of concrete is localized in finite region with softening behavior and it governs ultimate load of concrete. In this Paper, concrete under strain localization was modeled with localization region and non-localization region and lc~calization behavior was formulated based on averaging concept of heterogeneous material. By using the formulation, the localization phenomena of concrete under uniaxial loadings were well predicted. The analytical results show that size of localization region of concrete under uniaxial compression is three times of maximum aggregate size and the size effect of concrete is well predicted. The use of tension-softening curve obtained from direct tension test is suitable for well prediction of localization of concrete under uniaxial tension.

• Computational Structural Engineering
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• 제17권3호
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• pp.22-27
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• 2004

• Journal of the Korea institute for structural maintenance and inspection
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• 제24권6호
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• pp.25-33
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• 2020

To investigate the relationship between strain distribution and tensile properties of brittle material, five types of tensile coupon of carbon fiber reinforced polymer (CFRP) modified the tab portion in order to have a strain distribution including S0, SD1, SD2, SV1, SV2 were tested. The ultimate stress and strain of SD2 and SV2 which was intended to have larger strain distribution were smaller than those of SD1 and SV1, that was more clearly shown in the test results of the symmetric coupons (SV series) than the asymmetric coupons (SD series). In addition, the ultimate stress and strain of most coupons with strain distribution in this study were decreased when compared to the control group with uniform strain. These results were analyzed in various ways through 1) the average of the strain values directly measured by the strain gages, 2) the converted strain calculated by dividing the total deformation by the effective length, and 3) the ultimate effective strain derived from both the elastic modulus and the ultimate load. The values measured by strain gage indicates response of the local region precisely, but it does not represent the response from whole section. However, the converted strain and effective strain can supplement disadvantage of gage because they represent the average response of whole section. In particular, the effective strain can provide rupture strain conservatively, which can be utilized in practice, when the value obtained by strain gage was not effective due to gage damage or abnormal gage readings near ultimate load. This value provides a value that can be used even when partial rupture has occurred and is reasonably useful for specimens with strain distribution.

• Journal of the Korea Academia-Industrial cooperation Society
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• 제13권7호
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• pp.3207-3215
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• 2012

In this paper, we study the bending and free vibration analysis of nano plate, using a nonlocal elasticity theory of Eringen with a third-order shear deformation theory. This theory has ability to capture the both small scale effects and quadratic variation of shear strain and consequently shear stress through the plate thickness. Analytical solutions of bending and vibration of a laminated composite nano plate are presented using this theory to illustrate the effect of nonlocal theory on deflection of the nano plates. The relations between nonlocal third-order and local theories are discussed by numerical results. Further, effects of (i) nonlocal parameters, (ii) laminate schemes, (iii) directions of the fiber angle and (iv) number of layers on nondimensional deflections are investigated. In order to validate the present solutions, the reference solutions are used and discussed. The results of anisotropic nano plates using the nonlocal theory may be the benchmark test for the bending analysis.