• Advances in concrete construction
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• 제9권6호
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• pp.597-610
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• 2020

Stress-strain models of fibre reinforced polymer (FRP) confined concrete have been widely investigated; however, the existing load which is always supported by structures during the retrofitting phase, namely 'preload', has been neglected. Thus, preload effects should be clarified, providing insightful information for FRP retrofitting of structures with preload conditions. Towards this aim, experiments were performed for 27 cylinder concrete specimens with the diameter 150 mm and the height 300 mm. Three specimens were used to test the compressive strength of concrete to compute the preloads 20%, 30% and 40% of the average strength of these specimens. Other 24 specimens were divided into 2 groups; each group included 4 subgroups. Four subgroups were subjected to the above preloads and no preload, and were then wrapped by 2 FRP layers. Similar designation is applied to group 2, but wrapped by 3 FRP layers. All specimens were tested under axial compression to failure. Explosive failure is found to be the characteristic of specimens wrapped by FRP. Experimental results indicated that the preload decreases 12-13% the elastic and second stiffness of concrete specimens wrapped by 2 FRP layers. The stiffness reduction can be mitigated by the increase of FRP layers. Preload negligibly reduces the ultimate force and unclearly affects the ultimate displacement probably due to complicated cracks developed in concrete. A mechanism of preload effects is presented in the paper. Finally, to take into account preload effects, a modification of the widely used model of un-preload FRP confined concrete is proposed and the modified model demonstrated with a reasonable accuracy.

• 콘크리트학회논문집
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• 제11권3호
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• pp.89-100
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• 1999

The purpose of this study is to develop an analytic model of the concrete column strengthened with laminated CFS, and to provide a basic guideline for the strengthening design by CFS considering orthotropic properties of laminate. In this study, an analytical stress-strain model of laminated CFS is presented based on Tsai-Hill failure criterion. This model has been implemented in an algorithm which can evaluate the confinement effect of CFS. Through this algorithm, the stress-strain relationship of confined concrete is obtained and compared with experimental results of other studies. Using the constitutive relationships, section analyses of concrete column strengthened with CFS are done, and load-moment and load-curvature interaction curves are obtained. In addition, the strengthening effects of CFS according to various laminated angles are analyzed. Analytical results show that the strengthening effects of the strengthened concrete columns are significantly different in compression, flexure, and ductility according to the laminated ways. In compressive direction of principal stress shows the superiority, where an in flexural strengthening effects, [0/90]s does. In the aspect of ductility, [90]s shows the best effect.

• Computers and Concrete
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• 제33권5호
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• pp.545-557
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• 2024

A real-case incident occurred where a 9-meter-high segment of a pre-fabricated concrete separation wall unexpectedly collapsed. This collapse was triggered by improperly depositing excavated soil against the wall's back, a condition for which the wall segments were not designed to withstand lateral earth pressure, leading to a flexural failure. The event's analysis, integrating technical data and observational insights, revealed that internal forces at the time of failure significantly exceeded the wall's capacity per standard design. The Lattice Discrete Particle Model (LDPM) further replicates the collapse mechanism. Our approach involved defining various parameter sets to replicate the concrete's mechanical response, consistent with the tested compressive strength. Subsequent stages included calibrating these parameters across different scales and conducting full-scale simulations. These simulations carried out with various parameter sets, were thoroughly analyzed to identify the most representative failure mechanism. We developed an equation from this analysis that quickly correlates the parameters to the wall's load-carry capacity, aligned with the simulation. Additionally, our study examined the wall's post-peak behavior, extending up to the point of collapse. This aspect of the analysis was essential for preventing failure, providing crucial time for intervention, and potentially averting a disaster. However, the reinforced concrete residual state is far from being fully understood. While it's impractical for engineers to depend on the residual state of structural elements during the design phase, comprehending this state is essential for effective response and mitigation strategies after initial failure occurs.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2008년도 추계 학술발표회 제20권2호
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• pp.265-268
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• 2008

슬래브-기둥 접합부는 많은 구조물의 시공에 사용되고 있다. 그러나 횡하중을 받는 슬래브-기둥 접합부의 파괴거동 및 극한강도를 예측하는 것이 매우 어렵기 때문에 현행 구조물 설계기준은 횡하중을 받는 슬래브-기둥 접합부의 파괴 거동을 명확하게 설명하지 못하고 있다. 본 논문에서는 횡하중을 받는 슬래브-기둥 접합부의 극한해석과 설계를 위하여 응력교란영역을 가지는 3차원 구조의 해석과 설계를 위하여 제안된 3차원 격자 스트럿-타이 모델 방법을 파괴실험이 수행된 43개의 횡하중을 받는 슬래브-기둥 접합부의 극한강도 평가에 적용하고, ACI 318-05 기준과 FIB 1999 기준에 의한 극한강도 평가결과와 비교함으로써 3차원 격자 스트럿-타이 모델 방법의 타당성을 검토하였다.

• 콘크리트학회논문집
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• 제21권1호
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• pp.75-84
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• 2009

이전 연구에서 제안된 변형률 기반 전단강도모델에 근거하여, 프리스트레스트 콘크리트 보의 전단강도를 예측하기 위한 해석모델을 제안하였다. 전단보강 되지 않은 콘크리트 보에서는 일반적으로 인장대보다 콘크리트 압축대가 주로 전단력에 저항한다. 콘크리트의 전단성능은 콘크리트의 재료 파괴기준을 통해 정의된다. 압축대의 전단성능은 단면에 작용하는 수직응력과의 상관관계를 고려하여, 경사 파괴면을 따라서 산정된다. 압축대의 수직응력 분포는 부재의 휨변형에 따라 변화하므로, 압축대 단면의 전단성능은 휨변형에 대한 함수이다. 보의 전단강도는 전단성능 곡선과 전단수요 곡선의 교점에서 결정된다. 제안된 해석모델을 기존 연구자들의 실험 연구 결과와 비교한 결과, 실험체의 전단강도를 정확하게 예측하였다.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2005년도 봄학술 발표회 논문집(I)
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• pp.175-178
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• 2005

The major object of this paper is to propose a nonlinear finite element analysis(FEA) technique of steel coupling beams-wall connections governed panel shear failure using ABAQUS. Detailed finite element models are created by studying the monotonic load response of the designed steel coupling beams-wall connections. The developed models account for the effect of material inelasticity, concrete cracking, panel shear failure and geometric nonlinearity. In order to verify the proposed FEA model, this study attended experiment considered parameters to the steel beam : face bearing plates, and horizontal ties. And the analytical result attended by the proposed FEA model validated through comparisons with the experimental results. Finally, the study estimated the analytical values compared with ASCE Design Guidelines. At this time, the analysis showed good agreement between the theoretical and experimental results.

• 한국전산구조공학회논문집
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• 제30권2호
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• pp.137-143
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• 2017

본 논문에서는 파괴에너지이론에 기초하여 요소의존성을 최소화할 수 있는 인장파괴기준식을 제안하고 HJC(holmquist johnson cook), CSC(continuous surface cap), Orthotropic 모델을 이용한 폭발수치해석을 통해 기준식을 검증하였다. 폭발하중으로 인한 RC 보의 시간에 따른 중앙지점의 처짐을 실험결과와 비교하였다. 그 결과 기준식을 통해 산정된 파괴변형률을 수치해석상에 적용해줌으로써 해석결과의 요소의존성이 감소하였고 해의 정확성 또한 향상되는 것을 파악할 수 있었다.

• Computers and Concrete
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• 제16권4호
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• pp.587-604
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• 2015

The hybrid-type penalty method (HPM) is suitable for representing failure phenomena occurring during the transition from continua to discontinua in materials such as concrete. Initiation and propagation of dominant cracks and branching of cracks can easily be modeled as a discrete crack. The HPM represents a discrete crack by eliminating the penalty that represents the separation of the elements at the intersection boundary. This treatment is easy because no change in the degrees of freedom for the discrete crack is necessary. In addition, it is important to evaluate the correct deformation of the continua before the crack formation is initiated. To achieve this, we implemented a constitutive model of concrete for the HPM. In this paper, we explain the implemented constitutive model and describe the simulation of an anchor bolt pullout test using the HPM demonstrating its capability for evaluating progressive failure.

• Advances in concrete construction
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• 제14권2호
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• pp.131-137
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• 2022

Based on the design of reinforced concrete columns in Chinese design codes, the failure function of reinforced concrete (RC) columns cannot be expressed as a linear function. This makes it difficult to reveal the level of reliability control in Chinese design code. Therefore, the failure function of dimensionless form is established in this paper, and the typical components (Industrial plant columns) are selected for analysis. At last, numerical simulation proves that the proposed model can be used to analysis reliability of columns. The results based on this model indicate that there is a strong difference in the reliability of RC columns designed with different design parameters, and the reliability would be lower when the eccentricity produced by crane load is smaller.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2002년도 봄 학술발표회 논문집
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• pp.897-902
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• 2002

The failure of flat plate connection is successive failure process accompanying with stress redistribution, hence it is necessary to compute the contributions of each resistance components at ultimate state. In the present study, the interactions of resultant forces at each faces of connection, i.e. shear, bending moment and torsional moment are considered in the assessment of strength of slab. As a result the strength prediction model for connection is made up as combination of bending resistance, shear resistance and torsional resistance. The proposed method is verified by the experimental data and numerical data of continuous slabs.