• 복합신소재구조학회 논문집
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• 제4권1호
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• pp.40-46
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• 2013

This paper presents the design, fabrication and performance of a reinforced concrete beam strengthened by GFRP box plate and its possibility for structural rehabilitations. The load capacity, ductility and failure mode of reinforced concrete structures strengthened by FRP box plate were investigated and compared with traditional FRP plate strengthening method. This is intended to assess the feasibility of using FRP box plate for repair and strengthening of damaged RC beams. A series of four-point bending tests were conducted on RC beams with or without strengthening FRP systems the influence of concrete cover thickness on the performance of overall stiffness of the structure. The parameters obtained by the experimental studies were the stiffness, strength, crack width and pattern, failure mode, respectively. The test yielded complete load-deflection curves from which the increase in load capacity and the failure mode was evaluated.

• Steel and Composite Structures
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• 제28권1호
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• pp.63-71
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• 2018

This paper reports an experimental study that was accomplished to assess the seismic behavior of steel tube reinforced concrete bridge columns (SBCs). The motivation of this study was to verify a supposition that the core steel tube may be terminated at a rational position in the column to minimize the material cost while maintaining the seismic behavior of this composite column. Four SBC specimens were tested under combined constant axial load and cyclic reversed lateral loads. The unique variable in the test matrix was the core steel tube embedment length, which ranged from 1/3 to 3/3 of the column effective height. It is observed that SBCs showed two distinctly different failure patterns, namely brittle shear failure and ductile flexural failure. Tests results indicate that the hysteretic responses of SBCs were susceptible to the core steel tube embedment length. With the increase of this structural parameter, the lateral strength of SBC was progressively improved; the deformability and ductility, however, exhibited a tendency of first increase and then decrease. It is also found that in addition to maintained the rate of stiffness degradation and cumulative energy dissipation basically unchanged, both the ductility and deformability of SBC were significantly improved when the core steel tube was terminated at the mid-height of the column, and these were the most unexpected benefits accompanied with material cost reduction.

• Computers and Concrete
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• 제25권4호
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• pp.355-367
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• 2020

This paper proposed a numerical investigation based on finite elements analysis (FEA) in order to study the punching shear behavior of reinforced concrete (RC) flat slabs using ABAQUS and SAP2000 programs. Firstly, the concrete and the steel reinforcements were modeled by hexahedral 3D solid and linear elements respectively, and the nonlinearity of the used materials was considered. In order to validate this model, experimental results considered in literature were compared with the proposed FE model. After validation, a parametric study was performed. The parameters include the slab thickness, the flexure reinforcement ratios and the axial membrane loads. Then, to reduce the time of FEA, a simplified modelling using 3D layered shell element and shear hinge concept was also induced. The effect of the footings settlement was studied using the proposed simplified nonlinear model as a case study. Results of numerical models showed that increase of the slab thickness by 185.7% enhanced the ultimate load by 439.1%, accompanied with a brittle punching failure. The punching failure occurred in one of the tested specimens when the tensile reinforcement ratio increased more than 0.65% and the punching capacity improved with increasing the horizontal flexural reinforcement; it decreased by 30% with the settlement of the outer footings.

• Structural Engineering and Mechanics
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• 제59권5호
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• pp.853-866
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• 2016

This paper examines a methodology for computing the probability of structural failure of reinforced concrete beams subjected to fire. The significant load variables considered are dead load, sustained live load and fire temperature. Resistance is expressed in terms of moment capacity with random variables taken as yield strength of steel, concrete class (or grade of concrete), beam width and depth. The flexural capacity is determined based on the design equations recommended in Indian standard IS456:2000. Simplified method named $500^{\circ}C$ isotherm method detailed in Eurocode 2 is incorporated for fire design. A transient thermal analysis is conducted using finite element software ANSYS$^{(R)}$ Release15. Reliability is evaluated from the initial state to 4h of fire exposure based on the first order reliability method (FORM). A procedure is coded in MATLAB for finding the reliability index. This procedure is validated with available literature. The effect of various parameters like effective cover, yield strength of steel, grade of concrete, distribution of reinforcement bars and aggregate type on reliability indices are studied. Parameters like effective cover of concrete, yield strength of steel has a significant effect on reliability of beams. Different failure modes like limit state of flexure and limit state of shear are checked.

• 콘크리트학회논문집
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• 제22권3호
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• pp.345-356
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• 2010

직접전단과 불균형모멘트를 재하받는 슬래브-기둥 내부 접합부에 대한 대체설계방법이 개발되었다. 슬래브-기둥 접합부는 뚫림전단파괴에 앞서서 휨균열에 의해서 손상을 받으므로, 이 연구에서는 위험단면의 압축대에서 대부분의 전단저항이 발휘된다고 가정하였다. 뚫림전단강도의 산정을 위하여, 슬래브 휨모멘트와 불균형모멘트에 의해서 유발되는 압축수직응력의 영향을 고려하였다. 압축수직응력과 전단응력 사이의 상관관계를 고려하기 위하여, Rankine의 콘크리트 재료파괴기준을 사용하였다. 제안된 강도모델은 실험 결과와의 비교를 통하여 검증하였다. 검증 결과, 제안된 설계방법은 ACI 318과 Eurocode 2 보다 우수한 강도추정능력을 가지고 있으며 직접전단 또는 직접전단-불균형모멘트 복합하중을 재하받는 슬래브-기둥 접합부의 설계에 사용될 수 있다는 점이 밝혀졌다.

• 콘크리트학회논문집
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• 제14권6호
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• pp.961-972
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• 2002

횡하중을 받는 플랫 플레이트 구조는 슬래브-기둥 접합부의 취성 전단파괴에 대하여 취약하며, 이러한 접합부의 취성적 파괴를 방지하기 위해 접합부의 강도 및 연성능력이 반드시 확보되어야 한다. 그러나 이전 연구에 의하면 현행 설계기준이 플레이트-기둥 접합부의 강도를 정확히 예측하지 못하는 것으로 밝혀졌다. 본 연구에서는 비선형 유한요소해석을 이용한 변수연구를 내부 접합부에 대해 실시하였으며 수치해석 결과에 근거하여 접합부에 대한 설계방법을 개발하였다. 접합부 주위의 위험단면에서는 중력하중과 횡하중에 의해 발생된 휨모멘트와 전단력이 공존하며, 이 휨모멘트와 전단력의 상호작용을 고려하여 최대 허용편심전단응력을 제안하였다. 제안된 강도모델은 현 설계기준에 비하여 접합부의 강도를 보다 정확히 산정 할 수 있으며, 연속 슬래브에 대한 비선형 해석결과와 기존의 실험결과와의 비교를 통해 그 유효성을 검증하였다.

• Smart Structures and Systems
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• 제26권2호
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• pp.147-156
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• 2020

This numerical study demonstrates the porosity conditions and the intensity of the interactions with the aggressive agents. It is established that the density as well as the elastic modulus are correlated to ultrasonic velocity The following investigation assessed the effects of cement grade and porosity on tensile strength, flexural and compressive of Ultra High Performance Concrete (UHPC) as a numerical model in PLAXIS 2d Software. Initially, the existing strength-porosity equations were investigated. Furthermore, comparisons of the proposed equations with the existing models suggested the high accuracy of the proposed equations in predicting, cement grade concrete strength. The outcome obtained showed a ductile failure when un-corroded reinforced concrete demonstrates several bending-induced cracks transfer to the steel reinforcement. Moreover, the outcome also showed a brittle failure when wider but fewer transverse cracks occurred under bending loads. Sustained loading as well as initial pre-cracked condition during the corrosion development have shown to have significant impact on the corrosion behavior of concrete properties. Moreover, greater porosity was generally associated with lower compressive, flexural, and tensile strength. Higher cement grade, on the other hand, resulted in lower reduction in concrete strength. This finding highlighted the critical role of cement strength grade in determining the mechanical properties of concrete.

• 대한토목학회논문집
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• 제35권5호
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• pp.1015-1024
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• 2015

본 연구에서는 유리섬유강화폴리머 판을 영구거푸집 및 인장 보강재로 활용한 현장타설 고강도콘크리트 합성보를 대상으로 판 하부의 잔골재 부착여부, 웨브의 천공유무 및 간격, 상부플랜지 폭을 변수로 하여 휨 파괴실험을 수행하였다. GFRP 판 웨브를 천공하지 않은 경우 잔골재 부착효과 여부를 위한 실험 결과, 잔골재를 부착한 경우 미부착의 경우 보다 약 43% 높은 극한하중 값을 보여주었으며, 웨브의 천공유무 및 간격효과는 잔골재를 부착하지 않은 경우 천공간격이 3배인 경우가 약 23% 정도 높은 극한하중 값을 보여주었으며, 잔골재를 부착한 경우 천공 간격이 5배인 경우가 약 11% 정도 높은 극한하중 값을 보여주었다. 상부플랜지 영향을 살펴보면, 폭 20mm 경우가 40mm에 비해 약 12% 정도 큰 극한하중 값을 보여주었다.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2008년도 춘계 학술발표회 제20권1호
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• pp.197-200
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• 2008

이전 연구에서 제안된 변형률 기반 전단강도모델을 휨-압축 부재에 적용하여, 프리스트레스트 콘크리트 보의 전단강도를 예측하기 위한 해석모델을 제안하였다. 전단보강 되지 않은 콘크리트 휨-압축 부재에서는 균열발생 이후, 일반적으로 인장대보다 콘크리트 압축대가 주로 전단력에 저항한다. 압축대 콘크리트의 전단성능은 콘크리트의 재료 파괴기준을 통해 정의된다. 그리고 압축대의 전단성능은 단면에 작용하는 수직응력과의 상관관계를 고려하여, 주응력방향에 의해 결정되는 파괴면을 따라서 산정된다. 압축대의 수직응력 분포는 부재의 휨변형에 따라 변화하므로, 압축대 단면의 전단성능은 휨변형에 대한 함수이다. 부재의 전단강도는 전단 성능 곡선과 수요 곡선의 교점에서 결정된다. 제안된 해석모델을 기존 연구자들의 실험 연구 결과와 비교한 결과, 실험체의 전단강도를 정확하게 예측하였다.

• Computers and Concrete
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• 제22권2호
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• pp.167-182
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• 2018

The modeling of loss of bond between reinforcing bars (rebars) and concrete due to corrosion is useful in studying the behavior and prediction of residual load bearing capacity of corroded reinforced concrete (RC) members. In the present work, first the possibility of using different methods to simulate the rebars-concrete bonding, which is used in three-dimensional (3D) finite element (FE) modeling of corroded RC beams, was explored. The cohesive surface interaction method was found to be most suitable for simulating the bond between rebars and concrete. Secondly, using the cohesive surface interaction approach, the 3D FE modeling of the behavior of non-corroded and corroded RC beams was carried out in an ABAQUS environment. Experimental data, reported in literature, were used to validate the models. Then using the developed models, a parametric study was conducted to examine the effects of some parameters, such as degree and location of the corrosion, on the behavior and residual capacity of the corroded beams. The results obtained from the parametric analysis using the developed model showed that corrosion in top compression rebars has very small effect on the flexural behaviors of beams with small flexural reinforcement ratio that is less than the maximum ratio specified in ACI-318-14 (singly RC beam). In addition, the reduction of steel yield strength in tension reinforcement due to corrosion is the main source of reducing the load bearing capacity of corroded RC beams. The most critical corrosion-induced damage is the complete loss of bond between rebars and the concrete as it causes sudden failure and the beam acts as un-reinforced beam.