• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2000년도 봄 학술발표회 논문집
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• pp.787-790
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• 2000

This paper presents an experimental study on flexural behavior of structural member enlarged with epoxy mortar system. The main test variable is flexural tensile strength. A series of 4 test beams was tested to shoe the corresponding effect of each variables on maximum load capacity, load-deflection and moment-curvature relationship, interface behavior and failure mode. The results show that the flexural tensile strength of retrofitted materials have no relation load-deflection, but to load-strain, and failure mode.

• Computers and Concrete
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• 제3권4호
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• pp.261-284
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• 2006

The flexural behaviour of symmetrically reinforced concrete (RC) columns cast of normal- and high-strength concrete under both monotonic and cyclic loading is studied based on an analytical procedure, which employs the actual stress-strain curves and takes into account the stress-path dependence of concrete and steel reinforcement. The analysis is particularly extended into the post-peak stage with large inelastic deformation at various applied axial load level. The effect of axial load on their complete flexural behaviour is then identified based on the results obtained. The axial load is found to have fairly large effect on the flexural behaviour of RC columns under both monotonic and cyclic loading. Such effects are discussed through examination of various aspects including the moment-curvature relationship, moment capacity, flexural ductility, variation of neutral axis depth and steel stress.

• Structural Engineering and Mechanics
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• 제87권6호
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• pp.541-554
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• 2023

An unbraced cantilever beam subjected to loads which cause bending about the major axis may buckle in a flexuraltorsional mode by deflecting laterally and twisting. For the efficient design of these structures, design engineers require a simple accurate equation for the elastic flexural-torsional buckling load. Existing solutions for the flexural-torsional buckling of cantilever beams have mainly been derived by numerical methods which are tedious to implement. In this research, an attempt is made to derive a theoretical equation by the energy method using different buckled shapes. However, the results of a finite element flexural-torsional buckling analysis reveal that the buckled shapes for the lateral deflection and twist rotation are different for cantilever beams. In particular, the buckled shape for the twist rotation also varies with the section size. In light of these findings, the finite element flexural-torsional buckling analysis was then used to derive simple accurate equations for the elastic buckling load and moment for cantilever beams subjected to end point load, uniformly distributed load and end moment. The results are compared with previous research and it was found that the equations derived in this study are accurate and simple to use.

• 한국구조물진단유지관리공학회 논문집
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• 제7권3호
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• pp.223-230
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• 2003

본 연구의 목적은 탄소섬유쉬트(CFS)로 보강된 RC보의 보강시 상재하중의 유무에 따른 보강효과와 휨거동을 실험적으로 고찰하는 것이다. 실험변수는 인장철근비(0.85, 1.32, 1.91%)와 상재하중(무보강보의 항복내력의 80%)으로 한다. 보강보의 구조적 거동을 항복하중과 극한하중, 하중-중앙부 처짐 관계, 연성, 보강 효과의 항으로 비교하였다. 실험결과로부터, CFS로 보강된 RC보의 극한 내력과 휨파괴거동이 원부재와 부착된 CFS 간의 초기응력에 의해 변화하는 것으로 나타났다.

• Computers and Concrete
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• 제8권3호
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• pp.343-355
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• 2011

This paper presented the model to predict the chloride diffusion coefficient in tension zone of plain concrete under flexural cyclic load. The fictitious crack based analytical model was used together with the stress degradation law in cracked zone to predict crack growth of plain concrete beams under flexural cyclic load. Then, under cyclic load, the chloride diffusion, in the steady state and one dimensional regime, through the tension zone of the plain concrete beam, in which microcracks were formed by a large number of cycles, was simulated with assumptions of continuously straight crack and uniform-size crack. The numerical analysis in terms of the chloride diffusion coefficient, $D_{tot}$, normalized $D_{tot}$, crack width and crack length was issued as a function of the load cycle, N, and load level, SR. The nonlinear model as regarding with the chloride diffusion coefficient in tension zone and the load level was proposed. According to this model, the chloride diffusion increases with increasing load level. The predictions using model fit well with experimental data when we adopted suitable crack density and tortuosity parameter.

• Steel and Composite Structures
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• 제34권3호
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• pp.453-465
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• 2020

Influences of different variables that affect the effective flexural rigidity of reinforced concrete (RC) members are not considered in the most seismic codes. Furthermore, in the last decades, the application of steel fibers in concrete matrix designs has been increased, requiring development of an accurate analytical procedure to calculate the effective flexural rigidity of steel fiber reinforced concrete (SFRC) members. In this paper, first, a nonlinear analytical procedure is proposed to calculate the SFRC members' effective flexural rigidity. The proposed model's accuracy is confirmed by comparing the results obtained from nonlinear analysis with those recorded from the experimental testing. Then a parametric study is conducted to investigate the effects of different parameters such as varying axial load and steel fiber are then investigated through moment-curvature analysis of various SFRC (normal-strength concrete) sections. The obtained results show that increasing the steel fiber volume percentage increases the effective flexural rigidity. Also it's been indicated that the varying axial load affects the effective flexural rigidity. Lastly, proper equations are developed to estimate the effective flexural rigidity of SFRC members.

• Computers and Concrete
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• 제20권4호
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• pp.439-448
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• 2017

Reinforced concrete (RC) infrastructures often require strengthening due to error in design, degradation of materials properties after prolong utilization and increases load carrying capacity persuaded by new use of the structures. For this purpose, a newly proposed Side Near Surface Mounted (SNSM) composite technique was used for flexural strengthening of RC beam specimens. Analytical and non-linear finite element modeling (FEM) using ABAQUS were performed to predict the flexural performance of RC specimens strengthened with S-NSM using steel bars as a strengthening reinforcement. RC beams with various SNSM reinforcement ratios were tested for flexural performance using four-point bending under monotonic loading condition. Results showed significantly increase the yield and ultimate strengths up to 140% and 144% respectively and improved failure modes. The flexural response, such as failure load, mode of failure, yield load, ultimate load, deflection, strain, cracks characteristic and ductility of the beams were compared with those predicted results. The strengthened RC beam specimens showed good agreement of predicted flexural behavior with the experimental outcomes.

• Computers and Concrete
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• 제6권5호
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• pp.357-376
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• 2009

In the design of concrete columns, it is important to provide some nominal flexural ductility even for structures not subjected to earthquake attack. Currently, the nominal flexural ductility is provided by imposing empirical deemed-to-satisfy rules, which limit the minimum size and maximum spacing of the confining reinforcement. However, these existing empirical rules have the major shortcoming that the actual level of flexural ductility provided is not consistent, being generally lower at higher concrete strength or higher axial load level. Hence, for high-strength concrete columns subjected to high axial loads, these existing rules are unsafe. Herein, the combined effects of concrete strength, axial load level, confining pressure and longitudinal steel ratio on the flexural ductility are evaluated using nonlinear moment-curvature analysis. Based on the numerical results, a new design method that provides a consistent level of nominal flexural ductility by imposing an upper limit to the axial load level or a lower limit to the confining pressure is developed. Lastly, two formulas and one design chart for direct evaluation of the maximum axial load level and minimum confining pressure are produced.

• 한국지반공학회논문집
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• 제34권12호
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• pp.133-143
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• 2018

수평하중에 대한 말뚝의 휨강도를 증대시키기 위해 얇은 두께의 강관 내부에 PHC말뚝을 합성한 콘크리트 충전 강관(PCFT)말뚝이 개발되었다. PCFT말뚝의 휨강도를 강관말뚝과 비교하기 위하여 직경이 동일한 PCFT말뚝과 강관 말뚝에 대해 휨강도시험을 수행함과 동시에 한계상태설계법으로 P-M 상관도를 작도하였다. 그리고 PCFT말뚝의 하단에 PHC말뚝을 연결한 PCFT 복합말뚝의 수평지지력과 수평거동을 기존의 강관 복합말뚝(HCP) 및 강관말뚝과 비교하기 위하여 총 4본의 시험말뚝을 시공하고 수평재하시험을 수행하였다. 휨강도시험 결과 PCFT말뚝의 휨강도는 두께 12mm의 강관말뚝보다 18.7% 향상되었고, 동일한 휨하중에서 말뚝의 변위량은 강관말뚝보다 50% 감소하였다. 그리고 P-M 상관도로부터 연직하중을 받는 PCFT말뚝은 강관말뚝보다 휨내력이 크게 증가한 반면, 인발하중을 받는 PCFT 말뚝은 강관말뚝보다 휨내력이 감소함을 알 수 있었다. 또한 시험말뚝에 대한 수평재하시험의 결과에 따르면 상부말뚝의 길이가 동일한 경우 PCFT 복합말뚝은 HCP보다 수평지지력이 60.5% 컸고, 두께가 12mm인 강관말뚝보다 35.8% 큰 것으로 나타났다.

• Computers and Concrete
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• 제6권5호
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• pp.421-435
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• 2009

Chloride induced corrosion is a concern that governs the durability of concrete structures in marine environments, especially in tidal environments. During the service lives of concrete structures, internal cracks in the concrete cover may appear due to imposed loads, accelerating chloride penetration because of the simultaneous action of environmental and service structural loads. This paper investigated the effects of cyclic flexural loads on chloride diffusion characteristics of plain concretes, and proposed a model to predict the chloride penetration into plain concretes subjected to both tidal environments and different cyclic flexural load levels. Further, a new experiment was performed to verify the model. Results of the model using Finite Difference Method (FDM) showed that the durability of concretes in tidal environments was reduced as cyclic flexural load levels, SR, increased, and the modeling results fitted well with the experimental results.