• 한국지진공학회:학술대회논문집
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• 한국지진공학회 1997년도 춘계 학술발표회 논문집 Proceedings of EESK Conference-Fall 1997
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• pp.182-190
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• 1997

A new method to prevent reinforced concrete columns from brittle failure. The method is called transversely reinforcing method in which only the critical regions are confined in steel tube. The steel tubes can change the failure mode of the latter columns from the shear to the flexure. The steel tubes also increase the compressive strength, shear strength and deformation capacity of the infilled concrete. The following conclusions are reached on bases of the study on the seismic performance of the high-strength RC rectangualr short columns confined in steel tube with shear span tho depth ratio of 2.0 The brittle shear failure of high-strength reinforced concrete short columns with large amount of longitudinal bars, which cannot prevented by using the maximum amount of welded hoops, can be prevented by using the steel tube which confines all the maximum amount of welded hoops, can be prevented by using the steel tube which confines all the concrete inclusive of cover concrete. High-strength RC short columns confined in rectangular steel tube provided excellent enhancement of seismic performance but, found that plastic buckling of the steel tube in the hinge regions tended to occur when the columns were subjected to large cyclic lateral displacements. In order to prevent the plastic buckling when the columns lies on large on cyclic lateral displacements, the steel ribs were used for columns. Tests have established that the columns provide excellent enhancement of seismic performance of inadequately confined columns.

• Structural Engineering and Mechanics
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• 제18권2호
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• pp.151-166
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• 2004

The interaction between concrete core expansion and deformation of perimeter ties has been known to have a significant effect on the effective confinement of rectangular reinforced concrete (RC) tied columns. This interaction produces passive confining pressure to the concrete core. Most existing models for determining the response of RC tied columns do not directly account for the influence of flexural stiffness of the ties and the variation of confining stress along the column height. This study presents a procedure for determining the confined compressive strength of RC square columns confined by rectilinear ties with various tie configurations considering directly the influence of flexural flexibility of the ties and the variation of confining stress along the vertical direction. The concept of area compatibility is employed to ensure compatibility of the concrete core and steel hoop in a global sense. The proposed procedure yields satisfactory predictions of confined strengths compared with experimental results, and the influence of tie flexibility, tie configuration and degree of confinement can be well captured.

• Computers and Concrete
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• 제27권3호
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• pp.225-239
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• 2021

Carbon fiber reinforced polymer (CFRP) has extensive use in strengthening reinforced concrete structures due to its high strength and elastic modulus, low weight, fast and easy application, and excellent durability performance. Many studies have been carried out to determine the performance of the CFRP confined concrete cylinder. Although studies about the prediction of confined compressive strength using ANN are in the literature, the insufficiency of the studies to predict the strain of confined concrete cylinder using ANN, which is the most appropriate analysis method for nonlinear and complex problems, draws attention. Therefore, to predict both strengths and also strain values, two different ANNs were created using an extensive experimental database. The strength and strain networks were evaluated with the statistical parameters of correlation coefficients (R2), root mean square error (RMSE), and mean absolute error (MAE). The estimated values were found to be close to the experimental results. Mathematical equations to predict the strength and strain values were derived using networks prepared for convenience in engineering applications. The sensitivity analysis of mathematical models was performed by considering the inputs with the highest importance factors. Considering the limit values obtained from the sensitivity analysis of the parameters, the performances of the proposed models were evaluated by using the test data determined from the experimental database. Model performances were evaluated comparatively with other analytical models most commonly used in the literature, and it was found that the closest results to experimental data were obtained from the proposed strength and strain models.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2003년도 봄 학술발표회 논문집
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• pp.487-492
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• 2003

High-strength concrete(HSC) is a new construction material with enormous potential. Structures using high-strength concrete are to be coming more and more popular. But high-strength reinforced concrete columns show brittle behavior. It, therefore, is necessary to improve the ductility of HSC members. The purpose of this study is to investigate the ductility and strength of high-strength columns with variable lateral confinement under concentric axial load. Five HSC columns with compressive strength 68㎫ are designed with variable lateral confinements such as carbon fiber sheet(CFS), glass fiber sheet(GFS), and metal lath. Test results indicate that specimen confined by CFS show 11% higher maximum strength, 2.74 times ductility than A specimen using hoop. On comparing with the specimen A and B confined metal lath instead of hoop, strength decrease of 3%, and ductility increase of 1.21 times were observed.

• Steel and Composite Structures
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• 제17권4호
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• pp.431-452
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• 2014

The present study focuses on the mechanical behaviour of concrete filled double skin steel tubular (CFDST) stub columns confined by fiber reinforced polymer (FRP). A series of axial compression tests have been conducted on two CFDST stub columns, eight CFDST stub columns confined by FRP and a concrete-filled steel tubular (CFST) stub column confined by FRP, respectively. The influences of hollow section ratio, FRP wall thickness and fibre longitudinal-circumferential proportion on the load-strain curve and the concrete stress-strain curve for stub columns with annular section were discussed. The test results displayed that the FRP jacket can obviously enhance the carrying capacity of stub columns. Based on the test results, a new model which includes the effects of confinement factor, hollow section ratio and lateral confining pressure of the outer steel tube was proposed to calculate the compressive strength of confined concrete. Using the present concrete strength model, the formula to predict the carrying capacity of CFDST stub columns confined by FRP was derived. The theoretically predicted results agree well with those obtained from the experiments and FE analysis. The present method is also adapted to calculate the carrying capacity of CFST stub columns confined by FRP.

• Structural Engineering and Mechanics
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• 제18권1호
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• pp.21-40
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• 2004

In this paper, we modify the L-L model (Li et al. 2003) and extend the application of this model to concrete confined by both steel reinforcement and CFRP. Thirty-six concrete cylinders with a dimension of ${\varphi}30{\times}60$ cm were tested to verify the effectiveness of the proposed model. The experimental test results show that different types of steel reinforcement have a great effect on the compressive strength of concrete cylinders confined by steel reinforcement, but the different types of steel reinforcement have very little effect on concrete cylinders confined by both steel reinforcement and CFRP. Compared with the stress-strain curves of confined concrete cylinders, we can conclude that the proposed model can provide more effective prediction than others models.

• 콘크리트학회논문집
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• 제15권1호
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• pp.110-116
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• 2003

근년, 콘크리트구조물이 고층화, 대형화됨에 따라 고강도, 고유동, 고내구성인 고성능 콘크리트의 수요가 많아지고 있다. 이러한 고성능 콘크리트는 보통콘크리트에 비하여 압축강도가 크고, 시공성 및 내구성이 우수한 것이 장점이지만, 보통강도 콘크리트에 비하여 파괴형태가 취성적인 것이 단점으로 제시되고 있다. 따라서, 본 연구는 W/B 30% 및 40%에서 메탈라스, 유리섬유 및 탄소섬유로 횡구속된 고성능 콘크리트의 역학적 특성을 분석하여 압축강도 및 인성개량방법을 제안하고자 하였다. 연구결과 압축강도는 횡구속재의 횡구속력의 증대에 기인하여 메탈라스, 탄소섬유 및 유리섬유의 순으로 증가하였다. 또한, 횡구속재 변화에 따른 응력-변형도곡선에서 플레인의 경우는 최대하중 이후 취성파괴로 나타난 반면, 횡구속된 경우로, 특히 메탈라스로 횡구속하였을 때에는 인성증가로 변형율이 증가하여 어느 정도 취성이 개량됨을 알 수 있었다. 탄성계수는 보강하지 않은 콘크리트와 비교하여 약간 큰 값으로 압축강도의 경향과 비슷한 양상이었다.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2002년도 봄 학술발표회 논문집
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• pp.563-568
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• 2002

This paper is a fundamental study on the mechanical properties of the high performance concrete confined with metal lath, glass and carbon fiber laterally. According to the results, it shows that the compressive strength increases by 9%, 8% and 6% in metal lath carbon fiber and glass fiber in case of W/B 30% respectively. In case of W/B 30% and 40%, flecxural strength shows largely in order of carbon fiber, metal lath, glass fiber. In strain-stress curve with the kinds of material for lateral confinement, while brittleness failure occurs in plain concrete just after maximum load, it is improved in some degree in confined concrete due to increase of the strain by increase of toughness. But, elastic modulus shows the similar tendency between confined concrete and plain concrete. Length change ratio by drying shrinkage shows little a bit in order of carbon fiber, glass fiber and metal lath due to confinement.

• 한국구조물진단유지관리공학회 논문집
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• 제19권5호
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• pp.10-21
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• 2015

콘크리트 구조물의 내력성능을 향상시키기 위해 탄소섬유쉬트(Carbon Fiber-Reinforced Plastic Sheet, 이하 CFRP sheet)로 보강된 콘크리트에 대해 많은 연구가 수행되어 왔다. 본 연구는 CFRP sheet로 구속된 콘크리트에 대한 연구 중 미비한 부분을 보완하기 위하여 보강겹수, 시험체의 크기, 형상비, 겹이음길이를 변수로 하여 연구를 수행하였다. 각 시험체별 응력-변형률 곡선을 통해 콘크리트의 거동을 비교하였으며, 최대압축강도를 통하여 CFRP sheet의 보강효과를 확인하였다. 보강겹수의 증가에 따라 콘크리트의 압축성능은 크게 개선되었으며, 시험체의 크기와 형상비의 변화를 통해 이론적인 부분을 검증하였고, 겹이음길이는 둘레의 5%이상으로 해야만 보강효과에 영향이 없는 것으로 확인하였다. 또한 본 연구의 시험결과와 기존 시험결과를 정리하고 이를 기준으로 기존 강도추정모델을 통계 분석함으로 모델의 정확성과 신뢰성을 검증하였다.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2003년도 가을 학술발표회 논문집
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• pp.351-354
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• 2003

Triaxial behavior of concrete cylinders wrapped with FRP material has been investigated for the increase of concrete strength by lateral confinement. Using the model by Richart et al., a modified empirical equation was proposed to estimate the strength of concrete cylinders with FRP confinement based on the linear relationship between the concrete strength and lateral confining pressure. From the experimental stress-strain result of the cylinder specimens having similar confining pressure, less ductility was observed for higher strength concrete. But the compressive strength of the specimen was linearly increased by lateral confinement. The confinement effectiveness coefficient for the strength enhancement of the cylinders by FRP wrap was obtained as 2.27 from the regression analysis.