• Computers and Concrete
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• 제27권5호
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• pp.437-445
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• 2021

Retrofitting of structures has gained importance over the recent years. Particularly, Reinforced Cement Concrete (RCC) column strengthening has become a challenge to the structural engineers, owing to the risks and complexities involved in it. There are several methods of RCC column strengthening viz. RCC jacketing, steel jacketing and Fiber Reinforced Polymer (FRP) wrapping etc., FRP wrapping is the most promising alternative when compared to the others. The large research database shows FRP wrapping, through lateral confinement, improves the axial load carrying capacity of the columns under concentric loading. However, its confining efficiency reduces under eccentric loading. Hence a relative newer technique called Near Surface Mounting (NSM), in which Carbon FRP (CFRP) strips are epoxy grouted to the precut grooves in the cover concrete of the columns, has been thrust domain of research. NSM technique strengthens the column nominally under concentric load case while significantly under eccentric case. A novel configuration of NSM in which the vertical NSM (VNSM) strips are being connected by horizontal NSM (HNSM) strips was numerically investigated under both concentric and eccentric loading. It was found that the configuration with 6 HNSM strips performed better under eccentric loading than under concentric loading, while the configuration with 3 HNSM strips performed better under concentric loading than under eccentric loading. Hence an optimum of 4 HNSM strips is recommended as strengthening measure for the given column specifications. It was also found that Aluminum alloy cannot be used instead of CFRP in NSM applications owing to its lower mechanical properties.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2004년도 춘계 학술발표회 제16권1호
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• pp.80-83
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• 2004

The FRP plate or sheet bonding technology was widely used for strengthening deficient RC structures. The strengthened structure using FRP bonding scheme, however, experience the complex interfacial behaviour which is difficult to predict. Therefore, the unbonded scheme using some anchorage device can be is an alternative for more reliable design. In this study, wedge-type anchor for FRP plate is developed for the unbonded flexural strengthening scheme. Some parameter study using 2D finite element method is performed. The analysis parameters are taken as wedge-guide friction coefficients, wedge- FRP ,.friction coefficient and wedge inclination angle. Based on the parameter study, more efficient anchors are designed and tested. The test result show that the developed anchor assure about $80\%$ FRP strength, which is higher performance than typical bonding scheme. Last, 3D finite element analysis is performed.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2006년도 춘계 학술발표회 논문집(II)
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• pp.333-336
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• 2006

In general, polymer materials undergo degradation when exposed to ultraviolet radiation, which can cause dissociation of chemical bonds. FRP composites which are used in strengthening existing structure are usually adhered on the concrete surface, its mechanical properties as well as appearance such as color, surface conditions are affected by sunlight and expecially ultraviolet light. In this study, variations of tensile strength after exposure for certain period of time through accelerated exposure by Xe arc methods specified in KS F 2274 are measured in order to examine strength degradation characteristics of FRP composite. As a result of ultraviolet light test for FRP composite after accelerated exposure for 0, 500, 1000, 1500 hour, discoloration of FRP composite occurs according to the passage of time. But, few strength degradations of FRP composite are observed due to exposure of ultraviolet ray with an small variation of tensile strength.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2006년도 춘계 학술발표회 논문집(II)
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• pp.345-348
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• 2006

FRP composites which are used in strengthening existing structure are usually adhered to the concrete surface, their performance are directly affected by environmental condition such as freezing-thawing and moisture. Accordingly, it is required to evaluate bond durability between FRP composite and concrete as well as FRP materials itself. The durability characteristics of FRP composite for freezing-thawing are evaluated in this study with the variables of concrete strength, type of FRP composite, freezing-thawing conditions and freezing-thawing cycle. In addition, material durability of GFRP sheet for high temperature/high humidity condition are examined in this experimental study.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2006년도 추계 학술발표회 논문집
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• pp.125-128
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• 2006

Many research have been carried out concerned with the flexural performance of FRP composite in a various ways. Most of them, however, have used a small-scale specimen, so haven't been fully verified by full-scale model test. In this study, a full-scale RC beam model test for flexural strengthening with CFRP composites has been performed in order to verify test results obtained through a series of small-scale model test with respect to FRP stiffness affecting strengthening performance in the previous studies. A total of 4 specimens have been manufactured including control beam. The specimens strengthened with CFRP composites consist of 3 different CFRP stiffness with 2 types of CFRP composite. Consequently, the purpose of this study is to estimate influence of the size effect of specimens and FRP stiffness on the flexural performance. As a result, the effective strain of FRP composite is inversely proportional to FRP stiffness and ensures the same performance with small-scale model test.

• Structural Engineering and Mechanics
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• 제64권5호
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• pp.557-566
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• 2017

Fiber reinforced polymer (FRP) sheets are the most efficient structural materials in terms of strength to weight ratio and its application in strengthening and retrofitting of a structure or structural elements are inevitable. The performance enhancement of structural elements without increasing the cross sectional area and flexible nature are the major advantages of FRP in retrofitting/strengthening work. This research article presents a detailed study on the inelastic response of conventional and retrofitted Reinforced Concrete (RC) frames using Carbon Fibre Reinforced Polymers (CFRP) and Glass Fiber Reinforced Polymers (GFRP) subjected to quasi-static loading. The hysteretic behaviour, stiffness degradation, energy dissipation and damage index are the parameters employed to analyse the efficacy of FRP strengthening of brick in-filled RC frames. Repair and retrofitting of brick infilled RC frame shows an improved load carrying and damage tolerance capacity than control frame.

• International Journal of Concrete Structures and Materials
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• 제8권2호
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• pp.141-155
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• 2014

The use of fiber reinforced polymer (FRP) composites in strengthening reinforced concrete beam-column subassemblies has been scrutinised both experimentally and numerically in recent years. While a multitude of numerical models are available, and many match the experimental results reasonably well, there are not many studies that have looked at the efficiency of different finite elements in a comparative way in order to clearly identify the best practice when it comes to modelling FRP for strengthening. The present study aims at investigating this within the context of FRP retrofitted reinforced concrete beam-column subassemblies. Two programs are used side by side; ANSYS and VecTor2. Results of the finite element modeling using these two programs are compared with a recent experimental study. Different failure and yield criteria along with different element types are implemented and a useful technique, which can reduce the number of elements considerably, is successfully employed for modeling planar structures subjected to in-plane loading in ANSYS. Comparison of the results shows that there is good agreement between ANSYS and VecTor2 results in monotonic loading. However, unlike VecTor2 program, implicit version of ANSYS program is not able to properly model the cyclic behavior of the modeled subassemblies. The paper will be useful to those who wish to study FRP strengthening applications numerically as it provides an insight into the choice of the elements and the methods of modeling to achieve desired accuracy and numerical stability, a matter not so clearly explored in the past in any of the published literature.

• 한국철도학회논문집
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• 제12권5호
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• pp.641-648
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• 2009

최근 철도차량의 속도가 증가함에 따라 철도시설물에도 철근콘크리트 구조물이 많이 적용되고 있는 실정이다. 하지만 이러한 콘크리트 구조물은 공용년수의 증가에 따라 필연적으로 구조적인 보강이 요구된다. 강판보강법 및 섬유복합체(FRP)를 활용한 보강법 등이 가장 일반적으로 적용되는 실정이지만 각 공법마다 나름대로의 단점 역시 존재 한다. 최근 화재나 기타 환경적인 공격에 대하여 강한 내구성을 가진 재료의 개발이 요구되고 있으며 이에 따른 현무암으로부터 추출한 Basalt 섬유를 활용한 섬유보강재가 많은 관심을 받고 있다. 이에 본 연구에서는 Basalt 섬유쉬트를 보강재로 사용할 경우 중요한 특성인 콘크리트와의 부착특성에 관하여 연구를 수행하였다. 실험변수는 보강폭, 길이, 보강겹수를 포함한다. 실험결과, 파괴형태는 계면파괴, 섬유파단, 그리고 rip-off의 형태가 관측되었으며 보강길이보다는 보강폭이 보강강도에 더 많은 영향을 미치는 것으로 판단되었다. 또한 보강길이가 전부 유효하게 작용하지는 않았으며 이에 유효보강길이를 산정하고 이에 따른 부착강도를 산정하였다. 이를 다른 종류의 FRP재료를 활용한 경우에 유효 보강길이와 비교하여 Basalt 섬유쉬트의 부착특성을 분석하였다.

• 콘크리트학회논문집
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• 제22권5호
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• pp.719-725
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• 2010

최근 콘크리트 구조물에 충격하중, 폭발하중 등 극한의 외력이 작용하는 경우가 빈번하게 발생하고 있다. 이 연구에서는 강섬유보강 RC보와 carbon FRP 시트를 이용하여 보강한 RC보를 이용하여 충격실험을 진행하였다. 강섬유보강 RC보의 경우 0.75%부피비로 강섬유를 혼입하였으며 carbon FRP 시트의 경우 에폭시 레진을 이용하여 보강을 한후 보 부재를 완성하였다. FRP 시트 보강은 부재의 하단을 휨 보강하였으며 충격하중이 부재에 작용할 때 발생하는 shear-plug 균열을 제어하기 위하여 충격하중이 가해지는 국부에 CFRP 전단보강을 실시하였다. 실험진행은 drop-weight test 방식으로 직접 기기를 만들어 실행하였다. 각각의 부재에 단계별로 충격하중을 가하여 실험을 진행하였으며 균열과 균열폭을 측정하였다. 실험결과 강섬유보강 RC보가 일반 RC보에 비하여 균열폭 및 shear-plug 균열제어 그리고 스폴링파괴에 더 높은 성능을 나타내었다. FRP로 부재의 하단을 휨 보강한 부재의 경우 균열의 제어에 어느정도 효과를 나타내고 있으나 충격하중이 가해질 시 콘크리트와 FRP 시트의 부착면에서 박리파괴가 빠르게 진행되었다. FRP 시트로 부재의 하단과 측면을 CFRP로 휨, 전단보강한 부재의 경우 shear-plug 균열제어에 가장 높은 저항성능을 보이고 있음을 확인할 수 있었다. 하지만 충격하중이 보강이 이루어지지 않은 부분에 작용할 경우 오히려 보강이 되지 않은 RC보에 비하여 콘크리트 스폴링 파괴에 더 취약함을 알 수 있었다.

• 한국구조물진단유지관리공학회 논문집
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• 제14권2호
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• pp.153-160
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• 2010

다양한 요인에 의해 성능이 저하된 철근콘크리트 구조물은 보수 보강 공법이 요구된다. 현재 다양한 공법과 신소재를 이용한 보강법의 개발이 진행 중에 있다. 최근에 섬유보강 복합체(FRP)를 이용한 보강공법이 주목받고 있으며, 많은 연구와 개발이 진행 중에 있다. 본 논문에서는 FRP-알루미늄 유공복합보로 보강된 RC보의 화재거동에 관한 실험결과를 제시하고자 한다. 사전가력으로 손상시킨 RC보에 FRP-알루미늄 유공복합보로 보강후 화재노출시킨 결과, 손상율이 높아질수록 화재노출에 더욱 많은 영향을 받았으며, 보강효과가 떨어짐을 실험결과 나타났다.