• 한국구조물진단유지관리공학회 논문집
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• 제8권3호
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• pp.149-158
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• 2004

본 연구는 유효전단스팬에 대한 깊이의 비가 1.0인 깊이가 큰 보에 대해서 유효전단영역내에 개구부에 대한 파괴 메카니즘의 변화와 전단파괴된 후 보수 보강에 따른 부재 내력의 복원력에 관한 연구로서, 그 결론는, 전단파괴한 유공보 시험체의 초기사균열 하중은 시험체 간에 큰 차이가 없어 시험체의 배근형태에 영향을 받지 않는 것으로 나타났으며, 아라미드 시트로 보강된 시험체의 균열 및 파괴형태는 중앙부의 휨 균열과 전단지간의 사균열이 동시에 발생한 후, 최대내력근처에서 유공측의 전단균열이 확대되어, 시트면의 중앙부위가 박리되면서 전단파괴 되었다. 전단파괴된 깊이가 큰 보 시험체를 아라미드 섬유시트로 보강한 결과 보강전과 비교하여 최대내력은 최소 34.4%, 최대 83.8%의 증가를 나타내어 파괴전의 내력을 복원하는 것으로 나타났다.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2008년도 춘계 학술발표회 제20권1호
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• pp.169-172
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• 2008

FPR(Fiber Reinforced Polymer)는 중량에 비해 높은 강도, 높은 내부식성 등 우수한 역학적 특성으로 인해 최근 건설분야에 적용되는 사례가 많아지고 있으며, 특히 콘크리트 구조물 보강에 가장 활발히 적용되고 있다. FRP를 이용한 전통적인 보강방법은 인장면에 FRP를 부착하는 부착공법이었으나, 부착공법은 FRP의 박리 또는 부착파괴와 같은 조기파괴 문제점과 고정하중과 분담과 사용성 개선이 어려운 단점을 갖고 있다. 이러한 FRP 부착공법의 문제점들을 해결하기 위한 노력으로 최근에는 CFRP 판에 프리스트레스를 도입하는 공법에 대한 연구들이 시작되었다. 판형태의 CFRP를 이용하여 구조물에 긴장력을 도입하면 주인장철근의 응력을 경감시킬 수 있을 뿐만 아니라, 구조물의 균열폭과 휨변형도 감소시킬 수 있으며, 추가되는 활하중뿐만 아니라 고정하중도 일부 분담할 수 있게 되어 고가의 CFRP를 효율적으로 활용할 수 있는 방법이 된다. CFRP 판 긴장공법을 위해 최우선적으로 해결되어야 하는 것은 CFRP 긴장재를 정착하기 위한 적절한 정착장치의 개발이다. 본 연구에서는 CFRP 판 긴장재를 위한 정착장치를 개발하고자 CFRP 판의 정착단부 상세를 변수로 한 정착장치 인장실험을 수행하였으며, 기존 상용 정착구와 비교하여 저비용으로 제작 가능한 CFRP 판 긴장재용 몰드형 정착구의 성능을 검증하였다. 몰드형 정착장치에 대한 성능실험 결과 CFRP 판 긴장재의 표면이 거칠게 처리된 시편이 가장 정착성능이 우수한 것으로 나타났으며, 정착단부의 형상변화는 정착성능에 기여하지 못하는 것으로 나타났다.

• 한국구조물진단유지관리공학회 논문집
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• 제14권1호
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• pp.125-132
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• 2010

최근 건설 사업에서 FRP를 단순 부착하여 구조물을 보강하는 공법은 현재 가장 널리 사용되고 있는 보수보강법이다. 본 논문에서는 FRP로 보강된 철근콘크리트 구조물은 지속하중을 받고 있기 때문에 크리프와 건조수축의 영향을 받는다. 이로 인하여 FRP의 보강효과도 달라지며, 처짐 및 변형의 회복성능, 잔존 내력 역시 크게 달라진다. 따라서 CFRP, GFRP가 휨성능에 영향을 미치는 보강 성능을 파악하고, 일정 시간이 흐른 후 하중을 제거하여 장기 변형 및 처짐의 회복성능을 파악하고, 잔존하는 내력을 알아보고자 정적 재하 실험을 수행하였다. 실험한 결과, FRP 보강 실험체는 즉시 처짐을 제어하는 측면은 매우 효율적이고, 즉시변형 회복량 또한 즉시 변형량보다 큰 결과를 보였다. 잔존강도 실험을 통하여 CFRP로 보강된 실험체가 가장 큰 내력을 가지는 것으로 나타났다. FRP로 보강된 보는 지속하중에 의한 부착성능 및 잔존내력에는 영향이 없었던 것으로 판단된다.

• Steel and Composite Structures
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• 제30권5호
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• pp.417-432
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• 2019

This paper presents the results of axial compression testing and numerical modeling on reinforced concrete columns (RCC) with normal concrete (NC) and high-strength concrete (HSC), RCC confined by glass-fiber reinforced plastic pipes (GRP) casing as well as carbon fiber reinforced polymer (CFRP), The major parameters evaluated in the experiments were the effects of concrete type, GRP casing and CFRP wrapping, as well as the number of CFRP layers. 12 cylindrical RCC ($150{\times}600mm$) were prepared and divided into two groups, NC and HSC. Each group was divided into two parts; with and without GRP casing. In each part, one column was without CFRP strengthening layer, a column was wrapped with one CFRP layer and another column with two CFRP layers. All columns were tested under concentrated compression load. Numerical modeling was performed using ABAQUS software and the results of which were compared with experimental findings. A good agreement was found between the results. Results indicated that the utilization of CFRP wrapping and GRP casing improved compression capacity and ductility of RCC. The addition of one and two layer-FRP wrapping increased capacity in the NC group to an average of 18.5% and 26.5% and in the HSC group to an average of 10.2% and 24.8%. Meanwhile, the utilization of GRP casing increased the capacity of the columns by 3 times in the NC group and 2.38 times in the HSC group. The results indicated that although both CFRP wrapping and GRP casing increased confinement, the GRP casing gave more increase capacity and ductility of the RCC due to higher confinement. Furthermore, the confinement effect was higher on NC group.

• Smart Structures and Systems
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• 제23권5호
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• pp.495-506
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• 2019

This paper presents the results of axial pressure testing on reinforced concrete columns (RCCs) filled with confined normal concrete (NC) and high-strength concrete (HSC) using glass-fiber reinforced plastic pipes (GRP) casing as well as fiber reinforced polymer (FRP). This study aims to evaluate the behavior and mechanical properties of columns confined with GRP casing and FRP wrapping under pressure loads. The major parameters in the experiments were the type of concrete, the effect of GRP casing and FRP wrapping, as well as the number of FRP layers. 12 cylindrical RCCs (150*600) mm were prepared and divided into two groups, NC and HSC, and each group was divided into two parts. In each part, one column was without FRP strengthening layer, a column was wrapped with one FRP layer and another column with two FRP layers. All columns were tested under concentrated compression load. The results of the study showed that the utilization of FRP wrapping and GRP casing improved compression capacity and ductility of RCCs. The addition of one and two layers-FRP wrapping increased compression capacity in the NC group to an average of 18.5% and 26.5% and to an average of 10.2% and 24.8% in the HSC group. Meanwhile, the utilization of GRP casing increased the compression capacity of the columns by 4 times in the NC group and 3.38 times in the HSC group. The results indicated that although both FRP wrapping and GRP casing result in confinement, the GRP casing resulted in increased compression capacity and ductility of the RCCs due to higher confinement. Furthermore, the confinement effect was higher on columns made with NC.

• Computers and Concrete
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• 제30권5호
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• pp.339-355
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• 2022

The high cost of ultra-high-performance engineered cementitious composite (UHP-ECC) is currently a crucial issue, especially in terms of the polyethylene (PE) fibers use. In this paper, cheap calcium carbonate whiskers (CW) were evaluated on the feasibility of hybrid with PE fibers. Diverse combinations of PE fibers and CW were employed to investigate the multi-scale enhancement on the UHP-ECC performance. A probabilistic-based UHP-ECC tensile strain reliability analysis approach was utilized, which was in general agreement with the experimental results. Furthermore, a multi-dimensional integrated representation was conducted for the comprehensive assessment of UHP-ECC. Results illustrated that CW improved the compressive strength and energy dissipation capacity of UHP-ECC owing to the microscopic strengthening mechanism. CW and PE fiber further promoted the saturated cracking of composite by multi-scale crack arresting effect. In particular, PE1.75-CW0.5 specimen possessed the best overall performance. The ultimate cracking width of PE1.75-CW0.5 group had 98 ㎛, which was 46.18% lower compared to PE2-CW0 group, the 28d compressive strength were slightly improved, the tensile strain capacity was comparable to that of PE2-CW0 group. The results above demonstrated that combinations of PE fiber and CW could significantly enhance the comprehensive performance of UHP-ECC, which was beneficial for large-scale engineering applications.

• International Journal of Concrete Structures and Materials
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• 제6권2호
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• pp.123-134
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• 2012

There is significant concern in the engineering community regarding the safety and effectiveness of fiber-reinforced polymer (FRP) strengthening of RC structures because of the potential for brittle debonding failures. In this paper, previous research programs conducted by other researchers were reviewed in terms of the debonding failure of FRP laminates externally attached to concrete. This review article also discusses the influences on bond strength and failure modes as well as the existing experimental research and developed equations. Based on the review, several important conclusions were re-emphasized, including the finding that the bond transfer strength is proportional to the concrete compressive strength; that there is a certain bond development length that has to be exceeded; and that thinner adhesive layers in fact lower the chances of a concrete-adhesive interface failure. It is also found that there exist uncertainty and inaccuracy in the available models when compared with the experimental data and inconsistency among the models. This demonstrates the need for continuing research and compilation of data on the topic of FRP's bond strength.

• Structural Engineering and Mechanics
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• 제20권6호
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• pp.727-745
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• 2005

The present study is an experimental investigation into the behaviour of high strength concrete square short columns subjected to biaxial bending moments and strengthened by GFRP laminates. The main objectives of the study are: to evaluate the improvement in the structural performance of HSC short square columns subjected to small biaxial eccentricity when strengthened by externally applied FRP laminates, and to investigate the optimum arrangement and amount of FRP laminates to achieve potential enhancement in structural performance especially ductility. The parameters considered in this study are: number of FRP layers and arrangement of wraps. The load eccentricity is kept corresponding to e/t = 0.125 in two perpendicular directions to the columns principal axes, and the wraps are applied in single or double layers (partial or full wrapping). In the present work, test results of five full scale concrete columns are presented and discussed. The study has shown that FRP wraps can be used successfully to enhance the ductility of HSC columns subjected to biaxial bending by 300%.

• Structural Engineering and Mechanics
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• 제75권3호
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• pp.389-399
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• 2020

An infill wall made of high-performance fiber-reinforced cementitious composites (HPFRCC) was utilized in this study to strengthen the reinforced concrete (RC) frame structures that had not been designed for seismic loads. The seismic performance of the RC frame structures strengthened by the HPFRCC infill walls was investigated through the experimental tests, and the test results showed that they have improved strength and deformation capabilities compared to that strengthened by the RC infill wall. A simple numerical modeling method, called the modified longitudinal and diagonal line element model (LDLEM), was introduced to consider the seismic strengthening effect of the infill walls, in which a section aggregator approach was also utilized to reflect the effect of shear in the column members of the RC frames. The proposed model showed accurate estimations on the strength, stiffness, and failure modes of the test specimens strengthened by the infill walls with and without fibers.

• Advances in Computational Design
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• 제2권2호
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• pp.147-168
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• 2017

Over the past couple decades, externally bonded fiber reinforced polymer (FRP) composites have emerged as a repair and strengthening material for many concrete infrastructure applications. This paper presents an analytical investigation of the use of carbon FRP (CFRP) for a specific problem that occurs in concrete bridge girders wherein the girder ends are damaged by excessive exposure to deicing salts and numerous freezing/thawing cycles. A 3D finite element (FE) model of a full scale prestressed concrete (PC) I-girder is used to investigate the effect of damage to the cover concrete and stirrups in the end region of the girder. Parametric studies are performed using externally bonded CFRP shear laminates to determine the most effective repair schemes for the damaged end region under a short shear span-to-depth ratio. Experimental results on shear pull off tests of CFRP laminates that have undergone accelerated aging are used to calibrate a bond stress-slip model for the interface between the FRP and concrete substrate and approximate the reduced bond stress-slip properties associated with exposure to the environment that causes this type of end region damage. The results of these analyses indicate that this particular application of this material can be effective in recovering the original strength of PC bridge girders with damaged end regions, even after environmental aging.