• Steel and Composite Structures
• /
• 제21권6호
• /
• pp.1307-1325
• /
• 2016

Nonlinear behavior of two-span, continuous composite steel-concrete girders strengthened with Carbon Fiber Reinforced Polymers (CFRP) bonded to the top of concrete slab over the negative moment region was evaluated using a non-linear Finite Element (FE) model in this paper. A three-dimensional FE model of continuous composite girder using commercial software ABAQUS simulated and validated with experimental results. The interfacial regions of the composite girder components were modeled using suitable interface elements. Validation of the proposed numerical model with experimental data confirmed the applicability of this model to predict the loading history, strain level for the different components and concrete-steel relative slip. The FE model captured the different modes of failure for the continuous composite girder either in the concrete slab or at the interfacial region between CFRP sheet and concrete slab. Through a parametric study, the thickness of CFRP sheet and shear connection required to develop full capacity of the continuous composite girder at negative moment zone have been investigated. The FE results showed that the proper thickness of CFRP sheet at negative moment region is a function of the adhesive strength and the positive moment capacity of the composite section. The shear connection required at the negative moment zone depends on CFRP sheet's tensile stress level at ultimate load.

• Computers and Concrete
• /
• 제15권1호
• /
• pp.1-20
• /
• 2015

Many existing reinforced concrete (RC) columns in structures tend to become substandard RC ones due to updated standards or environmental changes. These substandard columns may alter the behaviors of the whole structure and therefore are in urgent need of seismic retrofitting. Owing to their superior advantages, carbon fiber reinforced polymer (CFRP) composites are widely used to retrofit RC columns. The applications mainly focus on various substandard RC columns, but few deals with substandard columns with deteriorated concrete, especially damaged by earthquake. The purpose of this paper is to investigate the seismic behaviors of CFRP reinforced partially deteriorated RC columns and to evaluate the effect of CFRP sheets on them. Six flexure-dominant columns were tested under a constant axial load and transverse cyclic displacements. It is found that the seismic behaviors of partially deteriorated columns can be recovered by wrapping CFRP sheets on them. Numerical analysis is then conducted using finite element methods and verified with experimental results. The effects of the axial load ratio, the ratio of the thickness of CFRP sheet to the column diameter, and the slenderness ratio on the seismic behaviors of CFRP reinforced RC columns are evaluated. Finally, a method is proposed to determine the required thickness of CFRP sheet.

• 복합신소재구조학회 논문집
• /
• 제4권2호
• /
• pp.1-7
• /
• 2013

In recent years, fiber reinforced polymer plastic composites are readily available in the construction industry. Fiber reinforced polymer composite has many advantages such as high specific strength and high specific stiffness, high corrosion resistance, light-weight, magnetic transparency, etc. In this paper, we present the result of investigation pertaining to the flexural behavior of flange strengthened I-shape pultruded fiber reinforced polymer plastic (PFRP) member using carbon fiber sheet (CFRP sheet). Test variable is consisted of the number of layers of strengthening CFRP sheet from 0 to 3. From the experimental results, flexural strengthening effect of flange strengthened I-shape PFRP member using CFRP sheet is evaluated and it was found that 2 layers of strengthening CFRP sheet are appropriate considering efficiency and workability.

• 대한토목학회논문집
• /
• 제42권3호
• /
• pp.311-322
• /
• 2022

본 연구에서는 분포형 광섬유 시트와 탄소섬유 시트를 콘크리트 표면에 부착하여 철근 콘크리트를 사용하는 구조물의 보강 효과 및 BOTDR 센서를 활용한 상태 평가를 4점 휨 실험을 통해 수행하였다. 부착 정도에 따른 보강 효과를 확인하기 위하여 탄소섬유 시트의 부착 형태를 다양하게 제작하였으며, BOTDR 센서의 활용성을 확인하기 위하여 실험체에 다수의 전기저항식 변형률 게이지를 부착하여 BOTDR 센서의 변형률과 비교하였다. 실험 결과를 살펴보면, 우선 CFRP시트 부착 정도에 따른 보강 효과에 분명한 차이가 나타나는데, 이는 부착 면적보다는 부착 형태에 더 영향을 받는 것으로 확인되었다. BOTDR 센서로부터 계측된 변형률로부터 하중 증가에 따른 철근 콘크리트 실험체의 구조적 거동을 시각화 할 수 있었으며, CFRP 보강 부위에서 하중이 집중되는 것을 알 수 있다. BOTDR 센서에서 계측된 변형률이 전기저항식 게이지로부터 계측된 변형률과 유사하게 계측되는 것을 알 수 있는데, 이를 통해 대형 토목 구조물의 전체적 거동을 분석하는데 BOTDR 센서가 효과적일 수 있음을 확인하였다. 다시 말해서, 국부적 변형률을 측정하는 전기식 변형률 게이지로 계측을 하면 계측 오차는 상당할 수 있는 반면에, 분포형으로 측정되는 BOTDR 센서는 이러한 문제를 줄일 수 있는 대안으로 판단된다. 마지막으로, CFRP 시트 탈락이 발생되는 부분에서 계측 BOTDR 센서 변형률이 높게 나타나는데 이를 활용하면 CFRP 시트의 국부적 손상 위치를 효율적으로 추적할 수 있을 것으로 판단된다.

• 한국구조물진단유지관리공학회 논문집
• /
• 제11권6호
• /
• pp.95-102
• /
• 2007

교량의 노후화와 교통량의 증가로 성능개선이 요구되어 질 경우, 경제적인 측면에서 신축 보다는 보수 보강을 통한 성능개선이 보다 바람직한 유지관리이다. 많은 보강공법중 시공방법의 편리와 빠른 시공기간으로 교량의 성능향상을 위해 FRP 재료를 이용한 표면부착공법이 많이 이용되고 있다. 특히, FRP 재료는 철근보다 경량이고 인장강도는 약 10배정도 우수한 재료이다. 이를 이용한 보강성능을 평가하기 위하여 CFRP 쉬트와 GSP를 이용하여 실험을 수행하였다.

• 한국구조물진단유지관리공학회 논문집
• /
• 제19권2호
• /
• pp.151-159
• /
• 2015

본 연구에서는 기존 철근콘크리트 구조물 보-기둥 접합부의 내진성능의 개선을 위해 보-기둥 접합부 영역을 FRP보강재 (탄소섬유시트, 아라미드섬유시트, 매입형 CFRP Rod)를 사용하여 보강한 후 내진성능을 평가하였다. 총 7개의 실험체를 제작하고 실험을 수행하여 내진성능을 평가하였으며, 본 연구의 실험결과를 근거로 다음과 같은 결론을 얻었다. 기존 철근콘크리트 보-기둥 접합부의 접합부 영역을 보강한 결과, 초기 재하시 접합부 영역의 균열억제 효과와 재하 전 과정을 통하여 보강재의 구속효과로 인하여 균열억제 효과가 커서 안정적인 파괴형태 및 내력향상 효과를 나타내었다. 매입형 CFRP Rod와 탄소섬유시트를 활용한 R/C 외부 보-기둥 접합부 실험체 LBCJ-CRUS는 표준실험체 LBCJ와 비교하여 변위연성 4, 7에서 각각 최대내력은 1.54배, 에너지소산능력은 2.36배 증가하였다. 그리고 실험체 LBCJ-CS, LBCJ-AF시리즈는 변위연성 7에서 표준실험체 LBCJ 보다 에너지소산능력이 각각 2.04~2.34, 1.63~3.02배 증가하였다.

• Structural Engineering and Mechanics
• /
• 제40권2호
• /
• pp.215-231
• /
• 2011

The axial compressive strength of unidirectional FRP is generally quite lower than its axial tensile strength. This fact decreases the advantages of FRP as main load bearing member in engineering structure. In order to restrain the lateral expansion and splitting of GFRP, and accordingly heighten its axial compressive bearing capacity, a project that to confine GFRP pole with surrounding CFRP sheet is suggested in the present study. The Experiment on the CFRP sheet confined GFRP poles showed that a combined structure of high bearing capacity was attained. Basing on the experiment research a theoretical iterative calculation approach is suggested to predict the ultimate axial compressive stress of the combined structure, and the predicted results agree well with the experimental results. Then the influences of geometrical parameters on the ultimate axial compressive stress of the combined structure are also analyzed basing on this approach.

• Structural Engineering and Mechanics
• /
• 제35권1호
• /
• pp.1-18
• /
• 2010

Bonding of carbon fiber reinforced polymer (CFRP) composites has become a popular technique for strengthening concrete structures in recent years. The bond stress between concrete and CFRP is the main factor determining the strength, rigidity, failure mode and behavior of a reinforced concrete member strengthened with CFRP. The accurate evaluation of the strain is required for analytical calculations and design processes. In this study, the strain between concrete and bonded CFRP sheets across the notch is tested. In this paper, indirect axial tension is applied to CFRP bonded test specimen by a four point bending tests. The variables studied in this research are CFRP sheet width, bond length and the concrete compression strength. Furthermore, the effect of a crack- modeled as a notch- on the strain distribution is studied. It is observed that the strain in the CFRP to concrete interface reaches its maximum values near the crack tips. It is also observed that extending the CFRP sheet more than to a certain length does not affect the strength and the strain distribution of the bonding. The stress distribution obtained from experiments are compared to Chen and Teng's (2001) analytical model.

• Structural Engineering and Mechanics
• /
• 제63권4호
• /
• pp.447-456
• /
• 2017

The primary objective of this paper is to study the effectiveness of anchorage on the performance of shear deficient beams externally strengthened with CFRP composites. The overall behavior of the tested beams loaded up to failure, the onset of the cracking, and crack development with increased load and ductility were described. The use of CFRP composites is an effective technique to enhance the shear capacity of RC beams by using CFRP strips anchored into the tension side and from the top by 15-34% based on the investigated variables. Bonded anchorage of CFRP strips with width of 0.1h-0.3h to the beam resulted in a decrease in average interface bond stress and an increase in the effective strain of the FRP sheet at failure, which resulted in a higher shear capacity as compared with that of the U-wrapped beams without anchorage as well as delay or mitigate the sheet debonding from the concrete surface.

• Steel and Composite Structures
• /
• 제14권5호
• /
• pp.453-472
• /
• 2013

This paper presents the structural behavior of CFRP (carbon fiber reinforced polymer) strengthened CFT (concrete-filled steel tubes) columns under axial loads. Circular and square specimens were selected to investigate the retrofitting effects of CFRP sheet on CFT columns. Test parameters are cross section of CFT, D/t (B/t) ratios, and the number of CFRP layers. The load and ductility capacities were evaluated for each specimen. Structural behavior comparisons of circular and rectangular section will be represented in the experimental result discussion section. Finally, ultimate load formula of CFRP strengthened CFT will be proposed to calculate the ultimate strength of CFRP strengthened circular CFT. The prediction values are in good agreement with the test results obtained in this study and in the literature.