• Steel and Composite Structures
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• 제10권4호
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• pp.361-371
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• 2010

Enhancement in the seismic buckling capacity of steel tanks caused by the addition of fiber reinforced polymers (FRP) retrofit layers attached to the outer walls of the steel tank is investigated. Three-dimensional non-linear finite element modeling is utilized to perform such analysis considering non linear material properties and non-linear large deformation large strain analysis. FRP composites which possess high stiffness and high failure strength are used to reduce the steel hoop stress and consequently improve the tank capacity. A number of tanks with varying dimensions and shell thicknesses are examined using FRP composites added in symmetric layers attached to the outer surface of the steel shell. The FRP shows its effectiveness in carrying part of the hoop stresses along with the steel before steel yielding. Following steel yielding, the FRP restrains the outward bulging of the tank and continues to resist higher hoop stresses. The percentage improvement in the ultimate base moment capacity of the tank due to the addition of more FRP layers is shown to be as high as 60% for some tanks. The percentage of increase in the tank moment capacity is shown to be dependent on the ratio of the shell thickness to the tank radius (t/R). Finally a new methodology has been explained to calculate the location of Elephant foot buckling and consequently the best location of FRP application.

• Computers and Concrete
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• 제33권2호
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• pp.163-173
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• 2024

Fiber-reinforced polymers (FRP) have a proven strength enhancement capability when installed into Reinforced Concrete (RC) beams. The brittle failure of traditional FRP strengthening systems has attracted researchers to develop novel materials with improved strength and ductility properties. One such material is that known as polyethylene terephthalate (PET). This study presents a numerical investigation of the flexural behavior of reinforced concrete beams externally strengthened with PET-FRP systems. This material is distinguished by its large rupture strain, leading to an improvement in the ductility of the strengthened structural members compared to conventional FRPs. A three-dimensional (3-D) finite element (FE) model is developed in this study to predict the load-deflection response of a series of experimentally tested beams published in the literature. The numerical model incorporates constitutive material laws and bond-slip behavior between concrete and the strengthening system. Moreover, the validated model was applied in a parametric study to inspect the effect of concrete compressive strength, PET-FRP sheet length, and reinforcing steel bar diameter on the overall performance of concrete beams externally strengthened with PET-FRP.

• 콘크리트학회논문집
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• 제19권6호
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• pp.727-734
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• 2007

철근과 fiber-reinforced polymer (FRP)의 물리적, 역학적 특성의 차이 및 슬래브 상부 보강재의 기둥 인접부 집중 배근, 그리고 기둥 인접부 슬래브에 강섬유 콘크리트 (SFRC)의 타설 등에 따른 2방향 슬래브의 펀칭 전단 거동에 대한 효과를 평가하였다. 펀칭 전단강도, 강성, 연성, 변형률 분포 그리고 균열 제어 성능 등을 파악하였다. 실험 결과 기둥 인접부의 슬래브에 집중 배근을 하거나 SFRC를 타설하는 것은 glass fiber-reinforced polymer (GFRP) 바로 보강된 슬래브의 펀칭 전단 거동을 향상시켰다. 기둥 인접 구역에 집중 배근된 슬래브의 실험 결과를 다양한 설계기준과 타 연구자에 의해 제안된 예측식과 비교하였으며, 집중 배근으로 인한 이점을 예측식에 반영할 수 있도록 집중 배근된 슬래브의 철근비를 산정하는 합리적인 방법도 제안하였다.

• Structural Engineering and Mechanics
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• 제56권3호
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• pp.473-490
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• 2015

This paper presents the analysis of intermediate crack-induced (IC) debonding failure loads for reinforced concrete (RC) beams strengthened with adhesively-bonded fiber-reinforced polymer (FRP) plates or sheets. The analysis consists of the energy release and simple ACI methods. In the energy release method, a fracture criterion is employed to predict the debonding loads. The interfacial fracture energy that indicates the resistance to debonding is related to the bond-slip relationships obtained from the shear test of FRP-to-concrete bonded joints. The section analysis that considers the effect of concrete's tension stiffening is employed to develop the moment-curvature relationships of the FRP-strengthened sections. In the ACI method, the onset of debonding is assumed when the FRP strain reaches the debonding strain limit. The tension stiffening effect is neglected in developing a moment-curvature relationship. For a comparison purpose, both methods are used to numerically investigate the effects of relevant parameters on the IC debonding failure loads. The results show that the debonding failure load generally increases as the concrete compressive strength, FRP reinforcement ratio, FRP elastic modulus and steel reinforcement ratio increase.

• Structural Engineering and Mechanics
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• 제73권4호
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• pp.381-395
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• 2020

Study on the inelastic response of bare and masonry infilled Reinforced Concrete (RC) frames repaired using Carbon Fibre Reinforced Polymers (CFRP) and Glass Fiber Reinforced Polymers (GFRP) subjected to quasi- static loading is presented in the work. The hysteresis behaviour, stiffness retention, energy dissipation and damage index are the parameters employed to analyze the efficacy of FRP strengthening of bare and brick in-filled RC frames. It is observed that there is a significant improvement in load carrying capacity of brick infilled frame over bare RC frame. Also FRP strengthened brick infilled frame performs much better than FRP repaired bare frame under quasi static loading. 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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• 제6권1호
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• pp.41-47
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• 2012

Fiber-Reinforced Polymers (FRP) are used to enhance the behavior of structural components in either shear or flexure. The research conducted in this paper was mainly focused on the shear-strengthening of reinforced and prestressed concrete beams using FRP. The main objective of the research was to identify the parameters affecting the shear capacity provided by FRP and evaluate the accuracy of analytical models. A review of prior experimental data showed that the available analytical models used to estimate the added shear capacity of FRP struggle to provide a unified design equation that can predict accurately the shear contribution of externally applied FRP. In this study, the ACI 440.2R-$08^1$ model and the model developed by Triantafillou and Antonopoulos$^2$ were compared with the prior experimental data. Both analytical models failed to provide a satisfactory prediction of the FRP shear capacity. This study provides insights into potential reasons for the unsatisfactory prediction.

• Structural Engineering and Mechanics
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• 제87권6호
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• pp.585-599
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• 2023

Geopolymer concrete (GC) can be competently utilized as a practical replacement for cement to prevent a high carbon footprint and to give a direction toward sustainable concrete construction. Moreover, previous studies mostly focused on the axial response of glass fiber reinforced polymer (glass-FRP) concrete compressive elements without determining the effectiveness of repairing them after their partial damage. The goal of this study is to assess the structural effectiveness of partially damaged GC columns that have been restored using carbon fiber reinforced polymer (carbon-FRP). Bars made of glass-FRP and helix made of glass-FRP are used to reinforce these columns. For comparative study, six of the twelve circular specimens-each measuring 300 mm×1200 mm-are reinforced with steel bars, while the other four are axially strengthened using glass-FRP bars (referred to as GSG columns). The broken columns are repaired and strengthened using carbon-FRP sheets after the specimens have been subjected to concentric and eccentric compression until a 30% loss in axial strength is attained in the post-peak phase. The study investigates the effects of various variables on important response metrics like axial strength, axial deflection, load-deflection response, stiffness index, strength index, ductility index, and damage response. These variables include concentric and eccentric compression, helix pitch, steel bars, carbon-FRP wrapping, and glass-FRP bars. Both before and after the quick repair process, these metrics are evaluated. The results of the investigation show that the axial strengths of the reconstructed SSG and GSG columns are, respectively, 15.3% and 20.9% higher than those of their original counterparts. In addition, compared to their SSG counterparts, the repaired GSG samples exhibit an improvement in average ductility indices of 2.92% and a drop in average stiffness indices of 3.2%.

• Steel and Composite Structures
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• 제11권4호
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• pp.325-340
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• 2011

Based on the experimental data presented in part I of these companion papers, a semi-empirical model is proposed for axial stress-strain curves of reinforced high-strength concrete square columns confined by aramid fiber reinforced polymer (FRP) jackets. Additionally, a three-dimensional finite element model is developed to simulate the mechanical behaviors of the columns. In the finite element model, both material nonlinear and contact nonlinear are taken into account. Moreover, the influence of contact nonlinear (i.e., the end friction on the contact surface between test machines and specimens) is investigated deeply. Predictions from both the semi-empirical model and the finite element model agree with the experimental results, and it is also demonstrated that the friction coefficient of end friction notably affect the properties of columns when it ranges from 0.00 to 0.25.

• 콘크리트학회논문집
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• 제19권6호
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• pp.763-771
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• 2007

철근부식은 철근콘크리트 구조물의 내구수명을 현저히 저하시키며, 유지보수 비용의 증가를 가져온다. 이와 같은 문제의 해결을 위해 피복두께의 증가, 고성능콘크리트의 사용, 에폭시 코팅 철근의 사용 등이 연구되었으나 완전한 해결책은 되지 못하고 있다. 최근 철근부식 문제를 근본적으로 해결하기 위한 새로운 대안으로 대두되고 있는 것이 FRP (fiber reinforced polymer) 복합재료를 이용한 철근대체제의 사용이다. 그러나 취성적 거동과 낮은 탄성계수로 인하여 철근콘크리트와는 다른 거동을 보이며 이에 대한 많은 연구가 필요한 상황이다. 본 연구에서는 FRP 보강근을 사용한 일방향 슬래브의 구조 실험을 통하여 철근콘크리트 슬래브와 거동 특성을 비교하였다. 균열 및 파괴모드, 처짐, 연성 등의 평가를 통하여 철근 대체제로서의 가능성을 평가하였으며, 해외의 제안식들을 사용하여 처짐 및 균열예측에 대한 식의 적정성을 평가하였다.

• Structural Engineering and Mechanics
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• 제59권4호
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• pp.775-793
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• 2016

This paper presents a numerical method for estimating the curvature, deflection and moment capacity of FRP-reinforced concrete encased steel composite beams (FRP-RCS). A sectional analysis is first carried out to predict the moment-curvature relationship from which beam deflection and moment capacity are then calculated. Comparisons between theoretical and experimental results of tests conducted elsewhere show that the proposed numerical technique can accurately predict moment capacity and deflection of FRP-RCS composite beam. The numerical results also indicated that beam ductility and stiffness are improved when encased steel is added to FRP reinforced concrete beams. ACI, ISIS and Bischoff models for deflection prediction compared well at low load, however, significantly underestimated the experimental results for high load levels.