Bond behavior of FRP-to-concrete under cyclic fatigue loading of RC structures strengthened with EB-FRP composites

Abstract

Reinforced concrete (RC) structures such as bridge girders are subjected, during their service life, to cyclic fatigue loading, mainly in the form of traffic loads. These structures are prone to progressive damage and may experience shear failure, which is often characterized by brittle rupture without any prior warning. Hence, retrofitting RC structures deficient in shear calls for the application of appropriate strengthening systems. The use of externally bonded (EB) fiber reinforced polymer (FRP) composites features numerous advantages and is a promising technology for shear strengthening of RC structures. However, the performance of EB-FRP retrofitted concrete structures can be highly influenced by the bond at FRP-to-concrete interface, as interfacial debonding can lead to the premature failure of the strengthening system. Limited investigations have been carried out on the FRP-to-concrete bond behavior of EB-FRP strengthened concrete structures under cyclic fatigue loading, and therefore, further related research will contribute to a better understanding of this complex research area. The present research study aims to investigate the fatigue bond behavior at the FRP-to-concrete interface of EB-FRP strengthened RC structures. To this end, in the first phase of this study, a literature-review is conducted to identify the parameters affecting the fatigue bond mechanism at the FRP-to-concrete interface. Indeed, it is indicated that carbon FRPs (CFRPs) can provide better fatigue resistance than other FRP composites, such as glass and aramid FRPs. An experimental investigation is conducted in the second phase of this study to fill existing gaps in the literature regarding the FRP-to-concrete bond behavior. A series of double-lap shear tests on CFRP-to-concrete bonded joints are designed to evaluate the interfacial behavior as a function of different variables, such as the FRP composite type (CFRP laminate vs. CFRP fabric sheet), the FRP-to-concrete width ratio (bonded FRP width to concrete width), and the FRP bond length under both monotonic and cyclic loading. The results of this experimental program demonstrate the superior performance of the CFRP composite bonding system using fabric sheet over the CFRP laminate in terms of bond ultimate resistance under monotonic loading and bond fatigue life under cyclic loading. Furthermore, increasing the CFRP-toconcrete width ratio was found to improve the bond behavior against the debonding failure mode under both loading conditions. As for the bond length, further discussions are presented to evaluate this parameter on the bond behavior, with emphasis on determining the effective bond length under both monotonic and cyclic loading conditions. By incorporating the current experimental results and research data available in the literature, analytical studies are conducted to develop the following two models: 1) a bond stress-slip relationship under monotonic loading; and 2) a fatigue-life prediction model of CFRP-toconcrete bond under cyclic loading. Both models are shown to perform satisfactorily when validated against the selected database and can be an effective tool for predicting the bond behavior at the CFRP-to-concrete interface of concrete structures strengthened in shear with CFRP composites.

Date	4 Jul 2023
Original language	American English
Awarding Institution	École de technologie supérieure
Supervisor	Georges El-Saikaly (Supervisor) & Omar Chaallal (Co-supervisor)