Experimental examination of CFRP strengthened RC beams under high cycle fatigue loading

The aim of current study is to investigate the effect of Carbon Fiber Reinforced Polymer (CFRP) composites on the fatigue response of reinforced concrete beams. 6 reinforced concrete (RC) beams from which 3 were retrofitted with CFRP sheets, were prepared and subjected to fatigue load cycles. To predict and trace the failure occurrence and its growth, a small notch was induced at the middle span in bottom surface of all RC specimens. At the certain points, strains in concrete and CFRP were measured in each cycle. The upper limit of applied load was considered at the level of design service load of bridges. In addition, strain measurements facilitated to the calculation of interfacial shear stresses between concrete substrate and the CFRP layer. The variation of such stresses through load cycles has been presented and discussed. Also, a discussion on possibility of the local debonding phenomenon resulted from such interfacial stresses was presented. Load–deflection curves, strain responses and propagation of tensile cracks provided an insight on the performance of the CFRP strengthened beams subjected to different cycles of fatigue loading. Variation of load-deflection curves through fatigue load cycles depicted stiffness degradation which was discussed in the research.