Experimental Examination of Intact and CFRP Retrofitted RC Beams under Monotonic and High Cycle Fatigue Loadings

The aim of this research is to investigate the effect of Carbon Fiber Reinforced Polymer (CFRP) composite fabric on monotonic and fatigue behaviors of reinforced concrete beams. To control the failure occurrence, a small notch was induced at the middle span in bottom surface for all of the studied RC specimens. Totally ۱۲ beams were tested from which ۶ beams tested under monotonic and ۶ other tested under fatigue cyclic loading. Every ۶ tested beams consisted of ۳ intact and ۳ CFRP retrofitted RC beams. The specimens were ۱۵۰×۱۵۰×۱۰۰۰ mm in dimensions and  a ۱۵۰ mm-deep notch was cut at the center. The experimental examination was conducted to study stresses distributed throughout the critical regions in reinforced concrete and carbon fiber reinforced plastic (CFRP) strengthened RC beams. Fundamentally, these critical regions are cracked zones in CFRP-retrofitted RC beams. Results from monotonic and fatigue tests were compared to each other. In the monotonic test, shear stress distribution and stiffness measurements were carried out until the failure of specimens. In the fatigue test, the ceiling of applied load was considered at the level of design service load for bridges. In addition, strain measurements led to the calculation of interfacial shear stresses between concrete substrate and the CFRP layer. The variation of such stresses through load cycles will be presented and discussed. Load–deflection curves, strain responses and propagation of tension cracks would provide an insight on the performance of the CFRP strengthened beams subjected to different cycles of fatigue loading.