FATIGUE BEHAVIOUR OF THE STRENGTHENED CONCRETE BEAMS WITH PRESOAKED CFRP LAMINATES UNDER CYCLE AND RANDOM LOADING

Externally bonded fiber reinforced polymer (FRP) materials are well suited to the rehabilitation and reinforcement of civil engineering structures due to their high specific strength, specific stiffness and corrosion resistance. In this paper, the static and fatigue performance of the presoaked CFRP strengthened concrete structures were probed. The 3-point bending experiments of RC beams strengthened with CFRP under static, cycle and random loading were performed. And the flexural fracture and fatigue behavior were analyzed. The linear curve between fatigue strength and the logarithm of fatigue life was obtained under cycle loading. The failure modes go through concrete cracking, CFRP debonding from concrete and steel bars yielding with increasing cycles of fatigue loading. Bonded CFRP increases the ductility of strengthened RC beam and results in dense distribution of cracks, and it's bending stiffness at damage state as well. The fatigue damage evolvement shows three stages of nucleation, steady expansion and failure. Compared with CFRP strengthened RC beams under cycle loading, CFRP strengthened RC beams scatter sparser cracks under random loading related to the peak loads. Then the failure mechanism was studied and an accumulative damage model was proposed to describe the fatigue damage and fracture process of CFRP strengthened RC beams under cycle loading and random loading.