Recently Carbon Fiber Reinforced Polymer (CFRP) is used to strengthen structural parts of reinforced concrete bridges. Nowadays, the research in this area is not so deep and mature although lots of experts all over the world have done a great deal of tests and theory analysis about strengthening the reinforced concrete beams by using CFRP. Especially, there is no further research on the ductility of RC beams strengthened with CFRP. This paper is based on our past research, to test and discuss the ductility of RC beams strengthened with CFRP. A series of RC beams were strengthened with CFRP and tested. According to comparison of the P~V curves, mid-span deflection, cracking load, strain within different teams, the authors analyze the ductility of the beams. It shows that the ductility of RC beams using the CFRP can be decreasing. This phenomenon must be paid attention in the construction. Finally, some conclusion and future works are given. IntroductionThe structure will go into elastic and plastic deformation when in the intense earthquake situation. Compared with the elasticity, the deformation of plasticity is too large to make the structure crack, and debond or even damage. On the other hand, because of the decreasing of structure stiffness on the elastic and plastic state, the period of self-oscillation increases. It changes the earthquake reacting characteristic of the structure. The non-elasticity un-recoverable distortion may consumes the input earthquake energy and decreases the affection of earthquake on the structure. On the nonlinear state, whether the structure is damaged or not is decided by the deformation of plasticity or dissipation energy instead of the intensity. Because one can not use the intensity condition to evaluate the anti-earthquake ability of the structure. To efficiently use the dissipation energy ability of the structural nonlinear deformation, at the same time, avoiding the damage caused by over large intense loss, over big plastic deformation and over long crack, it is
Externally bonded carbon fiber reinforced polymer (CFRP) materials are well suited to the rehabilitation and reinforcement of civil engineering structures due to their high specific strength, specific stiffness and corrosion resistance. To probe the fatigue behavior of CFRP strengthened concrete structures, three point bending experiments of reinforced concrete (RC) beams strengthened with carbon fibre laminate (CFL) under constant amplitude loading were performed. The histories of midspan flexibility and bending stiffness of strengthened beams were recorded automatically. And the linear curve between fatigue strength and the logarithm of fatigue life was obtained. The failure modes go through concrete cracking, CFL debonding from concrete and steel bars yielding and fracture with increasing cycles of fatigue loading. Bonded CFL increases the ductility of strengthened RC beam and results in dense distribution of cracks compared with normal RC beam, and it’s bending stiffness at damage state as well. The fatigue damage evolvement shows three stages of nucleation, steady expansion and failure. Then the failure mechanism was studied and a cumulative damage model was proposed to describe the fatigue damage and fracture process of CFL strengthened RC beams under constant amplitude loading.
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