Crack Failure Study Of Carbon-fiber Composite Reinforced Concrete Beams

The Carbon Fiber Reinforced Plates (CFRP) strengthening technique of concrete structures, as a new strengthening method and advanced technique, has a good researchful value, broad application, very huge social and economic benefit. Among the various of reinforced structures technique, application of carbon fiber reinforced plates (CFRP) has been gradually becoming the focus by the staff who enjoyed the study of it since it excels in convenience for constructing, reinforced effects, and huge social and economic benefit. In this paper, the concrete beam externally bonded with CFRP was studied by using the finite element method exclusively together with experimental method of carbon fiber reinforced concrete beams. The failure mechanism of CFRP structures with initial crack was studied and the effects on failure pattern of CFRP structures was also discussed.Considering the concrete characteristics, the crack progressing in the concrete structures was analyzed. Based on the fundamental idea of Fictitious Crack Model proposed by Hillerborg in Sweden, a finite element calculating analysis model suitable for the study was presented for carbon fiber reinforced structures. It was supposed that both concrete and FRP are isotropic and elastic materials in the finite element analysis. According to the calculating model, the finite element method analysis for carbon fiber reinforced structures was conducted. It shows that, for carbon fiber reinforced structures, there exist three over-loading zones. They lie at the tip of initial crack, the end of carbon fiber reinforced plate bonded externally and the concrete zone in the vicinity of interface between concrete and CFRP, respectively. The concrete was considered as crack progressing once the maximal principle of stress in the concrete reached the ultimate stress of concrete according to the theory of maximal tension stress. This paper also presents an effect of the depth of initial crack, the length of bonding carbon fiber reinforced plate and the end of carbon fiber reinforced plates bonded externally on the stress of over-loading zone, studying the discipline of CFRP structures and discussing the failure mechanism of CFRP structures. Finally, the failure discipline of concrete beam externally bonded with CFRP was found, predicting the failure pattern of it under three point loading centrally. On the other hand, an experimental study on concrete beam with bonded CFRP externally was also presented, studying the effects of various bonding length of CFRP, various bonding length of CFRP and various bonding layers of CFRP on the structures externally bonded with CFRP in the experiment. It shows that the results of finite element method and results of experiment are agreed.