Study On Interface Shear Failure Forms And Rules Of GFRP Reinforced Concrete Compound Beam

GFRP reinforced concrete compound beam structure is a new kind of reinforcedconcrete structure proposed on the basis of the mechanism of crack-resistance infracture mechanics. This new structure makes the most of crack-resistance of GFRP tostrengthen the property in the thought of crack-controlling by “resistance”.The thesis starts from the interface of GFRP and reinforced concrete, and analyzesthe relation between the interface destruction of GFRP and reinforced concrete, and thebearing capacity, deformation properties and crack distribution of GFRPreinforced concrete compound beam. The following conclusions have beendrawn:①By conducting the bending tests of both GFRP reinforced concretecompound beam and the common beam, the relation between the thickness ofGFRP and cracking loads, limit bearing capacity, yielding reinforcement capacity,structure stiffness and ductility indicators of reinforced concrete compound beam.The contrast shows that GFRP’s performance improves significantly with thethickness of GFRP increasing.②When the GFRP is rather thin, it is distinguished by a sudden tensile failure. Butwhen it reaches a certain thickness, it is not characterized by this any more. Instead, it isdistinguished by the dehiscence, expansion and destruction with the reinforced concrete.The stable expansion of interface crack and the increase of the deflection goes through arather long progress from the beginning of debonding to the unstable interfacedebonding. During this period, GFRP manifests good plastic deformation capacity.Experiments show that when GFRP reaches a certain thickness, its loading property andplastic deformation capacity does not grow with the thickness.③Inthe tracing analysis on the distribution of cracks of the FFRP reinforcedconcrete compound beams with different thicknesses and the change of maincrack width with different loads, it shows that:1）The number of cracks increasegradually, while the width and height decreases gradually. Overall, thedistribution of cracks changes from “sparse and broad” to “thick and narrow”;2）The main cracks fork even more frequently in the interface, and take on a look offingernail cracks;3) When the beams are in the state of ultimate destruction, Themain cracks near midspan grow smaller and smaller, while the main cracks besidethe midspan grow bigger and bigger. The three cracks turn into two and come together in the shape of arcuation;4) The same crack decreases with the increaseof thickness of GFRP under the same load.④This article analyzes the interfacial strain of compound beams of differentthicknesses in three stages: cracking, reinforcement yielding and the failure of thebeam. It illustrates the synergetic relation among the reinforcement, concrete andGFRP, as well as the inner relation among interfacial concrete, GFRP strain andthe failure mode. Mechanism of interfacial debonding and the Principle of BeamLoading Property Evaluation based on interface destruction is based on theseillustrations.⑤The finite element analysis indicates that: The stress intensity factor of the cracktip is in proposition to the closing force. But the closing force grow with the thicknessof GFRP, which makes the cracking capacity grow with the thickness of GFRP.⑥By comparing GFRP in the same size and GFRP reinforced concrete compoundbeam in cracking load, yielding reinforcement capacity, ductility and otherindicators, a conclusion that the two strengthening materials should be selected inan optimum way due to their own inferiors and superiors can be drawn.