Research On Strength Of RC Beams With Externally Bonded FRP Sheets Under Debonding Failure Modes

To improve the mechanical performances of structural members, the techniques of strengthening and restoring reinforced concrete beams with externally bonded fiber reinforced plastic (FRP) sheets are extensively applied. However, this newly arisen method is associated with brittle debonding failure modes-flexural strength of the compound beams without omen cannot reach that under ductile failure modes,even that of unreinforced members. According to different failure mechanism and displaying part, the failure modes are divided into plate end debonding failure and intermediate crack induced interfacial debonding failure.In this paper, the two debonding failure modes of the compound beam externally glued by FRP sheets are comprehensively studied. Its displaying part, style, condition, influential factors, mechanism and the comparative analysis of the two type of damage is investigated. Based on analysis and comparison of existing test data applied to existing ultimate strength prediction models, interfacial stress at the end of plate is deduced, and the judgment based on the damage is raised. For the end plate damage , the parameters corresponding to our new standard is transformed on the basis of the literature data.After formulas for calculating the effective moment of inertia for FRP-strengthened beams being revised and adjustment coefficient related to nominal main steel reinforcement ratio and curtailment length ratio being put forward, strength prediction formulas of compound beams under plate end debonding failure are established. In analysis of strength of compound beams under intermediate crack induced interfacial debonding failure mode, several bond strengths and their relation are introduced. Strength prediction formulas are established based on axially shear bond strength, among which involve several coefficient deduced from test scheme. The formulas for the two debonding failure modes are examined by their related data, and the calculation results agree with the test results with reasonable reliability.