Research On Debonding Failure Of Strengthening RC Beam With CFRP

Carbon fiber reinforced polymer(CFRP) has been widely used to reinforce or repair the reinforced concrete(RC) members because of the excellent properties of CFRP composites. The performance of RC structures strengthened with CFRP sheets depends on the bond behavior between CFRP sheets and concrete. At present, the studies are mainly focused on the bond performance between CFRP sheets and undamaged concrete. However, the concrete structures strengthened by CFRP sheets have been damaged to varying degrees in the actual projects. In this paper, in order to study the interfacial bond performance of the damaged concrete beams strengthened with CFRP sheets, the static test on damaged prestressed RC beams strengthened by CFRP sheets was carried out considering some parameters, such as damage degree, prestressed degree, surface treatment method and so on. The main contents are as follows:(1) The static loading test program was designed and this test was conducted to investigate the static interfacial bond performance of the damaged concrete beams strengthened with CFRP sheets considering the variables including damage degree, prestressed degree and surface treatment method,(2)Test results show that the failure of the strengthened beams were due to the CFRP sheets debonding between two loading points. The debonding of CFRP sheets initiated from the main crack near midspan. The bond carrying capacity between CFRP sheets and concrete decreased with increasing damage degree, but was enhanced if the concrete surface was notched.(3)Based on the test data and results, the CFRP sheet strain variation curve with the load, the beam displacement variation curve with the load, the strain distribution curve along the beam, the steel strain variation curve with the load and the bond-slip curve of the CFRP sheet- concrete interface were presented. The effects of the factors including damage degree, prestressed degree and surface treatment method for the interfacial bond performance of the damaged concrete beams strengthened with CFRP sheets was analyzed.(4)The interfacial bond-slip model of damaged concrete beams strengthened with CFRP sheets was proposed based on the existing bond-slip model. The proposed mode is in good agreement with the test results.