Prediction Of The IC Debonding Failure Of FRP-Strengthened RC Beams Considering Multi-Parameter Coupling

In recent years,externally pasted FRP(Fiber Reinforced Polymer)has become a common method to reinforce RC structures.The load on the structure transfers the effective stress to FRP through the interfacial bond layer,thus enhancing the carrying capacity of the structure.The debonding of the interface between FRP and concrete is a common form of flexural failure of RC beams strengthened with FRP.The debonding failure may occur at either the FRP end or the Intermediate Crack(IC).Compared with plate end debonding,IC debonding is difficult to avoid and the mechanism is complex.In the past 20 years,scholars around the world have done a lot of research on the calculation model of IC debonding bearing capacity of reinforced beams,but there is still a lack of a generally accepted model.At present,the debonding strain prediction model with a high degree of recognition at home and abroad is convenient to calculate,but it is highly empirical in the process of model establishment,with few influence parameters to be considered.Moreover,relevant literature shows that the prediction results of some debonding strain prediction models are relatively high in discretization,which cannot quantitatively reflect the influence of bad working conditions on IC debonding behavior of reinforced beams.Based on the theory of cohesive zone,a new prediction model of IC debonding of RC beams strengthened with FRP is proposed in this paper.The main research contents and conclusions are as follows:(1)A prediction model for IC debonding of RC beams strengthened with FRP was established based on the cohesive zone model.The model considers the coupling effect of many parameters,and has the advantages of high precision and concise expression.This model extends the existing theoretical model of the FRP reinforced line elastic precrack plain concrete beam based on the theory of cohesive zone to the FRP reinforced concrete beam.In order to verify the accuracy of the model,an experimental database of IC debonding of 155 RC beams strengthened with FRP was established in this paper.In order to test the reliability of the model,it is compared and analyzed with the current five representative strength models with high accuracy,and the results show that the prediction results of the new model have high accuracy.(2)The prediction model of IC debonding of RC beams strengthened with FRP under complex working conditions was established.Prediction model of FRP reinforcement IC debonding under ideal conditions,on the basis of the complex conditions of IC debonding down the influence of the change of the material constitutive relation,reinforcement beam deformation and FRP and concrete interface constitutive relation of the three aspects of change,from these three aspects analysis of debonding bearing capacity prediction model parameters change,the influence of the complex working conditions applicable to a variety of operating mode was established based on parameter change of multiple parameters of FRP reinforced RC beam IC debonding prediction model.By comparing the predicted results with the experimental data,it is proved that the model can effectively predict the crack stripping capacity of RC beams strengthened with FRP under complex working conditions.The results of parameter analysis show that the attenuation of frp-concrete interface bond is the main factor to reduce the bearing capacity of IC debonding.