Study On The Interface Bonding Performance Between FRP Bars And MPC

Near surface mounted(NSM for short)fiber reinforced polymer(FRP for short)reinforcement method is favored in the engineering field at home and abroad because of its good reinforcement effect,wide application range and low difficulty in construction.The MPC-NSM-FRP reinforcement method using magnesium phosphate cement(MPC for short)as the interface binder,which can effectively make up for the lack of durability of traditional epoxy binder,prolong the service life of the reinforced structure,and promote the application of NSM-FRP reinforcement method,has significant research significance and application value.The weak link of MPC-NSMFRP reinforcement system is the bonding interface,which determines the reinforcement effect.The key content missing from existing studies is the interface bonding performance between FRP bars and MPC,thus,it is necessary to carry out a systematic research on the interface bonding performance between FRP bars and MPC.Therefore,based on the experimental study and the mathematical statistical analysis,a study on the interface bonding performance between FRP bars and MPC was carried out in this thesis.The main work and achievements include the following four aspects:(1)Experimental study on shear fracture performance of MPC.The propagation of cracks in MPC under the bonding stress is a significant cause of interface bonding failure between FRP bars and MPC.In this thesis,based on the fracture mechanics theory,the shear fracture energy of MPC was used to quantitatively characterize the effect of MPC fracture performance on the interface bonding behavior between FRP bars and MPC.A total of 21 MPC cube specimens with double notch were designed and prepared.The shear fracture performance of MPC were studied by double-sided direct shear tests.The failure mode and failure mechanism,the load-slip relationship,the shear strength and the shear(mode ?)fracture energy were analyzed.Furthermore,the size effect of MPC shear fracture energy was studied based on the boundary effect theory,and the true fracture energy of MPC was calculated from the measured fracture energy.(2)Experimental study on interface bonding performance between FRP bars and MPC.The effects of MPC shear fracture energy,FRP bars diameter,bonding length and FRP bars surface form on the bonding performance were studied in this thesis.A total of 86 center pull-out specimens were designed and prepared,and the interface bonding performance between FRP bars and MPC were studied experimentally.The failure mode and failure mechanism,the bond-slip relationship,the characteristic bond strength and the characteristic slip value were analyzed.The significant factors for the interfacial bonding performance were determined by range analysis and variance analysis based on an orthogonal experiment.The effect of each factor on the interface bonding performance was analyzed in sequence using the control variable test design method.The local bond stress-slip relationship was calculated from the measured FRP surface strain,and the position function of bond stress distribution was obtained through curve fitting.(3)Study on the interface bond-slip constitutive model between FRP bars and MPC.Based on the analysis of the measured bond-slip curves and the existing typical bond-slip models,a piecewise average bond-slip constitutive model between FRP bars and MPC was proposed.The local bond-slip model,with the effect of position variation taken into account,was then established by introducing the position function.A theoretical analysis was carried out based on the proposed bond-slip model to reveal the bond-slip transfer mechanism in different stages as well as the interface bonding failure mechanism.(4)Study on the calculation method of bond-slip characteristic values.The characteristic bond strength and the characteristic slip value are the critical control variables for the bond-slip constitutive model.Based on the test results and analysis,the calculation models for bond-slip characteristic values were established with the effect of key factors taken into account using ordinary least squares(OLS for short).Besides,calculation models for the pull-out resistance,the basic anchorage length of FRP bars and the fracture energy of interface between FRP bars and MPC were also proposed.Through contrastive analysis,it was illustrated that the bond performance between FRP bars and MPC is better than that between FRP bars and concrete.The model factor was determined and the correlation analysis was conducted to determine the source of model systematic error.By regression analysis,the core function was determined,the correlation function was built,and the model was then modified.In addition,the quantile regression models for the bond-slip characteristic values were established using quantile regression.The distributions of characteristic values and the effect trend of each factor at different quantile levels were described.Thus,the regression model based on OLS method was supplemented and extended.