STUDY ON BOND BEHAVIOR OF BFRP BARS AND CONCRETE UNDER MEDIUM AND LOW LOADING RATES

BFRP bar is a new type of fiber composite material used in civil engineering field instead of steel bar. The bonding performance of BFRP bars and concrete under medium and low loading rates is an important premise to ensure the joint action of BFRP bars and concrete under dynamic loading. 16 groups of bonding specimens are designed according to the orthogonal test method, and the pull-out test is carried out on the BFRP bar-concrete specimens under different loading rates (0.005 mm/s-5 mm/s) by using the MTS test system, and the influence of loading rate, of concrete strength and of the diameter of BFRP bars on the bonding performance is studied. Based on the existing calculation model for bond strength, the bond characteristic parameters are modified, a formula is proposed for calculating the dynamic bond strength of BFRP bars and concrete under medium and low loading rates, and the bond-slip constitutive relationship model is further established for BFRP bars and concrete. The results show that the specimens fail due to the pull-out failure or the splitting failure, and bond stress-slip curves can be divided into a sliding stage, a declining stage and a residual stage. The bond strength increases with the increase of loading rate and of concrete strength, but decreases significantly with the increase of the diameter of BFRP bars. The theoretical calculation results are in good agreement with the experimental results, which provides an effective method for predicting the bonding properties of BFRP bars and concrete under medium and low loading rates.