Refined modeling of the interfacial behavior between FRP bars and concrete under different loading rates

Abstract

Fiber-reinforced polymer (FRP) bar can be served as a promising alternative to steel rebars due to its lightweight, high corrosion resistance and wider working temperatures, etc., especially for the structure sensitive to weight or in aggressive environments. In order to lay the foundation for a more scientific design of structures reinforced with FRP bars, the bond behavior of FRP bars to surrounding concrete subjected to pull-out loadings with different loading rates was investigated with a refined numerical model in the present study. In the model, the surface features of FRP bars and the heterogeneity of concrete were explicitly reflected. The interaction between the two materials was modeled with a surface-to-surface contact strategy. The effectiveness of the model was verified by the good agreement between the simulation results and the available experimental observations. With the help of the numerical model, taking basalt FRP (BFRP) bars as an instance, the cracking process and failure patterns, bond-slip curves, bond strength and peak slip at the FRP bar to the concrete interface were simulated and analyzed. The influences of fiber types and surface characteristics of FRP bars were discussed. Based on the simulation results, an empirical formula was given to predict the dynamic bond-slip relationships of FRP bars in concrete. It was indicated that the failure patterns of the FRP bar to concrete interface under various strain rates do not show much difference within the scope of the present study. The elastic modulus of FRP bars mainly affects the bond stiffness and peak slip instead of bond strength. The density of FRP bars has a slight influence on the bond strength and peak slip while ignorable on bond stiffness. The variation in rib height of FRP bars changes the bond strength and the descending part of bond-slip curves, showing no regularity on bond stiffness and peak slip. The influence of rib spacing on bond performance is irregular. As the strain rate increases, the bond strength of FRP bars to concrete is increased continuously while the peak slip is reduced firstly and then increased. The empirical formula in the form of two power functions, considering the strain rate effect of bond strength and peak slip, can reasonably reproduce the dynamic bond-slip relationships between FRP bars and concrete to a certain degree.