Static bond performance between BFRP bars and concrete with stirrup confinement: A refined modelling

Abstract

Determining the bond performance between fiber-reinforced polymer (FRP) bars and concrete has been one of the crucial issue for effective application of FRP bars in concrete structures. This study adopted a refined numerical method to investigate the pull-out behavior of embedded basalt FRP (BFRP) bars in concrete with or without BFRP stirrup confinement. In the numerical model, the inherent heterogeneous nature of concrete and surface profiles of the main deformed BFRP bar were explicitly expressed, where the concrete-bar interface was represented using a surface-to-surface contact strategy. The numerical model was calibrated by test results in available literatures and then utilized to conduct a parametric analysis on the bond behavior of BFRP bar-concrete interface. The investigated parameters included thickness-to-diameter ratio (c/d), stirrup ratio, and embedment length. The effect of these parameters on the failure modes, bond stress-slip response, and bond strength were discussed. It was found that the stirrup confinement can change the failure mode from brittle splitting to ductile pull-out and improve the interfacial bond strength, for specimens with c/d less than 3.75. However, the improvement in bond strength becomes insignificant after the stirrup ratio exceeds a critical value. Moreover, after c/d beyond 3.75, the application of stirrup has slight influence on the bond properties. Finally, based on the numerical results, considering the confinement effect of BFRP stirrups, a regression-based equation was derived for the bond strength between BFRP bar and concrete with or without stirrup confinement. The reasonability of the proposed equation was verified by the numerical and collected experimental data.