Analytical solution for FRP-to-concrete bonded joints considering local unloading and reloading

Abstract The mechanical performance of the interface between fiber reinforced polymer (FRP) laminates and concrete is essential for the analysis of FRP-strengthened concrete structures through external bonding. This paper presents an analytical solution for the pull-off behavior of FRP-to-concrete bonded joints considering local unloading and reloading. With the interfacial slip at the free end as the control variable, the focus of the analysis is to model the mechanical responses of the FRP-to-concrete interface under loading, unloading, and reloading. Based on a three-parameter nonlinear bond stress-slip model for the FRP-to-concrete interface, the interfacial slip and the strain in the FRP laminate are derived in an analytical manner. With the analytical solution, the snap-back phenomenon is analyzed. The critical bond length, and the interfacial slips at the start of unloading and at the termination of reloading are determined. Finally, the analytical solution is verified with existing test results through comparing the axial tensile force-slip relationship at the loaded end and the strain profiles in the FRP laminate.