Bond Behavior between ETS-GFRP strengthening bars and concrete at elevated temperatures: A preliminary analytical and numerical study

The bond behavior of an embedded through-section-glass fiber-reinforced polymer (ETS-GFRP) bar‒concrete interface at elevated temperatures is investigated. An analytical bond‒slip model is first developed to include both mechanical and thermal variables. By using the finite element method (FEM), the ETS-GFRP bar–concrete interface is simulated with the thermo-mechanical bond–slip curves varying at different temperatures. Various temperatures at the bond interface of 20°C, 23°C, 48°C, 70°C, 89°C, 107°C, and 123°C are examined. The results obtained from the developed bond model for the ETS-GFRP bar-to-concrete joint at elevated temperature show similar trend with those achieved from the FEM simulation with the developed thermo-mechanical bond–slip model. The bond fracture energy (GfT) and ductility index (BfT) govern the bond response of the ETS-GFRP bar‒concrete interface at elevated temperature. When the thermal loading is below the glass transition temperatures of the GFRP bar and adhesive, a slight reduction in the bond stiffness and capacity is observed by the thermo-mechanical bond–slip model. The degradation in bond performance is significant at high temperature levels. The bond force, interfacial shear stress, and strain due to the mechanical loading have opposite directions to those due to thermal loading.