Prediction of tension stiffening behaviours of FRP sheet strengthened RC tensile members by discrete modeling

Bond of FRP sheet/concrete interface not only influences loading capacity and ductility of FRP sheets strengthened RC members which usually fail due to premature interface debonding at ultimate limit state (ULS), but also influences the serviceability limit state (SLS) design, like control of concrete crack opening, member stiffness and deformation. The latter is closely related to concrete tension stiffening. A discrete analytical program based on rigid body spring
model (RBSM) is developed to simulate tension stiffening behaviors of RC prisms externally bonded with FRP sheets, which were experimentally investigated in previous studies. Difference from conventional discrete approach, which needs to embed concrete cracks before analysis, RBSM can simulate random cracking process of concrete because of using spring networks and meshing in random element shape using Voronoi geometry. Fracture energy based nonlinear bond-slip model developed by the authors and CEB-FIP bond-slip model are
implemented for FRP sheet-concrete interface and steel-concrete interface respectively in the current program. Comparison with experimental results verifies accuracy of the present discrete analytical modeling and its advantage in simulating fracture process of FRP sheet strengthened RC members. By using the program, further numerical experimentations are also performed to study the effects of end anchorage, interfacial fracture energy, and shear stiffness
of FRP sheet/concrete interfaces on concrete tension stiffening and overall load-deformation responses of FRP sheets strengthened RC tensile members. It has been clarified that optimum serviceability and ultimate limit states can be achieved by providing suitable interface property if mechanical anchorage is unavailable between FRP and concrete at anchorage areas.