Flexural time-dependent cracking and post-cracking behaviour of FRP strengthened concrete beams

The time-dependent flexural cracking behaviour of reinforced concrete beams strengthened with externally bonded composite materials is investigated with a focus on the creep effects. A theoretical model is developed, which accounts for the creep of the different materials involved, and which also accounts for the time-dependent cracking and the tension-stiffening phenomenon. The deformability of the adhesive layer in shear and through its thickness, as well as its ability to transfer shear and vertical normal stresses, is considered in the model. The incremental governing equations are formulated via the variational principle of virtual work based on an incremental exponential algorithm for the creep modelling. The capabilities of the model are demonstrated through numerical examples including a comparison with test results available in the literature. The results show that creep causes a significant redistribution of the internal forces and the interfacial stresses at the adhesive interfaces with time, which should be carefully considered in the design of FRP strengthened members.