Investigation into the time-dependent behaviour of reinforced concrete specimens strengthened with externally bonded CFRP-plates

This paper deals with the influence of an external CFRP-reinforcement on the time dependent behaviour of flexural concrete beams. For this purpose, four reinforced concrete beams are tested in relaxation under three-point bending. Three of the four are strengthened with a composite plate bonded to their tensile soffit. The latter is not strengthened. The phenomenon of relaxation leads to a decrease in the loading force in the course of time. The test results are analysed in three ways: the first is a comparison between the global behaviour of the four beams. The second is a detailed analysis of the internal equilibrium of the beams in the course of time. The third is a global approach based on an incremental method suited to time analysis of composite structures. It can be concluded that composite reinforcement has a positive influence on the long term behaviour of strengthened beams. Their time dependent behaviours are different depending on whether the beam is pre-cracked before being strengthened. This difference may be taken into account using a coefficient of influence applied to the composite reinforcement. The existence of a period of loading before strengthening has a positive influence on the long-term behaviour of the beam.