Fatigue-loading effect on RC beams strengthened with externally bonded FRP

Externally bonded carbon-epoxy fiber-reinforced polymers (CFRPs) have been widely used to restore or increase the capacities of reinforced concrete beams (Meier et al., 1992; Neale and Labossière, 1997; Varastehpour and Hamelin, 1997). A typical reinforced concrete bridge deck may experience up to 7x10 stress cycles during the course of a 120year life span (Barnes and Mays, 1999), while an overpass on a typical highway with a design life of 40 years can experience a minimum of 58x10 loading cycles of varying intensities. In contrast to the fairly extensive experimental and analytical studies conducted on the monotonic behavior of FRPstrengthened RC members, relatively little research has been carried out on the fatigue behavior of concrete beams strengthened with FRPs. However, some key research (Barnes et Al. 1999, Gheorghiu et Al. 2006, Ferrier et Al. 2005) has clearly shown that FRP-strengthened structures present better fatigue performances than unstrengthened ones. In most cases, it has been observed that the failure of the structure is initiated by successive yielding of the reinforcing steel in tension, in one or several locations. When debonding of the FRP laminate occurred, it was considered to be a secondary failure mode resulting from yielding and failure of the steel rebars. For serviceability limit state considerations, the overall behavior of a reinforced concrete beam strengthened with FRPs has to be evaluated. In the present work, this behavior is studied using a model which was designed for the evaluation of the beams’ mechanical properties. The fatigue modelling of beams strengthened by FRP is then validate thanks to an experimental investigation on 6 large scale beams. ABSTRACT: External bonding of fiber reinforced polymers (FRP) on concrete beams is particularly attractive for the strengthening of civil engineering structures in order to increase their mechanical resistance. The composite material is generally bonded on the tensile part of the beam. In order to design these bonded reinforcements, an iterative computational method based on section equilibrium and material properties (concrete, steel, adhesive and composite) has been developed: this method can be extended to describe the fatigue behavior of RC beams. This paper focuses on the damage behavior of concrete structures subjected to fatigue loading. A specific modeling coupled with an experimental investigation on large-scale beams made it possible to compare the theoretical and experimental fatigue behaviors of RC beams with and without composite reinforcements Results showed that the beam deflection and the strain in each material could be calculated with a sufficient accuracy, so that the fatigue behavior of the FRP strengthened beams was correctly estimated by the model.