Fatigue behaviour of CFRP-repaired corroded RC beams

Corrosion and deterioration can be a major problem in marine structures and bridges. Such structures are often subjected to oscillating loads that cause fatigue, significantly reducing the life of the structure. With the use of fibre reinforced plastics (FRPs) to rehabilitate and extend the life of structures, the remaining fatigue life after the repair must be assessed. This research is focused on the use of CFRP for the repair of corroded reinforced concrete beams. A series of twelve beams, four corroded and repaired with mortar, four corroded and repaired with mortar and strengthened with CFRP and four control specimens, were tested in fatigue. Extensive strain measurements on the CFRP and concrete surfaces were taken. While the CFRP delayed the fatigue failure it did not restore the cyclic resistance of the beams to that of the control specimens. A size effect was observed with a decreasing fatigue capacity of the repaired specimens with increasing size. This is attributed firstly to higher fatigue lives of smaller diameter bars and, secondly, to the presence of slip between the steel and surrounding concrete. This slip reduces strain localisation and, hence, stresses in the steel bar at the cracks. Also in this study, a finite element (FE) model is developed for concrete beams repaired using FRP. Existing constitutive models were adapted and included in the FE program RECAP for the modelling of fatigue behaviour of the concrete and steel reinforcing bars. The concrete was modelled using 2D membrane elements and the steel with 1D bar elements. A new 1D interface element was developed to connect the repair material to the parent concrete with cyclic fatigue included in the material model. The models were tested against FRP bond-shear fatigue tests and flexurally strengthened members with reasonable correlations observed for the numerical results with the test data. It was also shown that the slip in the reinforcing steel-concrete interface is a significant factor in modelling the behaviour of the smaller beams