Finite element modelling and testing of two-span concrete slab strips strengthened by externally-bonded composites and mechanical anchors

Ten three-dimensional finite element (FE) models were developed in this paper to simulate the nonlinear behaviour of two-span reinforced concrete (RC) slab strips. Two slabs were unstrengthened and eight slabs were strengthened in either the sagging or the hogging region by externally-bonded carbon fiber-reinforced polymer (EB-CFRP) laminates with or without mechanical anchors. The tensile steel in the strengthened region was approximately 30% of that of the unstrengthened region to represent a continuous RC flexural element in need of strengthening. Laboratory tests were carried out to verify the accuracy and validity of the FE models. Each specimen had a total length of 3800 mm, a width of 400 mm and a depth of 125 mm. The provision of mechanical anchors in the hogging strengthening prevented the CFRP debonding mode of failure, slightly improved the strength gain, and significantly improved the slab ductility. Failure of the slab strips strengthened in the sagging regions was not dominated by CFRP debonding, and hence, the effect of including mechanical anchors in the sagging strengthening was concealed. Unstrengthened specimens exhibited significant deviations from the elastic response. Sagging strengthening decreased the deviation from the elastic response. Specimens strengthened in the hogging region exhibited insignificant moment redistribution ratios. The developed FE models captured the nonlinear behaviour of the tested slab strips with good accuracy. The inclusion of an interfacial bond stress-slip model in the analysis between the CFRP and the concrete had insignificant effect on the predicted response of strengthened specimens.