Analytical Model for Predicting Response and Flexure- Shear Resistance of Composite Beams Combining Reinforced Ultrahigh Performance Fiber- Reinforced Concrete and Reinforced Concrete

The addition of an external layer of reinforced ultrahigh performance fiber-reinforced concrete (R-UHPFRC) on top of reinforced concrete (RC) floor slabs and bridge decks is an emerging technique for strengthening RC structures. As an additional reinforcement, a layer of R-UHPFRC significantly increases the maximum resistance and deformation capacity of RC elements, thus creating a composite element that herein is referred to as RU-RC elements. This paper presents an elastic-plastic fictitious RU-RC composite hinge model for the damage caused by flexural and flexure-shear cracks in the RC element of the composite members. The model accounts for the nonlinear interaction of the two elements due to intermediate-crack-induced debonding (ICD) zone in the near-interface concrete. The model determines the force-deflection response and force in the RU-RC composite tension chord. Furthermore, the contribution of the R-UHPFRC element and the shear resistance envelope of the member are calculated. Comparison with available experimental results shows that the model can accurately predict the member response, resistance and failure mode. A simplified formulation for the shear resistance of the composite members is proposed. The models in this paper are needed for the design of the structural behavior of RC beams strengthened with R-UHPFRC.