Finite element modeling of reinforced concrete beams strengthened with carbon fiber composites

This paper presents the results of a comparison between a finite element model and experimental data of reinforced concrete beams strengthened with carbon fiber reinforced plastics. For the experimental program, simply supported beams, with 12 x 20 cm cross section and 2.25 m long span were tested. These beams have been submitted to short-term static loading tests from which it has been possible to evaluate the stresses and strains, the displacements, the crack widths and the failure mode. Strains gauges glued to the composite surface allowed the analysis of the behavior at the interface. The tensile and shear stresses at interface could be estimated. The numerical model consisted of a nonlinear finite element model for the flexure-shear response. The concrete was represented through plane stress isoparametric, eight nodes, finite elements. The concrete two-dimensional constitutive law was based on the orthotropic model proposed by Darwin. The concept of uniaxial equivalent strain and the two-dimensional failure criterion of Kupfer and Gerstle were adopted. The reinforcement was represented through an embedded model. Each steel bar was considered as a more rigid line inside of the concrete element, which just resists to axial efforts. The model includes a special interface element to simulate the bond between concrete and the external composite plate which is represented by truss elements