Analytical prediction of the behaviour of R.C. strengthened beams

This paper examines the behaviour of concrete beams strengthened with an additional layer placed in the tensile region. Analytical and numerical methods are used to predict the behaviour of strengthened beams and the results are compared with experimental data from a previous research. The analytical method uses equations that describe the behaviour of the composite member and involved writing a computer program in order to facilitate calculations. The numerical method used a Finite Element Analysis Computer Program (ANSYS). Three different types of finite element simulate the behaviour of the strengthened beams. Three-dimensional elements capable of cracking in tension and crushing in compression model the concrete, spar elements represent the steel and special contact elements simulate the interface between the beam and the new concrete layer. The results of these two methods approach the experimental results when a monolithic specimen is considered. By performing several analyses, using both methods and different contact conditions at the interface of the composite member, the appropriate contact conditions that correspond to the experimental results are determined. In addition, when considering the numerical results, it is noted that improving the contact conditions increases the concrete and steel strain in the additional layer while the corresponding strains in the initial beam reduce. Furthermore, peaks in sliding and friction stress occur near to the supports of the beam.