Strengthening reinforced concrete beams with external unbonded bars: theoretical investigation

The paper describes the development of a numerical model for analysis of beams retrofitted with external unbonded reinforcement. The experimental phase of the investigation is described in a companion paper, which also outlines the advantages of the method. Because external reinforcement is not bonded to the beam throughout its span, but is anchored only at the ends, normal plane section behaviour assumptions cannot be used. The numerical model is based on section analysis, and incorporates non-linear material behaviour and non-linear geometric effects. The model is first validated against results from an experimental programme comprising 35 physical tests on laboratory specimens. The model is then used to supplement the experimental study by exploring parameters which could not receive adequate experimental coverage. The influence of the shape of the bending moment diagram and of span/depth ratio, parameters which were not adequately explored in the experimental investigation, are reported. Deflectors were typically calculated to double strength enhancement at shorter span/depth ratios; the benefits were greater with higher ratios. Their use will be advantageous in the majority of situations.