Ultimate strength of continuous beams with exposed reinforcement

This paper describes an experimental and numerical investigation into the effect of reinforcement exposure during the patch repair process on the ultimate strength of continuous beams. The parameters investigated were the position of breakout within the member and the areas of flexural reinforcement at the intermediate support and within the span. Reinforcement layouts were designed to vary both the moment redistribution demand for the full plastic collapse load to be attained and the redistribution capacity at the location where the first hinge would form. Exposure of reinforcement and the consequent loss of bond has two major effects. Firstly, it reduces beam stiffness at the exposed location, and shifts the balance of moments away from the location at which bars are exposed to other parts of the beam, Secondly, loss of composite interaction alters the pattern of flexural strains at the exposed section, increasing the strain at the extreme compression fibre and reducing section ductility. Results show that the moment capacity of a section with reinforcement exposed is not reduced if the exposed reinforcement yields before concrete crushing, but reductions in ultimate flexural strength are likely in heavily reinforced and therefore less ductile sections.