Shear strengthening of existing concrete bridges

Abstract

The shear capacity of existing concrete bridge beams is often inadequate and unable to meet current code requirements. This is often due to increased traffic loads, inadequate shear-resistance provision in the original design or deterioration of materials due to aggressive environments. This paper deals with a new type of shear strengthening for existing concrete bridges. It is proposed that vertical steel or fibre-reinforced plastic bars be inserted into pre-drilled holes and fastened in place using epoxy resin. This method has the advantage that only the soffit of the concrete bridge beam (or slab) is required for access, allowing the top surface to remain undamaged during strengthening. This could allow the bridge to be used during strengthening works, with traffic relatively unhindered by work being carried out below. Further, no threaded bars and plates are required in this scheme, solving the notorious installation and maintenance problems associated with present shear-strengthening schemes. Ten laboratory tests are presented here to demonstrate the system, and comparisons are made against current code predictions for the strength of such concrete beams with and without transverse reinforcement. An upper-bound plasticity-based solution is also provided as a means to explain enhancement in shear capacity in specimens with very few embedded vertical bars. The results of this work show that the proposed strengthening scheme is effective and provides significant improvement in the shear-carrying load capacity. Additionally, code predictions for capacity of the strengthened beams are rather accurate, so that this strengthening method may be adopted with confidence.