Deep embedment of FRP for concrete shear strengthening

The shear capacity of existing concrete structures is often unable to meet current standards requirements. This may be attributable to increased load requirements, inadequate shear provisions in the original design, deterioration of materials or an increased demand in shear capacity owing to flexural strengthening. There are various approaches to the repair and strengthening of existing concrete structures in shear using fibre-reinforced polymer (FRP), involving the use of plates or fabrics externally bonded to the web, prestressed straps wrapped around the beam or the use of bars mounted near the surfaces of the web. However, when only the top or bottom faces of the concrete member are accessible, as in the case of bridge beams made contiguous within a deck or for corbels, a different approach is proposed, called the deep embedment technique: vertical holes are drilled into concrete upwards from the soffit in the shear zones, high-viscosity epoxy resin is injected and then FRP or steel bars are embedded into place. In this paper, the results of a series of tests on unstrengthened and strengthened small-scale and large-scale reinforced concrete and prestressed concrete specimens with and without stirrups are presented. The proposed technique is shown to be feasible, successful and potentially more effective than other shear strengthening approaches. A simple model derived from the truss analogy is shown to be able to predict the capacity of the strengthened beams and can therefore be used as a design tool for the scheme.