Vertical shear interaction model between external FRP transverse plates and internal steel stirrups

A convenient and proven technique for increasing the vertical shear capacity of reinforced concrete beams is to externally bond fibre reinforced polymer (FRP) to the sides of the beam with the fibres orientated in the transverse or vertical direction. The FRP, which can be in the form of pultruded plates or applied in the wet lay-up procedure, acts as external FRP stirrups resisting vertical shear in the same way as the conventional internal steel stirrups. However, internal steel stirrups are ductile as they are both fully anchored and can yield, which is in contrast to external FRP stirrups that can debond in a brittle fashion and do not yield. Hence, there is no guarantee that the peak vertical shear forces that can be resisted by the steel stirrups and by the transverse FRP plates coincide. In this paper, a partial-interaction model has been developed that quantifies the vertical shear interaction between transverse FRP plates and steel stirrups.