Towards calculating the load-deflection response of anchored FRP-strengthened RC slabs

Tension face bonded fibre-reinforced polymer (FRP) composites can increase the flexural resistance of reinforced concrete (RC) flexural members such as beams and slabs. The propensity of the FRP to debond, at strain levels well below the strain capacity of the FRP, limits the effectiveness of the strengthening. This effectiveness can, however, be enhanced by the addition of mechanical anchorage and FRP anchors offer a viable solution. FRP anchors, which are installed at discrete locations along the length of the FRP strengthening, delay the propagation of debonding cracks and thus enhance the strain capacity of the FRP strengthening. It is important for design engineers to be able to quantify both the strengthening effect of the FRP in addition to the anchorage provided by the FRP anchors. The modelling of the complete load-deformation response of the strengthened and anchored system can be accomplished reasonably simply provided certain assumptions are made and a full-interaction sectional analysis is undertaken. The assumption of a pre-defined moment-curvature relationship enables closed-form solutions for the load-deflection response to be obtained. Such equations have been presented previously by the authors for FRP-strengthened members without anchorage. In this paper, the theory is extended to consider the effect of anchorage.