Modeling the influence of anchor spikes on the bond behavior of FRCM applied to curved masonry substrates

A phenomenological numerical model for the prediction of the bond behavior of Fiber Reinforced Cementitious Matrix (FRCM) strengthened curved stack bond masonry prisms subjected to single lap shear tests, additionally equipped with spike anchors, is presented. The model lumps all non-linearity in a zero-thickness interface layer between reinforcement, assumed elastic, and curved substrate, supposed rigid. Furthermore, anchor spikes are modeled by means of a linear spring connecting the reinforcement layer located on the free edge side with that positioned between the spike and the loaded edge. A standard second-order non-linear differential equation is derived to describe the mechanical behavior. Numerically, the problem is tackled explicitly, making use of a standard Runge-Kutta in-house developed kernel where the boundary condition at the loaded edge is transferred to the free one. Comparisons with a wide experimental program carried out by the authors on laboratory-scaled curve masonry prisms assembled from stacked units and mortar layers, reinforced with FRCM and equipped with a central spike confirm the predictive capabilities of the simple model proposed, underscoring (i) the role played by curvature in modulating the post-peak response, with an enhanced relative energy dissipation gain in the presence of spike anchors despite an overall reduction with increasing curvature, and (ii) the very moderate effect in terms of peak strength improvement. This post-peak enhancement should therefore be interpreted as a conditional benefit associated with the presence of the spike anchor, contrasting the detrimental role played by curvature.