Experimental study on the influence of spike anchors on the bond of FRCM systems applied to curved masonry specimens

This paper experimentally investigates the influence of spike anchors on the bond behavior of Fiber Reinforced Cementitious Matrix (FRCM) strengthening systems applied to curved masonry specimens. Indeed, while the effect of spike anchors has been recently studied in Fiber Reinforced Polymer (FRP) applications, their use in FRCMs remains less explored, especially for curved supports. The experimental program involved single-lap shear tests on flat and curved specimens with two curvature radii, strengthened at the intrados with PBO-FRCM and a spike positioned at mid-bond length. Two anchoring layouts were examined: fibers fanned (i) on the fabric surface and (ii) on the outer matrix layer. Results in terms of global load-displacement curves, crack propagation, and failure mechanisms triggered are presented and critically discussed. They show that spike anchors improve structural performance by delaying debonding, slightly increasing peak load (up to about 10–15 %) and significantly enhancing deformation capacity, with ultimate slip values up to several times those of unanchored configurations. Curvature plays an important role in the effectiveness of spike anchors, with failure modes mainly characterized by debonding at the inner fiber–matrix interface between the loaded edge and the spike, followed by fiber sliding in the segment between the anchor and the free edge. The study provides one of the first experimental comparisons of different spike anchorage layouts in PBO-FRCM systems applied to curved masonry substrates. • Spike anchors enhance bond and ductility of PBO-FRCM systems on masonry. • Single-lap shear tests reveal delayed debonding and higher deformation capacity. • Curvature strongly affects anchor efficiency, especially for smaller radii. • Anchor fan position governs pre- and post-peak ductility behaviour. • Failures shift from brittle debonding to progressive fiber sliding near the spike