Closed-form solution to the debonding of mortar based composites on curved substrates

Steel Reinforced Grout (SRG) composites are becoming a common technique for strengthening masonry arches and vaults. These composites are made of Ultra High Tensile Strength Steel unidirectional textiles applied to the substrate by means of inorganic mortar. The structural performance is generally controlled by the bond properties of the interface between the matrix and the textile, which in the case of arches or vaults is also affected by the curved geometry of the substrate. In this work, a closed-form analytical solution of the debonding process of a thin plate bonded to a rigid substrate with constant curvature is proposed. The work provides an upgrade of the model previously proposed by the author [1]. In the present work the substrate curvature is such that the normal stresses arising at the interface are tensile, as in the case of the reinforcement applied to the intrados of the vault [1] or compressive, as for the reinforcement applied to the extrados of the vault. The proposed model describes the interfacial stresses transfer mechanism in the framework of fracture mechanics, adopting two cohesive material laws to model the interfacial behaviour in normal (pure opening mode: Mode I) and in tangential (in plane shear mode: Mode II) direction. The coupling deriving from curvature is introduced directly in the cohesive laws that describe the bond properties. The outcomes of the proposed predictive model are validated by comparing them with the results derived from an experimental campaign of bond tests on straight and curved substrates made of brickwork strengthened with SRG. Finally, a simple design formula for the evaluation of the debonding load of a SRG-masonry joint in the case of curved substrate, is proposed.