Debonding of composites on a curved masonry substrate: Experimental results and analytical formulation Marialaura Malena, Gianmarco de Felice ⇑ Department of Engineering, University Roma Tre, Rome, Italy article info Article history: Available online 14 February 2014 Keywords: Masonry Bond Mortar based composites Textile reinforced mortar Curved substrate Analytical modelling abstract Externally bonded mortar based composites have become a popular technique for strengthening masonry arches and vaults. The effect of the curved substrate on the bond properties is one of the key factors affecting their structural behaviour. This paper presents the results of an experimental campaign of deb- onding tests on straight and curved substrates made of bricks assembled with mortar and strengthened either with Carbon Fibre Reinforced Cementitious Matrix (CFRCM) or Steel Reinforced Grout (SRG). The experimental results get insight into the failure mechanisms that take place in mortar based composites and disclose the effect of the substrate curvature on the interfacial strain distribution and on the load– displacement response. The experimental results are compared with the outcomes of a predictive model, proposed in this work, which provides a closed-form analytical solution to the debonding process of a thin plate on a rigid substrate with constant curvature. The model, which is based on an interface cohe- sive law, coupled in the tangential and normal directions, as a consequence of the curvature, is able to predict the decrease in bond stiffness and strength for increasing curvature, as shown by experimental results. Ó 2014 Elsevier Ltd. All rights reserved. 1. Introduction Increasing attention has been devoted in the recent years to the use of innovative materials, such as externally bonded reinforce- ment, for strengthening masonry constructions. Current applica- tions concern walls [1–3], arches and vaults [4,5], or columns [6] for either increasing the load carrying capacity or improving the behaviour under seismic events. Besides the well-established use of fibre reinforced polymers (FRP), the application of composites with inorganic matrix is receiving greater attention in current re- search and practice [7–11] thanks to the advantages in terms of permeability, fire resistance, cost, easier application. Fiber Rein- forced Cementitious Matrix systems (FRCM) appear particularly appropriated for application to architectural heritage because of theirs reversibility and chemical compatibility with the substrate [12]. For most strengthening systems, the bond between the ma- sonry and the reinforcement plays a key role in ensuring the load transfer. Several experimental debonding tests have been carried out on FRP systems, with different setups, either on clay bricks [13–15], stone elements [16] or on masonry prisms [7,17,18]. Most of the experimental results show that failure generally takes place with the detachment of a thin layer of masonry substrate. The adoption of an inorganic matrix affects the failure process that usually takes place within the matrix due to its lower mechanical strength, either by debonding at the fibre/mortar interface or by sliding of the fibres inside the mortar [9,13,19,20]. An analytical solution to the debonding problem is usually provided in the framework of fracture mechanics: in [21] a pre- diction of the ultimate load and the effective bond length is gi- ven, while in [22,23] a closed-form solution of the debonding process is provided for a bilinear and an exponential interface law, respectively. The number of contributions offered toward the comprehension of the mechanical behaviour of curved sub- strates is small, even though in current practice an increasing number of structural elements like arches or vaults are strength- ened with external bonded composites. Most of the experimental data available in the literature concern the structural behaviour of arches [4,5], but in such cases the local bond–slip law is hardly deducted from experiments. Direct shear bond tests on curved masonry prisms were described in [18] and simulated numerically in [24]. An analytical model for describing the inter- facial stresses between a thin plate bonded to a curved substrate was proposed in [25] and in [26]. http://dx.doi.org/10.1016/j.compstruct.2014.02.004 0263-8223/Ó 2014 Elsevier Ltd. All rights reserved. ⇑ Corresponding author. Tel.: +39 0657336268; fax: +39 0657336265. E-mail addresses: marialaura.malena@uniroma3.it (M. Malena), gianmarco. defelice@uniroma3.it (G. de Felice). Composite Structures 112 (2014) 194–206 Contents lists available at ScienceDirect Composite Structures journal homepage: www.elsevier.com/locate/compstruct