ORIGINAL ARTICLE Improving shear strength of unreinforced masonry walls by nano-reinforced fibrous mortar coating Luca Facconi • Antonio Conforti • Fausto Minelli • Giovanni A. Plizzari Received: 29 September 2013 / Accepted: 14 May 2014 Ó RILEM 2014 Abstract The limited tensile resistance of many existing un-reinforced masonry (URM) members may represent a matter of great concern, especially when masonry constructions are located in seismic areas. For this reason, the development of innovative strengthening and repairing techniques have been the subject of several experimental studies performed in the last few years by many researchers worldwide. The present paper concerns an experimental study based on quasi static reverse cyclic tests carried out on full- scale URM squat shear walls strengthened or repaired by means of a thin coating made of a calcium- aluminate steel fibre reinforced mortar (SFRM) containing nano-silica. This strengthening method represents a novelty with respect to both the nano- reinforced SFRM and the practical application proce- dure adopted. The experimental results show the enhanced performances provided by the proposed technique in terms of strength and stiffness increment. Keywords Masonry walls  Cyclic tests  Strengthening  Coating  Steel fibre reinforced mortar  Nano-reinforced mortar 1 Introduction The sustainable restoration of buildings erected after World War II is an important topic nowadays in Europe. Most of these buildings have already exhausted their design service life (as suggested by the Eurocodes, the typical service life for buildings is 50 years) and often have significant structural issues, with regards to both static and seismic actions. In fact, at the time of erection, buildings were designed and constructed in absence of any seismic standards (the first seismic provisions appeared in Italy in 1974 and the first official Italian seismic building code was issued in 1986) or any reference to good anti-seismic construction practice, with static loads lower than those today required by current codes [1]. Another issue concerns the efficient repairing of masonry walls damaged by an earthquake, which is necessary to allow inhabitants to return and live in their houses as soon as possible. As a consequence, the recurrent structural deficiencies of these buildings become even more significant, especially in seismic areas like the south Mediterranean European countries L. Facconi  A. Conforti  F. Minelli (&)  G. A. Plizzari DICATAM - Department of Civil, Environmental, Architectural Engineering and Mathematics, University of Brescia, Brescia, Italy e-mail: fausto.minelli@unibs.it L. Facconi e-mail: luca.facconi@unibs.it A. Conforti e-mail: antonio.conforti@unibs.it G. A. Plizzari e-mail: giovanni.plizzari@unibs.it Materials and Structures DOI 10.1617/s11527-014-0337-0