Experimental evaluation of shear and compression strength of masonry wall before and after reinforcement: Deep repointing M. Corradi a, * , C. Tedeschi b , L. Binda b , A. Borri a a Department of Civil and Environmental Engineering, University of Perugia, Italy b DIS-Dept. of Structural Engineering, Politecnico of Milan, Italy Received 16 December 2005; received in revised form 22 November 2006; accepted 22 November 2006 Available online 26 January 2007 Abstract Masonry presents some inadequacies due to its almost total lack of tensile strength. Typical damage to multiple leaf walls during earthquakes is the loss of bond between the leaves with consequent collapse of the external leaf. Retrofitting or repair of this damage is a very difficult task. In many cases grout injection or wall jacketing fail due to incompatibility with the construction technique of the walls. A complementary technique to the grouting has been proposed by the authors. Experimental results and applications of the technique on site have shown positive characteristics and the results of tests carried out on site show, in some cases, increases in shear strength and stiffness of the masonry walls. Ó 2006 Elsevier Ltd. All rights reserved. Keywords: Masonry; Shear strength; Reinforcement; Deep repointing 1. Introduction Multiple leaf walls of stone masonry structures are widely encountered in Italian and European historic cen- tres. Dwellings but also other important buildings of these centres are characterised by a typical construction tech- nique which is the double leaf wall with transversal connec- tions (diatons). Particularly in the case of dwellings, this connection is frequently missing or very rare (Fig. 1) due to poor workmanship or lack of large stones crossing the wall section. So the section of the wall consists of two exter- nal leaves with a gap between them filled with mortar, loose material and small pieces of stones. It is now well known by direct experience that under vertical and/or horizontal actions the two leaves tend to separate (Fig. 2) and a partial or total collapse of the wall can take place (out-of-plane mechanisms). This mechanism of collapse has frequently occurred during seismic events in Italy and elsewhere. One of the most difficult tasks for engineers and architects is the repair and/or retrofit of this damage. Traditional masonry works are also particularly suscep- tible to in-plane shear actions due to their very low tensile strength. Therefore, in order to predict properly the masonry shear capacity, it is necessary to identify first the most probable failure mechanisms, based on the knowledge of the involved materials. Reinforcement should prevent both out-of-plane and in-plane collapse mechanisms. After the major earthquake which hit Friuli in 1976 and badly damaged several historic centres, some reinforcing techniques were proposed to avoid the previous mentioned types of damage: (a) injection of grout in cases when at least the external leaves of the walls appeared in good con- ditions, (b) injections and jacketing with a reinforced cement rendering when also the bond between the stones of the external leaves were missing, (c) partial reconstruc- tion of the walls in the worst cases. These techniques were generally considered correct by the Italian seismic code and 0950-0618/$ - see front matter Ó 2006 Elsevier Ltd. All rights reserved. doi:10.1016/j.conbuildmat.2006.11.021 * Corresponding author. Fax: +39 075 585 3897. E-mail addresses: mcorradi@strutture.unipg.it (M. Corradi), te- deschi@stru.polimi.it (C. Tedeschi), binda@stru.polimi.it (L. Binda), borri@unipg.it (A. Borri). www.elsevier.com/locate/conbuildmat Construction and Building Materials 22 (2008) 463–472 Construction and Building MATERIALS