Experimental behavior on shear strengthened masonry panels

Traditionally a large percentage of the Italian building stock is made of masonry, with walls often made of hollow core clay bricks. These buildings are usually designed only for gravity loads, with no or little concern for seismic actions. Accordingly, they are extremely vulnerable to seismic actions, as shown by the recent earthquakes of L'Aquila (2009) and Emilia (2012). After the new seismic classification of the Italian territory, a large number of these buildings will need seismic retrofit works in order to be able to meet the new code requirements. Hence, seismic strengthening techniques for masonry buildings are rapidly gaining interest. In the present paper the effectiveness of a shear reinforcement technique on masonry panels is presentend. The specimens were reinforced by using an innovative strengthening system based on the combined use of a steel or glass fiber grid embedded in a base mortar. Such system is composed by two layers applied on both sides of the panels and connected by through joints made of steel bars of glass fiber wires. A series of one unreinforced masonry panel and four strengthened panels have been subjected to diagonal compression tests. This type of test was chosen to simulate the in-plane shear phenomenon of masonry. Several reinforcement configurations, with different combination of grid type, mortar type and connectors type, have been tested. Experimental results show the effectiveness of this technique to increase the shear strength and the ductility of the panels. The investigated technique does not significantly modify the stiffness of the structural elements confirming the compatibility of the intervention when used on existing buildings.