SHEAR STRENGTHENING OF URM CLAY WALLS WITH FRP SYSTEMS S. Grando*, M.R. Valluzzi*, C. Modena*, J.G. Tumialan** * Department of Transports and Construction, Università degli studi di Padova Via Marzolo 9 – 35131 Padova, Italy – email: granste@libero.it , valluzzi@caronte.dic.unipd.it , modena@caronte.dic.unipd.it ** Center for Infrastructures Engineering Studies 1870 Miner Circle – Rolla, Mo 65409-0030 USA – email: GTumialan@sgh.com Abstract This paper presents an experimental program dealing with the shear strengthening with FRP systems of URM walls built with concrete and clay units. Ten concrete and five clay masonry panels, strengthened with FRP composites in the form of laminates and rods, and stainless steel, were loaded along the wall diagonal to observe their shear performance. The dimension of the concrete masonry panels was 1.625 x 1.625 m. having a thickness of 152 mm, the masonry units were 203x152x406 mm. The clay panels were 1.22x1.22x0.1 m and the masonry units were 102x203x64 mm. For the rods the Structural Repointing technique was used. This technique consists in placing FRP rods in the masonry bed joints. On the contrary, for laminates, the Manual Lay-Up technique was used. The results demonstrated the effectiveness of FRP for increasing the shear performance of URM walls in terms of both capacity and pseudo-ductility. 1. Introduction It’s recognised that an infill URM wall can easily collapse when it’s loaded with an In-Plane force. This happens because this type of load generates a shear stress and a shear failure, identifiable by the cracks along the diagonals. The wall capacity, now, is totally lost and the panel can fall even under a low Out-of-Plane load, endangering human lives. It’s possible to resolve part of this problem by the use of FRP systems. Many experimental works showed that it’s possible to increase the ultimate capacity of a wall reinforcing it with FRP composites, without any addition in its weight and stiffness and avoiding dangerous consequences in case of seismic events. A main benefit is even the aesthetic and logistic advantage from the use of FRP: there is a minimal loss of usable space and with a plaster it’s possible to hide the strengthening material. 2. Material characterization Tests were concluded to characterize the mechanical properties of the materials used in this investigation. The average compressive strengths of masonry units resulted from the testing of prisms (ASTM C1314). The walls were strengthened with #2 GFRP bars having diameter of 6 mm, CFRP and GFRP laminates, stainless steel circular bars and internal steel nets. FRP and stainless steel bars were embedded into an epoxy-based paste and in a Latex Modified Cementitious Paste which, according to the manufactures and to test results (ASTM C–496–96), perform the mechanical properties as shown. All the properties are shown in Table 1: