Strengthened thin clay masonry infills: experimental analysis and validation of verification procedures

Masonry infill walls present a brittle behaviour when subjected to combined in-plane and out-of-plane actions due to seismic events. This characteristic is even more pronounced in thin infill walls, often characterised by masonry units with high void ratio, horizontal hole arrangement and low compressive strength. Thin infills are mainly employed as internal partitions in current construction practice, but they can be found also as external enclosures in many existing R.C. frame buildings. To overcome the intrinsic limits of this construction typology, three types of strengthening techniques are proposed: the first strengthening technique is characterised by the application of a bi-directional basalt mesh embedded in a special geo-polymeric plaster. The other two strengthening solutions consist of applying a fibre-reinforced limebased plaster, and one of them is also provided with an additional bi-directional basalt mesh. To validate the effectiveness of the proposed solutions, eight combined in-plane and out-of-plane tests on full-scale R.C. infilled frames (one-bay, one-storey) have been performed. Specimens have been tested firstly imposing increasing in-plane cyclic displacements at the frame top beam, and secondly monotonically loading the infill in the out-of-plane direction. This work presents an analysis of the obtained experimental results. The comparison with a reference plain masonry infill, tested in a previous experimental campaign, proves the effectiveness of the strengthening solutions in reducing infill damage and in increasing both the out-of-plane capacity and the deformability. Furthermore, since the currently adopted Italian building code lacks specific recommendations on the evaluation of masonry infills out-of-plane capacity, this article proposes simplified procedures together with their validation against experimental results. These simplified procedures take into consideration existing damage due to in-plane deformations as well as the improvement provided by the application of strengthening techniques.