SEISMIC ASSESSMENT OF MULTI-LEAF MASONRY STRENGTHEN WITH INJECTIONS OR TRANSVERSAL TIES

Recent earthquakes highlighted the vulnerability of multi-leaf walls, which tend to fail out-of-plane by disaggregation of the external leaves. Therefore, strengthening techniques are often necessary, in order to improve the transversal bond between the leaves, ensuring a monolithic behaviour of the wall. In the present paper a modelling strategy is presented which makes it possible to evaluate the response of rubble-stone masonry walls in presence of different strengthening interventions, including injections of mortar and insertions of tie bars throughout the thickness of the wall. The approach is based on the distinct element method, where the stonework is regarded as an assembly of rigid blocks and the mortar joints are simply regarded as non linear interfaces with cohesion and friction. Aiming at reproducing the shape and position of the stones within the wall, particular care is taken in the definition of the mesh, which is generated from the survey of existing masonry sections. The model proves able to capture the essential feature of the behaviour of ancient masonry, which relies on the morphology of the wall rather than on the mechanical properties of the components. Two boundary conditions are then investigated, i.e. cantilever wall and wall constrained at the top by means of a ring beam. The response of the stonework is finally evaluated by means of static push-over analyses. The results highlight the effects and efficacy of the strengthening techniques on the failure mechanism and on the out-of-plane capacity of multi-leaf masonry walls.