In-plane strength under seismic forces of multi-storey masonry walls reinforced by steel ties

The multi-storey wall with openings and large architraves, generally reinforced at floor levels by steel ties, is the more relevant resistant structural component of the masonry building under seismic action. The in-plane failure of the wall, occurring under constant horizontal forces with all the steel ties at yielding, is strongly conditioned by the presence of the panels situated above the openings. These panels, acting as diagonal struts, cause at the floor levels different horizontal displacements between the piers. Consequently, the horizontal ties are engaged in the mechanism. Horizontal cracks and corresponding hinges take place at different heights in the piers and high stresses occur in the steel ties. Local brittle failures can thus occur in advance, before the activation of the global collapse mechanism of the wall. Steel strengths of the ties have thus to be suitably chosen in order to avoid these local failures and ensure the development of the global failure of the wall. The strict application of the Limit Analysis can guarantee the development of the global failure by suitably dimensioning the yield strengths of the ties. This can be obtained checking the static admissibility of the internal stresses in the wall at the failure condition. The paper moves in this context and aims to give a general picture of the in-plane strength of the multi-storey masonry wall in the framework of the no-tension assumption for the masonry material.