A two-storey masonry wall under seismic loading: a comparison between simple and strengthened masonry.

Aim of the proposed paper is to present a method for checking the efficiency of reinforcing interventions adopted in order to strengthen a two-storey masonry wall with openings, by means of numerical simulation. Seismic excitation has been represented by a displacement history used as input base motion for a test, and the masonry wall has been discretized via FEM. The dynamic analysis has been performed via ANSYS code; the masonry wall has been discretized by means of a eight noded solid element, which allows to simulate a linearly elastic-brittle behaviour of material either in tension and compression, and to trace the onset and growth of cracks (opening, closure, re-opening in the principal directions) in the check points. The failure condition is represented by a multi-mode surface. The masonry wall has ben modelled by assuming the masonry material to be homogeneous and isotropic on the basis of average properties. The seismic response of the structure under investigation has been evaluated in either cases of simple and strengthened wall, the strengthening being represented by ''horizontal'' and ''vertical'' pretensioned steel bars. Storey-drift and stress time-histories, and crack patterns at failure have been reported in order to evaluate the efficiency of the strengthening. Comparing time-histories and crack patterns allowed to find out the ''key'' parameters, namely tensile strength of masonry material, shear transfer coefficients across the crack face. pretension level of reinforcing bars. Furthermore, unsafety of single ''vertical'' reinforcement is exhibited.