PSI - Issue 78

Elisabetta Bonaguro et al. / Procedia Structural Integrity 78 (2026) 1016–1023

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Fig. 4. Tensile strain pattern of a single SU referring to a) unreinforced condition; b) replacement of the first floor; c) replacement of both the two floors; d) replacement of all diaphragms; e) replacement of the roof only. 4. Unitaryretrofitonthefull cluster When theunitaryretrofit isimplemented at thelevel ofeach individual SU, i.e.,atthescaleoftheentire cluster, the outcomes are equivalent for the two-units configuration and for the whole cluster. The tensile strain pattern of the full cluster, throughout the floor stiffening process, shows a progressive inhibition of out-of-plane mechanisms, especially in the end units, occupying the most critical position when considering the +X loading direction. Indeed, while in the unreinforced condition (Fig. 5a, b) the damage is widespread, and more concentrated at the base of piers, in the strengthened one (Fig. 5c, d) strains migrateto spandrels and piers show low tensile damage. Moreover, shear-related damage is generally less significant, except in the walls of the north façade (Fig. 5d), which, being shorter of one storey and thus stiffer than the front façade, are more loaded by the pushover. a b

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Fig. 5. Tensile strain pattern of the whole cluster ’s elevations referring to flexible floors: a) south; b) north; and rigid slabs: c) south; d) north.

Rigid diaphragms provide additional interconnection among units, limiting relative nodal displacements and causing a reduction in the overall displacement capacity (Fig.6). A model with floors stiffened with an additional diagonal timber sheathing (G xy = 45 MPa; 8 cm thickness) represents an intermediate configuration between the unreinforced and replaced conditions. This model also highlights thereduction of the plastic field, typical of replaced mixed brick and concrete diaphragms with respect to a stiffened, but still flexible, diaphragm.