PSI - Issue 78

Ingrid Boem et al. / Procedia Structural Integrity 78 (2026) 457–464

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single-storey buildings are generally characterized by more compact configurations and, as noted, by a more effective coupling of piers provided by the spandrels;  the construction period generally seems not to affect the vulnerability of URM structures with a clear trend. However, focusing on 2-storey schools, an increase in vulnerability is observed for DL3 and DL4 in more recent constructions (≥1946). According to a qualitative analysis of the floor plans, this could likely be related to more complex structural configurations and longer spans (which increase the seismic demand on load-bearing walls), but these architectural features were not matched by an improvement in the material characteristics and/or walls thickness. Similarly, this tendency is observed in 1-storey schools, but it does not emerge in ≥3-storey buildings;  the considerations regarding the number of floors and construction age are generally maintained in RM buildings;  within a sub-typology, the dispersion tends to decrease for higher DL (values β ≤0.4 for DL3-4) and in most cases, in multi-storey structures, it does not undergo extreme variations in the transition from URM to RM;  the application of the CRM reinforcement brings evident benefits in the reduction of the seismic vulnerability, related to the increase of both strength and displacement capacity of the structures (as evident in Fig. 3);  the effectiveness of the intervention (as the ratio between the RM and URM median values of resisting acceleration) appears greater in 1-storey buildings (range 2.3-4.2 for DL1-2, 2.0-3.4 for DL3-5), compared to 2-storey (1.4-2.3 for DL1-2, 1.4-2.0 for DL3-4) or ≥3-storey buildings (1.2-2.2 for DL1-2, 1.5-1.8 for DL3-4), which already resulted more vulnerable in the URM condition. This is due to the uniform application of the strengthening configuration across all the floors, which lead to an over-strengthening of certain levels and, consequently, not allow the full exploitation of their plastic capacity (and associated ductility);  in 1- or 2-storey buildings, the effectiveness for DL3-4 tends to be slightly lower than for DL1-2, while an opposite trend emerges from the ≥3-storey buildings.

Fig. 4. Fragility curves for the URM (dashed lines) and RM (solid lines) school buildings, for different damage states (DS).