PSI - Issue 78

Gianrocco Mucedero et al. / Procedia Structural Integrity 78 (2026) 1959–1966

1963

zero days of downtime in achieving any recovery state. This indicates that such seismic events have a negligible impact on the buildings' ability to recover, suggesting that the buildings are well designed to withstand low-intensity earthquakes, regardless of the height or recovery state. As the return period increases to 475 years, recovery delays begin to appear and become more pronounced with building height and the stringency of the recovery objective. The two-storey building experiences modest delays, such as 12 days and 85 days for SiP and FR states, respectively. In contrast, four-storey buildings show larger delays, such as 121 and 273 days for SiP and FR states, respectively. The RT RO is almost similar to that obtained for FR. For a higher seismic intensity level, associated with the 975- and 2475 year return periods, the recovery time increases significantly, particularly for higher numbers of storeys. The RT SiP for six- and eight-storey buildings reaches 278 and 253 days, respectively, for the 975-year return period. The RT FR for those taller buildings is very similar for both the 975- and 2475-year return periods. In particular, the RT FR is 545 and 562 days for six- and eight-storey buildings at 975 years, respectively, whereas it reaches 706 and 790 days for the 2475 years return period. In contrast, smaller RT FR , such as 493 and 594 days, is obtained for two- and four-storey buildings, respectively. It is worth mentioning that, beyond a certain seismic intensity level, further increases in intensity level do not lead to proportionally longer recovery times, given that 790 days (two years) is the assumed reconstruction time. Some building types reach such a threshold for the 2475-year return period, thus, for return periods higher than 2475 years, the repair time is equal to the reconstruction time. The difference between RT RO and RT FR diminishes for high-intensity levels, particularly for higher-rise buildings, implying that much of the recovery effort must be undertaken regardless of whether the objective is RO or FR.

Fig. 2. Median downtime (in days) for FR, RO and SiP states, for different return periods.

To further clarify the need for introducing downtime-based performance criteria within the Italian seismic design code, indirect losses (i.e., the cost of relocating the displaced building occupants) were roughly estimated. A moderate daily relocation cost of €35 per person (€/day ⋅ person) (Calvi 2025) was assumed, along with an average occupancy of four persons per apartment and two apartments per storey. The number of relocation days per person was assumed to be equal to the median downtime (in days) required to achieve the RO state. Fig. 3 provides the total (direct and indirect) losses, and the indirect losses normalised by the replacement cost. Indirect losses follow a similar upward trend to the total losses. For the 475-year return period, the total losses are in the range of almost 0.5-0.8 times the reconstruction cost, with indirect losses in the range of 0.03-0.2 times the reconstruction cost, while from the 975-year return period above, the total losses exceed a normalised value of 1.0 and the indirect losses are almost half of the reconstruction cost. Such plots emphasise the growing importance of indirect losses as earthquake intensity increases, stressing the need for integrating seismic design with downtime recovery objectives, to reduce long-term economic consequences for building stakeholders, owners and occupants.