PSI - Issue 78

Lorenzo Principi et al. / Procedia Structural Integrity 78 (2026) 1681–1688

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while newer steel - concrete bridges (bridges built after 1980 with Bridge Design Code C) appear inland (Figure 5c), both using beam schemes; some culverts use slab schemes. Main obstacles are roads and rivers; natural discontinuities are more inland (Figure 5d). All bridges support up to 60 tons and have alternative routes. Seismic design is more prevalent inland, where PGA rises from 0.15 - 0.175 to 0.225 - 0.250 g (Figure 6e - f). (a) ADT ≤ 10k 10k – 25k ≥ 25k (b) ADTT ≤ 300 300 – 700 ≥ 700 (c) Deck Material R.C.

P.R.C. Hybrid (d) Obstacle Type River Road Natural Disc . (e) Seismic Design

(f) P.G.A.

Figure 5. Geospatial distribution of the input features along the SS77.

According to the predictions results (Table 9), m ost bridges fall into the M (53) and M - H (34) classes. This indicates a generally moderate - to - high seismic risk, likely influenced by regional PGA values and the presence or absence of Seismic Design considerations. Figure 6 shows that M - H and H class bridges are concentrated in the central section of the highway, while M class bridges are more common at the beginning and end. It is evident that higher - risk (M - H and H) bridges generally lack seismic design, unlike the modern, fully seismic - designed segment of SS77, which falls within the M class. The increased seismic risk in the central section is due to both older, non seismic structures and a higher number of crossings over primary and secondary roads (Figure 5d). Coastal bridges are mostly M class, likely because they span rivers more often than roads, resulting in lower exposure.

Table 9. Predictions of the CER.

L M-L M M-H H 0 0 53 34 8

(c) CER

Figure 6. Geospatial distribution of the CER predictions.