PSI - Issue 84

Alessandro Lipari et al. / Procedia Structural Integrity 84 (2026) 615–622

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2015, European Committee for Standardization, 2010), whereas for the traffic load a much longer return period was chosen (Bruls et al., 1996). Furthermore, both EC1-1-3 and EC1-1-4 give formulae to adjust the characteristic loads according to different return periods or probabilities of exceedance, and in Eurocode 8 part 1-1 the return period of the seismic action to be applied depends on the consequence class, i.e., it is related to the target β for the structure (European Committee for Standardization, 2024). In EC1-2 no such kind of adjustments are given or mentioned. Finally, it is worth noting that some authors use a 50- or 75-year return period for the assessment of existing structures (Caprani et al., 2012, Lipari et al., 2012, Enright and OBrien, 2013). Such return periods may be used for reliability-based design and assessment.

Q 1k = 300 kN; q 1k = 9 kN/m 2

Q 2k = 200 kN; q 2k = 2.5 kN/m 2

Q 3k = 100 kN; q 3k = 2.5 kN/m 2

Fig. 1. Load Model 1 (adapted from European Committee for Standardization (2023a)).

4. The Italian guidelines on existing highway bridges The Italian guidelines on the classification and management of risk, safety evaluation and monitoring of existing bridges (Ministero delle Infrastrutture e dei Trasporti, 2022) are based on a multi-hazard multi-level approach. The Level 4 consists of an “accurate assessment” for bridges that were previously classified with a “Class of Attention” Very High or failed the lower level of “preliminary assessment” (Level 3). In Level 4, the conditions of an existing highway bridge are defined as: • Adequate : verifications are fulfilled by using full loads and partial safety factors in the NTC; repairs may be planned if necessary. • Operational : verifications are fulfilled by using full loads in the NTC, but with reduced partial safety factors associated to a reference period t ref = 30 years; repairs must be planned and the bridge must be reported to the relevant authorities. • Transitable : verifications are fulfilled over a reference period t ref = 5 years while restricting the use of the bridge, for instance with lane closures, or limiting its load; traffic loading derives from: (1) the NTC or, (2) the vehicles allowed by the Italian road regulation ( Codice della Strada , CdS hereinafter) with maximum GVWs 44, 26, 7.5 or 3.5 t; repairs must be planned and carried out within t ref . The reliability indices β in the Italian guidelines are reduced to 1.8, 2.3 and 2.8 for Consequence Classes CC1, CC2 and CC3, respectively. The reduced partial safety factors were calibrated using the APFM. The partial safety factors for traffic actions γ Q are recapped in Table 1.

Table 1. Partial safety factors γ Q of road traffic loads for different bridge conditions and consequence classes. Conditions CC3 CC2 CC1 Adequate (*) 1.50 1.50 1.50 Operational 1.20 1.18 1.16 Transitable (1) 1.20 1.18 1.16 (*) as per the NTC; 1.35 k F . as per the Eurocodes.