PSI - Issue 62

Anna Rosa Tilocca et al. / Procedia Structural Integrity 62 (2024) 1043–1050 A.R. Tilocca et al. / Structural Integrity Procedia 00 (2019) 000 – 000

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5.1.1. Hazard (CDA sf ) Concerning to the hazard evaluation correlated to the structural-foundational risk, Italian Guideline indicates to take into account the maximum admissible passable mass on the infrastructure (commercial traffic) and the traffic-load frequency. For the present case study, railway bridge, “Class A” is considered without mass limitation according to the Italian design code (NTC, 2018) with a low frequency (≤ 300 commercial vehicle/day) due to the fact that the network is designed principally for the civil use . Moreover, the hazard classification for railway infrastructure is medium-high . 5.1.2. Vulnerability (CDA sf ) The vulnerability evaluation of the structural system in front of traffic-load actions is computed by the combination of 4 specific parameters: (i) degradation level of infrastructure, related to level 1, (ii) degradation rate, directly related to the age of construction, (iii) design code, related to the bridge class and (iv) static scheme/materials/span length. Railway bridge here analyzed has a degradation level equal to medium-low , as described before, and it was built in the ages 1980-1990, so the degradation rate is medium . Considering also that the viaduct category is a “Class B”, for bridges belonging to first category designed with code published between 1952-2005 with span length greater than 10m (25m), and knowing the static scheme used for the design process, simply supported beam in prestressed reinforced concrete, the vulnerability classification for the railway infrastructure is medium-high , as it possible to see in Figure 5. The number of spans is to be understood as the number of spans involved in a possible collapse mechanism. Consequently, the definitive vulnerability class increases by one level if the number of spans involved in a possible collapse mechanism is greater than 3. The class remains unchanged if the number of spans involved in a possible collapse mechanism is less than or equal to 3, as our case study with a railway bridge.

Figure 5. Flowchart for calculating vulnerability index CDA sf .

5.1.3. Exposure (CDA sf ) The evaluation of the exposure is based on 4 parameters that consider losses resulting from a collapse and its indirect consequences (what the bridge bypassing and entity of what), traffic/load interruptions (mean daily traffic-load index and alternative ways) and mean span length. Considering for our case of railway bridge with span length equal to 25m ( mean length ) and an average daily traffic-load with a low level (≤ 10000 vehicle/day), A1 highway bypassing is a high entity class while alternative ways are not available in our consideration. As reported in Figure 6, the final exposure class level is medium-high .

Figure 6. Flowchart for calculating exposure index CDA sf .

5.1.4. Final structural-foundational attention class index CDA sf The overall attention class index (CDA sf ) relating to structural and foundational risk is assigned based on the combination of the results of the previous assessments of hazard, vulnerability and exposure. No additional information is required, and the final level medium-high automatically derives from the previous information, as is possible to see in Table 1.

Table 1. Structural-foundational attention class index CDA sf .