PSI - Issue 44

Iolanda Nuzzo et al. / Procedia Structural Integrity 44 (2023) 1832–1839 Iolanda Nuzzo et al./ Structural Integrity Procedia 00 (2022) 000–000

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of Quarto Centro station and the other has a moderate distance for Quarto station, as shown in Fig. 2. Consequently, among the activities available for seismic risk management on this structure are interruption of train and/or road service and inspection of main structural components. Thus, the MAs and MSs proposed for seismic risk management of the case study are given below:

MA

MS

• • • • • • • • •

• • • •

MA 0 : No action required

MS 0 : MA 0

MA 1 : The train service remains in operation MA 2 : Technical inspection is required in medium urgency MA 3 : Immediate interruption of the train service MA 4 : Immediate interruption of the railway service MA 5 : Immediate technical inspection of the infrastructure MA 6 : Immediate technical inspection of the tracks

MS 1 : MA 1 + MA 2

MS 2 : MA 3 + MA 5 + MA 6

MS 3 : MA 4 + MA 5 + MA 6 + MA 7 + MA 8

MA 7 : Possible reopening of the service

MA 8 : Immediate closure of the roads below the viaduct

2.3 Step 3: Structural analysis for vulnerability assessment The viaduct is made of reinforced concrete and consists of 44 pairs of piers, 45 simply supported beams and two end abutments, with a total length of 1080 m. The beams have a length of 22.6 m, while the distance between the piers is 24.0 m. The single slab consists of two precast reinforced concrete box sections, which are connected by transverse rectangular beams, with a total width of 4.9 m. The beam height is 1.65 m with a 20 cm thick concrete top slab. Each beam is supported on a pair of reinforced concrete piers by means of a classic system of alternated fixed and sliding supports in the longitudinal direction to allow thermal expansions. All the supports do not allow movements in transversal direction. The piers have an octagonal section and a height varying between 6 m and 12 m, including a rectangular pier-cap at the top. The cross-sections of the piers have a maximum width of 3 m and a maximum height of 1.3 m. A 50 mm joint in both longitudinal and transverse directions is placed between the decks (Losanno et al., 2021). Therefore, the damage mechanisms potentially caused by a seismic event on the viaduct under study can be: local damage to the base of the piers (ranging from moderate to extreme levels); loss of support of the slabs; longitudinal pounding between slabs; transverse pounding between slabs. By combining the different damage mechanisms identified above, the moderate, DS1; severe, DS2; and extreme, DS3 damage states were considered for this study. 2.3.1 Vulnerability analysis of piers Two models were developed for the piers of the viaduct using the tools provided by SAP2000 and OpenSees software (Anh & Nguyen, 2016; Yuan et al., 2017). The cracking, yielding and collapse points of the moment curvature diagram of the piers were identified. In addition, incremental dynamic analyses (IDA) were implemented to determine the fragility curves, through the use of DYANAS software (Baltzopoulos et al., 2018). For this purpose, the backbone curve of the force-displacement behaviour of the piers was defined and corresponding hysteretic behaviour under cyclic loading set through the Clough model. Once the dynamic response of the system was obtained, the pseudo acceleration vectors associated with the three levels of displacement (i.e. cracking, yielding, and ultimate) were exported by DYANAS software. Then, the fragility function of an intermediate height pier (~7 m) was calculated using PGA as intensity measure (IM), see Fig. 3. 2.3.2 Vulnerability analysis of bearings From the analysis of the original drawings, it was identified that sliding supports and joints are characterized by a maximum stroke capacity of ± 25mm. From a preliminary analysis of the average annual thermal variation of the site, it was estimated a thermal displacement of ± 5mm. A tolerance of ± 2mm is assumed before any restraint is active in both directions of fixed supports and transverse direction of sliding supports.