PSI - Issue 62

Andrea Nettis et al. / Procedia Structural Integrity 62 (2024) 693–700 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

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the other components (superstructure and substructure) behave elastically. In such bridge typology, the preliminary deformations or relative differential displacements of bridge substructure components can involve significant strains lumped on bearing devices reducing their residual deformation capacity and determining increases of fragility. The influence of preliminary uncorrelated hazards on the seismic performance of bridge isolators is studied in previous research studies (Billah and Iqbal, 2022). In this study, a real case-study bridge is used. It is located in Southern Italy and experienced relevant bearing deformations after a few years since its construction because of the presence of an active slow-moving landslide. The sensitivity of bridge fragility considering several realistic landslide-induced differential settlement scenarios and variable isolator characteristics is studied. For the case study, seismic fragility curves considering specific settlement scenarios are computed and compared to the un-deformed condition to estimate the increase in fragility. 2. Methodology for the parametric analysis The adopted methodology for discussing the seismic performance and fragility of isolated continuous-deck bridges subjected to landslide-induced settlements is described in this section. First, the case-study bridge is presented. It is representative of continuous-deck bridges isolated through elastomeric bearings which were built in the last decades in seismic hazard-prone areas in Southern Italy. A parametric analysis is used to assess the fragility of the case-study bridge considering variation on the scenario of settlements and the typology of elastomeric bearing devices. Particularly, three elastomeric bearing typologies are considered to generate three bridge realisations. Each bridge realisation is analysed in its undeformed configuration and subjected to four landslide-induced settlement scenarios which are modelled as horizontal displacement patterns placed at the base of the piers in the transverse direction. Each bridge realisation paired with a given settlement scenario is analysed through 60 ground-motion excitations. The modelling and analysis strategy for the ground settlements and earthquake excitations is described. Finally, the adopted procedure for computing fragility curves, which are used for discussing the influence of settlement scenarios on the different bridge realisations is illustrated. 2.1. Case-study bridge and settlement scenarios The case-study bridge is part of the Bradanica highway in the Basilicata region (Southern Italy). The bridge was built in 2013 to overpass a river. The bridge is composed of six spans, having a length ranging between 28.00 and 30.00 m. The total length is equal to 180 m. The superstructure is composed of four pre-stressed U-shaped girders with a height of 1.80 m and a reinforced concrete deck whose thickness is equal to 0.30 m. The substructure is composed of reinforced concrete wall piers and seat-type abutments. The height of the piers ranges between 5.70 m and 8.90 m. Both piers and abutments have a variable number of piles. A graphic description of the case-study bridge is reported in Fig. 1. The girders are connected to the piers through a line of elastomeric bearings placed on baggies. After a few years of service, on-site inspections of the bridge reported relevant deformations of the bearing devices. On the basis of these observations, two specific topographic and geotechnical monitoring campaigns were addressed. The results showed differential displacement of the substructure components, mainly related to the transverse direction of the bridge, activated by a slow-moving landslide. A rigid movement of the substructure components is observed, while relevant deformations were lumped on the isolators. Because of this phenomenon, the bridge was closed.