PSI - Issue 62

Giovanna Pappalardo et al. / Procedia Structural Integrity 62 (2024) 460–467 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

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and u =9.76 mm, u/H =0.16%, for the unstrengthened and strengthened configurations, respectively (see Figure 5a-b). In terms of lateral drift, the current configuration of the bridge (the strengthened one) assures, even for the most loading scenario, a value lower than 0.2%, that can be still considered acceptable. In summary, the structural risk associated to the presence of the terrain laterally pushing the bridge can be considered low. Correspondingly, in Figure 6a-b, the deformed shapes are reported for the most sever thrusting scenario, showing how the main effect of the pressure of the landslide against the bridge is the rotation of the piers around their base; however, in the strengthened configuration the uplift at the uphill side is strongly limited by the enlargement of the foundation. In terms of damage pattern, Figure 6c-d, for both the configurations, the abutments are affected by a vertical cracking; in addition, a more extended crack pattern significantly involving the piers can be observed for the unstrengthened configuration.

(a)

(b)

(c) (d) Fig. 6. (a,b) Deformed shapes and (c,d) plastic strain maps for H t / H =1 of the landslide: (a,c) unstrengthened and (b, d) strengthened configurations. 3.3. Hydraulic risk As previously highlighted, the mobilization of the landslide results in the accumulation of material around the bridge piers, leading to a consequent reduction in the bridge spans. This paragraph discusses the increased risk of hydraulic insufficiency of the bridge due to this rise in the riverbed. The catchment basin at the bridge has a modest area of approximately 0.11 km 2 , with a main channel length of about 800 m (see Figure 7). The basin's time of concentration is approximately 0.15 hours based on the main channel length. Using the intense rainfall data recorded by the Maletto rain gauge station from 1948 to 2004, the rainfall probability curves parameters h = a t n were evaluated as reported in Table 2. Since the basin's time of concentration is less than one hour, as Ferro e Bagarello (1996) suggested, the exponent n for precipitation events lasting less than an hour should be replaced by the value n’ =0.386, valid for all Sicilian basins. Figure 8a illustrates rainfall probability curves for different return periods using the parameters described above. Due to the small extension of the basin, the peak flow rate can be estimated with the rational method Q C i A    , where C is the runoff coefficient (assumed here equal to 0.9 given the presence of clays), i is the rainfall intensity for a rain duration equal to the travel time and A is the catchment basin area. Table 3 shows the assessment of peak flow at the bridge for various return periods. Roughly, the flow passing through the bridge piers can be estimated using the assumption of uniform flow. Figure 8b depicts the variation of the freeboard concerning the rise in the riverbed elevation, considering, for safety purposes, the flow passage through the central span only.