PSI - Issue 84

Giovanni Stasi et al. / Procedia Structural Integrity 84 (2026) 789–796

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Having to consider the wide range of periods of interest for the structure, varying between 0.15 s and 3.5 s, did not allow for the signals to always be spectro compatible. a b

Fig. 5. Y-direction SLC response spectra: (a) 7 scaled natural signals, (b) average spectrum

In order to determine the main parameters of Magnitude (4.5 ≤ Mw ≤ 6.5 for SLV; 4.5 ≤ Mw ≤ 7 for SLC) and epicentral distance (0 ≤ R ≤ 30km for SLV; 0 ≤ R ≤ 20km for SLC), 2 disaggregation analyses were carried out. The seismic analysis considers signals from seismogenetic zone 915 of the ZS9 map, characterized by normal faults, with bidirectional effects evaluated through the simultaneous application of orthogonal recordings. Seven natural spectro-compatible signals were selected for the longitudinal direction, while their corresponding orthogonal components were scaled for transverse spectro-compatibility, neglecting vertical actions and spatial variability. The validation graphs display the response spectra for each signal alongside the average spectrum and the Type A soil elastic target spectrum, represented by a solid black line. These plots also include cyan dashed lines indicating the upper (+30%) and lower (-10%) tolerance limits relative to the target spectrum. The maximum peak ground accelerations of the scaled signals for the two directions are shown below in Fig. 6a and 6b a b

Fig. 6. (a) Peak ground accelerations of scaled signals in the X direction; (b) Peak ground accelerations of scaled signals in the Y direction.

5. Analysis of the existing structure The bridge was built in the absence of seismic regulations and in the absence of horizontal forces less than those of the wind with a pressure of 100kg/m 2 . The frame type of the substructures induces, in the presence of horizontal actions such as the earthquake (average PGA values of the 7 spectrum-compatible signals at the SLV equal to about 0.29g), considerable axial tensile and compressive stresses that cancel the effects of the weight at the base of one of the four walls. The presence of reduced gaps between the slabs, about 2cm, and the reduced flexural rigidity of the higher piers leads to a vulnerability of the decks under the hammering phenomena. Using a modal analysis with a design response spectrum (q = 1.5) at the SLV, the combined compressive and bending stress verification of the base section of the pier walls is satisfied with a seismic action equal to 60% (  E = 0.6) of that corresponding to a return period Tr = 950 years.