PSI - Issue 78

Franco Braga et al. / Procedia Structural Integrity 78 (2026) 2176–2183

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determined by the pseudo-acceleration spectrum obtained on the basis of the AMTS station recordings, scaled with q=1.5 5. Analysis results 5.1. Dynaic behavior of structures The modal analysis was performed considering 100 vibration modes and allowed to mobilize 100% of the translational mass in the horizontal direction and 98% of the translational mass in the vertical direction.

First vibration mode of the structure – T=0.63 sec Excites 76% of the seismic mass in the Y direction (E-W direction)

Third vibration mode of the structure – T=0.43 sec Excites 73% of the seismic mass in the X-direction (N-S direction)

Fig. 5. Main vibration modes

5.2. Comparison between project actions (L. 1684/1962), current (NTC08) and real (AMTS) actions The determination of the dynamic behavior of the analyzed structures allows us to identify the spectral accelerations relating to the two main modes (which, however, excite most of the seismic mass); in Fig. 6 it can be seen that in the E-W direction the spectral acceleration is slightly more severe for the NTC08 spectrum than that relating to the AMTS E-W spectrum, while for the N-S direction the situation is opposite, with the spectral acceleration relating to the AMTS N-S spectrum being decidedly higher than that relating to the NTC08 spectrum. The accelerations prescribed by the design standard (Law 1684/1962), increased, in accordance with § B.8.2. of the Ministerial Decree. 16.1.1996, with the coefficient γ E =1.5 to assimilate them to those of modern standards which provide for the Limit States approach rather than the Allowable Stress Desing approach, are considerably lower than those determined with the NTC08 and AMTS spectra.

Fig. 6. Comparison between project, current and real actions