PSI - Issue 78

Fadel Ramadan et al. / Procedia Structural Integrity 78 (2026) 859–866

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longer periods, the behavior reverses: soft soil sites tend to exhibit deamplification, while rock sites show a moderate amplification. The adjusted VH model has been recently employed to develop a newcode-based functional form for potential integration into construction norms, as proposed by Smerzini et al. (2025). The same concept has been adopted within the framework of the new generation of structural Eurocodes (CEN, 2004), specifically in EC8-1-1 (Labbè et al., 2022). The proposed formulation is designed to replace the traditional fixed factor (typically 2/3) often used in seismic design to approximate the vertical-to-horizontal (VH) ratio. Unlike the constant approach, the new functional form accounts for key parameters such as site classification and the horizontal peak ground acceleration (PGA), offering a more physically grounded and period-dependent representation.

Figure 3.1 Dependence of ITA18 and ITA18-NESS VH median spectra on (A) , (B) w, (C) SoF and (D) 30, After Ramadan et al. (2021). 4. GMM for Vertical Component in FAS In this section, we develop a novel GMM for the vertical component of Fourier Amplitude Spectrum (FAS) based on the ITA18 dataset and adopting the same functional form as the one proposed by Lanzano et al. (2022) for the horizontal component: ( ) ( ) ( )  + + + = + ,30 , , 10 log S V S R F W M D SOF F W M M Y a F (1)

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