PSI - Issue 78

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

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requiring excessively broad tolerance windows to force a match. As a consequence, the mean vertical spectrum of the selected suite significantly overestimates the target beyond short periods. A second selection is performed using the VH-ITA18-NESS target, based on the ITA18 ground motion model in terms of SA, which provides horizontal and vertical spectra for Italian sites. The same site classes (A and B), focal mechanism inclusivity, and general geographic parameters were used to ensure consistency with the previous test. Magnitude range (Mw or Ml): 5.9–6.0; epicentral distance: 0–20 km; horizontal period range: 0.1–2.0 s; vertical period range: 0–0.5 s; compatibility tolerance: –10% / +30%; maximum scale factor: 1.0 (no scaling). The selected suite achieved good 3D spectrum compatibility without the need for any scaling (Fig. 5.1. b). The average horizontal score is 0.142, and the vertical score is 0.121, demonstrating that the spectral shape of the target was well matched across the periods of interest. This underlines the advantage of using physics-based spectral models like ITA18, which allow for a more realistic representation of both horizontal and vertical components.

a)

b)

Figure 5.1. Vertical response spectra of the selected ground motion suite based on the NTC18 target spectrum (a) and VH-ITA18-NESS model (b). Solid colored lines represent the target vertical design spectra, while dashed lines indicate the upper and lower tolerance bounds. Thick black lines show the average response spectra of the final suite of 7 ground motion pairs. Selected records for selection on the left (a), coded according to ESM waveforms ID: I1.DHKQ.00.HN.IR-1978-0002, CI.WRC2..HN.EMSC-20190706_0000043, IV.T1241..HN.EMSC-20161030_0000029, BO.NIG27.00.HN.JP-2004-0002, HI.ARG2..HN.EMSC-20140203_0000008, BO.NIG1C.00.HN.JP-2004-0002, IV.T1214..HN.EMSC 20161030_0000029 (note that all spectra are scaled to their own PGA). Selected records for selection on the right (b): BO.KMM17.00.HN.USGS us20005i1a. NZ.CACS.20.HN.EMSC-20110221_0000047, HI.ARG2..HN.EMSC-20140203_0000008, E.SRC0.00.HN.IT-1976-0030, IT.PCB..HG.EMSC-20160824_0000006, IT.AMT..HG.EMSC-20160824_0000006, I1.SAT1.00.HN.EMSC-20120811_0000034.

6. Conclusion

This study has provided an overview of recent advances in vertical ground motion modelling in Italy and emphasized the importance of including the vertical component in seismic design, particularly for short-period structures and near source conditions, where vertical motion may exceed horizontal motion. Using the ITA18 and NESS1.0 datasets, a VH model was developed for Italy by Ramadan et al (2021), incorporating near-source effects and providing a code compatible formulation as an alternative to the traditional fixed VH ratio. Additionally, a vertical GMM in the Fourier domain has been proposed, showing that vertical motion dominates at high frequencies and short distances. These results support the integration of vertical ground motion into design practice and align with the shift toward energy based seismic representations. This also play a key role in ground motion simulation and structural demand assessment

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