Some considerations about vertical ground motions modelling in earthquake engineering

One of the current main challenges in Geotechnical and Structural Engineering is the analysis of the vertical component of site ground motion. In engineering practice, a simplified formulation of the Biot‘s equations is usually employed to model the coupled hydro-mechanical behaviour of saturated soils, namely the u–u formulation that neglects some terms of fluid inertial forces. This is in contrast with more refined formulations such as the u– u formulations that takes all inertial terms into account. The aim of this work is the validation of the u–u formulation as compared with the u–u formulation by means of numerical simulations, which are performed for different levels of permeability and different dynamic motions. The results are analysed in terms of frequency content and amplification rate, discussing the limits of applicability of the u–u formulation with respect to the u–u formulation.