Novel Aspects of Vertical Ground Motion Modelling in Earthquake Engineering

The analysis of the vertical component of site ground motion is one of the main challenges in Geotechnical and Structural Engineering due to recent observations of failure and damage of buildings and structures under seismic action. The most common approach employed in current engineering practice for saturated soils is the simplified u-p formulation of the Biot’s equations describing the coupled hydro-mechanical behaviour, although more refined formulations are available (e.g. the u-U formulation), which include all the inertial terms. The aim of this study is to perform a novel theoretical validation of the u-p formulation as compared with the u-U formulation for different levels of permeability and dynamic actions that are representative of a wide scenario of site ground properties and seismic hazard in the vertical direction. A detailed analysis of the response in term of acceleration and pore pressure time history, frequency content, acceleration response spectrum, and amplification rate of acceleration. This allows to extend the discussion of the limits of applicability of the u-p formulation to the context of a complex dynamic regime provided by the vertical components of real earthquake records.