Neo-deterministic definition of the seismic input at Nimis and its application to the seismic isolation of residential buildings Definizione neo-deterministica dell’input sismico a Nimis per l’applicazioall’edilizia residenziale

Nimis (Udine) has been included in seismic zone I by the new Italian seismic code, which specifies criteria for the design and construction of new buildings. The study presented in this paper deals with the deterministic definition of the seismic input in the municipality of Nimis, aimed at the design of residential seismic isolated buildings. The seismic input is defined by the computation of synthetic seismograms at different level of detail. In the first approximation a deterministic zoning at national scale has been defined to characterize the ground motion (in terms of displacement, velocity and DGA) at the bedrock. In this way a DGA value consistent with that one provided by the new Italian seismic code is obtained. In a second approximation the detailed modelling of seismic ground motion in Nimis has been performed considering selected scenario earthquakes and the specific local conditions at the site of Nimis. The most dangerous scenario considered, which corresponds to the source of the 1976 Friuli earthquake, leads to a peak ground acceleration al least twice than that obtained at national scale. This demonstrates the relevance of taking into account local geological conditions for a detailed modelling of ground motion. The corresponding horizontal response spectrum, calculated in the centre of the municipality using this source, has been used for the design of a residential seismic isolated building. This spectrum advises against the construction of a building with a fixed base, but it is compatible with the seismic isolation: the maximum displacement for the isolation system has been estimated about 15 cm, a value much lower than that provided by the code design response spectrum (28 cm). The importance of the realistic modelling is evident, as it allows for the optimisation of the structural design with respect to the site of interest.