An assessment of the NTC18 stratigraphic seismic amplification factors,Una valutazione dei fattori di amplificazione stratigrafica dell{'}azione sismica nelle NTC18

The present study aims at an evaluation of the simplified procedure for the prediction of stratigraphic amplification of the seismic action in the new Italian building code (NTC18). For this purpose, a stochastic database of ground response analyses has been implemented, by performing equivalent linear analyses on a collection of one-dimensional ground models. The models are representative of different subsoil conditions of engineering interest. The reference seismic input consists of collections of acceleration time histories, which are compatible with the seismological features of a number of sites with different seismic hazard. The results have been interpreted computing synthetic amplification parameters, allowing for the evaluation of the reliability of the subsoil classification system. The study also assesses the effect of some specific features, such as stiffness inversions or soil type. The results show that code prescriptions provide a reasonable estimate of seismic amplification. However, the large variability indicates that the simplified approach should be used with caution, especially for critical facilities.