Empirical models for the assessment of the number of equivalent cycles for Italian earthquakes

A number of procedures for liquefaction analysis are based on the comparison of the seismic demand, described by the earthquake irregular time-history of shear stress, and the liquefaction-resistance evaluated in the laboratory applying uniform series of cycles of shear stress to soil specimens. This comparison requires the conversion of the irregular shear stress history into an equivalent one which, in the soil specimens tested in laboratory, produces the ame pore pressure build-up caused at the site by the earthquake loading. Conversion procedures are available for evaluating the number Neq of cycles of the equivalent uniform shear stress time-history. As an alternative, Neq can be assessed using empirical predictive models available in the literature. The models relate Neq to magnitude, to site-source distance and to several parameters describing the energy, the frequency content and the significant duration of the reference ground motion. None of these models were derived with explicit reference to Italian seismicity and their accuracy was evaluated in the paper, comparing the values of Neq predicted by the models with those computed through a complete conversion procedure applied to a number of acceleration timehistories recorded during earthquakes occurred in Italy. The comparison showed that many of the considered empirical predictive models include seismic parameters poorly correlated to Neq. Thus, an existing empirical model was updated providing Neq as a function of suitable seismic parameters, that allows evaluating reliable values of the number of equivalent loading cycles of acceleration time-histories recorded during Italian earthquakes.