Site specific, spectrum compatible non synchronous motion

this paper aims to develop and validate structural design criteria which account for the effects of earthquakes spatial variability. In past works [Nuti and Vanzi, 2004, 2005] the two simplest forms of this problem were dealt with: differential displacements between two points belonging to the soil or to two single degree of freedom structures. Seismic action was defined according to EC8 [CEN, 2002]; the structures were assumed linear elastic sdof oscillators. Despite this problem may seem trivial, existing codes models appeared improvable on this aspect. For the differential displacements of two points on the ground, these results are now validated and generalized using the newly developed response spectra contained in the draft seismic Italian code [Ministero LL.PP., 2007]; the resulting code formulation is presented. Next, the problem of statistically defining the differential displacement among any number of points on the ground (which is needed for continuos deck bridges) is approached, and some preliminary results shown. It is also shown that the current codes (e.g. EC8) rules may be improved on this aspect.