ABSTRACT
Numerical noise, in the form of high frequency acceleration spikes, may become a major obstacle to the prediction of peak seismic ground acceleration and short period spectral accelerations. This problem is examined herein for the special case of liquefiable sites, where noise effects become more pronounced. It is shown that the acceleration spikes are not related to the numerical solution algorithm and to problem-specific modelling assumptions, but are associated to the abrupt changes in soil stiffness which occur during loading reversals, after the onset of soil liquefaction. The use of Rayleigh damping may moderate noise effects only in cases of low cyclic shear strain amplitude, as in the case of dry soil profiles. For liquefiable sites, where cyclic strains become large, numerical noise may be effectively eliminated by filtering separately the pre- and the post-liquefaction segments of the predicted acceleration time-histories, using different low-pass filters.
