Page 252 - Numerical Analysis and Modelling in Geomechanics

F.PERGALANI, V.PETRINI, A.PUGLIESE AND T.SANÒ 233

Figure 8.6 Non-stationary artificial acceleration time-histories (Pergalani et al., 1999).
Figures 8.8 and 8.9 show that the non-linearity can be very important for
strong ground motion for which a significant soil shear deformation exists.
Such non-linearity is accounted for by the use of equivalent linear analysis
(Seed et al., 1986) using an iterative procedure to obtain, in each iteration, the
characteristics of the soil compatible with the effective strain in each layer.
In performing the microzoning of the Umbria-Marche region, extensive use
was made of another computer program, called PSHAKE (Sanò and
Pugliese, 1991). This program allows the direct use of a response spectrum
instead of a time history as input. A power spectrum of a family of ground
motions on the outcropping rock is obtained through an iteration on the given
acceleration response spectrum, taking into account its exceedence probability.