Nonlinear Seismic Ground Response Analysis

One-dimensional seismic ground response analyses are often performed
using equivalent-linear procedures, which require few, generally well-known
parameters. Nonlinear analyses have the potential to more accurately simulate soil
behavior, but their implementation in practice has been limited because of poorly
documented and unclear parameter selection and code usage protocols as well as
inadequate documentation of the benefits of nonlinear modeling relative to equivalent
linear modeling. Regarding code usage/parameter selection protocols, the following are
described: (1) when input motions are from ground surface recordings, we show that the
full outcropping motion should be used without converting to a “within” condition; (2)
Rayleigh damping should be specified using at least two matching frequencies with a
target level equal to the small strain soil damping; (3) the “target” soil backbone curves
used in analysis can be parameterized to capture either the soil’s dynamic shear strength
when large-strain soil response is expected (strains approaching 1%), relatively
small-strain response