Effect of site amplification on inelastic seismic response

The available models for effective periods of site and structure are reviewed in context of frequency tuning in the inelastic seismic response of soil-structure system. The effect of seismic intensity and ductility demand, on the effective periods, is investigated, and inelastic site amplification is shown to be strongly correlated to the normalized effective period. Two non-dimensional parameters, analogous to the conventional site amplification factors in codes, are defined to quantify the inelastic site amplification. It is shown that the inelastic site amplification factor(i.e. ratio of constant ductility spectral ordinates at soil site to those at rock outcrop) is able to represent the site effects more clearly, as compared to the inelastic site amplification ratio(i.e. ratio of inelastic spectral ordinates at soil site to the corresponding elastic spectral ordinates at rock outcrop). Further, the peak in the amplification factor corresponding to the effective site period diminishes rapidly with increasing ductility demand.