Seismic site factors and design response spectra based on conditions in Charleston, South Carolina

Seismic site factors based on conditions typical of Charleston, South Carolina, are derived from the results of more than 13,000 one-dimensional equivalent linear and nonlinear dynamic response simulations. The site factors are plotted versus average shear wave velocity in the top 30 m (VS30) of soil and grouped by spectral acceleration and period. Median relationships for the site factors are expressed by a linear model for lower values of VS30 and a linear or exponential model for higher values. The computed factors are found to be somewhat different from the factors recommended in design codes. It is also found that amplifications greater than predicted by the common (or three-point) acceleration design response spectrum method can occur at periods greater than 1.0 s, particularly when VS30 < 200 m/s. Thus, when VS30 < 200 m/s, it is recommended that a multipoint response spectrum be constructed and compared with the three-point spectrum.