Vertical Seismic Response Spectra

Response spectra are derived from 30 historical vertical motion accelerograms recorded on hard or rock sites and used as a basis for a recommended design response spectra. Accelerograms were corrected for baseline and instrument errors using routine processing methods. Statistics are derived for the response spectra normalized to peak ground displacement, velocity, and acceleration. Effects of sample size are examined and a method for deriving confidence intervals for the statistical results is presented. Following approaches of previous investigators the results are used as a basis for recommendations of a smoothed design response spectra for vertical motion at hard or rock sites. The recommended vertical design spectra for rock sites are lower than recommendations of previous investigators for sites of intermediate hardness.