The Estimation of Peak Ground-motion Parameters from Spectral Ordinates

Relationships are derived between peak ground-motion parameters and the peaks in the corresponding 5% damped response spectrum. The relationships are based on a study of the smoothed spectra from a database of over 1,000 horizontal ground-motion records. A more consistent, but more complex, relationship is also derived between peak ground velocity (PGV) and an integration of the 5% damped spectrum, using random vibration theory. A recent proposal to estimate PGV from the 0.5 sec spectral ordinate is found to give less accurate results than the methods derived in this study, when compared with values derived from the strong ground-motion database; in particular, it consistently underestimates PGV for records with unusually long or short predominant periods. However, when compared with predictive equations for PGV, this method gives results comparable to the other two and is also much the simplest. Relationships between spectral ordinates and PGV are useful for the purpose of estimating PGV from a smoothed design spectrum or from a spectrum derived from ground-motion equations, for uses including estimation of structural damage and geotechnical effects. The relationships between response spectrum peaks and peak ground-motion parameters may also be useful in the selection of real time histories compatible with a smoothed design spectrum.