Correlations between the displacement response spectra and the parameters characterising the magnitude of the ground motion

Within a Displacement-Based Seismic Design approach, the seismic input is described through displacement design spectra. Until now, these spectra are commonly obtained from the corresponding pseudo-acceleration design spectra, widely used in a Force-Based Seismic Design approach, and are therefore affected by uncertainties regarding the schematization of pseudo-acceleration spectra.In this paper, the relationships between earthquake ground motion parameters and displacement spectra have been faced starting afresh to provide an updated schematization of the spectra which consciously accounts for the most representative ground motion parameters.First, in order to identify the fewest independent parameters which best describes the seismic input, for each record, different earthquake ground motion parameters have been computed and compared to each other through correlation analyses. The results indicate that the parameters Peak Ground Acceleration (PGA), Peak Ground velocity (PGV) and Peak Ground Displacement (PGD) are both necessary and sufficient to exhaustively characterize the seismic input.Second, on the basis of the well-established “tripartite” earthquake elastic response spectrum, analytical relationships have been derived between the PGA, PGV and PGV parameters and the average amplification factors of the structural response.Finally, simple formulas are proposed for the displacement spectrum which account for the PGA, PGV and PGD. Comparison with common code displacement spectra which accounts for the PGA only show that, to best capture the trend of real earthquake spectra and to avoid both over- and under-estimations, it is fundamental to take into account at least the PGV (if not also the PGD).