Scaling Methods for Earthquake Response Spectra

In current practice, design response spectra are normalized by the three peak ground motions. Alternative scaling factors are evaluated to reduce the dispersion encountered in normalized spectral ordinates. The scaling factors comprise two major groups, one based on ground motion data, and the other on response quanitities. Within the group based on ground motion values are the integrals of the squared acceleration, velocity, and displacement, and the associated root-square, mean-square, and root-mean-square motions. Included within the group based on response quantities are the spectrum intensity and the mean Fourier amplitude. The scaling parameters are evaluated statistically using response spectra for elastic, elastoplastic, and bilinear hysteretic systems, computed from a set of twelve representative earthquake recordings. The results show that a three parameter system of spectrum intensities, computed within low, medium, and high frequency regions, may provide a better means of scaling earthquake response spectra. Significant reductions in dispersion may be realized if elastic spectra are normalized by the spectrum intensities rather than the peak ground motions. The spectrum intensities also reduce the scatter for normalized inelastic spectra, for low to moderate displacement ductilities.