Many empirical scaling equations have been developed for scaling Fourier spectrum amplitudes of strong earthquake accelerations and for generation of artificial strong-motion accelerograms for the translational, torsional, and rocking components of strong motion. It has also been shown that rotational components of strong motion significantly contribute to the overall response of structures; however, little progress has been made in the development and deployment of strong-motion instruments to measure rotations. This article presents a simple approximate algorithm for generating torsional and rocking Fourier spectral amplitudes from the corresponding translational motions. The method can be used to generate torsion and rocking spectra from the translational Fourier spectra of actual records. Inverse Fourier transform can be used to generate torsional and rocking time histories.

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