SIMQKE-1 generates statistically independent accelerograms, performs a baseline correlation on the generated motions to ensure zero final ground velocity, and calculates response spectra.
One of the options in the program generates ground motions whose response spectra "match", or are compatible with, a set of specified smooth response spectra. The basis for the spectrum compatible motion generation is the relationship between the response spectrum values for arbitrary damping and the "expected" Fourier amplitudes of the ground motion (Vanmarcke, 1976).
The earthquakes are synthesized by superimposing sinusoidal components with pseudo-random phase angles, and by multiplying the resulting stationary trace by a user specified function representing the variation of ground motion intensity with time. The program SIMQKE-1 also has the capability to adjust, by iteration, the ordinates of the spectral density function to improve the agreement between computed and specified response spectra. Even without the last step, the average response spectrum (of a set of simulated motions) will match the smooth target spectrum very closely.
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