Generation of Seismic Floor Spectra

A simple method is presented for generation of floor response spectra directly from a given ground response spectrum. A common practice to generate floor spectra is to carry out time-history analysis for a ground spectrum-consistent accelerogram. Unless an ensemble of such accelerograms is used the response results cannot be relied upon, but the use of an ensemble of accelerograms is cumbersome and costly. A method which can directly use a prescribed spectrum is preferred. The proposed method is based on transfer characteristics of the structure for random excitation, and makes use of the structural frequencies, mode shapes and participation factors, and the prescribed spectrum to generate floor spectra. In the paper, the use of the proposed method is demonstrated by generating floor spectra of a building. The proposed method is simple and especially convenient for use on digital computers.