A general procedure is presented for a more accurate, rapid and economical computation of response from higher frequency modes, when the modal superposition time history or response spectra method is used for dynamic analysis of structures subject to uniform, translational seismic excitation. The procedure utilizes special amplification characteristics of earthquake loading for frequencies not less than a certain assigned value and certain properties of structural modal characteristics. The upper bound for the assigned value of frequency is usually 33 cycles/s. This procedure requires computation of only those frequencies that are lower than the assigned value, and other modal properties associated with these lower frequencies. For rigid structures (i.e., structures with frequencies not less than the assigned value), this procedure reduces itself down to the familiar static analysis.

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