Dynamic Design Analysis of Electrical Bus Runs and Supports to Withstand Earthquakes

Both foundation and building floor seismic response spectra, based upon a random type of earthquake input inotion, indicate that important quasi-resonance vibration buildup of about 5 to 10 times can occur in the usual 1 to 25 Hz frequency range of damaging seismic effects. However, dynamic analysis has shown that properly designed supports can be added to raise all bus run natural frequencies well-above 25 Hz, thereby causing the above-mentioned seismic vibration magnification to become negligible. The resulting stiffened and strengthened bus run configurations Would then be required to withstand only the specified earthquake-induced building floor motions amounting to about 0.2 to 0.5g. A steady vibration of 0.5g at 25 Hz results in an amplitude of only 0.008 in. Since such a small lateral deflection of a bus run section would produce only negligible bending stress, no strength failure or malfunction would be anticipated, provided there was no extreme relative motion in the building itself.