ABSTRACT
Prior to the 1971 San Fernando, California earthquake, nearly all damages to bridges during earthquakes were caused by ground failures, such as liquefaction, dierential settlement, slides, and/or spreading; little damage was caused by seismically induced vibrations. Vibratory response considerations had been limited primarily to wind excitations of large bridges, the great importance of which was made apparent by the failure of the Tacoma Narrows suspension bridge in the early 1940s, and to moving-loads and impact excitations of smaller bridges.
