Learning from recorded earthquake motion of buildings

Seismic records obtained during the Loma Prieta earthquake and the Whittler earthquake from 21 buildings were analyzed by a system identification method. The adequacy of current code specifications on building period estimation was discussed. A range of damping ratio was obtained for different building types. Characteristics of frame buildings and shearwall buildings were discussed in terms of the maximum story drift ratio envelope and the frequency ratio between higher modes and the fundamental mode. Torsional responses were found to be prevalent in several cases. The orthogonal effect was revealed indirectly by the concurrent nature of maximum story drift in the two horizontal directions. Large change of vibration frequency was found during the course of the earthquakes in many buildings.