Evaluation of variation in dynamic response of a building from seismic records using system identification

Natural frequencies and damping ratios are very important parameters characterizing the dynamic response of buildings. These dynamic characteristics vary during different earthquake excitations. To evaluate this variation, an instrumented building was studied. The dynamic properties of the building were ascertained using a time domain subspace state-space system identification technique considering 50 recorded earthquake responses. Relationships between identified natural frequencies and damping ratios, and the peak ground acceleration (PGA) at the base level of the building and peak response acceleration (PRA) at the roof level were developed. It was found that response of the building strongly depended on the excitation level of the earthquakes.A general trend of decreasing fundamental frequencies and increasing damping ratios was observed with increased level of shaking and response. It is concluded from the investigation that knowledge of variation of dynamic characteristics of buildings is necessary to better understand their response during earthquakes.