System identification of a five-story building using seismic strong-motion data

A full scale five-story reinforced concrete building was built and tested on the Large High Performance Outdoor Shake Table (LHPOST) at the University of California, San Diego in 2012. The main objective of the test program was to study the seismic response of the structure and the nonstructural components (NSCs) and their dynamic interaction at different levels of seismic excitation. The building specimen was first tested base-isolated and then fixed at its base. In the fixed-base configuration, a suite of six earthquake motions of various intensities was applied to the building to progressively increase the seismic demand. In this paper, the modal parameters of the fixed-base building are identified using the input-output dynamic data recorded during the seismic tests. The deterministic-stochastic subspace identification method (DSI) is employed to estimate the variations of the modal properties of the building during the seismic tests by employing a short-time windowing approach. The changes of the modal parameters during the seismic motions are tracked, analyzed, and compared to those previously obtained from ambient vibrations and low-amplitude white noise base excitation tests. The identified natural frequencies and equivalent damping ratios of the building changed with the intensity of the input motions and damage in the structure, while the mode shapes are found to be insensitive to them.