33. System Identification of a Three-Story Precast Concrete Parking Structure

A half-scale, three-story, precast concrete building resembling a parking garage was tested on the UCSD-NEES shake-table in May–July of 2008. This was the capstone test of a multi-university/industry research project aimed at the development of seismic design guidelines for precast concrete diaphragms. The shake-table tests were designed to induce damage on the building progressively through earthquake records of increasing intensity. Low-amplitude white-noise base excitations as well as scaled earthquake tests were performed between large-amplitude earthquake records. In this study, modal parameters of the test structures are identified using a deterministic-stochastic subspace identification method based on low-amplitude as well as high-amplitude seismic test data. The changes in the identified modal parameters are compared to the progressive damage of the building. Reduction of the identified natural frequencies and increase of the damping ratios indicate loss of stiffness and development/propagation of cracks, while the changes in the mode shapes point to the location of damage.