Modal Analysis of a Full-scale Four-story Reinforced-concrete Base-isolated Building Subjected to Random and Simulated Earthquake Shake Table Excitations

Full-scale dynamic earthquake engineering experiments are costly, yet they are vital for the advancement of seismic protection for large structures. The main goal of such large-scale studies is to accurately replicate the response of complex structures. E-Defense, a part of Japan's National Research Institute for Earth Science and Disaster Prevention (NIED), constructed and tested a four-story reinforced-concrete base-isolated building to study, among other objectives, how different energy dissipation devices in the building isolation layer improve the response subjected to strong impulsive and long period excitations. This structure was subjected in August 2013 to a series of tests. Analyzing the resulting acceleration responses from the random ground motion tests forms the first step in identifying the dynamic characteristics of this test structure. Specifically, enhanced canonical correlation analysis (ECCA) and the advanced numerical algorithm for subspace state-space system identification (N4SID), from the stochastic subspace identification (SSI) family of methods, were used to estimate the modal parameters. Additional identification was then performed using responses recorded during simulated earthquakes. The recovered modal parameters were compared against the nominal parameters to analyze the behavior of the building's isolation system, as well as the effectiveness of the identification methods.