Experimental Modal Analysis of a Full-Scale Seven-Story Shear Wall Based on Nonlinear Seismic Response

Abstract

In this study, the deterministic-stochastic subspace identification (DSI) method is used for estimating the instantaneous modal parameters of a full scale seven-story shear wall structure. Modal analysis is performed based on short time-windows of input-output data measured during different seismic base excitations on a shake table. The structure has been subject to four historical earthquakes with increasing intensities and various characteristics. At each time window, an equivalent global secant stiffness of the structure is estimated based on the hysteretic curve of base moment versus roof displacement. It is observed that the trend of identified instantaneous natural frequencies of the first vibration mode is strongly correlated with that of the square root of secant stiffness estimates. This observation encourages the use of experimental modal analysis for characterizing the stiffness behavior of nonlinear structures when subjected to nonstationary, large intensity excitations such as earthquakes.