Title : Application of system identification for dynamic characteristics of rocking foundations

Page : PP.167-178

Author(s) : Yu-Wei Hwang, Jiunn-Shyang Chiou, and Louis Ge

Keyword : damping ratio, footings, fundamental frequency, rocking foundations, shaking table tests, system identification

Abstract : 

This study applies system identification methods to analyze the change in the dynamic characteristics (fundamental frequency and damping ratio) of rocking foundation systems under earthquake excitation. Shaking table testing performed at the National Center for Research on Earthquake Engineering of Taiwan on a rocking-governed column-footing model is used for demonstration. Two methods of system identification, including short-time transfer function and autoregressive moving average (ARMA) model, are utilized to analyze the measured horizontal acceleration data. The segmental ARMA model is found effective to trace the change in the system fundamental frequency and damping ratio as well as the rotational stiffness of the footing. The system identification results show that during the shaking, the fundamental frequency (rotational stiffness of footing) and damping ratio of the system are not constant. As the shaking intensity increases, the fundamental frequency decreases along with the increasing damping ratio; however, the fundamental frequency goes up again and the damping ratio decreases as the shaking intensity decreases. Besides, the identified dynamic properties of the footing are consistent with those determined from the experimental moment-rotation curves of the footing.

Full Text : [Download]