A STUDY ON DYNAMIC CHARACTERS FOR RC PORTAL FRAME UNDER SHAKING TABLE TEST BY USING HHT APPROACH

The adaptive data analysis method adopted in this paper consists of essential empirical mode decomposition (EEMD) associated with down-sampling process and the Hilbert-Huang transform (HHT). Precise results can be obtained from data containing white noise in nonlinear system than the data from the common method of Fourier transform, which is based on the theory related to the linear systems. The reinforced concrete (RC) portal frame models had been tested by applying the 921 Chi-Chi earthquake acceleration data (TCU082NS) for shaking table tests. The investigation in this paper is aimed to analyze the dynamic characteristics according to these measured data during shaking table tests. The major goal in analyzing the earthquake data is to investigate the changes of frequencies decomposed to finite several intrinsic mode function (IMF), and the distributions of frequencies with respect to duration time, as well as the margin spectrum. The comparison studies of the HHT results for the frame, under nonlinear ultimate loading and linear elastic loading, might be able to ascertian the possible assessment approach for the frame. The finite element method is also adopted to analyze the stress distributions for the frame under ultimate loading and linear elastic loading respectively, and to figure out the differences between them. The possible assessment approach might be applied to health monitoring for RC structures such as buildings and bridges.