2 Master of the Department of Civil Engineering, NTUT, Taipei, Taiwan. Time and Frequency Domains Analysis on Bridges with Unequal Height Columns and Functional Unseating Prevention Devices Yeou-Fong Li1 and Cheng-Yi Chou2 1Professor of the Department of Civil Engineering , NTUT, Taipei, Taiwan . 2 Master of the Department of Civil Engineering, NTUT, Taipei, Taiwan. Abstract : In this thesis, the mechanical behaviors of bridge with functional unseating prevention devices (rubber bearing, restrainer, and shear key) were investigated by using the time and frequency domains analysis. The functions of the devices are to prevent bridge from unseating and to prevent most of the seismic force transfer to the bridge column. The non-linear dynamics analysis with SAP 2000 was used to simulate the bridges with unequal height column. The Hilbert-Huang Transform (HHT) was also used to transfer the time history response into the time-frequency domain and also to obtain the Hilbert spectrums of the rubber bearing displacement of bridges. The Hilbert spectrums can determine when the functional unseating prevention devices were operated and their operation sequences. The results of this thesis can provide bridge engineer to understand the mechanical behaviors of unseating prevention devices with unequal height columns and how to design functional unseating prevention devices in bridge with different column height ratio. Keywords： Unequal height columns, Functional unseating prevention devices, Non-linear dynamics analysis, Hilbert-Huang Transform Columns height 7.5 m-10 m of bridge for different functional unseating prevention devices displacement The rubber bearing displacement for column height 7.5 m-10 m Different gap of shear key for different peak ground acceleration 2D Hilibert spectrum of bridge with rubber bearing, restrainer and shear key