| Summary: | 碩士 === 中原大學 === 土木工程研究所 === 100 === In the last several decades, cable-stayed bridges have become popular due to their aesthetic appearance, structural efficiency, ease of construction and economic advantage. This type of bridge, however, is light and flexible, and has a low level of inherent damping, resulting in the fact that they are susceptible to seismic loads. Since the geometric and dynamic properties of the bridges as well as the characteristics of the seismic loads are complex, it is necessary to fully understand the mechanism of earthquake-induced vibrations of cable-stayed bridges, which is used to provide the essential information to accurately calculate the dynamic responses of the bridges under seismic excitations. The objective of this study is to present the spectral analysis of cable-stayed bridges under seismic loads. Based on the results of the initial shape, modal and seismic analyses in the previous work, the one-element cable system and multi-element cable system models of the symmetric harp cable-stayed bridge are developed to calculate the power spectral density functions of nodal displacement and internal force using the fast Fourier transform. The findings indicate that the global and local modes in the low frequency range can be successfully captured by the nodal displacement, whereas the global and coupled modes covering a variety of frequency ranges can be efficiently obtained by the internal force.
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