| Summary: | 碩士 === 國立交通大學 === 土木工程學系 === 101 === Environment induced vibrations should be controlled under very small level to precisely operate a synchrotron Χ light source. This work measures the ambient vibrations of the storage ring building in its various construction stages in National Synchrotron Radiation Research Center. The measurement shows a couple of important facts. The predominant frequency of the site is around 3 Hz, and there are external stable vibration sources with frequencies of 28~32 Hz and 57~60 Hz. The mat foundation of the building considerably reduces the vibrations with frequencies larger than 5 Hz. The root mean square values of displacement in the range of 4 to 100 Hz decrease from 80 nm to 30 nm in horizontal directions and from 85 nm to 40 nm in vertical direction. The auto-regressive vector time series model is applied to identify the modal parameters of the building from the measured ambient vibration responses. The building is divided into two parts by expansion joints, namely internal ring building and external ring building. Seven and nine modes are identified for the internal and external buildings, respectively. These identified natural frequencies are significantly larger than those obtained from the finite element model for design. The identified first fundamental frequencies of the internal ring and external ring buildings are larger than the designed ones by 45% and 70%, respectively. The identified 1st and 4th mode shapes of the external ring building and the 1st and 3rd mode shapes of the internal ring building show reasonable agreement with those obtained from the finite element model with MAC larger than 0.6. The inconsistency between the identified results and the analytical results of finite element model indicates the significant differences between the constructed building and the design one. The real stiffness of the building is larger than the designed.
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