| Summary: | 博士 === 國立臺灣科技大學 === 營建工程系 === 97 === In foundation vibration problems, the assumption of foundations being rigid is not always valid. Hence, this dissertation develops a new modal flexibility method and an efficient ring method to efficiently calculate modal impedance functions and evaluate dynamic response of a circular flexible foundation subjected to horizontal, vertical, and rocking motions. The displacement of flexible foundations is expressed in terms of modal shapes corresponding to free vibration of a circular plate, and dynamic interaction effects between the foundation and the underlying soil are represented using modal impedance functions.
Comparing with existing solutions, both developed methods are found to provide accurate results with less computational effort. Verified by SASSI program, it is also found that the coupling effect between horizontal and rocking motions can be considered adequately by the proposed methods.
In addition, parametric analysis are performed to investigate the influence of the load distribution, the vibration frequency range, the foundation mass, boundary-contact condition, and the relative stiffness between the foundation and the soil medium on the dimensionless modal response. The required numbers of modes for different load distributions and the relative stiffness ratio and justification for flexible foundations to be considered as rigid are suggested. Besides, the modal impedance functions and approximate solutions for the dynamic displacement of flexible foundations can be easily obtained, and the effect of flexible foundations can also be quickly evaluated.
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