| Summary: | 博士 === 國立臺灣大學 === 土木工程學研究所 === 94 === In engineering practice, a rigid-base model is often used to calculate the response of a structure subjected to earthquake excitations. This kind of analysis is based on an assumption that the deformability of foundation soils can be ignored, so that the interaction between the structure and supporting soils is negligible. However, for a massive structure founded on soft ground, the effects of soil-structure interaction (SSI) will significantly affect the response of structures. At present, most of the methods commonly used for SSI analysis are complicate computer codes. Therefore, the results obtained are very difficult to quantify the influence of SSI on the response of structures.
This study is to investigate the effects of Soil-Structure Interaction (SSI) on the dynamic response of a soil-structure system. An ideal model with a simple structure supported on elastic half space is utilized to derive the factor FSSI that can completely represent the effects of SSI. This factor is able to characterize both the change of predominant frequency and damping ratio of the system when compared to the conventional rigid-base type structural analysis. Based on that, an Equivalent Fixed-Base (EFB) model, which takes the effects of SSI into account, can be constructed. Associating the EFB model with traditional modal analysis, the SSI modal analysis can further be applied to determine the dynamic responses of a multi-degree of freedom soil-structure system. The earthquake response of the EFB model can also be calculated by using conventional rigid-base type programs which is very convenient for engineering applications.
The proposed EFB model has been used to simulate the dynamic responses of in-situ tests and earthquake response measurements in the Hualien LSST field test program. Cases selected for analysis include two forced vibration tests and four earthquake events with various magnitudes, including the Chi-Chi earthquake case. Although the computations have been greatly simplified, the results obtained are very satisfactory.
To incorporate the effects of SSI into the structural design, the most important issue is to quantify the effects of SSI for a soil-structure system. For design purpose, it is well recognized that the natural frequency and associated damping ratio are the key parameters for structural analysis. The natural frequency and associated damping ratio of the Equivalent Fixed-Base model constructed can be calculated through explicit equations, and can represent the dynamic characteristics of the original soil-structure system. Accordingly, the SSI response spectra analysis method can be directly used to estimate the dynamic response of a soil-structure system by using the conventional rigid-type foundation analysis.
|
|---|
