Simplified Analysis of Soil-structure Interaction System：Lumped-parameter Models to Represent the Soil and Fixed-base Models for the Whole System

• Main Authors: Cheng-Yin Chen, 陳承胤
• Other Authors: Wen-Hwa Wu
• Format: Others
• Language: zh-TW
• Published: 2000
• Online Access: http://ndltd.ncl.edu.tw/handle/48417800666087796253

碩士 === 國立雲林科技大學 === 營建工程研究所 === 88 === A number of frequency-independent lumped-parameter models to replace the continuous soil for a simplified analysis have been developed and shown to have good accuracy. However, the associated intricate arrangement of vibration units and numerous artificial internal degrees of freedom to introduce may still limit their popular application to engineering practice. A new methodology is developed in the first part of this thesis to construct consistent lumped-parameter models for representing the horizontal, vertical, rocking, and torsional vibrations of rigid foundations. A spring and a dashpot are first attached in parallel to a mass to constitute a single-degree-of-freedom (SDOF) oscillator. Depending on the requirement of accuracy, the lumped-parameter model is then designed to consist of one or several SDOF oscillators connected in series. The effectiveness of these models is demonstrated by simulating the impedance functions for different types of foundations and further application to complete soil-structure interaction (SSI) analysis. Compared with the other lumped-parameter models to achieve the same degree of accuracy, the models proposed in this study have the advantages in requiring less parameters to fit, inducing less artificial internal degrees of freedom and featuring a more systematic composition. An alternative methodology to simplify the analysis of soil-structure interaction systems is to represent the total structure-foundation-soil system with a lumped-parameter model similar to a fixed-base structure. In other words, the SSI effects are considered in the fixed-base models through modifying the structural parameters. Several fixed-base models have been recently developed and shown to have excellent accuracy. However, the modified mass and damping matrices of these models do not hold the properties of symmetry and orthogonality, which are usually valid or assumed for ordinary structural systems. In the second part of this thesis, this problem is further explored to establish a fixed-base model possessing classical normal modes. An iteration algorithm is suggested to incorporate the Gram-Schmidt orthogonalization process and the formulation in the modal space for the determination of orthogonal mode shapes, natural frequencies, and modal damping ratios. It is demonstrated with a numerical example that this new fixed-base model also preserves good accuracy. Consequently, the complicated SSI systems can be analyzed directly using conventional computer codes for structural dynamics with the fixed-base model developed in this study.