關鍵字 : 直接基礎、搖擺反應、不等高橋墩案例、週期延長 ;Abstract There have been so many examples of bridge damage due to the earthquake throughout the world. One of the seismic isolation methods that have been proposed to effectively decrease the damage by the earthquake is rocking effect of the spread foundation. Although the rocking effect can cause larger displacement at the superstructure, it is capable of decreasing the seismic force from the ground to the superstructure by prolonging the period to keep the bottom of the structure from the major damage. This research shows that the comparison of the reaction at the superstructure and the substructure between the fixed behavior and the rocking effect. It also compares the results from a symmetrical model and two unsymmetrical models which are referred to Japan specification. Models with rocking effect use nonlinear soil springs to simulate the interaction between the foundation and the soil. In addition, the comparison between a symmetrical model and two unsymmetrical models depends on what entire stiffness the whole model is. This research also uses Hilbert-Huang Transform, which is capable of dealing with the nonlinear and non-steady state signals appropriately to get the instantaneous frequency that shows the energy-frequency-time relationship. Besides comparing the distribution and the change of the frequency between the fixed models and rocking effect models by using HHT, the relationship between the frequency descending proportion and either the reaction at the superstructure or the substructure would be shown when the rocking effect is applied on each of the model. Keywords : Spread foundation , Rocking effect , Irregular-height bridge case , Period prolongation
