Abstract
In this paper, the authers deal with the filtering effect of foundation slab for earthquake inputs. The subject of this paper is divided into two main parts. One is the theoretical discussion of the filtering effect based on the Kausel's theoretical formulation. In this formulation, the filtering effect is given by the earthquake response analysis in which the mass of structure is ignored. The other is the discussion on the filtering effect of foundation slab based on earthquake observation records of a inground tank. And, the simulation is performed to verify the above theory using the finite element method (FEM). The conditions of inground tank is very suitable to study the filtering effect, because this tank could be assumed generously as "a massless rigid foundation" which is a basic model to understand the filtering effect. After the examination of observed records, the filtering effect of foundation slab is very clearly recognized. For example, the higher frequency components than 2.5 Hz of earthquake responses on the foundation are less intensity under 40 percent than that of adjcent free field. The results of the simulation agree with those of observations very well. Then, in the FEM program used in this paper, the earthquake input is assumed as the shear waves which propagate vertically in the ground right under the structural foundation. Therefore, the following important idea is pointed out. As before, we paid attention to the filtering effect on the only bottom of the foundation slab. However, in the real situation, it seems likely that the filtering effect is produced more on the side walls than on the bottom of the foundation.
