ABSTRACT A vibration isolation system using spring units and visco ...

(2) Result
According to the tests, the damping coefficient decreases and the stiffness increases with
increasing frequency.
Fig. 9 shows the displacement dependency of the damping coefficient. The horizontal damping
coefficient decreased down to 87 % compared to that at random noise excitation when the
amplitude was 30 mm. The vertical damping coefficient decreased down to 60 % compared to that
at random noise excitation when the amplitude was 45 mm.
4. SEISMIC RESPONSE ANALYSIS OF THE VIBRATION ISOLATED BUILDING
4.1 Analysis model
The analysis model is shown in Fig. 10
(1) The upper parts of the building were assumed as concentrated masses connected by springs.
(2) The ground floor was assumed as a solid slab.
(3) The spring elements and visco-elastic dampers were put under the columns of the ground floor.
(4) The analysis model was designed as a three dimensional model.
The data for the analysis are shown in Table 1.
Fig. 10 Analysis model of the building
4.1.1 Modelling of the springs
The spring coefficients of the spring depend on the deformation of the spring. The model of the
spring (shown in Fig. 11) was, therefore, composed of a vertical spring and a multi spring element
for the horizontal shear direction. Both elements were given restoration characteristics gained from
the experiments. The response calculation was done step by step with the tangential stiffness at
each step.