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

4.1.2 Modelling of the damper
The damping coefficients have a displacement dependency according to the experiments. These
dynamic characteristics of the damper are introduced into a four parameter model as shown in
Fig 12,
Fig. 11 Isolation spring element Fig. 12 4 parameter model Table 2 Parameters of the 4 parameter model
where the damping coefficients and the damper stiffnesses are taken into account according to the
experiments for every frequency. According to Fig. 9 the damping coefficients were reduced to
87 % in the horizontal direction and to 60 % in the vertical direction. The parameters of the
4 parameter model are shown in Table 2.
4.2 The procedure of the response analysis
With the help of a three dimensional frequency response analysis program and a three
dimensional time history response analysis program the response analysis was done as follows.
(1) The spring rates of the spring unit were assumed to be linear. In this way the three dimensional
frequency response analysis program was run. Next, the three dimensional time history response
analysis program was run. Then the similarity of the two wave forms gained from the two analysis
was compared.
(2) The spring was modeled as a combination of a vertical spring element and a multi spring
element for the horizontal shear direction. The damper was modeled as a four parameter model as
shown in Fig. 12. Then the three dimensional frequency response analysis program was run.
4.3 Earthquake records used
Earthquake records used in this analysis were modified from those of El Centro, Taft and
Hachinohe Earthquakes. The strength levels of the earthquake records were 50 kine for the
horizontal NS and EW direction vectors.