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confirmed in the X direction. Because the equipment had a small width in the X direction,
rocking occurred more outstanding in the X direction than in the Y direction.
The acceleration response magnification at the center of gravity was about 2.5 in case N, and
about 2.0 in case A and case B. The acceleration response spectra in Fig. 4 indicate that the
damping factor was about 5% in case N, and about 7% in case A and case B.
Characteristic Difference In Two Types Low-Stiffness
and High-Damping Rubber
Fig. 6 shows shear strain of the low-stiffness and high-damping rubber at every level of seismic
test. Shear strain increased as greater ground motion was applied in case A and B. Shear strain
of type B was greater than type A. The shaking table test found no significant difference in
vibration control effect of type A and type B.
Physical Damage To The Equipment
Physical damage to the equipment is discussed below. In case N, the welding, the major
structural elements of the equipment, suffered damage, like cracking, at AT08. As a result, the
acceleration response magnification at the top of the equipment at AT08 was lower than at
AT06 (see Fig. 5). In case A and case B, neither permanent deformation of major structural
elements nor cracking in the welding occurred at AT08. Thus, vibration control effect was
confirmed.
CONCLUSIONS
The application of vibration control device that reduces horizontal seismic force, which affects
the equipment, has been developed. Inserting low-stiffness and high-damping rubber between
the bottom of the equipment and the floor could attain the reduction of the seismic force
considered the lower floor response of buildings against earthquakes. Through the shaking
table test, the following conclusions were obtained.
(1) Installing low-stiffness and high-damping rubber between the bottom of the equipment and
the floor could reduce response acceleration of seismic motion 4 m/s 2 and 6 m/s 2 by 13%
to 29%. Damage to the equipment could be prevented against seismic motion 8 m/s 2 .
(2) Vibration control will become more effective even at higher levels of input seismic motions
by considering the way to reduce the rocking of the equipment.
Reference
INABA, T., DOHI, H., OKUTA, K., and SATO, T. (1998). Vibration Control of Equipment Using High
Damping Rubber. Second World Conference on Structural Control, ABSTRACTS, JUNE, 28-JULY1, 170.