Special Issue; Products for Industrial Machinery - NTN

“SSB” of Sliding Aseismic Isolution Unit Multi-ply Rubber
the severity of the seismic vibration is dampened by
seismic isolation to prevent damage to the structures
and maintain the functionality and habitability of the
buildings.
3. Reasons Why Low-Friction Sliding
Bearings Are Needed for Buildings
The time required for a building to vibrate once is
called its natural period. For many seismic vibration
modes, it is known that the severity of the vibration is
greatest for periods of 1 second or less and that these
seismic vibration periods are approximately the same
as the natural periods of structures that are not
seismically isolated. Thus, resonance vibration occurs
in these structures and consequently they can be
severely damaged. As schematically illustrated in Fig.
2 1) ,, SSBs can provide buildings with longer natural
vibration periods because of their low friction
coefficients. More specifically, compared to
conventional sliding bearings made from a
combination of PTFE sliding material and a noncoated
stainless steel plate, our SSBs succeeded in
reducing the vibrating force (seismic force) affecting
the building to approximately 1/3 of its original value.
As a result, since the sizes and numbers of pillars and
beams can be decreased, building designers can
create larger dwelling spaces.
schematically illustrated in Fig. 3, and the materials in
its major components are summarized in Table 1. The
SSB is comprised of a multi-ply rubber integrated
structure with laminated rubber and steel members, as
well as sliding members arranged in series. The SSB
has the following features.
Features of the multi-ply rubber SSB
1) Compared with a conventional single-ply rubber
SSB, the authors’ new design features a greater
rubber component shape factor (= rubber
diameter/4 x thickness of one ply of rubber). As a
result, the new design boasts greater vertical
rigidity and smaller rubber deformation.
2) Compared with a conventional single-ply rubber
SSB, the NTN’s new design features a long-term
carrying load that is approximately twice as great.
In addition, the combination of the thickness of
each rubber ply and the total number of rubber plies
can be altered arbitrarily. This feature allows
greater freedom in designing aseismic structures.
3) NTN’s new design involves a unique combination
that is comprised of a sliding member made of
PTFE and a corresponding sliding plate made of
Flange
Intermediate steel plate
Rubber
Flange
Intermediate steel plate
Rubber
Backing steel plate
Sliding member
Elastic
bearing
4. Composition and Features of the
Multi-Ply Rubber SSB
Backing steel plate
Sliding member
Length
The composition of a multi-ply rubber SSB is
Sliding plate + coating
Displacement and acceleration
are greater on the upper floors.
Displacement and acceleration
are virtually equal on all the floors.
Sliding plate mounting plate
Elastic bearing
Width
Earthquake resistant structure
(non-aseismic structure)
Natural period: 0.6 sec.
Seismically isolated structure
Conventional sliding bearing
(: approx. 0.10)
Natural period: 2-4 sec.
Displacement and acceleration are reduced further.
Sliding plate + coating
Sliding plate mounting plate
Fig. 3 Outlined structure of SSB
Table 1 Material of major parts of SSB
SSB=0.024
Natural period: 4-6 sec.
Fig. 2 Comparison of vibration strength of the building
with seismic isolated structure
Member NTN part designation Composition
Multi-ply rubber member
Sliding member
BEAREE ER4080
BEAREE FL3045
Natural rubber
PTFE w/ filler
Coating member BEAREE SP7001 Thermo-setting resin w/ filler
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