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1) Lead Rubber Bearing (Seismic Isolator)
Seismic Isolator is installed as a Damping Equipment under building structures so as to control the
tremor of structure against the loads of earthquake.
Base Isolation System, which is a branch of manual technique to reduce the tremor of structure, is widely
applied to the large sized structures such as road bridges, rail bridges and nuclear power station to
minimize damages from dynamic loads like earthquake. Also because it has the economic and functional
efficiency with comparative perfection, the Base Isolation System is studied and used in the world,
especially in USA and Japan.
So many bridges and buildings to which the Base Isolation System is applied are constructed in many
countries including USA and Japan all over the world, and the constructed structures showed so high the
function of isolation from earthquake that they proved the safety when arising the earthquake in practice.
Also the installation of Earthquake Absorbing Bearing is likely to be required in the world in order to get
the efficiency of seismic force damping function and of constructive cost down for the lower parts of
2) Special Features of Lead Rubber Bearing
* Strong Points
As it is made of vulcanized rubber layers, reinforced thin steel plates laid alternatively in the elastomeric pad, and
one or several lead cores inserted through the elastomeric pad and top & bottom steel plate, Earthquake
Absorbing Lead Rubber Bearing not only controls the volume of displacement with resisting the first horizontal
loads, but also prevents the bridge from falling down with absorbing the second horizontal loads at the time of
* Property of Lead as a Suitable Material for Earthquake Absorbing Work
Lead is a suitable material used for earthquke absorbing work owing to the followings; first, as lead has a high
malleability, it is able to be transformed from small to large range at a low temperature, second, the melting
point of lead, it is 20°C, which is lower than other metal, makes it easily possible for lead to return to original
* The Economic Design
* The More Excellent Safety
* Easy Installation
3) General Characters of Lead Rubber Bearing
A) Function & Applicable Bridge
The Earthquake Absorbing Lead Rubber Bearing is made so as to fulfill the earthquake absorbing function
as well as general bridge bearings
* Applicable Bridge
This bearing is mainly applicable to small & medium bridge and not suitable for large bridge because of
installation with a limit of dimensional height and volume according to the displacement moved from earthquake
or impact load So it's restricted on the scale of bridge.
B) Types of Lead Rubber Bearing
Because of the earthquake absorbing function, this Lead Rubber Bearing is manufactured for free movement to
C) Mechanical Properties of Lead Rubber Bearing
Earthquake Absorbing Lead Rubber Bearing shows following mechanical properties toward the loads of both
in a short and long term.
If Lead Rubber Bearing takes loads in a short term such as live loads from wind or earthquake on a little scale, it
will control the tremor of structure by the action of reinforced steel plate, laminated rubber and the first stage of
stiffness of lead, on the other side, if Lead Rubber Bearing takes loads in a long term such as live loads from the
change of temperature or earthquake on a large scale, it not only shall control the tremor of structure but also
ensure the safety of movement by the action of lead core which absorb the horizontally large energy after yield of
The horizontal hysteresis properties are shown as a following hysteresis curve combined the elasticity of steel
laminated rubber with the plastic transformation of lead core.
D)Vertical load dependence
The vertical load on the lead rubber bearing varies when an earthquake occurs. Effect of the vertical load on hysteresis loops over a range of σ=5,10, 15MPa was analyzed from the tests in section 3.2 and found to be very small. In Figure values of damping factor and stiffness normalized to σ=10MPa is shown. The ratio values at the shear strain of 100% were as follows: Heq(50)/Heq(100)=0.9, Heq(150)/Heq(100)=1.09; Kh(50)/Kh(100)=0.99, Kh(150)/Kh(100)=0.98.