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What is a seismically isolated bridge?
Its girders are supported by seismic isolation bearings to cope with an earthquake of the Great Hanshin-Awaji Earthquake’s magnitude, and the bridge is immune from an earthquake due to its longer period and the damping of seismic motion.
Laminated rubber (isolator)
The ability to bear a load and absorb rotation
Rubber reinforced with steel plates firmly supports the bridge.
Compared to rubber alone, it is more rigid in the vertical direction and it provides stable support for a structure.
The elasticity of the rubber absorbs rotation and deflection of the girder.
Bearing a load
Horizontal elasticity (lengthens the period)
The isolator converts seismic shaking into gentle movement.
It is pliable in the horizontal direction, so it softens the violent swaying of an earthquake and it lengthens the period of bridge swaying.
Horizontal elasticity and a longer period
Memory
Returns the structure to its original position.
After the earthquake subsides, the memory of the rubber returns the structure to its original position.
Lead core (damper)
Vibration damping and suppression of displacement
The lead core dampens substantial swaying of the structure.
The lead core plastically deforms as the laminated rubber deforms. It absorbs seismic energy and quickly dampens vibrations, minimizing the changes caused by an earthquake.
Trigger
The lead core reduces non-seismic shaking.
The high rigidity of the lead core holds the structure in place until a certain force is applied, preventing swaying due to storms and other causes.
The ability to dampen vibrations and suppress displacement
Vibration damping and suppression of displacement
The lead core dampens substantial swaying of the structure.
The lead core plastically deforms as the laminated rubber deforms. It absorbs seismic energy and quickly dampens vibrations, minimizing the changes caused by an earthquake.
