Seismic isolated building technology
Seismic Isolation Technology Used to Absorb the Impact of Seismic Vibrations Flexibly and to Protect Lifelines of Buildings
Difference between Seismic Resistance and Seismic Isolation
There are two concepts, "seismic resistance" and "seismic isolation," to preserve buildings against earthquakes.
Principles of Seismic Isolation and "4-second Seismic Isolation"
The seismic isolation structure is a principle to prevent seismic energies being transmitted to buildings by insulating buildings from the ground using the properties of laminated rubber, hard in the vertical direction and soft in the horizontal direction.
It is difficult to precisely predict the frequency components of earthquakes. The response of a building to earthquake vibrations, however, becomes almost constant regardless of the types of seismic waves when the primary natural oscillation cycle of the seismic isolation structure is made to be 4 seconds or longer. Accordingly, the level of response also becomes smaller. Figure 1 illustrates that the strength of oscillation becomes remarkably smaller at 4 seconds or after.
This means, if a "4-second seismic isolation" can be achieved, even the buildings built on soft ground can maintain stability.
Fig. 1 Correlation between the primary natural oscillation cycle of a building and strength of vibration
”RSL Seismic Isolation System" which Achieves 4-second Seismic Isolation
The "RSL seismic isolation system" is often used to build seismic isolation buildings.
The "RSL seismic isolation system" is a seismic isolation system which uses a combination of layered natural rubber compounds (Rubber), a steel damper (Steel) and a lead damper (Lead).
Roles of each seismic isolation component
- ・Using the layered rubber isolator: Using the 4-second seismic isolation system, buildings are isolated from the seismic vibrations of the ground.
- ・Lead damper: This is used to absorb vibrations at the time of earthquakes of a moderate level.
- ・Seismic isolation U type damper and steel bar damper: These are used to quickly converge impacts from large earthquakes.
The synergy of these products makes possible the preservation of buildings and safety inside of the buildings against the strongest earthquakes.
Laminated rubber isolator made of natural rubber compound
This laminated rubber isolator is an important product which has a role to reduce transmission of seismic forces to buildings by supporting the building load and flexibly transforming its shape in the horizontal direction during earthquakes.
Kurashiki Kako's laminated rubber isolator has a reinforced structure without central holes. The laminated rubber isolator without a central hole has a rigid axis and demonstrates excellent performance under a high surface pressure circumstance.
U-shaped damper integrated with laminated seismic isolation rubber mount
By integrating laminated rubber compound and a U-shaped damper, customers can share the advantages of reducing the time for installation. When an earthquake occurs, this absorbs the seismic energy and reduces seismic vibrations using its property of stable restoring force.