Earthquake isolation (foundation isolation) system can be used to prevent damage caused by seismic forces in high-rise buildings. In the earthquake isolation system, suspension or a series of carrier bearings are placed between the substructure and the superstructure. When the ground shakes due to seismic forces, the suspension can prevent or reduce the force transmission from the ground to the superstructure.
What is an earthquake isolator?
Earthquake isolators are designed to absorb energy and create a damping effect on the building. Buildings are not exposed to earthquake-induced movements, as flexibility is gained to the structure obtained with this system. This method was introduced in the 1900s but reached a practical stage in the design of seismic resistant buildings in the 1970s.
In traditional tall buildings, the foundation is rigidly constructed. In other words, during an earthquake, the superstructure moves together with the foundation and soil due to the load transfer from the ground to the structure. Displacement will be greater in the upper parts of the building, reaching up to 2/3 the height of the building. Since the structure is rigid, lateral forces from earthquakes can cause damage and even cause buildings to collapse (resonance).
Since seismic forces cannot be controlled, making the structure flexible is a better way to protect buildings from seismic forces. This is accomplished by placing earthquake isolators at the foundation of the structure. These insulators have a great influence on the lateral forces on the structure due to ground motion. The ground and substructure move with seismic forces and the isolator provides flexibility between the substructure and superstructure.
In this way, the superstructure is less affected by the earthquake. Foundation insulation effectively reduces the rigidity of the structure and reduces the inertial forces on the structure. It also lowers the natural frequency of the earthquake force and prevents the formation of resonance.
The structure with a rigid foundation will have a zero natural period. When the ground moves, an acceleration equals the ground acceleration occurs on the structure. Here the relative displacement between the ground and the structure will be zero. However, in a flexible structure (structures using earthquake isolators), the natural period is infinite. Therefore, no acceleration occurs on the structure when the ground moves and the relative displacement will be equal to the ground displacement.
Advantages of using earthquake isolator
- Providing foundation insulation is an effective way to construct an earthquake resistant building.
- It prevents damage to property inside buildings.
- It provides more stability to the structure.
- Foundation isolation is a good way to dissipate seismic energy over structures.
- Plastic deformation of building elements can be prevented during an earthquake.
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