This section provides an easy-to-understand explanation of the features and differences of the three typical technologies used to protect buildings against earthquakes: seismic resistance, vibration control, and seismic isolation.
Structural performance of buildings is classified into three categories: life protection, damage prevention, and functional maintenance.
The "protection of human life" is the minimum performance required to prevent a building from collapsing or falling and to prevent harm to the building's surroundings.
Damage prevention is the ability to prevent loss of property value in buildings due to earthquakes or to restore value by facilitating restoration. It also includes protecting the cultural value of the valuable building itself, which cannot be restored.
Functional maintenance" refers to the ability of a building to continue to function as expected after an earthquake. It also includes the protection of the building's internal accommodations.
Traditionally, seismic design has been used to protect these performances. In recent years, however, vibration control has been actively applied with the aim of satisfying these performance requirements to a higher degree.
Vibration control methods can be broadly classified into vibration control and seismic isolation. Both are based on seismic design, with the addition of vibration control functions.
Difference between "seismic resistance," "seismic control," and "seismic isolation
Earthquake Resistance] Withstands shaking.
This is a design method that strengthens the building itself to withstand the shaking of earthquakes. By making pillars and walls sturdier, the deformation of the building is reduced, preventing it from collapsing or falling down. From the viewpoint of protecting human life, earthquake-resistant structures can provide the necessary and sufficient performance. However, when severe vibrations occur, the building may be damaged, making it difficult to maintain its functionality.
In the 1995 Hyogo-ken Nanbu Earthquake, buildings built according to the new earthquake-proof design method (1981) were damaged but did not collapse. However, the buildings themselves were severely damaged, and many were demolished. In 2000, the new earthquake-proof standard, which was further strengthened in light of the 1995 earthquake, went into effect.
Figure 1: Image of building earthquake resistance
Seismic damping (vibration control)] Absorbs shaking
Seismic damping (vibration control) is a method of absorbing seismic shaking with a device to make it easier for the shaking to subside. It reduces the shaking of a building by applying a resistance force to the vibration and damping it.
Typical examples are vibration control dampers and mass dampers (TMD and AMD). They prevent amplification of building shaking and subdue it quickly, thus reducing damage to the building. Thus, in addition to protecting human life, they also prevent damage and maintain functionality.
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Figure 2: Image of building vibration control (vibration)
Seismic isolation] Shaking is blocked.
It is designed to block out shaking during earthquakes (to prevent shaking from being transmitted to the building).
Typical examples include devices such as laminated rubber installed at the foundation of a building. These devices prevent ground shaking from being transmitted to the building and significantly reduce the shaking applied to the upper building. In addition to protecting human life, these devices can achieve high performance in preventing damage and maintaining functionality.
Figure 3: Image of seismic isolation of a building
*References
The Architectural Institute of Japan (ed.) Easily Understandable Building Vibration Control