What is an isolation system and how does it work?

A seismic protection technique, an isolation system, separates the structure’s (superstructure) base from the building (foundation or substructure). It considerably reduces the energy delivered to the superstructure during an earthquake to separate the structure from its base.

These isolation systems frequently have one or more types of bearings to support the structure’s weight. Inverted pendulums, sliding plates, and elastomeric pads are a few examples of these parts. These parts can somewhat dissipate energy, although usually only by hysteretic damping. Hysteretic damping can occasionally trigger higher modes but has some restrictions on how much energy it can absorb.

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See also: How to ensure your home is earthquake proof?

Isolation system: Purpose

Wind and earthquake are the two main types of loads that call for the lateral design of a structure. Furthermore, since earthquake load cannot be regulated, it is impracticable to construct a structure to accommodate an infinite seismic demand. Accepting the demand and ensuring that the capacity surpasses the demand is the only practical course of action. The mass of the structure and the ground acceleration are inversely connected with the inertial forces produced by earthquakes. Enhancing the building’s flexibility or elastic strength is the most conventional method of handling seismic demand. Therefore, the goal of the isolation system is to decrease seismic demand rather than to increase capacity. Although it is impossible to control ground motion, we can change the demand on a structure by preventing or minimising the motions transported to the structure from the foundations.

Isolation system: Working principle

A basic idea behind the isolation system is to modify the building structure’s responsiveness so that the ground underneath it can move freely without exerting force on the structure above. It is accomplished by dividing or isolating the superstructure from its foundation on swaying ground. As a result, the building is less affected by earthquake forces.

The term “isolation” itself alludes to the diminished interaction between the ground and the main structure. “Base isolation” refers to the system’s provision beneath the structure.

In earthquake engineering, the isolation system falls under the passive vibration control technique. It is a concept for the structural design that aims to decouple the building from the harmful impacts of an earthquake’s ground motion.

The building behaves more flexibly due to the base isolation’s decoupling action, enhancing earthquake resistance.

Isolation system: Characteristics

An isolation system must have these fundamental characteristics:

• Flexibility
• Damping to reduce the amplitude of a resonance
• Isolation to impede the transmission of disturbing vibration
• Resistance to vertical loads or other service loads
• Resonance, which is a structure’s oscillation at a greater displacement than the input displacement.
• Transmissibility to measure the response of an isolator

Isolation system: How does it work?

Base isolation involves putting flexible bearings or pads between the building’s foundation and the structure above. These pads or bearings are made of layers of rubber and lead. By decreasing swaying and trembling during an earthquake, these base isolators move and stretch under pressure to absorb much of the impact of an earthquake.

Isolation system: Advantages 

• In addition to shielding buildings from seismic activity, the base isolation system also shields them from severe blast pressure because mobility reduces the explosion’s overall impact on the buildings.

• Compared to conventional structural components, base-isolated structures are far more reliable because they are predictable.

• Only an isolation system, whose components may be easily replaced, is damaged in the event of significant and unexpected earthquake activity.

• Retrofitting a base isolation system to a suitable existing structure is also an option. Also, the building can continue to be used while being renovated.

• Buildings that are seismically insulated or have a seismic insulation system from the base outperform those that are not. They have lower floor accelerations and drifts and are less prone to sustain structural damage.

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