What Are Isolation Systems?

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Overview

A famous quote says: "Earthquakes do not kill people. Buildings do."

Basically, buildings are giant blocks of concrete and steel that can collapse under the strong pressure of earthquakes, resulting in catastrophic consequences.

Each year, approximately 12,000 to 14,000 earthquakes occur, and although they can't be prevented, construction techniques and building resistance can lessen their effect and protect thousands of people.

Our main topic for today is securing buildings with isolation systems.

Therefore, let's get started and discover together the most effective isolation systems.

What Are Isolation Systems In A Building?

Installing isolation devices under a building to protect it from strong earthquakes is known as seismic isolation. Since the 1980s, the seismic isolation approach has been researched and applied to buildings.

The columns and beams in a traditional earthquake-resistant design are meant to be robust and flexible enough to withstand seismic shocks.

This strategy is used to design and construct the vast majority of buildings. When a traditional building is confronted with a significant earthquake, it can prevent its collapse and save the lives of its people.

Seismic isolation can significantly reduce building shocks thanks to the discovery of laminated rubber bearings that made the seismic isolation technology viable.

Moreover, the rubber bearings have low horizontal stiffness and are made up of many layers of thin rubber sheets and reinforcing steel plates.

After the Great East Japan Earthquake struck on March 11, 2011, sensors were able to record the isolator's behavior.

The greatest deformation of the rubber bearings was around 9 cm, and the effects on the second floor of each building were roughly reduced by half, which is evidence of how durable and reliable they are.

By using seismic isolation, not only is the structure of the building safe but also the individuals and properties within.

Based on the position of the isolators, seismic isolation methods can be divided into two categories, base isolation and mid-story isolation.

What Are Base Isolation And Mid-Story Isolation?

Base Isolation:

A base isolation system is a common device used to protect a structure from the effects of seismic forces. Dr. Bill Robinson of New Zealand created base isolation bearings in the 1970s.

Both new and modified buildings can be designed to be damage-resistant through the use of base isolation systems.

For that, this technology is known as a seismic base isolation system.

The main concept of a base isolation system is to change the building structure's responsiveness, allowing the ground underneath to move freely causing the pressures to affect the building structure above. This is accomplished by removing or isolating the superstructure from its oscillating ground-based substructure. As a result, the structure is less vulnerable to earthquake forces.

In earthquake engineering, the base isolation system is classified as a passive vibration control technique. It's a structural design method to isolate the structure from the harmful impacts of earthquake ground motion.

The decoupling effect of the base isolation allows the building to behave more flexibly, boosting its seismic resistance.

To better understand the principle, look at this example.

Consider a structure supported by frictionless rollers.

When the earth beneath the building begins to shake, the rollers start to roll freely, while the building remains stationary above.

This means that the ground movement has no effect on the structure, and it remains safe. Because the distance between the foundation pit's vertical wall and the building is so narrow that they may collide when the ground moves.

Now, consider the following scenario: Instead of rollers, the building mentioned above is put over flexible pads. Although the building does experience some ground shaking, this structure provides resistance to lateral movement in the event of a seismic force.

Base isolators are the name for these flexible pads.

Mid-Story Isolation:

This method entails installing a seismic isolation layer into the fourth floor, which is the structurally weakest, in order to boost the earthquake resisting ability by totally isolating the office and residential stories.

According to calculations, 24 rubber bearings and various dampers are needed, and the story's elevator shaft will be divided into upper and lower halves, necessitating the construction of additional elevators.

This strategy satisfies the need for continuous employment.

A mid-story system is mostly utilized on unusual structures like huge platforms and multi-tower constructions, which have one or several-story RC frame platforms at the base half and some multi-story buildings at the top portion.

It is simple to locate an isolation layer between conversion floors and lower structures in a complicated high-rise building with conversion stories.

Wire Rope Isolators As a Base Isolation System

Although these are two effective methods of isolation, they aren't the only ones.

You see, in recent years, the engineering world developed a decoupling method based on wire rope isolators, citing calculations and characterization tests. Laboratories tested the system for earthquakes using an electrohydraulic shaker machine.

It was decided to use wire rope isolators for their inherent flexibility, damping, and displacement capabilities. Temperature, humidity, and chemical agents do not affect the wire rope isolators, which can endure as long as the equipment they protect.

All around the world, wire rope isolators have been used to protect critical components of the power grid from earthquake damage.

Conclusion

Building seismic isolation and response control strategies have been investigated and implemented in structures since the 1980s to make them more earthquake resistant.

Shaking table tests, structural health monitoring, and earthquake reaction studies were used to verify the impacts of seismic isolation and response control approaches.

As for now, many new techniques and procedures are being researched to improve response reduction effects, and the number of people using them is rapidly increasing.

Most importantly, people's lives, property, housing, social infrastructure, and economic activities should all be protected from earthquakes, which is why earthquake-proof systems are a must.