42.3. Types of Base Isolation Systems

Uses alternating layers of rubber and steel shims. It provides flexibility in the horizontal direction while supporting vertical loads.

The elastomeric isolation system is a popular type of base isolation. It consists of layers of rubber and steel that are designed to offer flexibility when the ground moves during an earthquake. This flexibility allows the building to sway and move without transferring much of that movement into the structure itself. Importantly, while the system is flexible in the horizontal direction (like swaying side to side), it also provides the necessary support for the building's vertical weight.

Think of a trampoline. The rubber mat gives way and bounces when you jump, but it still holds you up while you’re in the air. Similarly, elastomeric isolators allow for movement during seismic activity yet support the building’s weight.

A central lead core is inserted in elastomeric bearings to provide additional energy dissipation through yielding of lead.

Lead rubber bearings are an enhanced version of elastomeric systems. They include a core made of lead which adds an additional layer of energy dissipation. When the building sways during an earthquake, the lead core effectively deforms. This deformation absorbs a significant amount of energy, reducing the overall movement passed to the building structure. This feature helps protect the integrity of the building during intense seismic events.

Imagine squeezing a stress ball filled with liquid. The liquid moves around and absorbs the pressure you apply, helping the ball maintain its shape. In the same way, the lead core in the bearings absorbs and dissipates energy, helping keep buildings stable during shaking.

Uses materials with low friction coefficients. Variants include:

• Pure Friction Sliding
• Friction Pendulum Bearings (FPB): Combine friction and restoring force due to curvature.

Sliding isolation systems rely on materials that create very little friction to allow the building to slide back and forth during movement. This type of system can be further classified into two types: pure friction sliding, which allows unrestricted sliding, and friction pendulum bearings, which not only allow for sliding but also use a curved surface to create a restoring force that pushes the building back to its original position after the shaking stops. This combination of sliding and restoring forces helps to minimize the energy transferred to the building.

Think of a sled on snow. When you push it, it slides easily because of the low friction. Similarly, a sliding isolation system allows the building to slide during shaking, minimizing damage. The friction pendulum is like a swing that naturally comes back to the center after being pushed.

Combine two or more types of isolators to achieve optimized performance.

Hybrid systems integrate components from different types of isolation methods to take advantage of their strengths. By using a combination of elastomeric and sliding systems, for example, these hybrid isolators can offer enhanced flexibility, energy dissipation, and overall performance under seismic loads. The goal is to optimize the isolation performance based on specific structural needs and site conditions.

Consider a hybrid car that combines an electric motor with a gasoline engine. This allows the vehicle to achieve better efficiency and power while using the strengths of both technologies. Similarly, hybrid isolation systems blend different techniques for better earthquake protection.

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