40.20. Base Isolation and Energy Dissipation Devices

Base Isolation

• Reduces seismic forces by introducing flexibility at foundation level.
• Types:
  • Lead rubber bearings (LRB)
  • Friction pendulum systems

Base isolation is a technique used in earthquake engineering to reduce the seismic forces that a building experiences during an earthquake. It works by adding flexible materials at the foundation level of the structure. This flexibility allows the building to move independently of ground motion, thereby minimizing the forces transmitted from the ground to the structure.

Two common types of base isolation systems include Lead Rubber Bearings (LRB) and Friction Pendulum Systems. LRBs are designed with rubber layers and a lead core that can deform and absorb energy. Friction pendulum systems allow the structure to slide over a curved surface during an earthquake, which also helps to absorb energy and reduce motion.

Think of a base isolation system like a pair of shock absorbers on a car. When you drive over a bumpy road, the shock absorbers help smooth out the ride by absorbing the bumps. Similarly, base isolation devices absorb the shaking caused by earthquakes, allowing the structure above to remain stable and safe.

Damping Devices

• Absorb earthquake energy:
  • Viscous dampers
  • Tuned mass dampers
  • Metallic yield dampers Not yet mandatory by code but considered in performance-based design.

Damping devices play a crucial role in minimizing the energy transmitted to a structure during an earthquake. They function by converting kinetic energy from motion into thermal energy, which dissipates and reduces the amount of energy that goes into damaging the structure.

There are several types of damping devices:

1. Viscous Dampers: These use a fluid that resists motion, helping to absorb energy. They are often used in various structures to reduce vibration.
2. Tuned Mass Dampers: These are large masses placed in a structure that move in opposition to the structure’s movements, thus helping to balance the forces.
3. Metallic Yield Dampers: These devices are designed to deform permanently under stress, absorbing energy as they yield.

Although these devices are recognized for their effectiveness in managing seismic loads, they are not yet mandatory by code, which means that their use is considered more in performance-based design rather than in standard building requirements.

Imagine a basketball player who anticipates a sudden move from an opponent and leans into their motion to absorb the push instead of falling over. Damping devices act like this player; when the building shakes, these devices absorb and manage the energy to prevent the structure from collapsing or suffering damage, allowing it to stay upright and stable.

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