43.3.3. Energy Dissipation Devices (Dampers)

• Resist motion through fluid viscosity • Common in retrofitting and high-rise structures

Viscous dampers are devices designed to resist motion by utilizing the viscosity of a fluid. When a structure experiences vibrations—such as during an earthquake—the damper allows fluid to flow through a mechanism that creates resistance against the motion. This helps to absorb and dissipate energy, reducing the amplitude of vibrations that the structure experiences. Viscous dampers are particularly useful in retrofitting existing buildings to enhance their earthquake resilience, as well as in new high-rise constructions where managing sway is critical.

Imagine if you tried to shake a bowl of jelly. The jelly's resistance to the movement slows down the shaking significantly. Similarly, viscous dampers slow down and reduce the vibrations a building experiences during an earthquake, just like jelly slows down your hand's movement in the shaking bowl.

• Dissipate energy by friction between surfaces • Simple, economical, and maintenance-free

Friction dampers work by converting kinetic energy from vibrations into heat energy through friction. They consist of two surfaces that rub against each other, and as the building sways or moves, this rubbing generates friction, which dissipates energy. These dampers are favored for their simplicity and cost-effectiveness, as they require little to no maintenance over their lifespan. In many cases, they can improve the performance of structures during seismic events without complex controls or systems.

Think of rubbing your hands together to generate heat. The more vigorously you rub, the more heat you produce. Friction dampers function in much the same way; as the building moves, the friction between the surfaces generates heat, which helps to reduce the energy from vibrations, making the structure more stable.

• Use yielding of steel or other metals for energy absorption • Reusable after moderate events

Metallic yield dampers absorb energy by relying on the yielding behavior of metals like steel. When subjected to stress, the metal undergoes a deformation process that allows it to absorb significant amounts of both energy and force. After a seismic event, these dampers can often be returned to their original state and re-used, making them a sustainable choice for energy dissipation in buildings. This ability to return to function after absorbing energy is important for maintaining the safety and integrity of structures.

Consider a spring that you can compress and then release. Each time you compress it, it can still return to its original shape. Metallic yield dampers act similarly; they absorb energy during an earthquake and can often be restored, like a spring that helps maintain the building’s stability.

• Use both viscous and elastic properties of materials • Temperature-sensitive and frequency-dependent

Viscoelastic dampers leverage materials that exhibit both viscous and elastic properties. This means they can deform under stress (viscous behavior) and return to their original shape (elastic behavior). These dampers are sensitive to temperature changes and the frequency of vibrations, which means their performance can change based on environmental conditions. This adaptability makes them effective for a wide range of vibrations, providing significant energy dissipation.

Think of chewing gum. When you pull on it gently, it stretches (elastic behavior), and when you chew it quickly, it becomes less springy and more resistant (viscous behavior). Just like chewing gum can behave differently based on how you use it, viscoelastic dampers adapt to different vibration frequencies and temperatures to help stabilize structures.

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