Another approach for controlling seismic damage in buildings and improving their seismic performance is by installing Seismic Dampers in place of structural elements, such as diagonal braces. These dampers act like the hydraulic shock absorbers in cars – much of the sudden jerks are absorbed in the hydraulic fluids and only little is transmitted above to the chassis of the car. When seismic energy is transmitted through them, dampers absorb part of it, and thus damp the motion of the building.
Commonly used Seismic Dampers
- Viscous Dampers (energy is absorbed by silicone-based fluid passing between piston cylinder arrangement),
- Friction Dampers (energy is absorbed by surfaces with friction between them rubbing against each other),
- Yielding Dampers (energy is absorbed by metallic components that yield).
- Viscoelastic Dampers (energy is absorbed by utilizing the controlled shearing of solids).
Thus by equipping a building with additional devices which have high damping capacity, we can greatly decrease the seismic energy entering the building.
How it Works?
The construction of a fluid damper is shown in (fig). It consists of a stainless steel piston with bronze orifice head. It is filled with silicone oil. The piston head utilizes specially shaped passages which alter the flow of the damper fluid and thus alter the resistance characteristics of the damper. Fluid dampers may be designed to behave as a pure energy dissipater or a spring or as a combination of the two.
A fluid viscous damper resembles the common shock absorber such as those found in automobiles. The piston transmits energy entering the system to the fluid in the damper, causing it to move within the damper. The movement of the fluid within the damper fluid absorbs this kinetic energy by converting it into heat. In automobiles, this means that a shock received at the wheel is damped before it reaches the passengers compartment. In buildings this can mean that the building columns protected by dampers will undergo considerably less horizontal movement and damage during an earthquake.
New Breed of Energy Dissipation Devices
The innovative methods for control of seismic vibrations such as frictional and other types of damping devices are important integral part of seismic isolation systems as they severe as a barrier against the penetration of seismic energy into the structure. In this concept, the dampers suppress the response of the isolated building relative to its base.
The novel friction damper device consists of three steel plates rotating against each other in opposite directions. The steel plates are separated by two shims of friction pad material producing friction with steel plates.
When an external force excites a frame structure the girder starts to displace horizontally due to this force. The damper will follow the motion and the central plate because of the tensile forces in the bracing elements. When the applied forces are reversed, the plates will rotate in opposite way. The damper dissipates energy by means of friction between the sliding surfaces.
The latest Friction-ViscoElastic Damper Device (F-VEDD) combines the advantages of pure frictional and viscoelastic mechanisms of energy dissipation. This new product consists of friction pads and viscoelastic polymer pads separated by steel plates. A prestressed bolt in combination with disk springs and hardened washers is used for maintaining the required clamping force on the interfaces as in original FDD concept.