DAMPERS

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Energy Dissipation System(Dampers)

• Mechanical system which dissipate earthquake energy into specialized devices which deforms or yield during earthquake.

• They enhance energy dissipation in a structure to which they are installed so that the structure has to resist lesser amount of earthquake forces.

• They are not used to support the structure.

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• When seismic energy is transmitted through them, dampers absorb part of it, and thus damp the motion of the building.

Behavior of Building with and without dampers• When ground seismic waves reach up and start

to penetrate a base of a building and the base of the building starts moving.

• Due to inertia the building continue to remain in the previous position.

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• Due to this the building suffers distortion and the distortion wave travels along the height of the structure.

• Continue shaking of the base causes the building to undergo series of oscillations which ultimately results in collapse of building.

• To avoid such a circumstance dampers are used.

• Dampers dissipate the wave energy inside a superstructure caused by seismic waves and thus controlling the oscillations of the building

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Function

• By proper configuration of lateral resisting system, the earthquake energy is directed towards these devices located within the lateral resisting elements, to intercept this energy.

• Due to the earthquake induced mechanical energy in the system is transformed into thermal energy within these devices

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• These devices enhance the damping characteristics of the structure and consequently the amplitude of the motion of the structure is damped, thereby reducing the forces on structural members.

• These may be provided in isolation or coupled with rubber pads in series or parallel.

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Types of DampersHydraulic Dampers(oleodynamic devices)

• Used with objective of permitting slowly developing displacements due to thermal movements, but limiting the response under dynamic actions.

• These system dissipate energy by forcing a fluid through an orifice.

• The fluid may be oil or very high molecular weight polymers. 9

• They constitute a piston moving axially in the polymer, inside the cylinder.

• They may also constitute a piston moving in every direction in viscous elastomers like silicon or bitumen.

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• Oil dampers require frequent maintenance so not commonly used.

Electro- Rheological Fluid Dampers(ERF-D)• Passive fluid dampers including friction type

forces.

• Operate under shear flow.

• Fluid viscous damping reduces stress and deflection because the force from damping is completely out of phase with stresses due to seismic loading.

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• This is because damping force varies with stroking velocity.

• Other types of dampers, such as yielding elements, friction devices, plastic hinges and visco- elastic elastomers, do not vary their output with velocity.

• Hence they can increase column stress while reducing deflection.

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METALIC DAMPERS• Utilize the hysteretic behaviour of metals in the

inelastic range.

• These can be fabricated from steel, lead or spherical shape memory alloys.

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• These systems are referred to as amplitude dependent systems.

• Since the amount of energy dissipated, which is hysteretic in nature, is usually proportional to force and displacements.

• It is most often located within the structural lateral load resisting elements such as braced frames.

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STEEL DAMPERS

• Fabricated from round steel bars for cross-braced structure.

• energy is dissipated by inelastic deformation of the rectangular steel frame in the diagonal direction of the tension brace.

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FRICTION DAMPERS• The friction surfaces are clamped with

prestressing blots.

• It exhibit perfect rectangular hysteretic behaviour.

• Referred to as displacement- dependent systems, since the amount of energy dissipated is proportional to displacement.

• Contact surfaces used are lead- bronze against stainless steel or teflon against stainless steel. 17

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LEAD EXTRUSION DAMPER

•Utilize the hysteretic dissipation properties of metal.

•Process of extrusion consists of forcing a lead piston through an orifice.

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Shape memory alloys• Also known as smart alloys, are metals that,

after being strained, revert back to their original shape.

• These enable large forces and movement actuation, as they can recover from large strain

• They have capability of dissipating energy without incurring damage, as in case of steel dampers, when they yield.

• Alloys used are NiTi, CuZnAl and CuAlNi.21