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Dampers

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Dampers used in building to control earthquake induced vibrations on buildings.

Publié dans : Ingénierie
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Dampers

  1. 1. DAMPERS 1
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  3. 3. 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. 3
  4. 4. • 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. 4
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  6. 6. • 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 6
  7. 7. 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 7
  8. 8. • 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. 8
  9. 9. Types of Dampers Hydraulic 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
  10. 10. • 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. 10
  11. 11. • 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. 11
  12. 12. • 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. 12
  13. 13. METALIC DAMPERS • Utilize the hysteretic behaviour of metals in the inelastic range. • These can be fabricated from steel, lead or spherical shape memory alloys. 13
  14. 14. • 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. 14
  15. 15. 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. 15
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  17. 17. 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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  19. 19. LEAD EXTRUSION DAMPER •Utilize the hysteretic dissipation properties of metal. •Process of extrusion consists of forcing a lead piston through an orifice. 19
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  21. 21. 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

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