its a case study on vibration isolation

1. VIBRATION ISOLATION
DEPARTMENT OF MECHANICAL ENGINEERING,
MUMBAI UNIVERSITY
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3. CONTENTS
 INTRODUCTION
 VIBRATION ISOLATORS
 FORCE TRANSMISSIBILITY (TR)
 TRANSMISSIBILITY VERSUS FREQUENCY RATIO
 MOTION TRANSMISSIBILITY
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4. INTRODUCTION
“Everything in Life is Vibration” – Albert Einstein
 Vibrations are produced in machines having unbalanced masses or forces. These
vibrations are transmitted to the foundation upon which the machines are
mounted, which is undesirable.
 Hence, it’s essential to isolation the machines from foundation so that the
adjoining structure is not set into heavy vibrations. These is known as vibration
isolation
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5.  The basic objectives of vibration isolation are...
(i) To protect the delicate machine from excessive vibration transmitted to it from its
supporting structure.
(ii) To prevent vibratory forces generated by machine from being transmitted to it’s
supporting structure.
 The effectiveness of isolation may be measured in terms of force or
motion transmitted to that existence. Accordingly it’s known as force isolation or motion
isolation. The lesser the force or motion transmitted the grater is the isolation
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6. VIBRATION ISOLATORS
 The vibration isolation may be obtained by placing isolation
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7.  The term isolation refers to reduced interaction between structure and the ground.
 When the seismic isolation system is located under the structure, it is referred as
“base isolation”.
 The other purpose of an isolation system is to provide an additional means of energy
dissipation, thereby reducing the transmitted acceleration into the superstructure.
 The decoupling allows the building to behave more flexibly which improves its
response to an earthquake.
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8. CONCEPT OF BASE ISOLATION
 The concept of base isolation is explained through an example building resting on
frictionless rollers.
 When the ground shakes, the rollers freely roll, but the building above does not
move.
 Thus, no force is transferred to the building due to shaking of the ground; simply,
the building does not experience the earthquake.
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10.  Now, if the same building is rested on flexible pads that offer resistance against
lateral movements, then some effect of the ground shaking will be transferred to
the building above.
 The flexible pads are called base-isolators, whereas the structures protected by
means of these devices are called base-isolated buildings.
 The main feature of the base isolation technology is that it introduces flexibility in
the structure.
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11.  So in flexible structures the structure will not move, the ground will.
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13. ISOLATION COMPONENTS
 Elastomeric Isolators
 Natural Rubber Bearings
 Low-Damping Rubber Bearings
 Lead-Rubber Bearings
 High-Damping Rubber Bearings
 Sliding Isolators
 Resilient Friction System
 Friction Pendulum System
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14.  Elastomeric Isolators
 These are formed of horizontal layers of natural or synthetic rubber in thin layers
bonded between steel plates.
 The steel plates prevent the rubber layers from bulging and so the bearing is able
to support higher vertical loads with only small deformations.
 Plain elastomeric bearings provide flexibility but no significant damping and will
move under service loads.
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15.  Methods used to overcome these deficits include lead cores in the bearing, specially
formulated elastomers with high damping and stiffness for small strains or other
devices in parallel.
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16.  Low Damping Natural or Synthetic Rubber Bearings
 Elastomeric bearings use either natural rubber or synthetic rubber (such as neoprene),
which have little inherent damping, usually 2% to 3% of critical viscous damping.
 For isolation they are generally used with special elastomer compounds (high damping
rubber bearings) or in combination with other devices (lead rubber bearings).
 They are also flexible at all strain levels.
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17.  Lead Rubber Bearings
 A lead-rubber bearing is formed of a lead plug force-fitted into a pre-formed
hole in an elastomeric bearing.
 The lead core provides rigidity under service loads and energy dissipation under
high lateral loads.
 Top and bottom steel plates, thicker than the internal shims, are used to
accommodate mounting hardware. The entire bearing is encased in cover
rubber to provide environmental protection.
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18.  When subjected to low lateral loads
(such as minor earthquake, wind or
traffic loads) the lead rubber bearing is
stiff both laterally and vertically.
 The lateral stiffness results from the
high elastic stiffness of the lead plug
and the vertical rigidity (which remains
at all load levels) results from the
steel-rubber construction of the
bearing.
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19.  Isolation Systems based on Sliding
 The second most common type of isolation system uses sliding elements between the
foundation and base of the structure.
 In this type of Isolation system, the sliding displacements are controlled by high-tension
springs or laminated rubber bearings, or by making the sliding surface curved.
 These mechanisms provide a restoring force to return the structure to its equilibrium
position.
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20.  Sliding isolator without Recentering
capacity
 This consists of a horizontal sliding
surface, allowing a displacement and
thus dissipating energy by means of
defined friction between both sliding
components and stainless steel.
 One particular problem with a sliding
structure is the residual displacements
that occur after major earthquakes.
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21.  Sliding Isolator with Recentering Capacity
 Compared with sliding isolators, sliding isolation pendula (SIPs) with recentering
capacity have a concave sliding plate.
 Due to geometry, each horizontal displacement results in a vertical movement of the
isolator.
 The potential energy, stored by the superstructure, which has been pushed to the top,
automatically results in recentering the bearing into neutral position.
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22.  They remain horizontally flexible, dissipate energy and recenter the
superstructure into neutral position.
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23.  Friction Pendulum System
 The Friction pendulum system (FPS) is a sliding isolation system wherein the weight of
the structure is supported on spherical sliding surfaces that slide relative to each other
when the ground motion exceeds a threshold level.
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24. Isolator Locations
 The requirement for installation of a base isolation system is that the building be
able to move horizontally relative to the ground, usually at least 100 mm.
 The most common configuration is to install a diaphragm immediately above the
isolators.
 If the building has a basement then the options are to install the isolators at the
top, bottom or mid-height of the basements columns and walls.
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26. BASE ISOLATION IN REAL BUILDINGS
 Seismic isolation is a relatively recent and evolving technology. It has been in
increased use since the 1980s, and has been well evaluated and reviewed
internationally.
 Base isolation is also useful for retrofitting important buildings (like hospitals and
historic buildings).
 By now, over 1000 buildings across the world have been equipped with seismic
base isolation.
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27.  In India, base isolation technique was first demonstrated after the 1993 Killari
(Maharashtra) Earthquake.
 Two single storey buildings in newly relocated Killari town were built with rubber
base isolators resting on hard ground.
 After the 2001 Bhuj (Gujarat) earthquake, the four-storey Bhuj Hospital building
was built with base isolation technique.
 All were brick masonry buildings with concrete roof.
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28.  The figure shows the base isolation technique used in the Bhuj Hospital building
with the help of Base Isolators.
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29. APPLICATIONS
 Base isolation provides an alternative to the conventional, fixed base design of
structures.
 Base Isolation minimizes the need for strengthening measures of adding shear
walls, frames, and bracing by reducing the earthquake forces imparted to the
building.
 Base isolation had the effect of reducing the earthquake force demands on the
superstructure to 30% of the demands for a fixed-base structure.
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30. CONCLUSION
 Seismic base isolation method has proved to be a reliable method of earthquake
resistant Design.
 The success of this method is largely attributed to the development of isolation
devices and proper planning.
 Adaptable isolation systems are required to be effective during a wide range of
seismic events.
 Efforts are required to find the solutions for the situations like near fault regions
where wide variety of earthquake motions may occur. 30

31. Thank You… !!!
To
Ms
)
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