introduction, principle, concepts, types of base isolation, application

1. BASE ISOLATION
1.What is base isolation system?
 Base Isolation Is One Of The Most Important Concepts For Earthquake Engineering
Which Can Be Defined Is Separating Or Decoupling The Structure From Its Foundation.
 Base Isolation Technique developed to prevent or minimize damage to building during
an earthquake.
 One of the most widely implemented seismic protection system is base isolation.
 The terms isolation refers to reduced interaction between structure and the ground.
2.Concept of base isolation system
 Base isolation is explained through an example of building resisting on frictionless
rollers.
 When the ground shakes, the roller freely roll, but the building is not move.

Thus, no force transferred to the building due
to shaking the ground. Because roller is absorbed whole shock. So building does not
experience the earthquake.
 High rise buildings or building rested on soft soil are not suitable for base isolators.
 Most suitable structures for base isolation are low or medium rise building.
3.Principle of base isolation system
 The fundamental principle of base isolation to modify the response of building so that
the ground can move below the building without transmitting these motion into the
building and other structure.
 The structure and ground moves the same amount.
 So in flexible structure the structure will not move with the ground.

2.  The structure is perfectly rigid will have zero period.
 Structure without base isolator is severe shaking with ground.
 Structure with base isolator is moving horizontally slow with isolators.
4.When base isolation system is suitable?
 The sub soil does not produce a long period ground motion.
 When the structure is jointed sufficiently with high column load.
Lateral load due to wind are less than approximately 10% of the structure weight.
5. Difference between fixed and isolated base structure
 When the earthquake is affected on fixed base structure at that time structure is not
defending against earthquake.
 But in base isolated structure the when earthquake is affected on the structure building
is defending against earthquake very well.
 In fixed structure, structure is moves with ground motion.
 In isolated structure, structure is not moves with ground motion. But isolation bearing is
moves with ground motion. So we can say the structure is safe.

3. Isolators
elastomeric isolators
Natural rubber
bearing
low damping
rubber bearing
lead rubber
bearing
High damping
rubber bearing
sliding isolators
flat sliding
bearing(resilient
friction system)
spherical sliding
bearing(friction
pendulum system)
6. Types of base isolators

4. 7. Elastomeric base Isolators
 These are formed of horizontal layers of natural oy synthetic rubber in thin layers
bonded between steel plates.
 The steel plate prevent the rubber layers, so the bearing is able to support higher
vertical loads with only small deformation.
 Plain elastomeric bearing provides flexibility and will move under service loads.
7(a). Low damping natural rubber bearing
 Damping ratio = 2% to 3%
 Manufacturing is easy. Response not strongly sensitive temperature, rate of loading and
aging.
 Shear strain is exceed up to 100%.
7(b). High damping natural rubber bearing
 Damping is increased by adding extra-fine carbon black, oils or resins and other fillers.
 Maximum shear strain = 200 to 350%
 Damping ratio = 10 to 20% at 100% shear strain
 Effective damping depends on:

5. -velocity of loads
-load history
-temperature
7(c). Lead rubber bearing
 Damping properties can be improve by plugging a lead core into bearing.
 Damping of the lead-plug bearing varies from 15% to 35%.
 The performance depends on the lateral force.
 Maximum shear strain = 125 to 200%
8. Sliding isolators
 The second most common type of isolation system uses sliding elements between
the foundation and base of the structure.
 By high tension springs or laminated rubber bearing by making sliding curved
surface.
 These mechanisms
provide a restoring
force to return the
structure to its
equilibrium position.

6. 8(a). Flat sliding isolators (resilient friction sys.)
 Two types of flat sliding isolators :
1. With recentering capacity
2. Without recentering capacity
8(b). Spherical sliding isolators (Rollers)
(Friction pendulum)
 the friction pendulum system is
sliding isolation system where in
the weight of the structure is
supported on spherical sliding
surfaces that slide relative to
each other when the ground
motion exceed a threshold level.

7. 9. Advantages
 Reduced the seismic demand of structure, thereby reducing the cost of structure.
 Less displacement during the earthquake.
 Improves safety of structure.
 Reduced damages caused during the structure.
10. Disadvantages
 Challenging to implement in an efficient manner.
 Allowance for building displacements.
 Inefficient for high rise buildings
 Not suitable for buildings rested on soft soil.
11. Applications
 Bridges
 Buildings
 Historic structure

8. 12. Real life applications
(1). Tomb-of-Cyrus, Iran.
World’s first base isolated structure.
(2). New hospital building, Bhuj
Base isolated building