2. Earthquake Protective
Systems
Passive Protective
Systems
Hybrid Protective
Systems
Active Protective
Systems
Tuned Mass
Damper
Energy Dissipation
Base Isolation
Active Isolation
Semi-Active
Isolation
Semi-Active Mass
Damping
Active Mass
Damping
Active Bracing
Adaptive Control
Base Isolation is the most common System

3. ActivePassive
 Base Isolation falls into general
category of Passive Energy
Dissipation, which also includes In-
Structure Damping.
 In-structure damping adds
damping devices within the
structure to dissipate energy but
does not permit base movement
Where isolation and/or energy
dissipation devices are powered
to provide optimum
performance.

4.  What is Base Isolation?
 It is a system that may be defined as a
flexible or sliding interface positioned
between a structure and its foundation,
for the purpose of decoupling the
horizontal motions of the ground from
the horizontal motions of the structure,
thereby reducing earthquake
damage to the structure and its
contents.

5. The concept of separating the structure from
the ground to avoid earthquake damage is
quite simple to grasp. After all, in an
earthquake the ground moves and it is this
ground movement which causes most of the
damage to structures. An airplane flying over
an earthquake is not affected.
So, the principle is simple. Separate the
structure from the ground. The ground will
move but the building will not move.

6. Ideal separation would be total. Perhaps
an air gap, frictionless rollers, a well-oiled
sliding surface, sky hooks, magnetic
levitation. These all have practical
restraints.
An air gap would not provide vertical
support; a sky-hook needs to hang from
something; frictionless rollers, sliders or
magnetic levitation would allow the
building to move for blocks under a gust of
wind.

7. The fundamental principle of base
isolation is to modify the response of the
building so that the ground can move
below the building without transmitting
these motions into the building

22.  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(As
shown in Fig (a)). Thus, no force is
transferred to the building due to the
shaking of the ground; simply, the
building does not experience the
earthquake.

24.  Now, if the same building is rested on the flexible
pads that offer resistance against lateral movements
fig (b), then some effect of the ground shaking will be
transferred to the building above. If the flexible pads
are properly chosen, the forces induced by ground
shaking can be a few times smaller than that
experienced by the building built directly on
ground, namely a fixed base building fig (c). 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.

25. As a result, a robust medium-rise masonry or
reinforced concrete building becomes extremely
flexible. The isolators are often designed, to absorb
energy and thus add damping to the system. This
helps in further reducing the seismic response of the
building. Many of the base isolators look like large
rubber pads, although there are other types that
are based on sliding of one part of the building
relative to other. Also, base isolation is not suitable
for all buildings. Mostly low to medium rise buildings
rested on hard soil underneath; high-rise buildings or
buildings rested on soft soil are not suitable for base
isolation.

26. The benefits of using seismic isolation and energy dissipation devices
(“isolators” for simplicity) for earthquake-resistant design are many:
1. Isolation leads to a simpler structure with much less complicated
seismic analysis as compared with conventional structures;
2. Isolated designs are less sensitive to uncertainties in ground motion;
3. Minor damage at the design level event means immediate
reoccupation;
4. The performance of the isolators is highly predictable, so they are
much more reliable than conventional structural components (e.g.
some ductile walls in the Christchurch earthquakes); and finally,
5. Even in case of larger-than-expected seismic events, damage will
concentrate in the isolation system, where elements can be easily
substituted to restore the complete functionality of the structure.

27. The three basic elements in seismic isolation systems that
have been used to date are :
A vertical-load carrying device that provides lateral
flexibility so that the period of vibration of the total system
is lengthened sufficiently to reduce the force response,
A damper or energy dissipater so that the relative
deflections across the flexible mounting can be limited
to a practical design level, and
A means of providing rigidity under low (service) load .

28. Factor of Safety = Column Strength/Earthquake force > 1
Factor of Safety = Capacity/Demand > 1
Capacity > Demand
The earthquake causes inertia forces proportional to
the product of the building mass and the earthquake
ground accelerations. As the ground accelerations
increases, the strength of the building, the capacity,
must be increased to avoid structural damage.

32. 1.SLIDING SYSTEMS
A layer with a defined
coefficient of friction will limit
the accelerations to this value
and the forces which can be
transmitted will also be limited
to the coefficient of friction
times the weight.

35. The building is supported by bearing pads that have a curved
surface and low friction. During an earthquake the building is free
to slide on the bearings. Since the bearings have a curved
surface, the building slides both horizontally and vertically. The
forces needed to move the building upwards limits the horizontal
or lateral forces which would otherwise cause building
deformations. Also by adjusting the radius of the bearings curved
surface, this property can be used to design bearings that also
lengthen the buildings period of vibration.

37. Elastomeric bearings 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. Under a lateral load the
bearing is flexible.

39. Lead-rubber bearings are the frequently-
used types of base isolation bearings. A lead
rubber bearing is made from layers of rubber
sandwiched together with layers of steel. In
the middle of the solid lead “plug”. On top
and bottom, the bearing is fitted with steel
plates which are used to attach the bearing
to the building and foundation. The bearing
is very stiff and strong in the vertical
direction, but flexible in the horizontal
direction.

44. There are some proprietary devices based
on steel springs but they are not widely used
and their most likely application is for
machinery isolation. The main drawback with
springs is that most are flexible in both the
vertical and the lateral directions. The
vertical flexibility will allow a pitching mode
of response to occur. Springs alone have little
damping and will move excessively under
service loads.

45. Rolling devices include
cylindrical rollers and ball
races. As for springs, they are
most commonly used for
machinery applications.
Depending on the material
of the roller or ball bearing
the resistance to movement
may be sufficient to resist
services loads and may
generate damping.

47. 'Earthquake-resistant' technology
enables the building to counter quakes
by making its strength and resilience
great enough to resist shakings. Although
it can protect the building safely, it is ac-
companied by a risk that the furniture
inside could fall or drop.
The technology called 'seismic isolation
structure' which turns destructive seismic
shakings into slower and softer ones
prevents possible damage. This structure
can evade the tremors, taking them in
stride and safeguarding the building, not
mention the human lives and property

48. Response of Base Isolated Buildings
The base-isolated building retains its original, rectangular
shape. The base isolated building itself escapes the
deformation and damage-which implies that the inertial
forces acting on the base isolated building have been
reduced. Experiments and observations of base-isolated
buildings in earthquakes to as little as ¼ of the
acceleration of comparable fixed-base buildings.
Acceleration is decreased because the base isolation
system lengthens a buildings period of vibration, the
time it takes for a building to rock back and forth and
then back again. And in general, structures with longer
periods of vibration tend to reduce acceleration, while
those with shorter periods tend to increase or amplify
acceleration.

49. Feasibility of seismic isolation
Structures are generally suitable for seismic isolation if the
following conditions exist:-
1.The sub soil does not produce a predominance of long period
ground motion.
2.The structure has two stories or more ( or is usually heavy).
3.The site permits horizontal displacements at the base of order 6inches.
4. The structure is fairly squat.
5.Wind lateral loads and other non-earthquake loads are less than
approximately 10% of the weight of the structure.
Each project must be assessed individually and early in design phase to
determine the suitability for seismic isolation.

50. It Includes:
Layout and installation details for the isolation
system depends on the site constraints,
Type of structure
Construction and other related factors.
The following details are provided as an aid in
determining the appropriate layouts for particular
projects and not intended to restrict the designer
in individual cases.
1. Bearing location
2. Connection details