This document provides a summary of base isolation as a seismic retrofitting technique. It defines base isolation as decoupling a structure from its foundation to protect it during earthquakes. It describes different types of base isolators using materials like rubber, lead and steel. Advantages include reducing structural damage, secondary damage, and maintenance costs. Disadvantages include challenges implementing for tall buildings. Examples of base isolated structures worldwide and in India are given. The document concludes with suggestions for government initiatives to develop this technology in India.

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BASE
ISOLATION
Report submitted by.
Sumeet Srivastav
3rd
year, Civil Engineering
B-tech
Section-CE (B),Roll No-27601312111.
Subject- Seminar
Subject code- CE 681

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CONTENTS
Acknowledgement.
Introduction.
What is Retrofitting?
Types Of Retrofitting.
What is Base Isolation?
Design principle of Base isolation
Difference between Base Isolation and Other Retrofitting Techniques.
Advantages of Base Isolation.
Disadvantages of Base Isolation.
Types Of Base Isolators.
Materials Used For Base Isolators.
Base Isolators Are Economic Solution.
Comparison Of Base Isolated Structures From Fixed Base Structures.
Base Isolation In India.
Famous Projects in the World Using Base Isolation.
Some Companies Using Base Isolation.
Government Initiatives.
An Advice for Developing This Kind Of Technology.
References.

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Acknowledgement
Before going into the report,I would like to thank and acknowledge my respected
faculties here for their help, their guidance and their support throughout the duration of
completion of this project.
Introduction
In this report the task is to describe the retrofitting techniques with Base Isolation as an
example, advantages of base isolation, compare its utilities to other techniques, discuss
about the government initiatives, brief discussion on how to make this technology
developed for future purposes.
Retrofitting
Seismic retrofitting is the modification of existing structures to make them more
resistant to seismic activity, ground motion, or soil failure due to earthquakes.
Types of Retrofitting Techniques

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Base Isolation
Base isolation, also known as seismic base isolationor base isolation system, is one of the most
popular means of protecting a structure against earthquake forces.It is a collection of
structural elements which should substantially decouple a superstructure from its
substructure resting on a shaking ground thus protecting a building or non-building structure's
integrity.
Base isolation is one of the most powerful tools of earthquake engineering pertaining to the
passive structural vibration control technologies. It is meant to enable a building or non-
building structure to survive a potentially devastating seismic impact through a proper initial
design or subsequent modifications. In some cases, application of base isolation can raise both
a structure's seismic performance and its seismic sustainability considerably.
Base isolation system consists of isolation units with or without isolation components, where:
1. Isolation units are the basic elements of a base isolation system which are intended to
provide the aforementioned decoupling effect to a building or non-building structure.
2. Isolation components are the connections between isolation units and their parts having
no decoupling effect of their own.
Design Principle Of Base Isolation
• The main principal of base isolation is to try and isolate the structure from the ground
movement so you could just about put it on ball bearings if you like and the ground
could move underneath it and the building stays still.
• Seismic isolation is important for two reasons, one it protects the structure, now it is
possible always to build a strong enough structure, however it may not be economic.
You can reduce the forces being transmitted to the building, in an earthquake, by
following a seismic isolation approach. Now the most important thing is that seismic
isolation protects the contents.

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Difference between Base Isolation and other Retrofitting
Techniques
Base Isolation is different because ….
It can be applied just under
the structure and still saves
a major amount of
destruction other than
other retrofitting
techniques.
The buildings which are
retrofitted , after an
earthquake has passed
,their maintanance cost is
higher than a base isolation
building.
The building with base
isolation is much cost
effective than a building
which is retrofitted.

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Advantages
Widely held misconception that seismic isolation is expensive.
Structural Damage is restricted when the structure is built on a suitable
seismic isolating system.
Damage to indoor services and facilities would be of little concern which
would normally affect gas, water or sewage leakage for unfortified structures. The
base isolation will protect the structure by preventing plastic deformation of
structural elements, because the super structure demonstrates elastic behavior
during initial and following excitation of the base.
Secondary damage as a result of falling furniture would be restricted. In other
words, the level of safety is increased significantly when using base isolation system
rather than conventional systems.
The function of buildings can be ensured during an excitation or even after a major
earthquake as super structure is designed to remain elastic. Therefore, plastic
deformation of structural elements can be prevented and the building is still a safe
place to remain and life can continue as normal.
Base isolation can be retrofitted to suitable existing structures but too many
variables to give meaningful indication of cost
Highly effective in reducing the peak acceleration transmitted to the
superstructure. Thus, the deflections and stresses generated in a base-isolated
structure are significantly lower than those of a fixed-base one
Structures can include buildings, bridges, storage containers, tanks, power facilities
and most other structures requiring protection from damagingforces of
earthquakes, and vibration in general.
Base isolation allows for a reduction in structural elements of the building with less
ductile detailing needed.

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Crawl spaces or basements can have multiple benefits e.g. in siting services,
additional income from a carpark, flexibility for future development.
Protection of the CONTENTS – with controlled movement caused by seismic
isolators contents are not subject to violent and sudden shakes thereby reducing
the impact on the contents.
Protection of the integrity of the internal structures e.g. stairs, internal walls, and
partitions.
Building is safer for occupants and contents are protected.
Continuity of operations is much more likely.
Widely held misconception that seismic isolation is expensive.
When viewed against the savings it can in some cases result in a slightly lower
construction cost overall
Building can remain serviceable throughout construction
Does not involve major intrusion upon existing superstructure
Isolates Building from ground motion
Lesser seismic loads, hence lesser damage to the structure.
Minimal repair of superstructure.
Disadvantages
Cannot be applied partially to structures unlike other retrofitting
Challenging to implement in an efficient manner
Allowance for building displacements

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Inefficient for high rise buildings
Not suitable for buildings rested on soft soil.
Coupled foundations allow motion of some modes of the structure to include a
participating soil mass which increases inertia for these modes, and would also allow
energy to radiate back into the soil. A Base Isolated building is decoupled from the soil
by the isolators. The lower support stiffness of the isolators makes the building more
susceptible to wind induced motion.
Types of Base Isolators
• Base isolation systems which uses Elastomeric Bearings
• Base isolation systems with Sliding System
Elastomeric Base Isolation Systems
• This is the mostly widely used Base Isolator.
• The elastomer is made of either Natural Rubber or Neoprene.
• The structure is decoupled from the horizontal components of the earthquake ground
motion.
A layer with low horizontal stiffness is introduced between the structure and the
foundation.
Fig: Steel Reinforced Elastomeric Isolators

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Sliding Base Isolation Systems
It is the second basic type of isolators.This works by limiting the base shear across the isolator
interface.
Spherical Sliding Base Isolation Systems
Spherical Sliding Isolation Systems are another type of base isolation.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 bearing. Since the
bearings have a curved surface the building slides both vertically and horizontally.

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Friction Pendulum Bearing
These are specially designed base isolators which works on the principle of simple pendulum.It
increases the natural time period of oscillation bycausing the structure to slide along the
concave inner surface through the frictional interface.It also possesses a re-centering
capability.
Fig: Cross-section of Friction Pendulum Bearing
Materials Used For Base Isolators
Lead rubber bearings were developed as base isolators in the 1970s. They consist of three
basic components – a lead plug, rubber and steel, which are generally placed in layers.
Rubber
The rubber provides flexibility through its ability to move but return to its original position. At
the end of an earthquake, if a building hasn’t returned to its original position, the rubber
bearings will slowly bring it back. This might take months, but it will return to its original
position.
Image: Lead rubber bearings

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Lead
Lead was chosen because of its plastic property – while it may deform with the movement of
the earthquake, it will revert to its original shape, and it is capable of deforming many times
without losing strength. During an earthquake, the kinetic energy of the earthquake is
absorbed into heat energy as the lead is deformed.
Steel
Using layers of steel with the rubber means the bearing can move in a horizontal direction but
is stiff in a vertical direction.
Base Isolators Are Economic Solution
1. Base isolation allows for a reduction in structural elements of the building with less
ductile detailing needed
2. Widely held misconception that seismic isolation is expensive
3. E.g. Union House built in Auckland in 1983 with base isolation produced an estimated
7% cost saving in the total construction cost of $6.6m which included a construction
time saving of 3 months due to the structural form requiring less seismic force, ductility
demands and structural deformations
4. As a general rule the inclusion of all aspects of seismic isolation in a new structure will
add no more than 3% to total construction cost and considerably less when assessed
against the benefits of isolation
5. Contrary to belief, seismic isolation devices require no maintenance during the life of
the building
6. Following any significant event they should be inspected to ensure bolts and load plates
are still in place.
7. Devices do not need replacing after an earthquake unless the event was in excess of their
design specification in which case we recommend the removal of some devices for testing.
8. Because the building is protected from major damage, repair costs following an
earthquake will be lower to non-existent

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9. We remain convinced of the effectiveness ONLY of seismic isolation in the protection
not only of the external structure but also the contents and in maximizing the potential
for immediate business continuation.
Comparison of Base isolated structures from Fixed Based
Structures:
COMPARISON OF STORY DISPLACEMENTS FOR THE FB AND IB STRUCTURE FOR LOAD CASE
DL+SLL+EQY
COMPARISON OF QUANTITY OF REINFORCEMENTS
Analytically it has been show that lead rubber bearings can bring about 20% savings in the
reinforcement used. Since the building does not undergo any deformation but only gets
displaced, the hospital is still serviceable after the occurrence of the design earthquake. A
further study can be made where a comparison of a building with shear wall with a building
equipped with base isolators is done in order to estimate the reduction in concrete quantity.

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Base Isolation In India
The idea of base isolation has not been fully integrated in our India.Though India also suffers
from Earthquake Zones 4 and Zones 5 which are under the area of Gujarat and Kashmir, Ran of
Kutch and the Himalayas, It still needs base isolation in these parts of India to protect the
buildings(official and residential) and hospitals and some historic buildings and monuments for
which India is famous for.
India is also in need of some techniques of base isolation which they could apply and be safe
from Earthquake damage and destruction. Since this technology is still growing in India, it’s a
little costly compared to India which is still developing.
Examples- Bhuji Hospital which was funded by the New Zealand Government as part of its International Aid
Programe. The new 30,000m² hospital is the first building in India to be fitted with the technology. It is reputed to be
able to stand a force 10 tremor on the Richter scale. The system is maintenance-free and does not incorporate
electronics. It's just rubber and lead..
BhujiHospital ,GujratProvince,India

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Famous Projects In the World Using Base Isolation
MM 21,JapanMM 21,JapanMM 21,JapanMM 21,Japan
XXXXindian Hospital, Taiwanindian Hospital, Taiwanindian Hospital, Taiwanindian Hospital, Taiwan
Berkeley Public SafetyBerkeley Public SafetyBerkeley Public SafetyBerkeley Public Safety
BuldingBuldingBuldingBulding

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Asian Art Museum,Asian Art Museum,Asian Art Museum,Asian Art Museum,
USAUSAUSAUSA
Coronado Bay Bridge, USACoronado Bay Bridge, USACoronado Bay Bridge, USACoronado Bay Bridge, USA
Utah State Capitol,Utah State Capitol,Utah State Capitol,Utah State Capitol,
USAUSAUSAUSA

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Name Of Some Companies Using Base Isolation
Dynamic Isolation Systems, USA
Holmes Consulting Group, New Zealand
Arup Group Limited
Seismic Isolation Engineering Incorporation,Emeryville, CA (USA)
Government initiatives:
As Government Initiatives, I would like to suggest,
1. Initiation of Base Isolation techniques in the concept of new buildings in
some required parts of India.
2. Setting up a full scale 3D Earthquake testing facility to test the behavior of 2
to 3 stories models of isolated buildings or retrofitted buildings before they
are actually developed in the project area.
3. As we are fully aware that the laborers in our country have limited
knowledge about technology going on in the world, so we must need to train
them and make them aware of such kind of technologies.
A Suggestion By Me
As a report maker I studied it as much as possible with in a very short period. So I would
like to suggest initiating some comparative studies on Base Isolation. Thus it can be used
easily in our country which can show an economic solution.

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References
Commercial Internet Sites:
www.wikipedia.com
http://www.youtube.com
http://www.robinsonseismic.com
www.ijetch.org
www.academia.edu
Some Universities And Organizations Papers
1. ISET Journal Of Earthquake Technology
2. Journal of Engineering Research and Applications
3. International Journal of Emerging Technology and Advanced Engineering
4. Indian Institute of Technology (Kanpur).
Thanking You.
Date of Submission: / /