Microsoft Word - BASE ISOLATION

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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 Safety Berkeley Public Safety Berkeley Public Safety Berkeley 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: / /