base isolation engineering

By:-Shreeja GuhaShaikh Aliya

Namrata RenukaAditi

Technical Seminar Report on

Guided by: Mr.

What is Base IsolationStudy of EarthquakeIntroductionEffects of EarthquakeBase IsolationPrinciple of Base IsolationIsolation ComponentsElastomeric IsolatorsSliding IsolatorsBase Isolators in real buildingApplicationsConclusions

What is Base Isolation?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”.

To know the detail of Base Isolation first of all we

need to know what is seismic waves.

Lets Start

Earthquake

An Earthquake is the result of a sudden release of

energy in the Earth’s crust that creates seismic

waves.

Introduction

Earthquake by itself, is not a disaster, it is natural phenomenon

result from ground movement, sometimes violent.

These produce surface waves, which cause vibration of the

ground and structures standing on top.

Depending on the characteristics of these vibrations, the ground

may develop cracks, fissures and settlements.

Here we can see that major part of India is prone to Earthquake, that’s

why need of Base Isolation is in high demand to meet the crisis.

The possible risk of loss of life adds a very serious dimension to

seismic design, putting a moral responsibility on structural

engineers.

In recent times, many new systems have been developed, either

to reduce the earthquake forces acting on the structure or to

absorb a part of seismic energy.

One of the most widely implemented and accepted seismic

protection systems is Base Isolation.

Introduction…

Effects of Earthquake

Base IsolationBase isolation is one of the most widely accepted seismic

protection systems in earthquake prone areas.

It mitigates the effect of an earthquake by essentially isolating the

structure from potentially dangerous ground motions.

(a) Conventional structure (b) Base isolated structure

BASE ISOLATION…

Seismic isolation is a design strategy, which uncouples the

structure for the damaging effects of the ground motion.

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.

Buildings with foundation base fixed to the

super structure are known as Fixed base.

Buildings with rubber or similar isolation

between to base foundation and structure

are known as Base isolated buildings.

BASE ISOLATION…

Principle of Base Isolation

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.

For this type of structure, when the ground beneath the structure

moves there will be zero acceleration induced in the structure and

the relative displacement between the structure and ground will

be equal to the ground displacement.

So in flexible structures the structure will not move, the

ground will.

Principle of Base Isolation…

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

Elastomeric Isolators

These are formed of horizontal layers of natural

or synthetic rubber in thin layers bonded

between steel plates.

Isolation Components…

Natural Rubber Bearing Low-Damping Rubber Bearing

Lear-core Rubber Bearing High-Damping Rubber Bearing


Sliding IsolatorsIn 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.


Friction Pendulum System

Resilient Friction System


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.

Base Isolation in Real Building

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.

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.

Any Queries???

Thank you

base isolation engineering

Technology