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A Seminar On Base Isolation using dampers in Civil Engineering CIVIL ENGINERING DEPARTMENT INDIAN INSTITUTE OF TECHNOLOGY VARANASI-221005 Prepared By: Shubham Dubey (11403EN001)

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Page 1: Shubham Dubey Seminar

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A

Seminar

On

“ Base Isolation using dampers in

Civil Engineering” 

CIVIL ENGINERING DEPARTMENT

INDIAN INSTITUTE OF TECHNOLOGY

VARANASI-221005

Prepared By: Shubham Dubey (11403EN001)

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CONTENTS

• What is seismic force?

• Difference between magnitude and intensity.

• Natural hazards due to earthquake.

• Basic concept of earthquake resistant diesign.

• Requirements and different types of base isolation devices.

• Case study –  Los Angeles city hall

• Bibliography.

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WHAT IS SEISMIC FORCE?

Seismic Forces is generated due to

Earthquake.

Earthquake is a natural disaster. It is a violent shaking of earth.

It happens due to mass shifting in

 bedrock.

Because it is a natural disaster so

we can’t control it. Only we can

try that the damage should be

minimum.

Bhuj Earthquake, 2001

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Different Seismic Zones In India

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MAGNITUDE AND INTENSITY

OF EARTHQUAKE1. MAGNITUDE

• The Magnitude (M) is a quantitative measure of its strength in

terms of energy released .

•  It is defined as logarithm to the base 10 of the maximum trace

amplitude, expressed in microns, which the standard short-

 period torsion seismometer would register due to theearthquake at an epicentral distance of 100 km.

It is measured in R ichter’s scale.

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2. INTENSITY

The intensity of an earthquake is measured qualitatively in

terms of damages caused by it at a particular location.

In general, larger the earthquake, greater is the intensity

It is indicated by a number according to the modified Mercalli Scale or

M.S.K. Scale of seismic intensities 

Magnitude of an earthquake is a measure of its

size. While intensity is an indicator of the severity

of shaking generated at a given location.

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HAZARDS DUE TO EARTHQUAKE

a) Liquefaction of Soils

 b) Ground Shaking

c) Surface Ruptured) Landslides

e) Lateral Spreading

f) Shear Failure of Foundation

g) Settlements of Structures

h) Failure of Retaining Wall

i) Tsunamis And Seiches

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CONVENTIONAL CONSTRUCTIONPRACTICE ASSUMES FIXED BASE

STRUCTURES

• The Dynamic Characteristics of Fixed Base Structures are

determined by the general characteristics of the structuralsystem

• The Designer can only slightly adjust those DynamicCharacteristics

•  As a matter of fact, most common Building Structures haveunfavorable Dynamic Characteristics that result in increasedSeismic Response

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EARTHQUAKE PERFORMANCE

OF FIXED BASE STRUCTURES

• Conventional Fixed Base Structures can not be realistically

designed to remain elastic in large seismic events (more soin regions of high seismicity)

• Common practice is to design them so that they experiencedamage in a controlled manner and have large inelastic

displacements potential

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EARTHQUAKE-RESISTANT DESIGN

Objective of Earthquake-Resistant Design is to make such

 buildings that can resist effect of ground motion and would not

collapse during the strong Earthquake.

All the components of the structure and foundations are

designed to resist inertia forces in addition to the normal

forces.

All the walls must be jointed properly, so that they can act

together against the earthquake shaking at the time of seismic

force transferring to the ground.

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BASE ISOLATION METHOD

The idea behind the Base Isolation is to detach (isolate) the building

from the ground in such a way that earthquake motions are not

transmitted up through the building, or at least greatly reduced.

If a building is rested on flexible pads that offer resistance against

lateral movements, 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. 

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BASIC IDEA BEHIND BASE

ISOLATION

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THE CONCEPT OF BASE

ISOLATION

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THE CONCEPT OF BASE ISOLATION

Fixed Base

Base IsolatedPeriod

Significantly Increase thePeriod of the Structure and the

Damping so that the Response

is Significantly Reduced

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EFFECT OF BASE ISOLATION

METHOD

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View of Basement in Bhuj Hospital Building

BASE ISOLATION METHOD

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• REQUIREMENT OF BASE

ISOLATION DEVICES

•  Isolating the building from the ground

•  Supporting the weight of building

•  Damping of response amplitude

•  Restoring the original position after an earthquake

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SEISMIC DAMPERS

Seismic Dampers are fixed in place of structural elements as

diagonal braces.

They absorb a part of seismic energy when it is transmitted through

them.

TYPES OF SEISMIC DAMPERS:

a. Viscous DampersEnergy is absorbed by silicone-based

fluid passing between piston-cylinder

arrangement.

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Viscous Damper

SEISMIC DAMPERS

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SEISMIC DAMPERS

 b. Friction Dampers

Energy is absorbed by surfaces with

friction between them rubbing against

each other

c. Yielding Dampers

Energy is absorbed by metallic

components. 

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Friction And Yielding Dampers

SEISMIC DAMPERS

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Steel damper

Lead

damper

BASE ISOLATION SYSTEM DAMPERS

Oil damper

Friction damper with

Coned disc springs 

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MAINTENANCE

•  Large relative displacement at isolation interface occurs during strong

earthquake. Thus, obstacles in or in the vicinity of isolation interface

spoil efficient seismic performances.

•  Some isolation devices deteriorate by aging. Aged deteriorations must beconsidered by heat accelerated tests and others at design stage.

•  Rubber bearings creep subjected to long term loads. Unexpected creeps

and external damages must be found out by regular examinations.

•  Breaks, water leakage and others may happen when piping and wiringhave insufficient deformation capacities.

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LOS ANGELES CITY HALL

• Building was severely damaged during the 1989 Loma

Prieta earthquake

• Building is listed on the historic register –  Retrofit had to

 preserve the interior architecture and the historic fabric ofthe building

• Both conventional fixed-base and base isolation retrofit

concepts were studied

• The most economical and effective method was determined

to be base isolation

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LOS ANGELES CITY HALL

Isolation System:

• 111 rubberisolation bearings

• 36 of them with

lead cores

Fixed Base Base Isolated

Earthquake Response

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LOS ANGELES CITY HALL

Critical Construction Issues:

• Temporary lateral bracing during construction period to

safeguard against possible earthquake occurrence

• Symmetric work sequence was important to reduce the

possibility of torsional response in the event of an

earthquake

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CONCLUSION

• Thus the conclusion is that

base isolation is the most

appropriate and economical

way of designing a seismic

load resisting multi storeystructure . Moreover, research

work is going on whether the

absorbed seismic energy can

be utilized in some or the

other way.

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BIBLIOGRAPHY

• Calvi, G.M., (2010). L’Aquila Earthquake 2009: Reconstruction between Temporary and

Definitive. Proceedings, NZSEE 2010 Annual Conference. Wellington.

• Christopoulos, C. and Filiatrault, A., (2006). Principles of Passive Supplemental Damping and

Seismic Isolation. IUSS Press. First edition. Pavia, Italia.

• Dowrick, D.J., (1988). Earthquake Resistant Design. John Wiley & Sons, Chichester, UK.

• Rodgers G.W., Solberg, K.M., Mander J. B., Chase, J.G., Bradley, B.A., and Dhaka R.P.,

(2011). ‚High-Force-to-Volume Seismic Dissipaters Embedded in a Jointed Pre-Cast Concrete

Frame‛. ASCE Journal of Structural Engineering (JSE), ISSN: 0733-9445, (In Press).

• Rodgers, G.W., Solberg, K.M., Chase, J.G., Mander, J.B., Bradley, B.A., Dhakal, R.P. and Li,

L.,

• (2008). ‚Performance of a damage-protected beam-column subassembly utilizing external

• HF2V energy dissipation devices‛. Earthquake Engineering and Structural Dynamics, Vol. 37,

No. 13, pp. 1549-1564.

• Skinner, R.I., Kelly, T.E., Robinson, W.H., (2000). ‚Seismic Isolation for Designers and

Structural Engineers‛. Robinson Seismic Ltd. and Holmes Consulting Group, Wellington.

• Zayas, V.A. et al., (1990). A Simple Pendulum Technique for Achieving Seismic Isolation. 

Earthquake Spectra.pp. 317, Vol.6, No.2.

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