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EARTHQUAKE RESISTANT

ARCHITECTURE

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Source: Kobe I EERI - Slide #43

E RTHQU KES

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Earthquakes are a natural phenomena, like drought, flood

and Cyclones.

Earthquakes in simple terms is a sudden trembling or shaking

movement of the earth surface.

Larger earthquakes usually preceded by tremors and some violent

shocks and followed by smaller earthquakes of diminishing size

called aftershocks.

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What are Earthquakes?

Source: www.earth.leeds.ac.uk/dynamicearth

- Energy is released.

- Movement of fault

blocks takes place

along a fault plane.

A sudden release of

energy accumulated indeformed rocks

causing the ground to

tremble or shake.

- Causes rupturingor brittle failure of

crustal rocks.

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INSIDE EARTH

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Layers of the Earth

By analyzing the seismograms from many

earthquakes, scientists have discovered

that three main levels o r shel ls existwithin the Earth:

MANTLE

The region just below

the crust and

extending all the way

down to the Earth'score is called the

mantle. The mantle, a

dense, hot layer of

semi-solid rock

approximately 2,900km thick.

CORE Beneath the mantle is the Earth's core.

The Earth's core consists of a fluid outer core and

a solid inner core.

CRUST

The Earth's outermost surface is

called the crust. The crust is

relatively light and brittle. Mostearthquakes occur within the crust.

Scientists believe that below the

lithosphere is a relatively narrow,

mobile zone in the mantle called the

asthenosphere (from asthenes, Greek for weak).

Source: www.thetech.org

http://www.thetech.org/exhibits_events/online/quakes/inside/mantle.html

http://www.thetech.org/exhibits_events/online/quakes/inside/core.html

http://www.thetech.org/exhibits_events/online/quakes/inside/mantle.html

http://www.thetech.org/exhibits_events/online/quakes/inside/crust.html

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BASIC TERMINOLOGY

Earthquake

Hypocentre or focus

Epicentre

Focal depth

Epicentral dis tance

Origin t ime

Foreshocks and Aftershock s

Fault

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Earthquake Magnitude

• It is measured on Richter Scale and is

related to the logarithm (base 10) of theamount of energy released by an

earthquake.

• The magnitude M of an earthquake isrelated to the energy released at the focus

of the earthquake, and is given by the

approximate formula

Log E ( ergs) = 11. 8 + 1.5 M

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• The smallest earthquake perceptible by

human being corresponds to the

magnitude of 2• largest and most destructive earthquake

so far known to have occurred has been

assigned a magnitude 8.7.• The damage from an earthquake starts

from magnitude 5 and above.

• Earthquakes are often classified intodifferent groups based on their size

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SEISMIC WAVES

Seismic waves are of two types

Body waves

Surface waves

Body waves consist of Primary waves (P-waves) and

Secondary

waves (S-waves)

Surface waves consist of Love waves and Rayleigh

waves

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Arrival of seismic wave at a site

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Types of Waves

Fastest waves

Do not travel through

liquid

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Seismic Hazards

• Ground shaking

• Structural hazards

• Liquefaction• Landslides

• Retaining structures failure

• Lifeline hazards• Tsuanami

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Classification of earthquakes• Based on location

– Interplate

– Intraplate

• Based on epicentral distance – Local earthquakes < 1º

– Regional earthquakes 1 - 10 º

– Teleseismic earthquakes > 10º• Based on Focal depth – Shallow depth 0-71 km

– Intermediate depth 71-300 km

– Deep earthquake > 300km

• Based on Magnitude

– Micro earthquake < 3 – Intermediate earthquake 3-4.9

– Moderate earthquake 5-5.9

– Strong earthquake 6-6.9

– Major earthquake 7-7.9

– Great earthquake > 8

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Indian Subcontinent: among the world’s most disaster proneareas

65% of land vulnerable to Earthquakes

8% of land vulnerable to Cyclones

5% of land vulnerable to Floods

> 1 million houses damaged annually + human, social, other losses

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PAST EARTHQUAKES IN INDIA

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Seismic Zone

Map of

India:

Year-1962

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Seismic Zone

Map of

India:

-1966

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Seismic Zone

Map of

India:

-1970

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Seismic ZoneMap of

India:

-2002 About 65 percent of theland area of India is

liable to seismic hazard

damage (about 26%

under MSK Intensity

VII, 18% under VIII and12% under IX and

higher).

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Earthquake Risk

•Hazard = Probability of ground motion

•Site effects = Soil properties, topography

presence of Reservoirs (RIS),

Mines (MIS)

• Vulnerability = Building types, Age

•Risk = Hazard x Site effects x Vulnerability

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VULNERABILITY

• 1819 Gujarat [Kutch] 8.0 (2000 deaths)

• 2001 Gujarat [Bhuj] 6.9 (13805 deaths)

•

Increased vulnerability in two centuries

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EFFECT OF SEISMIC FORCES

ON STRUCTURES

• Inertia Forces in Structures

– From Newton’s First Law of Motion, even

though the base of the building moves

with the ground, the roof has a tendency tostay in its original position

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– If the roof has a mass M and experiences an acceleration a, thenfrom

inertia force = Ma ( direction is opposite to acc.) Clearly, moremass means higher inertia force. Therefore, lighter buildings

sustain the earthquake shaking better.

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Twisting

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Design aspects of Earthquake

resistant buidings

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Design aspects of RCC

buildings

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