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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.

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

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BASIC TERMINOLOGY

Earthquake

Hypocentre or focus

Epicentre

Focal depth

Epicentral dis tance

Origin t ime

Foreshocks and Aftershock s

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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

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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:

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Seismic Zone

Map of

India:

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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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