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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
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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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