CT.Lakshmanan Assistant Professor (Selection Grade) School of Architecture & Interior Design SRM University Elementary Seismology Prepared by CT.Lakshmanan
Jan 26, 2016
CT.LakshmananAssistant Professor (Selection Grade)School of Architecture & Interior DesignSRM University
Elementary Seismology
Prepared by CT.Lakshmanan
The Vulnerability Profile - India
59% of land mass prone to earthquakes 40 million hectares (8%) of landmass prone to floods 8000 Km long coastline with two cyclone seasons Hilly regions vulnerable to
avalanches/landslides/Hailstorms/cloudburst 68% of the total area susceptible to drought Different types of manmade Hazards Tsunami threat 1 million houses damaged annually + human, economic,
social and other losses
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Prepared by CT.Lakshmanan
Hazard, vulnerability & disaster
Disaster = F (Hazard, Vulnerability)
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Ingredients of RiskH x V - C = R
Hazard x vulnerability – capacity = risk
H - potential threat to humans and their welfareV - exposure and susceptibility to loss of life or dignityC - available and potential resources R - probability of disaster occurrence
Capacity - “resources, means and strengths which exist in households and communities and which enable them to cope with, withstand, prepare for, prevent, mitigate or quickly recover from a disaster”
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Disaster Prevention, Mitigation & preparedness
• Prevention requires the elimination of risk while mitigation is the reduction of risk..
• Disaster Preparedness : Forecast and take precautionary measures in advance of an imminent threat.
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Prepared by CT.Lakshmanan
Seismology The term ‘Seismology’ is derived from Greek word
Seismo, which means earthquake and logos means science; hence the Seismology is Science of Earthquakes
Seismology can be defined in two ways:
1. The science of earthquakes and the physics of the earth’s interior
2. The science of elastic wave (seismic waves)
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CONTINENTAL DRIFT
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Source: from internetPrepared by CT.Lakshmanan
Fault A fault is nothing but a crack or weak zone inside the Earth. When two blocks of rock
or two plates rub against each other along a fault, they don’t just slide smoothly.
As the tectonic forces continue to prevail, the plate margins exhibit deformation as seen in terms of bending, compression, tension and friction. The rocks eventually break giving rise to an earthquake, because of building of stresses beyond the limiting elastic strength of the rock.
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DEPTH OF FOCUS
Shallow focus Earthquakes
< 70 km deep
Intermediate focus earthquakes
70 km ~ 300 km
Deep focus earthquakes
> 300 kmPrepared by CT.Lakshmanan
Magnitude Vs Intensity The magnitude of an earthquake is
determined instrumentally and is more objective measure of its size
Intensity of an earthquake is a subjective parameter based on assessment of visible effects. It depends on factors other than the actual size of the earthquake
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Prepared by CT.Lakshmanan
M > 8 Great Very great
7 - 7.9 Major Great
6 - 6.9 Strong Moderate
5 - 5.9 Moderate Moderate
4 - 4.9 Light Slight
3 - 3.9 Minor Slight
M < 3 Micro earthquake
EARTHQUAKE MAGNITUDE CLASS
USGS IMD
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Magnitude Annual Average No.
M > 8 2
7 - 7.9 20
6 - 6.9 100
5 - 5.9 3000
4 - 4.9 15,000
3 - 3.9 >100,000
GLOBAL EARTHQUAKE OCCURRENCE
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SEISMIC WAVES
Body Waves
Surface waves
Body Waves
Primary waves P-waves
Secondary waves S-waves
Surface Waves
Love waves
Rayleigh waves
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More than 60 % area is earthquake prone.
Zone V 12 %
Zone IV 18 %
Zone III 26 %
Zone II 44 %
Fig. courtesy: nicee
IS 1893:2002
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Casualties during past events
1004 768
8000
38 63
14000
0
2000
4000
6000
8000
10000
12000
14000N
um
be
r o
f d
ea
ths
Bh
uj
Ch
am
oli
Ja
ba
lpu
r
Kill
ari
Utt
ark
as
hi
Bih
ar
(198
8)
(199
3)
(199
7)
(199
9 )
(200
1)
(199
1)
Wh
ere
(w
hen
?)
?
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Earthquake Do Not Kill People
Improperly Designed Structures Do!Prepared by CT.Lakshmanan
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Earthquake Design Philosophy
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IMPORTANT CONSIDERATIONS TO MAKE A BUILDING EARTHQUAKE RESISTANT
1. Configuration
2. Ductility
3. Quality control
4. Base Isolation
5. Passive Energy Dissipating Devices
6. Active Control Systems
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A terminally ill patient , however effective the medication, may
eventually die.Similarly, a badly configured building
Cannot be engineered for an improved performance beyond a certain limit.
1. Configuration
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Regular Configuration• Regular configuration is seismically ideal. These
configurations have low heights to base ratio, symmetrical plane, uniform section and elevation and thus have balanced resistance.
These configurations These configurations would have maximum would have maximum torsional resistance due torsional resistance due to location of shear walls to location of shear walls and bracings. Uniform and bracings. Uniform floor heights, short spans floor heights, short spans and direct load path play and direct load path play a significant role in a significant role in seismic resistance of the seismic resistance of the building.building.Prepared by CT.Lakshmanan
Irregular Configuration
Buildings with irregular configuration
Buildings with abrupt changes in lateral resistance
Buildings with abrupt changes in lateral stiffness Prepared by CT.Lakshmanan
Re-entrant corner
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Discontinuity in diaphragm Stiffness
Discontinuity in Diaphragm Stiffness
FLEXIBLE
DIAPHRAGM
R I G I D
D I A P H R A G MO P E N
Vertical Components of Seismic Resisting System
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Out of plane Offsets
Shear Wall
Out-of-Plane Offset
in Shear Wall
Shear wallsNon-parallel system
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ELEVATION IRREGULARITIES
1) Soft-Storey/Pan-caked 2) Set-backs 3) Connections
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Pancaking
Soft storey
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ELEVATION IRREGULARITIES
4) Pounding 5) Breaks in Columns or Beams
6) Staggered Levels
7) In-fills
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Open ground storey building (soft storey)
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Right or Wrong…?
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Short column effect
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DuctilityLet us first understand how different materials behave. Consider white chalk used to write on blackboards and steel pins with solid heads used to hold sheets of paper together. Yes… a chalk breaks easily!!
On the contrary, a steel pin allows it to be bent back-and-forth. Engineers define the property that allows steel pins to bend back-and-forth by large amounts, as ductility; chalk is a brittle material.
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The currently adopted performance criteria in the earthquake codes are the following:i. The structure should resist moderate intensity of earthquake shaking without structural damage. ii. The structure should be able to resist exceptionally large intensity of earthquake shaking without collapse.
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The strength of brittle construction materials, like masonry and concrete, is highly sensitive to the
1. quality of construction materials
2. workmanship
3. supervision
4. construction methods Prepared by CT.Lakshmanan
Quality control
special care is needed in construction to ensure that the elements meant to be ductile are indeed provided with features that give adequate ductility.
Thus, strict adherence to prescribed standards of construction materials and construction processes is essential in assuring an earthquake-resistant building.
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Elements of good quality control.
1.Regular testing of construction materials at qualified laboratories (at site or away)
2. Periodic training of workmen at professional training houses, and
3. On-site evaluation of the technical work
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IS CODES
IS 1893 (Part I), 2002, Indian Standard Criteria for Earthquake Resistant Design of Structures (5th Revision)
IS 4326, 1993, Indian Standard Code of Practice for Earthquake Resistant Design and Construction of Buildings (2nd Revision)
IS 13827, 1993, Indian Standard Guidelines for Improving Earthquake Resistance of Earthen Buildings
IS 13828, 1993, Indian Standard Guidelines for Improving Earthquake Resistance of Low Strength Masonry Buildings
IS 13920, 1993, Indian Standard Code of Practice for Ductile Detailing of Reinforced Concrete Structures Subjected to Seismic Forces
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Base isolators
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While Hazards Are Inevitable, Each Hazard Need Not Convert
Into A Disaster… As What Comes In Between Is The Culture of Safety And Prevention
Let us Work Together to Build a Culture of Prevention !
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