The document discusses various topics related to earthquakes and seismic design including: 1. Plate tectonics theory explains how the lithosphere is broken into plates that move relative to each other, causing earthquakes along plate boundaries. 2. Earthquakes are measured on the Richter scale and can cause damage depending on factors like magnitude, distance from epicenter, and soil properties. 3. Seismic design codes aim to prevent collapse from major earthquakes through concepts like ductility, overstrength, and redundancy while allowing some damage from minor quakes. 4. Dynamic analysis methods like response spectrum and time history are used to design important structures, while the equivalent lateral force method is commonly used for other

1. Earthquakes and Seismic Design
By Dr. N. Subramanian
3rd Nov. 2012

2. Cross-section of Earth
Though we have explored Space above ground extensively, we
could go only about 7.6 miles below ground! Russian
geologists started drilling into the Kola Peninsula, near
Finland, in 1970 and after 22 years could not proceed further.

3. Plate tectonics- Alfred Wegener
, 1912
Dr. N. Subramanian

4. Plate tectonics (PT)
 Earlier theories assume gradual shrinking
(contraction) or gradual expansion of the globe.
 PT is based on continental drift & developed in early
20th century
 Lithosphere is broken up into 7-8 major tectonic
plates, and numerous smaller plates
 Tectonic plates move – because lithosphere has a
higher strength and lower density than the underlying
asthenosphere- Dissipation of heat from the mantle is
the source of energy
 Lateral relative movement of the plates- 0 to 100 mm
annually
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5. Three types of plate boundaries exist
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6. Global earthquake epicenters, 1963–
1998
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7. Aerial view of San Andreas Fault in the Carrizo
Plain, northwest of Los Angeles
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8. Earthquakes
• Around 500,000 earthquakes occur each
year, detectable with current instrumentation.
About 100,000 of these can be felt.
• Human activities that produce minor
earthquakes:
– Storage of large water behind a dam,
– Injecting liquid under high pressure into wells
(fracking to extract natural gas),
– Coal mining
– Oil drilling
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9. Recurrence of Earthquakes
• Average recurrence of Earthquakes are:
– Earthquake of M3.7–4.6 every year,
– Earthquake of M4.7–5.5 every 10 years,
– Earthquake of 5.6 or larger every 100 years.
• The United States Geological Survey
estimates that, since 1900, there have been
an average of 18 major earthquakes (M 7.0–
7.9) and one great earthquake (M 8.0 or
greater) per year.
Dr. N. Subramanian

10. Aftershocks
 An aftershock is an earthquake that occurs after a
previous earthquake, the mainshock.
 It occurs in the same region of the main shock but
always of a smaller magnitude.
 If it is larger than the main shock, the aftershock is
redesignated as the main shock and the original main
shock is redesignated as a foreshock.
 Formed as the crust around the displaced fault plane
adjusts to the effects of the main shock
 They are dangerous - usually unpredictable, can be of
a large magnitude, and can collapse buildings that are
damaged from the main shock
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11. Earthquakes-Epicenter
Epicenter is the point on the Earth's surface that is directly above the
hypocenter (where the Strain energy stored in the rock is first released)
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12. EARTHQUAKES
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13. Earthquake Prediction Instrument...
from ancient China
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14. Seismograph is used to measure wave
amplitude
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15. Can we predict earthquakes
correctly?
• Long ago, Catholic Church in Rome condemned
Galileo Galilei and put him under house arrest
for teaching ‘Earth revolves around the sun’!
• Now, (Oct 22, 2012) an Italian court convicted
seven scientists and experts for 6 years in prison
for failing to adequately warn citizens before an
earthquake struck central Italy in 2009, killing
more than 300 people.
Dr. N. Subramanian

16. Can we predict earthquakes
correctly?
• Scientists generally cannot predict the
time, location and magnitude of EQ - But they
did it once!
• On Feb. 4, 1975, seismologists issued a warning
to residents of Haicheng in northeastern
China, prompting people to seek safety
outdoors.
– A M7.3- EQ struck that evening, killing more than
2,000 people and destroying more than 90 percent of
the city.
– Without the warning, about 150,000 people would
have died!
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17. Characteristics of an Earthquake
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18. As the “quality” of the sediment decreases,
the amplitude of the waves increases
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19. Magnitude: Richter scale- Californian seismologist
Charles F. Richter, in 1930s
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20. P and S waves and Magnitude
• P waves are the first to arrive due to their high
displacement speed,
• Followed by the S waves.
Two parameters that determine magnitude:
• The time delay between the arrival of the first P
waves and S waves(proportional to the distance
between the seismograph and the hypocentre of the
earthquake), and
• Their amplitude.
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21. P and S waves
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22. Graphical solution of the mathematical formula for
determining magnitude on the Richter scale
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23. Intensity of earthquakes
• Modified Mercalli Intensity scale (MMI) and
MSK scale (Appendix D of Draft IS 1893)
• Initially developed early last century by
Giuseppe Mercalli.
• Both have twelve levels of intensity
– Level I – least perceptive
– Level XII – most severe
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24. Factors Influencing Seismic Damage
The following factors influence the
seismic damage:
Peak Ground Acceleration (PGA)
 Amplitude,
 Duration and frequency of ground
vibration,
 Magnitude,
 Distance from epicenter
 Geographical conditions between
the epicenter and the site,
 Soil properties at the site and
foundation type
Building type and characteristics.
Damage to a Steel building in
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25. Lateral Force Resisting Systems
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26. Better Performance in Earthquakes
Have simple and regular Plans
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27. Collapse of L-shaped building in
Ahmedabad, 2001
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28. Avoid Irregular Configurations
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29. Avoid Novel Structural Features
(If their EQ behavior is not known)
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30. Geometric vulnerabilities
- CCTV Tower, China
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31. Response Spectra for Different Strong
Earthquakes
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32. Response Acceleration coefficient as
given in IS 1893 (Part 1)-2002
Smoothened Elastic Design Acceleration
Response Spectrum (SEDRS) for 5% damping.
For Steel structures use 2% damping
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33. SEISMIC ZONES OF INDIA
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34. Probabilistic Seismic Hazard Map
(PSHM) of India
• The National Disaster Management
Authority, Govt. Of India, New Delhi has also
developed a Probabilistic Seismic Hazard
Map (PSHM) of India
•
http://ndma.gov.in/ndma/disaster/earthquak
e/India-psha-finalreport.pdf
Dr. N. Subramanian

35. Equivalent Lateral Base Shear Force
Procedure
Equivalent Lateral Base Shear Force :
Where Z= zone factor, I = importance factor, and R= Response reduction Factor
I = 1.5 for largely
crowded and imp.
Buildings, and
equal to 1.0 for
other buildings.
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36. Approximate Fundamental Period
The approximate fundamental natural period of vibration for a
moment resisting frame without brick infill panels is :
Ta = 0.085 h0.75 in seconds
where h = height of the building in m
For all other buildings, including moment resisting frame
buildings with brick in-fill,
Ta = 0.09h / √d in seconds
where d = base dimension of the building at the plinth
level, along the considered direction of the lateral force, in
meters.
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37. Equivalent Static Method
(seismic coefficient method)
Total design seismic base shear if determined by
VB = Ah W
Ah = Design horizontal acceleration spectrum value
W = Seismic weight of the building
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38. Fundamental natural periods of
structures differ over a large range
Adapted from: Newmark, (1970), Current trends in the Seismic Analysis and Design of High
Rise Structures, Chapter 16, in Wiegel, (1970), Earthquake Engineering, Prentice Hall, USA.
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39. Distribution of Base Shear to
Different Levels of the Building
 After the base shear force VB is determined it should be
distributed along the height of the building (to the
various floor levels) using the following expression:
After the Base shear is distributed, the frames may
be analyzed by any standard computer program to
get the internal forces!
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40. Dynamic Analysis
The dynamic analysis methods are grouped into:
Response spectrum method (multistory
buildings, irregular buildings, overhead water ranks
and bridge piers are often designed using this
method)
 Time-history response analysis (most important
structures such as nuclear reactors, large span
structures or very tall buildings are designed using this
method).
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41. EARTHQUAKE DESIGN PHILOSOPHY
The seismic design philosophy as per IS 1893(part 1) is:
 Minor and frequent earthquakes should not cause any damage to
the structure
 Moderate earthquakes should not cause significant structural
damage but could have some non-structural damage
 Major and infrequent earthquakes should not cause collapse
Hence design is done for much smaller forces than actual seismic
loads.
Note that this approach is different than that adopted in the case of
wind, dead, live and other loads, where the structure is designed
for the actual loads.
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42. Earthquake design philosophy
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43. Seismic Design Philosophy
Though the structure is designed for reduced earthquake loads, the
following contributing factors will prevent the collapse of the structure:
Over-strength,
Redundancy,
Ductility
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44. Ductile and Brittle performance
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45. CURRENT DESIGN CODES
Expected Performance:
The design requirements primarily are intended
to safeguard against major failures and loss of
life, NOT to limit damage, maintain functions, or
provide for easy repairs.
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46. Performance Based Design (PBD)
Future (PBD) Codes will be based on:
Desired performance chosen by owner.
Reduced business interruption
Reduced damage costs
Current Performance based design documents:
Vision 2000
FEMA 356/273
ATC 40
FEMA 310
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47. Load Combinations
In general consider the 8- load combinations:
(1) 1.5 (DL + IL) + 1.05(CL or SL)
(2) 1.2 (DL + IL) + 1.05(CL or SL) ± 0.6(WL or EL)
(3) 1.2 (DL + IL ± WL or EL) + 0.53 (CL or SL)
(4) 1.5(DL ± WL or EL)
(5) 0.9 DL ± 1.5 (WL or EL)
(6) 1.2 (DL + ER)
(7) 0.9DL + 1.2 ER
(8) DL + 0.35(IL + CL or SL) + AL
Where, DL = Dead load, IL = imposed load (live load),
WL = wind load, SL = snow load, CL = crane load
(vertical / horizontal), AL = accidental load, ER =
erection load and EL = earthquake load.
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48. Loading Combination for Non-
orthogonal buildings
Eight additional possibilities
should also be considered.
(1) ELx + 0.3 ELy
(2) 0.3ELx + ELy
(3) ELx – 0.3ELy
(4) 0.3ELx - ELy
(5) – (ELx + 0.3ELy
(6) (0.3ELx + ELy)
(7) – (ELx – 0.3ELy)
(8) – (0.3ELx – ELy)
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51. Seismically Active regions in India
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52. Past Earthquakes in India
Four Great
earthquakes (M>8)
occurred in a span of
53 years from 1897 to
1950; the January
2001 Bhuj earthquake
(M7.7) is almost as
large
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53. Past Earthquakes in India
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