CSE C4-I 2013
C4-I INTRODUCTION TO EARTHQUAKE
ENGINEERING AND SEISMICITY
Overview of Elements of
Seismic Design
Course Coordinator:
Dr. Carlos E. Ventura, P.Eng.
Instructor:
Dr. Carlos E. Ventura, P.Eng.
Certificate Program in Structural Engineering
Instructor: Dr. C.E. Ventura
Seismic Hazard
Certificate Program in Structural Engineering – C4
No. 2
Instructor: Dr. C.E. Ventura
Seismic Hazard
soil
Shaking at site depends on:
• proximity of sources
• return period
• path
• site conditions
Certificate Program in Structural Engineering – C4
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Instructor: Dr. C.E. Ventura
Plate Tectonics
Lisa Wald
USGS Pasadena
U.S. Department of the Interior
U.S. Geological Survey
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No. 4
Instructor: Dr. C.E. Ventura
Seismicity of Canada
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No. 5
Instructor: Dr. C.E. Ventura
Western N. America Tectonic Setting
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No. 6
Instructor: Dr. C.E. Ventura
Cascadia Subduction Zone
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No. 7
Instructor: Dr. C.E. Ventura
Significant Earthquakes Felt in SW B.C.
Ref. Geological Survey of Canada, 2002
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Instructor: Dr. C.E. Ventura
Earthquake Characteristics
Peak Ground Parameters
 Acceleration (PGA)
 Velocity (PGV)
 Displacement (PGD)
Certificate Program in Structural Engineering – C4
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Instructor: Dr. C.E. Ventura
Earthquake Parameters…
 Duration of Significant Shaking
 Frequency Content
1985 Mexico Earthquake (SCT 1A; N90E)
0.5g
1940 Imperial Valley Earthquake (El Centro; S00E)
1971 San Fernando Earthquake (Pacoima Dam; N76W)
0
10
20
30
40
50
60
Time (sec)
1991 Uttarkashi Earthquake (Uttarkashi, N75E)
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Instructor: Dr. C.E. Ventura
Response Spectra/Design Spectra
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Instructor: Dr. C.E. Ventura
Response Spectra
• A means of quantifying seismic response for a
structure subjected to earthquake excitation
• SDOF model of an actual structure is used
Oscillation of building
Inverted Pendulum Model
Characterized by the fundamental period T
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Instructor: Dr. C.E. Ventura
Response Spectrum…
Fundamental Natural Period T
Single
Storey
Building
0.05 sec
Elevated
Water Tank
4 sec
Large Concrete Gravity Dam:
0.8 sec
Low-rise
Building
0.4 sec
15 Storey
Building
1 sec
Reinforced
Concrete
Chimney
2 sec
Certificate Program in Structural Engineering – C4
Suspension Bridge
6 sec
No. 13
Instructor: Dr. C.E. Ventura
Response History Analysis
(t)
1940 El Centro 180o
Ground Motion
0.30
Acceleration (g)
0.20
0.10
0.00
-0.10
0
5
0.4
0.2
0
25
-0.4
-0.6
30
35
40
Displacement  , in.
2
20
35
40
Response Displacement
1.5
15
30
time seconds
0.6
10
25
-0.40
0.8
5
20
-0.20
Response Acceleration
-0.2 0
15
-0.30
T = .5 sec
Response Acceleration (g)
10
1
0.5
0
-0.5 0
5
10
15
20
25
30
35
40
-1
-1.5
-0.8
-2
Time (seconds)
Certificate Program in Structural Engineering – C4
Time (seconds)
No. 14
Instructor: Dr. C.E. Ventura
Response spectrum
Under the same earthquake shaking, maximum
response of a spectrum of structures
with different T and a given damping
Earthquake Shaking
Certificate Program in Structural Engineering – C4
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Instructor: Dr. C.E. Ventura
Response Spectrum…
• A graph of maximum response of SDOF
Systems versus T
• Same ground motion
• Different T
• Fixed damping 
max
N
4
3
2
Maximum
Displacement
1
N
3
4
2
1
Dmax
Natural Period T (sec)
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Instructor: Dr. C.E. Ventura
Response History Analysis
Max accel value = 0.71 g
(t)
Response Acceleration (g)
T=0.5sec
0.8
0.6
0.4
0.2
0
-0.2 0
5
10
15
20
25
30
35
40
-0.4
-0.6
-0.8
Time (seconds)
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Instructor: Dr. C.E. Ventura
Acceleration Response Spectra
.71g @ .5 seconds
Response Acceleration - g
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
0
1
2
3
4
5
Period T (seconds)
Certificate Program in Structural Engineering – C4
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Instructor: Dr. C.E. Ventura
Response History Analysis
Max  value = 1.74 in
(t)
2
T=0.5sec
Displacement  , in.
1.5
1
0.5
0
-0.5 0
5
10
15
20
25
30
35
40
-1
-1.5
-2
Time (seconds)
Certificate Program in Structural Engineering – C4
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Instructor: Dr. C.E. Ventura
Displacement - in
Displacement Response Spectra
10
9
8
7
6
5
4
3
2
1
0
1.74 in @ T=.5 sec
0
1
2
3
4
5
Period T (seconds)
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Instructor: Dr. C.E. Ventura
How to determine
Base Shear V?
~2.5-3.0 PGA
Actual
TS
Velocity–
sensitive
Region
PGA
Displacement–
sensitive
Region
Smoothened
Acceleration
sensitive
Region
Spectral Acceleration (PSA)
Acceleration Spectrum
TA
TV
Natural Period T (sec)
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Instructor: Dr. C.E. Ventura
The Effect of Soil Conditions…
Spectral Acceleration
Peak Ground Acceleration
IDEALIZED RESPONSE SPECTRUM
Soft-Medium Clay
Deep Cohesionless Soils
1
Stiff Soil & Rocks
0
1
2
3
Natural Period T (sec)
Certificate Program in Structural Engineering – C4
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Instructor: Dr. C.E. Ventura
Pseudo-Spectral Acceleration (PSA)
Effect of Damping
Low
Damping
High
Damping
Natural Period T (sec)
Certificate Program in Structural Engineering – C4
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Instructor: Dr. C.E. Ventura
Design Spectra
Smooth curve ->Remove sensitivity to calculation of T
g t 
u
Actual Ground Acceleration :
Random
0
Time t
Energy
Actual
Trend line
Energy
Intensive
Region
0
25
Long Period
Waves
Certificate Program in Structural Engineering – C4
Short Period
Waves
Frequency
(Hz)
No. 24
Instructor: Dr. C.E. Ventura
Response spectra for the 2010 Chile earthquake
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Instructor: Dr. C.E. Ventura
NBCC Seismic Hazard > Uniform Hazard Spectra
(UHS)
• UHS are defined by spectral ordinates at different periods
calculated at the same probability of exceedance 2% in
50 years in case of NBCC 2010)
• The ordinates of the UHS at different periods are affected
by the ground motions from earthquakes of different
magnitudes and distances from the site
UHS approach followed by NBCC since
the 2005 edition of the Code
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Instructor: Dr. C.E. Ventura
NBCC - “Robust” 2%/50 Year PGA
Hazard Map
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Instructor: Dr. C.E. Ventura
(Sa)
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Instructor: Dr. C.E. Ventura
NBCC Uniform Hazard Spectrum for Montreal
The design spectrum is defined by 4 Sa values
(at 0.2 sec, 0.5 sec, 1 sec, and 2 sec) –
see NBCC Appendix C
Certificate Program in Structural Engineering – C4
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Instructor: Dr. C.E. Ventura
Design Spectral Acceleration S(T)
The design spectral acceleration that includes the site soil
coefficients Fa and Fv (depending on soil class)
S(T) = FaSa(0.2) for T < 0.2 s
= FvSa(0.5) or FaSa (0.2) whichever is smaller for T= 0.5 s
= FvSa (1.0) for T = 1.0 s
= FvSa (2.0) for T = 2.0 s
= FvSa (2.0)/2 for T ≥ 4.0 s
Certificate Program in Structural Engineering – C4
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Instructor: Dr. C.E. Ventura
Certificate Program in Structural Engineering – C4
No. 31
Instructor: Dr. C.E. Ventura
Change in Probability Level: Vancouver and
Montreal
Sa(0.2) hazard curves for Vancouver and Montréal, showing
how increasing the 10% in 50 year median hazard by a factor
of two (2×) produces different increases in safety.
For Vancouver this would give ground motions with a 1/2400
per annum exceedance probability, but for Montréal the
ground motions would have a 1/1600 per annum exceedance
probability.
Clearly the same level of safety would not be achieved for
these two locations
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Instructor: Dr. C.E. Ventura
Seismic Performance
Objectives
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No. 33
Instructor: Dr. C.E. Ventura
Earthquake Resistant Design:
Key Objective
• Structures should be able to resist
• Minor (and frequent) shaking with no damage
• Moderate shaking with no structural damage,
but some non-structural damage
• Severe (and infrequent) shaking with structural
damage, but with NO collapse
Damage
Certificate Program in Structural Engineering – C4
Frequency
No. 34
Instructor: Dr. C.E. Ventura
Earthquake Performance…
Minor Shaking
Moderate Shaking
Strong Shaking
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No. 35
Instructor: Dr. C.E. Ventura
Code Seismic Provisions:
Performance Objectives
 To prevent major failure and loss of life
 Building structures should be able to resist
moderate earthquakes without significant damage
 Building structures should be able to resist major
earthquakes without collapse (collapse ≡ exit by
occupants impossible due to failure of primary
structure)
Certificate Program in Structural Engineering – C4
No. 36
Instructor: Dr. C.E. Ventura
Total Horizontal Earthquake Force
What is Satisfactory Seismic
Performance and How to Achieve it?
Ductile Performance
Non-ductile Collapse
Horizontal Movement of Roof
relative to its base
Certificate Program in Structural Engineering – C4
No. 37
Instructor: Dr. C.E. Ventura
Satisfactory Seismic Performance:
NBCC performance objectives:
Buildings should be able to resist major
earthquakes without collapse BUT damage is
expected
Designers must design and detail structures to
control the location and extent of damage
Certificate Program in Structural Engineering – C4
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Instructor: Dr. C.E. Ventura
Capacity Design Approach
Certificate Program in Structural Engineering – C4
No. 39
Instructor: Dr. C.E. Ventura
Capacity Design Approach
Every structure or a structural component has
several possible modes of failure, some of
which are ductile while others are brittle.
Satisfactory seismic response of structures
requires that brittle failure modes be avoided.
This is accomplished through the application of
a capacity design approach.
Certificate Program in Structural Engineering – C4
No. 40
Instructor: Dr. C.E. Ventura
Capacity Design Approach: Objective
To force the structure to yield in a ductile manner
without failing at the expected displacements
(including other components of the structure,
such as columns).
At the same time, the rest of the structure needs
to remain strong enough, say in shear, or flexible
enough not to fail under gravity loads at these
displacements.
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Instructor: Dr. C.E. Ventura
Chain Analogy for Capacity Design
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No. 42
Instructor: Dr. C.E. Ventura
Shear forcedeflection curves
for flexural and
shear failure
mechanisms
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Instructor: Dr. C.E. Ventura
Capacity Design
Concrete
 Ductile yielding generally means flexural yielding, plastic hinges
 Shear yielding usually means shear failure, and is normally a brittle
failure, not good
Steel - ductile yielding can be:
 Flexural
 Joint deformation
 Shear deformation if detailed adequately e.g. shear yielding in
eccentric braced panels
 Tension-compression yielding in buckling restrained braces
Wood
 Ductile shear walls – the nails deform plastically
 Special connections
Masonry
 Shear walls in flexure
Certificate Program in Structural Engineering – C4
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Instructor: Dr. C.E. Ventura
•
The Type of Damage
– Sudden versus gradual
• Example: Multi-storey Steel Building
– Beam Failure versus Brace Failure
Beams : Flexural yielding versus Local Buckling
•
F

Flexural Yield Response: Ductile
F
Local Buckling in Flexure : Non-ductile
Brace Failure: Non-Ductile
0
Certificate Program in Structural Engineering – C4
Δ
No. 45
Instructor: Dr. C.E. Ventura
Example: RC Frame Structures
Beam sidesway
mechanism (weak
beam-strong
column)
Column sidesway
mechanism (weak
column-strong beam)
Certificate Program in Structural Engineering – C4
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Instructor: Dr. C.E. Ventura
The collapsed building (identical to the one standing
on the left)
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Instructor: Dr. C.E. Ventura
Certificate Program in Structural Engineering – C4
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Instructor: Dr. C.E. Ventura
Certificate Program in Structural Engineering – C4
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Instructor: Dr. C.E. Ventura
2003 Algeria (M6.8)
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Instructor: Dr. C.E. Ventura
Plastic hinge at the top of a bridge pier (1995 Kobe,
Japan earthquake)
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Instructor: Dr. C.E. Ventura
Ductility
Certificate Program in Structural Engineering – C4
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Instructor: Dr. C.E. Ventura
Elastic and Inelastic Seismic
Response
Consider 2 structures: A and B
Structure A with sufficient strength to remain elastic during
the entire earthquake.
Structure B is elasto-plastic and has the same initial stiffness
as structure A, but with a smaller strength (Fy) as
compared to A.
Even though the structure B undergoes inelastic response
(and hence damage), it will not collapse if it has the
capacity to undergo the large displacements required by
the inelastic response.
Certificate Program in Structural Engineering – C4
No. 53
Instructor: Dr. C.E. Ventura
Elastic
response
Inelastic
response
Certificate Program in Structural Engineering – C4
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Instructor: Dr. C.E. Ventura
Elastic vs Inelastic Response

Total
Horizontal
Load
Fmax
Force
Force
Fy
0
0
∆max
Displacement
A - Linear Elastic System
∆y
∆max
Displacement
B - Inelastic (elasto-plastic) System
Certificate Program in Structural Engineering – C4
No. 55
Instructor: Dr. C.E. Ventura
Equal Displacement Principle
Force
Elastic
Ductile
Displacement
Equal displacement principle: elastic and elasto-plastic
systems with the same T subjected to the same ground
motions have approximately the same peak displacement
Certificate Program in Structural Engineering – C4
No. 56
Instructor: Dr. C.E. Ventura
Equal Displacement Principle:
When does it Apply?
Force
Force
Elastic
Elastic
Ductile
Ductile
Displacement
Short T Structures
(T < ~0.4 s)
Displacement
Intermediate/Large T Structures
(T > ~0.4 s)
Certificate Program in Structural Engineering – C4
No. 57
Instructor: Dr. C.E. Ventura
Inelastic (Ductile) Seismic Response
If the structure is detailed such that it is able to undergo
large displacements without collapse, it could be
designed to have a maximum lateral strength which can
be much lower than the maximum response of a
corresponding elastic structure.
Ductility is the capacity of a structure or a
member to undergo deformation beyond yield
without loosing the load-carrying capacity.
Certificate Program in Structural Engineering – C4
No. 58
Instructor: Dr. C.E. Ventura
Displacement Ductility Ratio

Total
Horizontal
Load
Total
Horizontal
Load
Idealised
Response
Fy
Actual
Nonlinear
Response
0
Ductility  
∆y
∆max
Roof
Displacement Δ
Maximum Displacement  max

y
Yeild Displacement
Certificate Program in Structural Engineering – C4
No. 59
Instructor: Dr. C.E. Ventura
NBCC Rd factor
Rd is the ductility factor used to reduce the design forces in
recognition of the fact that a ductile structure designed for
such lower forces is able to dissipate the energy input by the
earthquake through inelastic deformation without collapsing.
The Rd value is dependent on the ductility capacity of the
structure.
Certificate Program in Structural Engineering – C4
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Instructor: Dr. C.E. Ventura
Force modification/ductility factor Rd
 Related to the amount of ductility capacity the
structure is believed to possess.
 Varies from 1.0 (e.g. unreinforced masonry) to
5.0 (e.g. ductile steel moment frame).
 Don’t get reduction in force for nothing!!
For higher R values, material codes (e.g.
A23.3) have stricter detailing requirements.
Needed to achieve higher ductility capacity.
Certificate Program in Structural Engineering – C4
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Instructor: Dr. C.E. Ventura
Ductile Response of a Braced Steel Frames
• 1995 Kobe, Japan earthquake (M 7.0)
Certificate Program in Structural Engineering – C4
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Instructor: Dr. C.E. Ventura
Cyclic energy dissipation: different systems show different ability to absorb
energy through inelastic behaviour => different Rd values
Certificate Program in Structural Engineering – C4
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Instructor: Dr. C.E. Ventura
Ductile Response of Reinforced Masonry Shear Walls
Certificate Program in Structural Engineering – C4
Source: Shedid, Drysdale and El-Dakhakhni
(2008)
No.
64
Instructor: Dr. C.E. Ventura
Ductile Response of Reinforced Masonry Shear Walls
Certificate Program in Structural Engineering – C4
Source: Shedid, Drysdale and El-Dakhakhni
(2008)
No.
65
Instructor: Dr. C.E. Ventura
Force modification/ductility factor Rd
Fmax
Rd 
 f  , T 
Fy
If we can ensure ductility, we can design the
structure to yield at a reduced force of
(Fmax/R).
Force
Elastic
Higher ductility
Smaller
Force
Certificate Program in Structural Engineering – C4
Ductile
Displacement
No. 66
Instructor: Dr. C.E. Ventura
Elastic and Design Base Shear
Ve = elastic base shear
V = design base shear
Certificate Program in Structural Engineering – C4
No. 67
Instructor: Dr. C.E. Ventura
Lateral Displacements/Drift
Certificate Program in Structural Engineering – C4
No. 68
Instructor: Dr. C.E. Ventura
Lateral Displacements
V
k
Certificate Program in Structural Engineering – C4
V=k 
No. 69
Instructor: Dr. C.E. Ventura
Lateral Displacements and Drift
Lateral displacements or drift of a structural system under
wind or earthquake forces are important from 3
different perspectives:
1. Structural stability
2. Architectural integrity and potential damage to various
non-structural components
3. Human comfort during and after an earthquake
Certificate Program in Structural Engineering – C4
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Instructor: Dr. C.E. Ventura
P-delta effect
Olive View Hospital, the 1971 San Fernando
earthquake, California
Certificate Program in Structural Engineering – C4
No. 71
Instructor: Dr. C.E. Ventura
Lateral Drift
Drift = lateral deflection of one floor relative to the floor below
Drift ratio = drift divided by the storey height between the two floors
Certificate Program in Structural Engineering – C4
No. 72
Instructor: Dr. C.E. Ventura
Lateral drift - example
 2  1
• ∆2 – ∆1 the drift in the second storey
• (∆2 – ∆1)/h the drift ratio for 2nd storey
• ∆3/h3 the average drift ratio for the entire
structure
NBCC prescribes drift ratio limits
Certificate Program in Structural Engineering – C4
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Instructor: Dr. C.E. Ventura
Design Displacements/Drift
Design displacements
– obtained by
multiplying elastic
displacements due to
force V by RdRo/IE
Note: this is an approximate deflection estimate!
Certificate Program in Structural Engineering – C4
No. 74
Instructor: Dr. C.E. Ventura
RC Shear Walls: Elastic and Plastic Deflections
This is a more accurate deflection
estimate! (see Section B.2, Anderson
and Brzev)
Certificate Program in Structural Engineering – C4
No. 75
Instructor: Dr. C.E. Ventura
Resources:
•
Anderson,D.L., and Brzev,S., Seismic Design Guide for Masonry Buildings, Canadian
Concrete Masonry Producers Association, Toronto, 2009 (Chapter 1 and Appendix B)
(free download available from www.ccmpa.ca).
•
National Building Code of Canada 2010, National Research Council, 2010.
•
Mitchell, D., Paultre, P.,Tinawi, R., Saatcioglu, M., Tremblay, R.,Elwood, K., Adams, J.,
and DeVall, R., “Evolution of seismic design provisions in the National building code of
Canada,” Can. J. Civ. Eng. 37: 1157–1170 (2010)
Acknowledgement:
Many of the slides were kindly provided by Prof. Svetlana Brzev of BCIT.
Certificate Program in Structural Engineering – C4
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