Download - 17 Earthquake Engineering
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Earthquake Engineering
Civil & Environmental EngineeringUniversity College London
Earthquake Engineering
Dr Tiziana Rossetto
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Earthquake Engineering
Civil & Environmental EngineeringUniversity College London
Introduction
In the past 3 centuries over 3 million people have dieddue to earthquakes and earthquake related disasters.
The economic losses estimated for the period 1929-1950
are in excess of US$10 billion.
2/3 of the earths crust is seismically active, which means
that about 1,000,000,000 people are living in areas ofthe world that are prone to earthquakes.
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Earthquake Engineering
Civil & Environmental EngineeringUniversity College London
Introduction
For more developed countries the economic loss due to
an earthquake can be enormous even if the death toll isfairly low (Coburn and Spence 1992):
e.g. Kobe Earthquake (Ms 7.0, Japan, 1995) killed
5,420 people but caused US$ 150 billion economic loss
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Earthquake Engineering
Civil & Environmental EngineeringUniversity College London
cost of
damage perfatality
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Civil & Environmental EngineeringUniversity College London
Introduction
But cost is relative:
e.g. Managua earthquake (Ms 6.1, Nicaragua, 1972),caused 10,000 deaths and US$ 2 billion economic loss.
..but This loss = 40% of GNP
For more developed countries the economic loss due to
an earthquake can be enormous even if the death toll isfairly low (Coburn and Spence 1992):
e.g. Kobe Earthquake (Ms 7.0, Japan, 1995) killed
5,420 people but caused US$ 150 billion economic loss
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Earthquake Engineering
Civil & Environmental EngineeringUniversity College London
Introduction
What do we know?
Earthquakes cannot be prevented nor accuratelypredicted.
It is not ground shaking itself that causes life andeconomic loss but the collapse or damage of buildingsand infrastructure that are too weak to resist the groundshaking.
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Earthquake Engineering
Civil & Environmental EngineeringUniversity College London
What is Earthquake Engineering?
The application of civil engineering toreduce life and economic losses due toearthquakes,
(i.e to mitigate seismic risk)
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Earthquake Engineering
Civil & Environmental EngineeringUniversity College London
What is Seismic Risk from theengineers perspective?
the probability of losses occurring due to
earthquakes within the lifetime of astructure; these losses can includehuman lives, social and economic
disruption as well as material damage.
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Earthquake Engineering
Civil & Environmental EngineeringUniversity College London
What is Seismic Risk?
RISK = SEISMIC HAZARD x VULNERABILITY
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Earthquake Engineering
Civil & Environmental EngineeringUniversity College London
What is Seismic Risk?
RISK = SEISMIC HAZARD x VULNERABILITY
Probability of a potentially damagingearthquake effect occurring at the site ofplanned construction within its design life.
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Earthquake Engineering
Civil & Environmental EngineeringUniversity College London
What earthquake effects cause damage?
Ground shaking
Bhuj E/q, India 2001Loma Prieta, CA 1989
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Earthquake Engineering
Civil & Environmental EngineeringUniversity College London
Ground shaking
What earthquake effects cause damage?
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Earthquake Engineering
Civil & Environmental EngineeringUniversity College London
Ground shaking
Surface rupture
Chi Chi E/q, Taiwan
Hector Mines E/q, USA
What earthquake effects cause damage?
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Earthquake Engineering
Civil & Environmental EngineeringUniversity College London
Ground shaking
Surface rupture
Landslides
What earthquake effects cause damage?
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Earthquake Engineering
Civil & Environmental EngineeringUniversity College London
Ground shaking
Surface rupture
Landslides
Liquefaction
What earthquake effects cause damage?
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Earthquake Engineering
Civil & Environmental EngineeringUniversity College London
Ground shaking
Surface rupture
Landslides
Liquefaction
What earthquake effects causedamage?
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Earthquake Engineering
Civil & Environmental EngineeringUniversity College London
Ground shaking
Surface rupture
Landslides
LiquefactionTsunamis
What earthquake effects cause damage?
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Earthquake Engineering
Civil & Environmental EngineeringUniversity College London
What is Seismic Risk?
is the probability of the occurrence of
damage in a building when exposed to aparticular earthquake effect.
RISK = SEISMIC HAZARD x VULNERABILITY
Probability of a potentially damagingearthquake effect occurring at the site ofplanned construction within its design life.
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Earthquake Engineering
Civil & Environmental EngineeringUniversity College London
What is Seismic Risk?
DETERMINED BY MAN: CAN BE
REDUCED THROUGH SEISMICDESIGN
RISK = SEISMIC HAZARD x VULNERABILITY
DETERMINED BY NATURE:CANNOT BE REDUCED
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Earthquake Engineering
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Seismic Hazard and Seismic Design
Design Problem:An earthquake usually constitutes themost severe loading to which most civil engineeringstructures might possibly be subjected, and yet in mostparts of the world, even those that are highly seismic, there
is a possibility that an earthquake may not occur during thelife of the structure.
Note: Lateral loads imposed by winds = 1-3% of building weight.Lateral loads due to earthquakes = 25-30% of building weight.
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Earthquake Engineering
Civil & Environmental EngineeringUniversity College London
Seismic Hazard and Seismic Design
Design Problem:An earthquake usually constitutes themost severe loading to which most civil engineeringstructures might possibly be subjected, and yet in mostparts of the world, even those that are highly seismic, there
is a possibility that an earthquake may not occur during thelife of the structure.
Assessment Problem: Most buildings that exist have not
been designed to seismic codes. Can they withstand thetype of earthquake that might happen in their location?What will be the damage incurred if an earthquake doesoccur?
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Earthquake Engineering
Civil & Environmental EngineeringUniversity College London
Seismic Hazard and Seismic Design
Hence, engineers require seismic hazardassessments to provide not only a description of
the likely seismic loads (ground shaking) to beexperienced by an engineering structure, but alsoto attach probabilities of occurrence to these
earthquake loads.
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Earthquake Engineering
Civil & Environmental EngineeringUniversity College London
How do earthquake measurementstranslate into earthquake design loads?
Seismograms can be used directly as input to complicated
dynamic inelastic time history finite element analyses ofimportant buildings.
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Earthquake Engineering
Civil & Environmental EngineeringUniversity College London
How do earthquake measurementstranslate into earthquake design loads?Seismograms can be used directly as input to complicated
dynamic inelastic time history finite element analyses ofimportant buildings.
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Earthquake Engineering
Civil & Environmental EngineeringUniversity College London
How do earthquake measurementstranslate into earthquake design loads?
Seismograms used directly as input to complicateddynamic inelastic time history finite element analyses ofimportant buildings.
Earthquake Acceleration Spectra and Peak GroundAcceleration.
Spectral modal analysis methodsEquivalent lateral force methods
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Earthquake Engineering
Civil & Environmental EngineeringUniversity College London
Computation of Elastic ResponseSpectrum
Single degree
of freedom
systems
Plot maximum
response acceleration
vs fundamental period
of SDOF
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Earthquake Engineering
Civil & Environmental EngineeringUniversity College London
Elastic and Inelastic Spectra
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Civil & Environmental EngineeringUniversity College London
Design Spectra (EC8)
~2.5.ag
Shape will be different
for different soilconditions. i.e. site
amplification effects areconsidered
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Earthquake Engineering
Civil & Environmental EngineeringUniversity College London
Code-type zonation map
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Civil & Environmental EngineeringUniversity College London
T1 T2 T3
T1T2
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Civil & Environmental EngineeringUniversity College London
Equivalent Lateral Load
V = C.W ( ~ F=m.a)
I = Importance factor
Sa(T1) = spectral acceleration
for fundamental period, includessite effects
q = behaviour factor, represents
structures ability to dissipate energy
( )qSI
g
TSaC ...1=
V
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Earthquake Engineering
Civil & Environmental EngineeringUniversity College London
Conventional Seismic DesignNormal building life assumed to = 50years
Ultimate limit state design: Design a building to resist anearthquake with a return period of 475yrs (i.e. the designloads will have a 10% probability of being exceeded in the
structures life).
If a structure is very important (i.e. the consequences of its
damage are severe) these loads will be increased: e.g.Nuclear structures designed to resist a 10,000 year returnperiod event.
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Earthquake Engineering
Civil & Environmental EngineeringUniversity College London
Conventional Seismic DesignNormal building life assumed to = 50years
Ultimate limit state design: Design a building to resist anearthquake with a return period of 475yrs (i.e. the designloads will have a 10% probability of being exceeded in the
structures life).If we design for the seismic loads to be resisted bythe building without damage (i.e. for the building toreact elastically) the cost of construction would beprohibitive
So we design buildings to be damaged underearthquake loading
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Earthquake Engineering
Civil & Environmental EngineeringUniversity College London
Designing for Controlled DamageWe design buildings to be damaged and react inelastically:
meaning they dissipate the same energy, but will undergogreater deformation during the event
y
e
u
Displacement ()
Pi
Pe
Equal EnergyRule
Force (P)
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Earthquake Engineering
Civil & Environmental EngineeringUniversity College London
Designing for Controlled DamageWe design buildings to be damaged and react inelastically:meaning they dissipate the same energy, but will undergogreater deformation during the event
The location of the damaged areas is controlled to avoid
catastrophic failure.
Simple design rules andcapacity design
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Earthquake Engineering
Civil & Environmental EngineeringUniversity College London
Simple Design Criteria
Choose an adequate lateral load resisting system
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Civil & Environmental EngineeringUniversity College London
Adequate Lateral Load Resisting Systems
Concentrically
braced frame
Eccentrically
braced frames
Moment resistingframe:
RC up to 5 floors
Steel up to 2 floors
fuse
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Earthquake Engineering
Civil & Environmental EngineeringUniversity College London
Simple Design Criteria
Choose an adequate lateral load resisting system
Maintain regularity in plan and elevation (of stiffness andmass distribution)
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Civil & Environmental EngineeringUniversity College London
Regularity in Plan
U i it C ll L d
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Civil & Environmental EngineeringUniversity College London
Regularity in Elevation
University College London
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Civil & Environmental EngineeringUniversity College London
Regularity in Elevation
University College London
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Earthquake Engineering
Civil & Environmental EngineeringUniversity College London
Regularity in Elevation
MassIrregularity
StiffnessIrregularity
University College London
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Earthquake Engineering
Civil & Environmental EngineeringUniversity College London
Soft-storey Failure
University College London
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Earthquake Engineering
Civil & Environmental EngineeringUniversity College London
Soft-storey Failure
University College London
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Earthquake Engineering
Civil & Environmental EngineeringUniversity College London
Soft-storey Failure
University College London
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Earthquake Engineering
Civil & Environmental Engineeringy g
Simple Design Criteria
Choose an adequate lateral load resisting system
Maintain regularity in plan and elevation (of stiffness andmass distribution)
Ensure connection between structural elements
Connecting and anchoring of reinforcement Using appropriate materials
University College London
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Civil & Environmental Engineering
Poor Connection
Ci il & E i t l E i iUniversity College London
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Earthquake Engineering
Civil & Environmental Engineering
Premature shear failure throughinappropriate detailing
Fukae Viaduct, Kobe 1995
Ci il & E i t l E i iUniversity College London
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Earthquake Engineering
Civil & Environmental Engineering
Premature shear failure throughinappropriate detailing
Fukae Viaduct, Kobe 1995
Civil & Environmental EngineeringUniversity College London
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Earthquake Engineering
Civil & Environmental Engineering
Civil & Environmental EngineeringUniversity College London
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Earthquake Engineering
Civil & Environmental Engineering
Civil & Environmental EngineeringUniversity College London
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Earthquake Engineering
Civil & Environmental Engineering
Poor Connection
Civil & Environmental EngineeringUniversity College London
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Earthquake Engineering
Civil & Environmental Engineering
Simple Design Criteria
Choose an adequate lateral load resisting system
Maintain regularity in plan and elevation (of stiffness andmass distribution)
Ensure connection between structural elements
Avoid designing in locations of stress concentration
Civil & Environmental EngineeringUniversity College London
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Earthquake Engineering
Civil & Environmental Engineering
Local Stress Points
Shortcolumn
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Earthquake Engineering
Civil & Environmental Engineering
Short Column Failure
Shortcolumn
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Earthquake Engineering
C & o e ta g ee g
Simple Design Criteria
Choose an adequate lateral load resisting system
Maintain regularity in plan and elevation (of stiffness andmass distribution)
Ensure connection between structural elements
Avoid designing in locations of stress concentration Consider dynamic response in determining spacing
between buildings, so as to avoid pounding
Civil & Environmental EngineeringUniversity College London
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Earthquake Engineering
g g
Pounding
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Earthquake Engineering
g g
Pounding
Civil & Environmental EngineeringUniversity College London
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Earthquake Engineering
Simple Design Criteria Choose an adequate lateral load resisting system
Maintain regularity in plan and elevation (of stiffness andmass distribution)
Ensure connection between structural elements
Avoid designing in locations of stress concentration Consider dynamic response in determining spacing
between buildings, so as to avoid pounding
Adopt capacity design concepts to control the failuremode
Civil & Environmental EngineeringUniversity College London
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Earthquake Engineering
Capacity Design
Civil & Environmental EngineeringUniversity College London
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Earthquake Engineering
Bad Design
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Earthquake Engineering
Bad Design
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Earthquake Engineering
Bad Design
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Earthquake Engineering
Capacity Design
Civil & Environmental EngineeringUniversity College London
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Earthquake Engineering
Simple Design Criteria Choose an adequate lateral load resisting system
Maintain regularity in plan and elevation (of stiffness andmass distribution)
Ensure connection between structural elements
Avoid designing in locations of stress concentration Consider dynamic response in determining spacing
between buildings, so as to avoid pounding
Adopt capacity design concepts to control the failuremode
Be aware of damage potential on non-structural elements
Civil & Environmental EngineeringUniversity College London
Damage due to Non Structural
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Earthquake Engineering
Damage due to Non-StructuralElements
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Earthquake Engineering
Base-Isolation
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Base-Isolation
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Earthquake Engineering
Final RemarksDamage to buildings is the greatest cause of life loss, directdamage and business interruption in an earthquake.
New buildings should be designed considering earthquakeloading with the consequence of their damage in mind
during the design process.
Assess our existing structures for their earthquakeresistance
Predict the likely loss and intervene with structuralstrengthening if the risk is too high.
Civil & Environmental EngineeringUniversity College London
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Earthquake Engineering
Evening Seminar7th February 2006 at 6pm
The October 8, Pakistan Earthquake:Effects and Relief
Presentation by EEFIT Team and Oxfam
Venue: Chadwick Lecture Theatre, Dept of Civil and
Environmental Engineering, UCL
Open to All
Register your interest with me: [email protected]