seismology and earthquake engineering :introduction lecture 3
DESCRIPTION
Seismology and Earthquake Engineering :Introduction Lecture 3. Hall of Fame (famous earthquakes). 1906 San Francisco. Hall of Fame (famous earthquakes). 1964 Niigata. Hall of Fame (famous earthquakes). 1964 Alaska. Hall of Fame (famous earthquakes). 1960 Chile. - PowerPoint PPT PresentationTRANSCRIPT
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Seismology and Earthquake Seismology and Earthquake Engineering :IntroductionEngineering :Introduction
Lecture 3Lecture 3
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Hall of Fame (famous earthquakes)
1906 San Francisco
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Hall of Fame (famous earthquakes)
1964 Niigata
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Hall of Fame (famous earthquakes)
1964 Alaska
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Hall of Fame (famous earthquakes)
1960 Chile
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Hall of Fame (famous earthquakes)
1971 San Fernando
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Hall of Fame (famous earthquakes)
1985 Mexico City
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Hall of Fame (famous earthquakes)
1989 Loma Prieta
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Hall of Fame (famous earthquakes)
1994 Northridge
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Hall of Fame (famous earthquakes)
1995 Kobe
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Hall of Fame (famous earthquakes)
1999 Chi Chi (Taiwan)
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Engineering for Earthquakes
Geotechnical Engineering Considerations
• Site Response – modification of ground motions by local geologic conditions
• Ground Failure – mass movement of soil (liquefaction, settlement, landslides, etc)
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Site Response
Problem:
Predict the response of a soil deposit due to earthquake excitation
SourceSource
PathPath
SiteSite
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Site Response
Soil response depends on:• Type of soil• Thickness of soil • Stiffness of soil
Results:• Some soil deposits amplify bedrock motion• Some soil deposits de-amplify bedrock motion • Some soils do both
Bedrock
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Site Response1985 Mexico City Earthquake
M = 8.1Over 200 miles away
Younglake
deposits
University
CommunicationsBuilding
30 m soft clay
Rock
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Site Response1985 Mexico City Earthquake
M = 8.1Over 200 miles away
Rock – 0.03g
Soft clay – 0.15g
Soft clay amplified bedrock motions by
factor of 5
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Site Response1989 Loma Prieta Earthquake
M = 7.1Over 60 miles away
San Francisco
Oakland
Yerba Buena IslandTreasure Island
Yerba Buena Island
Treasure Island
Rock Soft soil
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Site Response1989 Loma Prieta Earthquake
M = 7.1Over 60 miles away
Rock – 0.06g
Soft soil – 0.15g Rock
Soft soil
Soft soil amplified bedrock motions by
factor of 2-3
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Ground Failure
Landslides
Yungay, Peru
Before
After
Engineering for Earthquakes
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Ground Failure
Landslides
Engineering for Earthquakes
Before After
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Ground Failure
Landslides
Engineering for Earthquakes
Before After
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Ground Failure
Landslides
Engineering for Earthquakes
TaiwanEl Salvador
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Ground Failure
Liquefaction
Engineering for Earthquakes
Loose SandHigh contact
forcesLow contact
forces
Earthquake shaking
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Ground Failure
Liquefaction
Engineering for Earthquakes
High contact forces
Low contact forces
Earthquake shaking
• Soil wants to densify• Water pressure increases• Contact forces decrease• Strength decreases
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Ground Failure
Liquefaction
Engineering for Earthquakes
Niigata, Japan
Niigata, Japan
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Ground Failure
Liquefaction
Engineering for Earthquakes
Moss Landing, California
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Engineering for Earthquakes
Structures
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Engineering for Earthquakes
Structural Engineering Considerations
• Design of new structures
• Retrofitting of existing structures
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Engineering for Earthquakes
Design Considerations
Performance objectives
Immediate Occupancy Life Safety Collapse Prevention
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Immediate OccupancyImmediate Occupancy
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Life SafetyLife Safety
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Collapse PreventionCollapse Prevention
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Seismic Loading on Structures
Earthquake motion
Gravity load (vertical)Weight of structureWeight of contents
Vertical seismic loads
Horizontal seismic loads
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Seismic Loading on Structures
Earthquake motion
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Seismic Loading on Structures
LengtheningShortening
Rotation
To prevent excessive movement, must restrain rotation and/or lengthening/shortening
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Types of structures
Moment frame
Strong beam/column connections
resist rotation
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Types of structures
Braced frameDiagonal bracing
resists lengthening and shortening
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Concrete Shear Wall
Shear wall resists
rotation and lenthening/shortening
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Structural Materials
MasonryVery brittle if unreinforcedCommon in older structuresCommon facing for newer structures
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Structural Materials
Timber
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Structural Materials
ConcreteHeavy, brittle by itselfDuctile with reinforcement
Rebar
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Structural Materials
Prestressed ConcreteStrands tensioned during fabrication
Prestressing strandsTensionTension
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Structural Materials
Prestressed ConcreteStrands tensioned during fabrication
Beam on ground – no stress
Unreinforced
Prestressed Rebar
Prestressingstrands
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Structural Materials
SteelLight, ductileEasy connections
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Structural Damage
Masonry
IranSan Francisco
Watsonville
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Structural Damage
Timber
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Structural Damage
Timber
Soft first floor
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Reinforced Concrete Column
Structural Damage
Reinforced Concrete
Axial
Lateral
Overturning
RebarRebar
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Structural Damage
Reinforced Concrete
Insufficient confinement
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Structural Damage
Reinforced Concrete
Increased confinement
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Structural Damage
SteelFractured weld
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Engineering for Earthquakes
Mitigation of seismic hazards
• Geotechnical
• Structural
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Soil Improvement
Mitigation of liquefaction hazards
• Densification
• Grouting/Mixing
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Soil Improvement
Densification
Dynamic compaction
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Soil Improvement
Densification
Vibroflotation
Gravel inserted as vibroflot is
extracted
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Soil Improvement
Grouting/Mixing
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Structural Retrofitting
Column jacketing Steel jacket
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Structural Retrofitting
Column jacketing External ties
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Structural Retrofitting
Column jacketing Fiber composite wrap
Composite wall retrofit
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Structural Retrofitting
Bracing
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Structural Retrofitting
Shear Walls
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New Structural Systems
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New Structural Systems
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Post Tensioned Bars (ungrouted)
Fiber Reinforced Grout
U Flexural Plate (UFP) Connector
Foundation
New Structural Systems
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New Structural Systems
Flexural connectors dissipate energy
Post-tensioned bars stretch as
walls rock
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New Structural Systems
Post-tensioned bars snap walls back into
place
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New Structural Systems
Base isolation
Ground shaking transmits force into
structure
Ground moves, structure doesn’t
Requires something
strong vertically, but soft laterally
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New Structural Systems
Base isolation
Rubber bearings
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New Structural Systems
Dampers – shock absorbers