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