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
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 Site Path Source
Site Response Soil response depends on: Type of soil Thickness of soil Stiffness of soil Bedrock Results: Some soil deposits amplify bedrock motion Some soil deposits de-amplify bedrock motion Some soils do both
Site Response 1985 Mexico City Earthquake M = 8.1 Over 200 miles away Communications Building 30 m soft clay Young lake deposits University Rock
Soft clay amplified bedrock motions by factor of 5 Site Response 1985 Mexico City Earthquake M = 8.1 Over 200 miles away Rock – 0.03g Soft clay – 0.15g Soft clay amplified bedrock motions by factor of 5
Site Response 1989 Loma Prieta Earthquake M = 7.1 Over 60 miles away Yerba Buena Island Treasure Island Oakland Yerba Buena Island Treasure San Francisco Rock Soft soil
Soft soil amplified bedrock motions by factor of 2-3 Site Response 1989 Loma Prieta Earthquake M = 7.1 Over 60 miles away Soft soil amplified bedrock motions by factor of 2-3 Rock – 0.06g Soft soil Soft soil – 0.15g Rock
Engineering for Earthquakes Ground Failure Landslides Before After Yungay, Peru
Engineering for Earthquakes Ground Failure Landslides After Before
Engineering for Earthquakes Ground Failure Landslides After Before
Engineering for Earthquakes Ground Failure Landslides El Salvador Taiwan
Engineering for Earthquakes Ground Failure Earthquake shaking Liquefaction High contact forces Low contact forces Loose Sand
Engineering for Earthquakes Ground Failure Earthquake shaking Liquefaction Soil wants to densify Water pressure increases Contact forces decrease Strength decreases High contact forces Low contact forces
Engineering for Earthquakes Ground Failure Niigata, Japan Liquefaction Niigata, Japan
Engineering for Earthquakes Ground Failure Liquefaction 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 Occupancy
Life Safety
Collapse Prevention
Vertical seismic loads Horizontal seismic loads Seismic Loading on Structures Vertical seismic loads Gravity load (vertical) Weight of structure Weight of contents Horizontal seismic loads Earthquake motion
Seismic Loading on Structures Earthquake motion
Seismic Loading on Structures Rotation Shortening Lengthening To prevent excessive movement, must restrain rotation and/or lengthening/shortening
Strong beam/column connections resist rotation Types of structures Moment frame Strong beam/column connections resist rotation
Diagonal bracing resists lengthening and shortening Types of structures Braced frame Diagonal bracing resists lengthening and shortening
Shear wall resists rotation and lenthening/ Concrete Shear Wall Shear wall resists rotation and lenthening/ shortening
Structural Materials Masonry Very brittle if unreinforced Common in older structures Common facing for newer structures
Structural Materials Timber
Structural Materials Concrete Heavy, brittle by itself Ductile with reinforcement Rebar
Structural Materials Prestressed Concrete Strands tensioned during fabrication Tension Prestressing strands
Structural Materials Prestressed Concrete Strands tensioned during fabrication Rebar Prestressing strands Beam on ground – no stress Unreinforced Prestressed
Structural Materials Steel Light, ductile Easy connections
Structural Damage San Francisco Masonry Watsonville Iran
Structural Damage Timber
Structural Damage Timber Soft first floor
Structural Damage Reinforced Concrete Axial Overturning Lateral Rebar Reinforced Concrete Column Rebar Lateral
Structural Damage Reinforced Concrete Insufficient confinement
Structural Damage Reinforced Concrete Increased confinement
Structural Damage Fractured weld Steel
Engineering for Earthquakes Mitigation of seismic hazards Geotechnical Structural
Soil Improvement Mitigation of liquefaction hazards Densification Grouting/Mixing
Soil Improvement Densification Dynamic compaction
Gravel inserted as vibroflot is extracted Soil Improvement Gravel inserted as vibroflot is extracted Densification Vibroflotation
Soil Improvement Grouting/Mixing
Structural Retrofitting Steel jacket Column jacketing
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
New Structural Systems Post Tensioned Bars (ungrouted) Fiber Reinforced Grout U Flexural Plate (UFP) Connector Foundation
Flexural connectors dissipate energy New Structural Systems Flexural connectors dissipate energy Post-tensioned bars stretch as walls rock
Post-tensioned bars snap walls back into place New Structural Systems Post-tensioned bars snap walls back into place
Requires something strong vertically, but soft laterally New Structural Systems Base isolation Requires something strong vertically, but soft laterally Ground shaking transmits force into structure Ground moves, structure doesn’t
New Structural Systems Base isolation Rubber bearings
New Structural Systems Dampers – shock absorbers