Seismology and Earthquake Engineering :Introduction Lecture 3

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Presentation transcript:

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