Seismology and Earthquake Engineering :Introduction Lecture 3.

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