HOW SEISMIC ISOLATIONWORKS

BEHAVIOUR OF CONVENTIONAL &BASE ISOLATED STRUCTURE

Basic ElementsHorizontal Flexible SupportDamping by Energy Dissipation

Acceleration Response Spectrum

Displacement Response Spectrum

Rollers

Lead Rubber Isolators

FlexibilityIncreased Flexibility May Make Structure More Responsive to Wind and Service Loads

FlexibilityLengthens PeriodReduces Acceleration and ForcesIncreases Displacements

Energy DissipationSubstantial Increases In Damping Will:1. Reduce Displacements2. Reduce Sensitivity to Earthquake Characteristics3. Provide Wind Restraint

Displacement Response Spectrum

Acceleration Response Spectrum

Force Displacement Trade-Off

Design Principles of Seismic IsolationPeriodEarthquake ForceCapacityEarthquake DemandIsolated DemandCode Design Force1 SEC2 SEC3 SEC

Design Principles of Seismic Isolation

Hysteresis LoopForceDisplacementPlastic Deformation

Our Objective Should Be -- And Can BeTo Eliminate Earthquake Damage as a Business Risk

In Summary...Seismic Isolation provides major economic advantages:Protection of occupants, contents, structureDramatic reduction in damageminimal business disruptionAnd.....for comparable costSeismically Isolated StructureDISSeismic Isolator

In Summary...Earthquakes are inevitableConsequences are frequently catastrophicMany businesses never recoverThe risks can be avoidedConventional Structure

Building CodesMinimum StandardBased on Past Earthquake ExperienceLife Safety OrientedDo Not Directly Protect Property Loss Do Not Directly Protect Business Disruption

Quote from SEAOC Blue Book Commentary, Source of the Uniform Building CodeThese Recommendations primarily are intended to safeguard against major failures and loss of life, NOT to limit damage, maintain functions, or provide for easy repairs.

Seismic Isolation GoalsProtection of LifeProtection of Building FrameProtection of ContentsProtection of Operation

SEISMIC ISOLATIONTECHNOLOGY

DISSEISMIC ISOLATOR TMCover RubberEnergy Dissipation CoreSteel Reinforcing PlatesInternal Rubber LayersBottom Mounting Plate(Top Mounting Plate Not Shown) Integral with Isolator Connects to structure above and below isolator Protects steel plates Provides lateral flexibility Reduces earthquake forces & displacements by energy dissipation Provides wind resistanceSeismic Isolation SystemIllustrated here is one ofseveral designs of seismicisolators. Vulcanized rubber layers that can move in anyhorizontal direction arelaminated between steelsheets to form a movable,flexible base.

USA Patent Nos. 4,117,637, 4,499,694 and 4,593,502 Provides vertical load capacity Confines lead core

During a Richter 8.0 Earthquake a Seismically Isolated Building Will Behave as if it Were Experiencing a 5.5 Earthquake

Global Cost IssuesFirst CostLife Cycle CostsEarthquake DamageDisruption/Security

Economic FeasibilityCost of ConstructionEarthquake Insurance PremiumCost of Earthquake DamageCost of Disruption

Total Damage Comparison

Short Term CostsSeismic IsolatorsArchitectural ModificationsUtility Connections

Conventional ApproachesStiff BuildingLow DriftsHigh AccelerationsFlexible BuildingLow AccelerationsHigh Drifts

Damage CostsCaused by HighFloor Accelerations

Ceiling & LightsBuilding EquipmentElevatorsContents

Caused by LargeInterstory Drift

Structural FramePiping & DuctworkFacade & WindowsPartitions

Damage MitigationHow Does Seismic Isolation Reduce Damage?

Essentially elastic response Reduces forces on structure Reduces floor accelerations Reduces interstory drift

Short Term SavingsReduced Member SizesReduced Equipment BracingAlternative Configurations and Materials

Long Term BenefitsIncreased SafetyReduced LossesReduced Repair Costs Continuous Operation

Good CandidatesHistoric Buildings

Good CandidatesExpensive ContentsManufacturing FacilityComputer Data CenterMuseum

Good CandidatesEssential FacilitiesHospitalsEmergency OperationsFireMilitarySecurity/Defense Police CommunicationsUtilitiesComputer Data Centers

Good CandidatesCosts of DisruptionAlmost any BusinessExamples:HotelsBanks Down-Time Causes Severe Economic Loss

DisruptionLoss of FunctionLost RevenueLiabilityEmployee ExpensesLost Market Share

Whats at RiskCorporateHeadquartersManufacturing and Process FacilitiesCommunication and Data Centers Research and Development Facilities Hospitals/EmergencyResponse CentersMuseums/Historical StructuresStructures

Whats at RiskPersonnelIndustrial EquipmentIn-Process ProductsSystems Equipment Research and Data Medical EquipmentHistorical Assets

Whats at RiskLoss of ProductionLoss of Market ShareLoss of Projected SalesLoss of Customer FulfillmentLoss of RevenueLoss of Stock Value Business Interruption

World Wide UseCanadaItalyChileJapanChinaMexicoEnglandNew ZealandFranceRussiaGreeceSouth AfricaIcelandUnited StatesIran/IraqYugoslavia

Retrofit GoalsReliable Capacity Exceeds Elastic Demand(Isolation)orCombined Ductility and Capacity is Sufficientto Resist Demand (Conventional)

Retrofit GoalsFunctionalityContents ProtectionInvestment ProtectionHistoric PreservationDesign Economy

Retrofitting with Seismic IsolationExisting Structural CapacityElastic Performance LimitsLimited Base ShearPlane of IsolationControl of Displacements

Retrofit Design IssuesCapacity of Existing BuildingPlane of IsolationFoundation LevelBasement LevelTop or Mid-Height at Columns

Benefits of Seismic Isolation RetrofitEliminates Ductility DemandWork is Primarily Confined to BasementBuilding Can Continue to be OccupiedOften the Most Economic Solution

Suitability of StructureHeight to Width Ratio Prevents Gross OverturningLocal Column Uplift is OK

Constructability1.Seismic Isolator Location2.Allow for Building Movement Above Seismic Isolators3.Allow for Mechanical and Electrical Service Movement4.Installation Details5.Access and Instrumentation

Practical LimitationsSoft SoilBuilding Period > 1.5 sec.Wind Load > 10% Building WeightInadequate Space to Move

Performance Based Code Choices Fully Operational Partially Operational Life Safety

Progress of Seismic Isolation Technology

Structural DescriptionNon-Ductile Reinforced Concrete Frame260,000 sq. ft. floor area8 Floors plus basement

SummaryWhen earthquake demand exceeds capacity, damage occurs.The ability to absorb this excess demand but not collapse is called ductility.Conventional construction is analogous to the Volvo automobile design. Damage occurs, but occupants are safe.Code buildings are not necessarily usable after an earthquake.Isolation by intent and design provides for post-earthquake functionality.

Earthquake Hazard MitigationPassive TechnologiesBase IsolationEnergy DissipationDevicesStructuralSystemHysteretic FrictionViscousMoment FrameSlip BoltedBase Isolation Controls Input to the SystemEnergy Dissipation Controls System Response to Input FCI Rubber HDR FPS W-B Lead Ext. Yield Steel Hydraulic Any Slider Materials 3MElasticSpringSlidingHystereticViscousVisco-elasticExoticFrictionDuctilityEnhance-ment

Earthquakes HappenLoma Prieta, CA 10/17/896.9 (Mw) moment magnitude earthquake15 seconds duration$7 billion in damageNorthridge, CA 01/17/946.7 (Mw) moment magnitude earthquake15 seconds duration$30 billion in damageKobe, JAPAN 01/17/956.9 (Mw) moment magnitude earthquake20 seconds duration$150-200 billion in damage4% of Japans GDP

Unimaginably ExpensiveLoma Prieta = $450 million per secondNorthridge = $2 billion per second!Kobe = $7.5 billion per second!!

Loma Prieta: October 17, 1989X axis = YearNorthridge: January 17, 1994Y axis = # of IsolatedKobe: January 17, 1995 Structures

1984 1986 1988 1990 1992 1994 1996Seismic Isolation Trends in JapanSince the 1995 Kobe Quake

Only Life Safety RiskCurrent Building Codes Provide for Life-Safety Protection OnlyRecommendations primarily are intended to safeguard against major failures and loss of life, not to limit damage, maintain functions, or provide for easy repair. (Source: SEAOC Blue Book)A high-value, heavily occupied building is, in effect, designed to the same performance level as a low-value farm building if the basic [building] code is merely followed. (Source: EQE Summary Report on the Kobe Earthquake, p. 91.)

Property Damage RiskMajor value lies in the facilities, equipment and product, not the structureAgain, earthquakes pose greater vulnerability to nonstructural damage

Whats at RiskStructures Corporate Headquarters Research & Development Manufacturing, Distribution Facilities & Process Facilities Hospitals/Emergency Data & Communications Response Centers Centers Museum/Historical StructuresAssets Personnel Research & Data Industrial Equipment Medical Equipment In-Process Products Historical Systems EquipmentBusinessInterruption Loss of Production Loss of Customer Fulfillment Loss of Market Share Loss of Revenue Loss of Projected Sales Loss of Stock Value

Retrofit Goals

Energy Dissipation -- How it WorksEnergy Dissipation vs. Without Energy Dissipation With Energy DissipationInter-story drift is reduced bya factor of approximately twowith the installation of energy dissipators.Without EnergyDissipation

One and Two Story Buildings

Applications30 U.S. Buildings75 Japanese Buildings90 U.S. Bridges400 Structures Worldwide

Isolated0.12gWest Japan Postal Savings Computer CenterKobe - January 17, 19950.40g0.12gAmplification of forces

ConventionalInstrumented Conventional StructureKobe - January 17, 19951.18g0.37gAmplification of forces0.37g

IsolatedUSC University HospitalNorthridge - January 17, 19940.11g0.49g0.37gAmplification of forces0.13gB1234567

ConventionalOlive View HospitalNorthridge - January 17, 19942.30gAmplification of forces0.80g0.80g

Business Interruption Can Be Fatal43% of business closed by a catastrophe never re-open

28% of those that do re-open, fail within 3 to 5 years

29% survive

The Goals of Seismic IsolationProtection of LifeProtection of Building FrameProtection of Non-Structural Components and ContentsProtection of Processes and FunctionProtection of Market ShareProtection of Research and Development Projects

Damped StructureUndamped StructurePerformance Comparison

20 Story Building in Japan

Recommendation: When you build your next new facility, you should know that for a 2-3% increase in the cost of of the building you can significantly reduce your business risk.

Probabilities are Small, But Significant67% chance of a 7.0 (Mw) moment magnitude earthquake in the Bay Area during the next 30 years 30 year timeline provides a false sense of remoteness and securityProbability converts to a 3.6% chance every year of the earthquake happening during that year