Basic Principles of Earthquake Loss Estimation - …

1 1A Campaign by theA Campaign by theEarthquake Engineering Research InstituteEarthquake Engineering Research InstituteNorthern California ChapterNorthern California ChapterBasic Principles ofEarthquake loss Estimation -PML and Beyond- Single-Site seismic RiskSeismic Risk Terminology Exposure: the buildings, contents, people andprocesses at risk Earthquake hazards : ground shaking, soilliquefaction, surface fault rupture, slopeinstabilities, tsunami, seiche, etc. seismic Vulnerability: fragility ordamageability, the relationship betweenhazard and damage, loss or disruption Risk: the relationship between loss severity andfrequency2 RiskRisk occurs at the intersection ofexposure, hazard and vulnerabilityR = E x H x VR = E x H x VRiskRisk has at least two dimensions: severity and frequency, or mean and varianceAnnual Frequencyof ExceedanceLoss, Damage, Casualties or Downtime3 Return Period vs.

2 Exposure Period andProbability of ExceedanceP=1- e-t Tt = exposure period (years)P = probability of exceedance in exposure period, tT = average return period190285475 seismic Risk StandardsDamage Relationships:ATC-13, ATC 13-1 NIBS Steinbrugge, Wiggins, Thiel & ZsuttySeismic Risk Terminology: ASTM E 2026-99 Rapid Visual Screening: FEMA 154 Vulnerability of Buildings: ASCE 31-03 (FEMA 310)Vulnerability of Contents: FEMA 74 Rehabilitation of Buildings: FEMA 3564 Qualifications for seismic RiskNeeded: Engineering JudgmentMinimum: or + lots of experienceSeismic Risk Assessment, Individual BuildingsExpertise in Seismology + Geology + StructuralEngineering and StatisticsSeismic Risk Assessment, Building PortfoliosExpertise in Seismology + Geology + StructuralEngineering + Actuarial Science + Systems AnalysisSeismic Risk ToolsATC 13-1 HAZUS-MH MR1 FEMA Benefit/Cost ToolsProprietary Tools Multi-Site tools for insurance RMS, AIR, ABS, URS For Engineers ST-Risk (Risk Engineering and Degenkolb) SiteRisk (URS)5 ASTM E 2026 99 Standard Guide for the Estimation of Building Damageability in EarthquakesProbable loss - a direct relationship between probability andearthquake damage, considering both the hazard anddamage function loss - estimates damage for a defined quake scenario.

3 Scenario Expected loss (mean estimate) Scenario Upper loss (90% estimate)_____ PML is redefined in ATC 13-1 for ..probable maximum lossstudies PML50 and PML90 are equivalent to SEL and SUL for earthquakehazards with a 475-year return periodASTM E 2026 99 Levels of Investigation Standard Guide for the Estimation of Building Damageability in EarthquakesHigher levels of investigation are required wherehigher hazards exist, and/or where higherconfidence is required in the hazards Ground shaking Surface fault rupture Soil liquefaction andsoil failures Slope instability TsunamiSeismic hazards Ground shakingHazard-recurrence: Use this where loss is related to a singleground motion parameter, with no magnitude dependenceGood Source: USGS National seismic Hazard Mapping Project [2002]7 seismic hazards Ground shakingUSGS National seismic Hazard Mapping Project 2002 Where losses are magnitudedependent, multi-site, ormulti-period, use an event setHazard-recurrence (single-site,single ground motion parameter) seismic hazards Ground shakingDamage from ground motions: which parameter works best?

4 Peak ground acceleration (PGA) Peak ground velocity (PGV) Spectral acceleration (SA) @ fundamental structural period Modified Mercalli Intensity (MMI) Arias Intensity8 seismic hazards Local HazardsLiquefaction,surface faulting, landslide, Site ClassSeismic hazards Local HazardsLiquefaction,surface faulting, landslide, Site Class9 Adjustment for Site ConditionsFa, Fv factors in SEI/ASCE 31-03and FEMA 356 AmplificationSoil Factorsare amplitude-dependent 10 Uncertainty in seismic HazardsLarge uncertaintyLocal hazards per HAZUS11 StructuralVulnerabilityAssessmentStructu ral Vulnerability AssessmentResources -- see BibliographyStructural EvaluationASCE 31-03 (previously FEMA 310, or FEMA 178)Building Codes (IBC, UBC, etc.)Damage RelationshipsATC 13 " Earthquake Damage Evaluation Data for California"Steinbrugge, various publicationsThiel & Zsutty, EERI Spectra, 1987 Wesson et al.

5 , EERI Spectra, 2004 Porter et al, CUREEHAZUS MHRelationship? > Engineering Judgment!12 Wish List for Documents for seismic StudiesStructural drawings (originals, mods, retrofits)Architectural drawingsGeotechnical report ( soils report )Construction photosEarthquake damage reportsAccelerometer recordingsComputer models (ETABS, SAP, ..)Also, access to Engineer-of-Record, ConstructorStructural EvaluationDamage RelationshipsCourtesy USGS13 Damage RelationshipsTwo parts to the damage relationship:1) Damage versus ground motion2) Variability of damageDamage to wood frame dwellings in Northridge [Wesson, Spectra, August 2004]DFCV(DF)Damage RelationshipsTwo parts to the damage relationship:1) Damage versus ground motion2) Variability of damageDamage to wood frame dwellings [Porter, CUREE-CalTech, 2002]DFCV(DF)14 ATC 13 Facility Class 6 California Construction(Zone 4?

6 ATC 13 Damage Probability MatricesDamage State1 None2 Slight3 Light4 Moderate5 Heavy6 Major7 DestroyedDamage Factor Range (%)00 11 1010 3030 6060 100100 Central Damage Factor (%) Class 6: Low-rise concrete shear wall15 ATC 13 Damage Probability MatricesFacility Class 6:Low-rise concreteshear wallVariability of Building DamageDamage Histograms from Wesson, 2004, Northridge Damage to DwellingsAnd Gamma function fitsPGA= Factor (DF)Damage Factor (DF)These are fat distributions -- high of Building DamageFit DF, CV to: Beta, Lognormal or Gamma distributionLevels of InvestigationTypical Levels of InvestigationLevel 0 DesktopLevel 1 Site Visit (visual survey, exteriors + interiors,nondestructive examination of readily availableareas)Level 2 Site Visit + review of design documentsLevel 3 Detailed Engineering Review (with computermodels, material testing)Compare: ASTM levels; ASCE 31-03 Tiers17 Levels of InvestigationLevel 0 DesktopLevel 1 Site VisitLevel 2 Site Visit + review of design documentsLevel 3 Detailed Engineering ReviewHow do we relate Levelof Investigation anduncertainty in the riskmodel?

7 Damage FactorProbabilityDensityFunctionModifyin g seismic vulnerability to reflect seismic do changes in strength, ductility, period, and damping,and increased regularity and redundancy, affect damage?Major Challenges18 seismic vulnerability relationshipsfor new ChallengesBuckling-restrained braceDemandCapacityMean Damage FactorMajor ChallengesRelating Damage to Code FrameMomentFrameShear Wall19 The Future? Damage vs. Demand-to-CapacityCasualtiesRelationship s for injuries and fatalitiesNote high variance!20 Contents DamageATC 13 damage relationships for equipment and contentsDowntime RelationshipsDependent upon building damage state + SocialFunction Class (occupancy)21 Risk AssessmentHAZUS-MH MR1 Advanced Engineering Building Module Scenario-based Building- and site-specific22 HAZUS-MH MR1 Advanced Engineering Building ModuleCapacity SpectrumHAZUS Fragility CurvesLightShakingModerateShakingSevereS haking23 HAZUS-MH MR1 Advanced Engineering Building Module HAZUS is scenario-based (deterministic or semi-probabilistic) and it can provide expected loss (SEL).

8 Uncertainty in damage state is listed, but HAZUS does notprovide upper-bound loss (SUL) or Probable loss (PL) High degree of user knowledge and expertise seismic Risks: SEL, SULA more complete answer is a loss curve or a distributionDFPDSELSUL@ 475 year return period24 Single-Site seismic Risks: Probable LossLoss Limit475 YearsTypical seismic Risk AnalysisComparing Scenario Losses and Probable Loss25 Average Annual loss (AAL) or Expected Annual loss (EAL) The long-term annual loss rateAAL is found by summing the product of each discreteloss state (Li) x its annual frequency of occurrence( i), over all loss states:AAL = ! Li x and variance AALPDS ingle-Site seismic RisksBenefit/Cost AnalysisThe reduction in Average Annual loss afforded byretrofit is an annual benefit. The present value of theloss reduction benefit can be compared with(present) cost of retrofit, to estimate a ratios are long-term, time-averaged expected values.

9 But retrofit for any singlestructure has a high uncertainty: what is theprobability that it will experience Earthquake hazardshigh enough to pay back the retrofit?26 Benefit/Cost Analysis Example5-Story nonductile concreteframe in San Bernardino, CA$25 retrofit to increase theeffective R from 4 to 6 and thedesign strength (USD) fromV= to V = frameBenefit/Cost Analysis Example27 Benefit/Cost Analysis ExampleR = 4V = = = 6V = = Analysis ExampleExcludesLife-safetyBenefits28 Benefit/Cost Analysis ExamplePayback AvgReturn Period= 29 yearsProbable LossOther benefits of seismic retrofit -- not included in asimple benefit-to-cost calculation: enhanced life-safety (fewer deaths and injuries) increased resale value and marketability ( ,salvage value and rentability) extended useful life for the building fewer customers lost due to interruption or delayof service possible lower insurance rates reduced need for insurance reduced demand on emergency resourcesBenefit/Cost AnalysisBeyond seismic RisksGeographic correlation of risksGeographic diversification!

10 Use multi-site 1100% CorrelatedIndependentProbability of ExceedanceLoss Severity [$] loss Severity [$] loss Severity [$]2 x Risk 12 x Risk 1 Uncertainties in seismic RisksGround Motion uncertainty in the selectedground motion parameter for damage, anduncertainty in annual frequency of occurrenceBuilding Performance variability (damage orloss, given the ground motion parameter)Risks from "Special" hazards (fault rupture,liquefaction, landslide, ..) are difficult to model30 Glossaries, WebsitesGLOSSARIESH azards: : :United States Geological Survey hazards In seismic Hazard Assessment Program P. Graf, , Earthquake RiskURS, Los