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)

3 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: 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.

4 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? Peak ground acceleration (PGA) Peak ground velocity (PGV) Spectral acceleration (SA) @ fundamental structural period Modified Mercalli Intensity (MMI)

5 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.

6 , 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?

7 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?

8 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).

9 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 = !

10 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. 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.