A Framework for Risk Assessment of Infrastructure in a Multi-Hazard Environment. Stephanie King, PhD, PE

Transcription

1 A Framework for Risk Assessment of Infrastructure in a Multi-Hazard Environment Stephanie King, PhD, PE Weidlinger Associates, Inc. AEI-MCEER Symposium New York, NY September 18, New York Cambridge Mt. View Washington DC New Jersey Los Angeles ABQ Edinburgh UK

2 Outline Introduction and Motivation The problem we are addressing Multi-hazard environment Basic Framework for Assessment Risk equation Multi-hazard modeling issues Simplified framework for assessment Limitations and use of results Concluding Remarks 2

3 The Problem ASCE Report Card for America s Infrastructure (2005): ASCE estimates that $1.6 trillion is needed over a five- year period to bring the nation's infrastructure to a good condition. Limited resources + competing priorities What are the risks? Which risks should be mitigated first? Which mitigation options are best? 3

4 Multi-Hazard Environment Hazards Natural and weather-related related Accidental and service-related related Intentional Varying probabilities of occurrence Varying consequences given occurrence Varying design and assessment methods 4

5 Multi-Hazard Environment Evaluation of Mitigation Options Ancillary benefits Increasing the risk for certain hazards Risk Perception Outcome vs. occurrence likelihood Most recent hazardous event Social and political issues Influences funding decisions Not always rational 5

6 Basic Risk Equation P [B] = P [A] P [B A] In terms of Expected Values E [B] = P [A] E [B A] Risk (outcome B) Occurrence (probability of event A) Vulnerability (outcome B given event A occurs) 6

7 Basic Risk Equation Quantifying Risk Rational basis for decisions Prioritization Cost-benefit comparisons Decompose Risk Components Occurrence Hazard modeling (events and loads) Vulnerability Damage and loss modeling (consequences) Impact of mitigations 7

8 Multi-Hazard Modeling Natural Hazards Accidental Hazards Intentional Hazards Wind Seismic Flood Snow Fire Fatigue Corrosion Impact Sabotage Crime Terrorism Hazard Models Damage Models Loss Models Empirical data Simulation Accepted probabilities Actuarial data Simulation Prevention Subjective Human intent Prevention Empirical data Analytical data Design methods Published models Actuarial data Testing data Analytical data Limited data Design methods Many variables Empirical data Analytical data Published models Actuarial data Analytical data Limited data Many variables Response 8

9 Framework for Assessment and Fault Tree Approaches Quantified value of risk Clear contribution of risk components Track influence of assumptions Simplifications to make trees manageable Typically implement in software 9

10 Example Fault Tree Analysis Unacceptable Consequence Loss L Loss Modeling OR Wind Damage W Seismic Damage S AND Flood Damage F Blast Damage B AND Fatigue Damage D Damage Modeling Soil Type = T Ground Motion G AND Structure Capacity C Impulse I Pressure P AND Structure Capacity C Hazard Modeling Magnitude M Site Distance S Blast Load L Stand-off X 10

11 Example Tree Analysis Hazard Modeling Damage Modeling Loss Modeling Wind Outcome 1 Occurs at Site Seismic Flood Size = A Size = B Loading < X Loading X Damage = I Damage = II Damage = III Outcome 2 Outcome 3 Size = C Damage = IV Blast Size = D Damage = V 11 Fatigue Size = E

12 Limitations on Results Risk assessment is a snapshot in time many things change Sensitivity of assumptions and simplifications Understand the uncertainties Combination of applicable models for various hazards Use of subjective information 12

13 Concluding Remarks Quantifying multi-hazard risk Decompose risk components Rational basis for decisions Prioritization Costs and benefits of mitigations Understanding risk is the first step; need to act on that understanding Funding issues Liability issues 13