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Geotechnical Fragility Analysis for Seismic Probabilistic Risk Assessment
Seismic probabilistic risk assessment (SPRA) analyses are carried out for new nuclear power plants and for existing nuclear power plants as part of Post-Fukushima effort. To support the SPRA analyses for post-seismic accident sequences, seismic fragility curves are developed for structures, systems, and components (SSCs). Fragility analyses of structures typically focus on failure modes related to yielding of shear walls or other structural members, excessive interstory drift, or impact with adjacent structures. Geotechnical failure modes such as liquefaction, slope stability, bearing capacity and excessive differential settlement are generally screened out and not explicitly considered in the probabilistic risk assessment (PRA) model. For geotechnical failure modes that are not screened out, there is no consensus on how the fragility calculations should be conducted and high confidence low probability failure (HCLPF) or median capacity should be determined. The conservative deterministic failure method (CDFM) approach was developed primarily for structural failure modes and was not calibrated for geotechnical problems. Therefore, using the CDFM for geotechnical fragility calculations can result in gross errors in HCLPF or median capacity estimates. The error can result from the way the uncertainty term β is assigned, the presence or lack of conservatism in the factor of safety calculations, and whether ductility is considered. Geotechnical capacity equations typically do not rely on codes like the structural capacity equations, thus, may not be always conservative. This paper identifies typical geotechnical failure modes for PRA, provides examples on the screening out criteria, and, for non-screened out modes, provides recommendations on how the fragility calculations may be conducted, considering both simplified approaches, such as CDFM, and more comprehensive approaches such as Monte Carlo simulations.
Geotechnical Fragility Analysis for Seismic Probabilistic Risk Assessment
Seismic probabilistic risk assessment (SPRA) analyses are carried out for new nuclear power plants and for existing nuclear power plants as part of Post-Fukushima effort. To support the SPRA analyses for post-seismic accident sequences, seismic fragility curves are developed for structures, systems, and components (SSCs). Fragility analyses of structures typically focus on failure modes related to yielding of shear walls or other structural members, excessive interstory drift, or impact with adjacent structures. Geotechnical failure modes such as liquefaction, slope stability, bearing capacity and excessive differential settlement are generally screened out and not explicitly considered in the probabilistic risk assessment (PRA) model. For geotechnical failure modes that are not screened out, there is no consensus on how the fragility calculations should be conducted and high confidence low probability failure (HCLPF) or median capacity should be determined. The conservative deterministic failure method (CDFM) approach was developed primarily for structural failure modes and was not calibrated for geotechnical problems. Therefore, using the CDFM for geotechnical fragility calculations can result in gross errors in HCLPF or median capacity estimates. The error can result from the way the uncertainty term β is assigned, the presence or lack of conservatism in the factor of safety calculations, and whether ductility is considered. Geotechnical capacity equations typically do not rely on codes like the structural capacity equations, thus, may not be always conservative. This paper identifies typical geotechnical failure modes for PRA, provides examples on the screening out criteria, and, for non-screened out modes, provides recommendations on how the fragility calculations may be conducted, considering both simplified approaches, such as CDFM, and more comprehensive approaches such as Monte Carlo simulations.
Geotechnical Fragility Analysis for Seismic Probabilistic Risk Assessment
Tastan, Erdem O. (author)
Geo-Risk 2017 ; 2017 ; Denver, Colorado
Geo-Risk 2017 ; 399-411
2017-06-01
Conference paper
Electronic Resource
English