QUANTIFICATION OF CONSERVATISMS IN SEISMIC RISK ESTIMATES THROUGH ENGINEERING ADVANCEMENT OF SEISMIC PRA

SIGNIFICANT CONSERVATISM IN MODERN SEISMIC PRA DERIVES FROM SIMPLIFICATIONS IN GROUND-MOTION CHARACTERIZATION AT THE INTERFACE OF SEISMIC HAZARD AND FRAGILITY METHODOLOGIES. THIS CONSERVATISM ARISES BECAUSE A SINGLE COMPOSITE-MAGNITUDE, BROAD-BAND, GROUND-MOTION SPECTRUM IS USED TO DERIVE FRAGILITY FUNCTIONS, WHEREAS THE MAJORITY OF MOTIONS CONTRIBUTING TO SITE HAZARD HAVE (LESS-DAMAGING) NARROW-BAND SPECTRA. THIS RESEARCH REFINES MOTION CHARACTERIZATION, USING EXPLICIT MULTIPLE, MAGNITUDE-DEPENDENT SPECTRA, AND DEVELOPS MAGNITUDE-DEPENDENT FRAGILITIES AND MAGNITUDE-DECOMPOSED HAZARDS, TO QUANTIFY CONSERVATISMS IN SEISMIC PRAS. FOR AN EXISTING PRA, THIS WORK WILL FIRST IMPLEMENT ADVANCED LINEAR AND NONLINEAR STRUCTURAL AND COMPONENT MODELS, AND CALIBRATE THESE AGAINST EXISTING PRA FRAGILITIES, USING MOTIONS CHARACTERISTIC OF THE COMPOSITE-MAGNITUDE SPECTRUM. THEN, NEW, MAGNITUDE-DEPENDENT FRAGILITIES WILL BE DEVELOPED WITH THE CALIBRATED MODELS, USING SEVERAL SITE-SPECIFIC GROUND MOTIONS. SIMULATIONS USING AVAILABLE BOOLEAN LOGIC WILL BE CONDUCTED TO CONSTRUCT PLANT-LEVEL, MAGNITUDE DEPENDENT FRAGILITIES. SEISMIC HAZARD WILL BE COMPUTED AND DECOMPOSED INTO MAGNITUDE RANGES SPECIFIC TO THE NEW FRAGILITIES. FINALLY, HAZARD/FRAGILITY CONVOLUTIONS WILL BE PERFORMED TO OBTAIN AN ACCURATE SEISMIC CORE-MELT FREQUENCY DISTRIBUTION. COMPREHENSIVE COMPARISON OF THE PRA AND THE NEW ASSESSMENT WILL BE MADE, DELINEATING THE SPECIFIC NATURE OF CONSERVATISMS IN CURRENT PRACTICE.