SGH previously performed a deterministic seismic evaluation of MFC-704 for the Performance Category 3 (PC-3) Design Basis Earthquake (DBE) in accordance with DOE-STD-1020 criteria. Since this evaluation was performed under consideration of current requirements, we were able to cost-effectively adapt the available results from our previous assessment and did not need to analyze the entire structure again. SGH developed more realistic seismic capacities by extracting conservative assumptions introduced into the PC-3 DBE ground response spectra by enveloping and broadening spectra generated by the site response analysis.
For this evaluation, unacceptable structure performance was defined as structure collapse. We developed seismic fragilities for several structure failure modes, including base mat punching shear, roof beam moment and shear, roof joist shear, wall out-of-plane moment, pilaster moment, concrete masonry unit (CMU) wall moment and tension, and CMU strongback base connection bearing. By considering more realistic seismic capacities and response, we found that the median and high confidence of low probability of failure capacities for the controlling structure failure modes are much greater than the mean 2,500 year horizontal ground response spectrum corresponding to recently postulated earthquake ground motion update.