SIMPLIFIED METHOD FOR EVALUATING THE SEISMIC BUCKLING CAPACITY OF UNSTIFFENED STEEL CONTAINMENT STRUCTURES

A simplified method is presented for evaluating the seismic buckling c apacity of unstiffened, free-standing steel containment structures. Th e method is consistent with current US Nuclear Regulatory Commission s eismic design standards and with containment buckling interaction equa tions given in the American Society of Mechanical Engineers Boiler and Pressure Vessel Code which includes the influence of geometrical impe rfections of the shell on buckling. Stresses to be considered in the i nteraction equations are determined from beam theory using standard re sponse spectrum analysis. An empirical correction factor is developed to account for hoop 'stresses that are not explicitly represented in t he beam theory. As the results of these analyses are very sensitive to the damping that is assumed, the extensive three-dimensional finite e lement analyses that were performed to develop the hoop stress reducti on factor were also used to study the sensitivity of containment buckl ing to the assumed damping. Experiments on model containment structure s were then performed to further investigate the damping properties ex hibited by these structures. The study is concluded by showing that th e simplified method reasonably predicts seismic buckling capacities wh en compared with independently determined predictions from detailed fi nite element analyses.