Buckling and post-buckling behavior of the ACS support columns

Computer program development and modeling procedures for above-core structures (ACS) have recently focused on modeling the buckling and post-buckling behavior of the ACS support columns. These developments are directed toward two considerations: (1) the prediction of the forces exerted by the column in a hypothetical core-disruptive accident (HCDA) in order that the motion of the ACS can be predicted in a coupled fluid-structure analysis, (2) the calculation of the strains and deformations of the support columns so that situations which lead to complete failure can be identified. One of the aims of this study was to examine the effect of the change in cross section, previously not treated, on the behvior of the support columns. For this purpose, models have been developed in which the portions of the column which undergo significant changes in cross section are modeled by plate elements. Results are presented for two sets of studies. In the first set, results are presented for a series of Stanford Research International scale model tests. Comparison of the tests with the computed results shows reasonable agreement. In the second, the column was displaced with a constant velocity at one end to examine its resistance as a function of displacement. The behavior of support columns consisting of two concentric cylinders has also been studied. The interesting feature of this design is that when one of the cylinders buckles, it moves laterally against the other, which may not have buckled. An effective but simple model was developed for representing the interaction between the columns. Results are presented for an HCDA corresponding to a release of 1000 MJ. (orig.)