Simplified model and seismic response of integrated nuclear containment system based on frequency adaptive lumped-mass stick modeling approach

Finite element analysis based on solid elements can be used in the seismic analysis of integrated nuclear containment systems, which include structural components (nuclear containment building) and non-structural components (reactor vessel, steam generator, etc.). However, this solid element based FE modeling requires long computational times or high costs to acquire the analysis results; this is due to the large number of nodes and the resulting large matrix during the integration and assembly of all elements. These long computational times present several difficulties for seismic engineers in the preliminary design steps since the large number of earthquake data are used in the analysis and several design parameters need be changed. This paper presents a new simplified modeling technique for an integrated nuclear containment system, named “frequency adaptive Lumped Mass Stick (LMS) model”. This technique consists of a smaller number of stick elements and lumped masses, and it determines the amount of lumped masses to be identical to the frequencies of the original or actual structures. The frequency adaptive LMS modeling technique is applied to all structural and non-structural components of the nuclear containment building system. The integrated system is obtained considering the connecting boundary conditions of each component. Seismic analysis of the integrated system is performed using the simplified model and the results are compared to those of the solid based finite element model.