[en] In this paper different types of idealization for a dynamic analysis of underground concrete ducts with protective slab are discussed and compared. Ducts between reactor and control building of a nuclear power plant are to be designed for loadings produced by an aircraft crash. These ducts have a height of about three to four meters and are two to eight meters wide. They are designed with a protective slab of about 1.5 m in thickness at ground level and with an intermediate layer of earth of about one meter in thickness. To prevent impact on the sides of the ducts the protective slab overlaps the ducts. With a 1.5 m thickness, perforation in the direct loading area through aircraft impact will not occur. Thus reinforcement in the protective slab and dimensions and reinforcement of the ducts have to be designed to withstand bending moments and shear forces during the time dependent loading based on the loading diagram for aircraft crash used in the Federal Republic of Germany. (Auth.)