Erdbebenberechnungen von unterirdisch angeordneten Reaktorgebäuden

Embedding the buildings, in soil changes their seismic response behaviour as compared to surface buildings, i. e. higher, stiffness and increased radiation damping is attained. Finite element models are, best suited for determining the effects of embedment and of layered subsoil. The code used was the LUSH2-programme, which is applicable to 2-dimensional problems and provides an approximate treatment for non-linear dynamic soil behaviour. For embedded buildings there is a good agreement between 2- and 3-dimensiqnal models of the response for points below the soil surface. It is therefore permissible to use the less costly 2-dimensionalprogrammes. To simulate earthquake, three different acceleration-time histories, derived from actual measurements and from artificial synthesis, with differing response spectra were fed in. The soil characteristics assumed are applicable to a representative site in Germany. Three different types of models were examined, using analytical models with only a few elements for parametric studies and with up to 716 elements for more precise calculations. A comparison was made between the semi-embedment, the total embedment, and installation of the reactor building above-ground. The results of the calculations show that the three, acceleration- time histories lead to different peak stresses due to different spectral intensities, but that the acceleration patterns as a function of depth are similar. It does not even change significantly with variations in the dynamic shear modulus and critical damping of the soil layers. The acceleration pattern is strongly influenced by the thickness of the soil layer between the rigid base and the foundation plate of the building. In the case of thick strata, accelerations will decrease towards the soil surface, whereas they increase with less thick strata(amplification). This phenomenon is independent of the level of embedment of the reactor building. To answer the question as to which siting will involve lower accelerations a distinction must be made between the reactor building proper and the internals which are excited via the foundation plate. In general, the embedded reactor building is less stressed than in the case of siting above-ground. In general it may also be said, that in the case of thick soil strata, the internals are slightly less affected by stressing due to the increase in accelerations than in the case of the building being sited below ground level : The shift of maximum response towards higher frequencies was confirmed by the investigations. Calculations have resulted in a similar behaviour in earthquake conditions for semi- and totally embedded reactor buildings. The height of the coverage and the thickness of a superimposed concrete slab have no significantinfluence on earthquake response