Variation of floor vibrations due to earthquake in reactor building structures

We have studied floor vibration of a generic reactor building subjected to seismic loads, with the aim of quantifying the variability of vibrations within each floor. A detailed 3D building model founded on the bedrock, was excited simultaneously to three directions by artificial accelerograms compatible with Finnish ground response spectra. The material model of the reinforced concrete walls, columns
and beams was linear, whereas water in the spent fuel storage pools was modelled with mass elements. The dynamic simulation of 20 seconds was carried out using explicit time integration. The extracted results of the simulation were accelerations in three directions and pseudo-acceleration spectra (PSA) in several floor locations. At first, locations were estimated by engineering judgement
to arrive to a feasible number of floor nodes and locations for post processing. It turned out that engineering judgment was not enough to depict locations, which resulted in conservative vibration estimates. For this reason we took a more systematic approach, where nodes of the floors were selected with a 2 m grid. With this method, besides the highest PSA peaks in all directions we are able
to give the full plot of the vibration distribution in each floor. The statistical evaluation of the floor responses was also carried out in order to define floor accelerations and PSA’s with high confidence of non-exceedance. The conclusion is that in-floor variability can be as high as 50-60% and more extensive models with enough dense node grids should be used in order to have the conservative
estimate of floor vibration under seismic action.