Assessment of the floor response spectra due to pounding between adjacent structures during earthquakes: An alternative approach to study local amplifications. (15th March 2022) - Bodnar, B.
Highlights: An alternative approach to describe pounding between two adjacent multi-story buildings during earthquakes is proposed, in order to study the local amplifications of the floor response spectra (FRS) at floor level. Impact loadings are firstly computed by using simplified beam models and are then applied to the 3D mesh of the first building, decreasing CPU time. The results highlight propagation of transversal shock waves and underline local amplifications of the FRS at the edges of the floors in the high frequency range. A comparison of the responses given by detailed 3D finite element analyses and spectral modal analyses (SMA) proves that with an error less than 10%, the SMA method may be regarded as acceptable to design equipment in case of pounding between adjacent multi-story buildings. A sensitivity analysis shows that the error between detailed 3D finite element analyses and SMA increases when the damping of the structure is low in the high frequency range. Abstract: The capability of safety structures, systems and devices to withstand dynamic loadings (earthquakes, impacts, pounding, falling of heavy objects, etc.) is part of the design basis of nuclear power plants or facilities. In order to ensure their correct design, it is necessary to assess, beforehand, the admissible load. However, the validity of the Response Spectrum Analysis (RSA) largely used in the community can be legitimately questioned since it does not account for local high dynamic phenomena and is strongly dependent on the choice of parameters to get a satisfactory assessment of the calculation results. In this paper, the reliability of the RSA to design devices in case of pounding loading is studied. An alternative approach to describe pounding between two adjacent structures during earthquakes is proposed, in order to assess the floor response spectra (FRS) with a reasonable computation time. The loading demand is then computed at the bottom of a device located at floor level, from a step-by-step calculation and by performing a RSA. The reliability of the RSA in case of earthquake induced pounding is assessed by comparison of these results. To perform calculations, the impact forces are firstly assessed using linear beam models with the same modal characteristics as the ones of the building under study. Then, the pounding loading is applied to a three-dimensional mesh of the first structure made from shell and beam finite elements. The results highlight the propagation of shock waves and underline local amplifications of the FRS at the edges of the floors. The loading demand given by the RSA shows that the error related to the step-by-step calculation decreases when the pounding is considered. It turns out that the impact loading leads to higher horizontal displacements and reduces the rotations at floor level. Its amplitude increases when the damping of the structure is low, especially in the high frequency range. With an error of less than 10%, the RSA method may be regarded as acceptable in case of pounding between adjacent multi-storey buildings.