Potential of Winkler type platform models for SSI problems considering flexibility of base mat

• Published in: Nuclear engineering and design 2013-10, Vol.263, p.18-31
• Main Author: Tyapin, Alexander
• Format: Article
• Language: English
• Subjects: Asymptotic properties; Computer aided manufacturing; Flexibility; Format; Mathematical models; Nuclear reactor components; Platforms; Seismic response; Soil structure interactions; Spectra
• ISSN: 0029-5493; 1872-759X
• DOI: 10.1016/j.nucengdes.2013.04.003

•Base mat's flexibility affects different seismic response parameters in different ways.•The most sensitive are the internal seismic response forces in the base mat itself.•Vertical response accelerations in the centers of the rooms are sensitive too.•Shaped Winkler model generally gives better results than the conventional flat one.•Even shaped Winkler model cannot reproduce the response in two sensitive formats. Linear soil-structure interaction (SSI) analysis seems to be well understood nowadays and can be performed, for example, by convenient combined asymptotic method (CAM). However, CAM is asymptotically accurate for rigid base mats only – this is a limitation. So, the additional research is needed to find out (a) what is the impact of the base mat's flexibility to the seismic response; (b) how can one account for this impact using the conventional tools. In the first part of the paper a sample “wave” solution is obtained in the frequency domain using SASSI2000 code, without CAM at all. Different formats of the seismic response (e.g., in-structure response spectra, soil-structure interaction forces, in-structure internal forces) have proved to have different sensitivity to the base mat's flexibility. In the second part of the paper this wave solution is a benchmark for the different “platform” models with “soil” springs and dashpots distributed over the base mat (this is a broad definition of Winkler type model). Different shapes of distribution, starting from the conventional Winkler's flat shape and up to the “optimal” shape, are compared to each other in the second part of the paper. It is shown that even the most advanced “shaped” models of the Winkler type are limited in their ability to reproduce seismic response in the most sensitive format – the internal forces in the mat. This is the result of (a) local nature of Winkler's model, and (b) frequency independence of its’ parameters.