FLAT-BOTTOM SILOS FILLED WITH GRAIN-LIKE MATERIAL REFINEMENTS OF THE SILVESTRI THEORY

Seismic behavior of squat flat-bottom silos containing grain-like material still presents strong uncertainties and current design codes tend to provide too conservative formulations. Over the years, many researchers focused on the overall dynamic behavior of such silos mainly through numerical investigations. Only recently, Silvestri et al. (2012) obtained the analytical expression of the pressures exerted by the ensiled grain on the silo walls in accelerated conditions, by means of plain dynamic equilibrium considerations. In the present paper, refinements to the original theory proposed by Silvestri et al. (2012) are presented. In detail, the static and the dynamic actions on the silo walls (as effect of the ensiled material) are idealised in a more consistent way, as far as the distribution of the vertical normal pressure is concerned. A direct comparison with the consolidated Janssen and Koenen (1895) theory for design of silos is also performed in order to check the theoretical model in static conditions. Once again, the findings confirm that, in case of squat silos, i.e. characterized by low, but usual height/diameter slenderness ratios, the portion of ensiled material that interacts with the silo walls turns out to be noticeable smaller than the total mass of the grain and the effective mass suggested by EC8 for seismic design.