Seismic design of flat bottom silos containing grain-like material

This paper proposes an innovative methodology for the seismic design of flat-bottom silos containing granular, grain-like material. In the general issues concerning the actions provoked by earthquake ground motion on the walls of flat-bottom grain silos, the assessment of the horizontal actions seems to be of particular interest. Up to date, the horizontal actions due to the seismic event are usually evaluated under the hypotheses (i) of stiff behaviour of the silo and its contents and (ii) that the grain mass corresponding to the whole content of the silo except the base cone with an inclination equal to the internal friction angle of the grain is balanced by the horizontal actions provided by the walls (supposing that the seismic force coming from the base cone is balanced by friction and therefore does not push against the walls). This paper presents analytical developments devoted to the evaluation of the effective behaviour of flat-bottom silos containing grain, as subjected to earthquake input. The analyses are developed by simulating the earthquake ground motion with constant vertical and horizontal accelerations (time-history dynamic analyses are not carried out) and lead to the subdivision of the ensiled material into three different portions (depending on the interaction with the container) by means of plain dynamic equilibrium considerations that take into consideration the specific mutual actions developing in the ensiled grain. Two portions push (in different ways) into the silo walls, while the third one does not push into the silo walls. The findings indicate that, in the case of silos characterized by specific (but usual) height/diameter slenderness ratios, the portion of grain mass that interacts with the silo walls turns out to be noticeably lower than the total mass of the grain in the silo.