On the evaluation of the horizontal forces produced by grain-like inside silos during earthquakes

This paper presents analytical developments devoted to the evaluation of the effective behavior of grain in flat-bottom silos during an earthquake. Based on the results achieved from this study, the paper proposes an innovative methodology for the seismic design of flat-bottom silos containing granular and grain-like materials, which allow for substantial reductions (with respect to the traditional approaches adopted by the codes) in the design seismic actions for silos characterized by squat geometrical configuration. The analyses are developed by simulating the earthquake ground motion with constant vertical and horizontal accelerations 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. The findings indicate that, in the case of squat silos (characterized by low, 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.