ASESGRAM Assessment of the Seismic Behaviour of Flat‐bottom Silos Containing Grain‐like Materials ‐ Final Report ‐

This document reports the results and the preliminary interpretation of an experimental test campaign devoted to the evaluation of the actual pressures induced by the ensiled grain on the walls of flat-bottom silos during an earthquake. According to Eurocode 8, the seismic design of such silos is currently developed estimating the inertia forces caused by earthquakes upon these structures using a “crude” evaluation (80% of the mass of the grain-like material multiplied by the Peak Ground Acceleration). An alternative theory has been recently developed by the authors (Silvestri et al. 2012). The analytical research work starts from all the same basic assumptions of Eurocode 8 except for the one regarding the horizontal shear forces among consecutive grains. Only this difference leads to a new physically-based evaluation of the effective mass of the grain which horizontally pushes on the silo walls. The analyses are developed by simulating the earthquake ground motion with time constant vertical and horizontal accelerations and are carried out by means of simple dynamic equilibrium equations that take into consideration the specific mutual actions developing in the ensiled grain. The findings indicate that, in case of squat silos (characterized by low, but usual, height/diameter slenderness ratios), the portion of the grain mass that interacts with the silo walls turns out to be noticeably lower than the total mass of the grain in the silo and the effective mass adopted by Eurocode 8. The main goal of the current ASESGRAM project is to experimentally verify the analytical findings obtained by the authors (Silvestri et al. 2012) regarding the actions induced by grain like material upon the walls of flat-bottom silos. In more detail, the objective of the shaking-table tests is to investigate the pressures given by a grain like material, under constant horizontal acceleration, confined in a stiff cylindrical element, in order to compare them with the analytical formulation and with the Eurocode 8 provisions. This final report contains: (a) a brief summary of the analytical theory developed by the authors; (b) the description of the silo specimen and the test instrumentation; (c) the characteristics of the materials involved in the tests; (d) the program of the experimental tests; (e) the results of the first session of tests; (f) the results of the second session of tests; (g) the results of the third session of tests; (h) a preliminary interpretation of the experimental results in order to understand the actual behaviour of the silo contacting grain-like material under various accelerated conditions; (i) some concluding remarks containing preliminary but yet clear indications regarding the behaviour of silo under dynamic base excitation.