Pressures measurements of maize grain in cylindrical steel silos and comparison with different international standards

Flat bottom cylindrical silos are employed worldwide to store granular products of high commercial value. However, many gaps still remain in relation to pressure estimation and structural failures still occur. Moreover, there are few full-scale experimental stations in the world to facilitate advances in this line of research. Therefore, in this work, pressures were evaluated in a metallic cylindrical pilot silo that allows geometry adaptations. The pressures were analyzed for two slenderness ratios (2 and 3, respectively) with a flat bottom, using maize, a free-flowing product, as the stored product. The pressures were analyzed during loading and discharge conditions. The experimental results were compared with those recommended by means of the current standards EN 1991-4 and ANSI/ASAE S433.1 and the theory of Jenike et al. (1973). The results obtained show that the discharge pressures for the H/D ratio equal to 2 may exceed those obtained by the calculation method proposed by ANSI/ASAE S433.1, showing that the coefficients used in the standard are not sufficient to promote safety in projects of this configuration. Among the analyzed standards, EN 1991-4:2006 best fitted the experimental discharge pressures for the H/D ratio equal to 3. However, the theory of Jenike et al. (1973) presented theoretical values closer to the experimental ones in all analyzed depths. It is clear that further experimental studies are still needed to understand the underlying physical phenomena and the relationships between the pressures, silo geometry and flow pattern of the stored material.