Current Design of Rectangular Steel Silos: Limitations and Improvement

Abstract

Abstract This study proposes a modification for the current design approach for rectangular silos that accounts of silos’ wall flexibility. First, the authors investigated the effect of wall stiffness, symbolized by the wall width-to-thickness ratio (a/t), on the wall-filling pressure using a recently validated 3D finite element model (F.E.M.). The model was then employed to predict the pressures acting on flexible-wall silos accounting for the stress state in stored granular materials. Most design formulas and guidelines assume silos’ walls to be rigid. This assumption is acceptable for the case of thick-wall concrete silos; it is questionable for thin-wall, metal silos, however. Consequentially, it is crucial to determine the minimum wall stiffness necessary to secure the applicability of the current design rigid wall assumption, and to propose a way to deal with more flexible walls. To this end, several wall pressure distributions that correspond to filling steel silos with varied wall thicknesses were studied. A new adjustment to the Janssen technique was proposed for a better estimate of the wall-filling pressures for square or rectangular silos. In the case of square silos, the Eurocode uses the Janssen equation together with an equivalent radius of a corresponding circular silo (with the same hydraulic radius) to determine the wall pressure. This method predicts pressure values that are practically accurate for rigid-wall silos, but its accuracy decreases for flexible-wall silos. As a remedy, the Janssen equation was modified in this research to generate more accurate pressure estimates based on the equivalent volume concept. The finite element results of several developed models with the same granular material were compared to the estimations of the newly established approach to verify the broad range of its applicability.