On the definition of design values for loads on silos and tanks

Abstract

Silos and tanks are both industrial storage containers, so it may be imagined that they can be treated in a common manner for structural design. However, the statistical base of reliability theory shows that tanks are exceptionally invariant in their loading, while loads in silos are possibly the most unpredictable of all structural engineering loads. This article sets out the arguments why the statistical scatter of loads on tanks should be seen as very small indeed. It then treats the problems of loads on silos at length, showing that a wide range of different factors dramatically influence the safety of the structure, leading to a situation in which the use of a single value for the partial factor on stored solid loads could be either very uneconomic or else unsafe. It shows that the known key parameters that define the form of the structure, the aspect ratio, the properties of the stored solids, the manner of filling and discharge, and the frequency of usage of the silo should all play a strong role in determining appropriate values of design partial factors. The recommended values for the partial factors should therefore be evaluated using rules placed in EN 1991-4.