Influencing factors on effective width of compressed zone in joint column - cylindrical shell of steel silo

Abstract

In order to ensure unloading of whole amount of stored product by gravity, steel silos are often placed on supporting structure. The simplest way to design these complicated facilities is to divide cylindrical shell on two parts in our minds - discretely supported ring beam and continuously supported shell above it. Obviously, to ensure continuously support of shell, bending stiffness of ring beam should be high. In European standard EN 1993-4-1, that concept is recognized but it keeps silence about recommended stiffness of ring beam. Another way to design is to know law of distribution of compressive axial stresses due to discrete column reactions R, by height of shell. Knowing it, we could calculate the effective width l_eff of distribution of compressive stresses on every level. Where effective width is equal to distance between discrete supports, there critical height of shell ends and above it cylindrical body is continuously supported. Unfortunately the above quoted standard EN 1993-4-1 does not give an information how to calculate l_eff. The questions here are; should we accept linear distribution of compressive forces by height? In addition, could we use directly the results of Whitmore (1952), where angle of distribution α = 30°? Or, even to accept a far more brave opinion that α = 45°, used by many of the elder designers? Moreover, is value of angle α constant or does it depend on various influencing factors?