Locally supported cylinders with rigid stiffeners: elasto-plastic failure

Steel silos [1] are thin-walled cylindrical shell structures which are frequently supported by local supports or engaged columns. These discrete supports introduce high forces into the shell wall, resulting in axial compressive stress concentrations in the shell wall directly above the supports. Consequently, both buckling and yielding resistance are reduced due to these elevated compressive stresses. This premature instability phenomenon should be avoided at any time. Because of this, a local stiffening configuration near the supports is added to improve the buckling strength, as material is added in the region of elevated stresses. Vanlaere [2] considers a configuration consisting of 2 longitudinal stiffeners with limited length above each support, combined with circumferential stiffeners at top and bottom (Fig. 1). These stiffeners are welded to the shell wall and are made from flat steel plate. The stringer stiffeners assist with the introduction of the supporting load into the shell wall, while the two ring stiffeners ensure that the shell wall remains its circular form. Moreover, the lower ring assists with the introduction of loads form the hopper into the barrel. Obviously, it is not the intention that the added local stiffening members fail before the ultimate strength of the shell wall is reached. Rather, the stiffening members must withstand higher loads than the shell wall itself. Fig. 1 shows an example where this condition is not met.