Wind induced buckling of large circular steel silos with various slenderness

Large steel silos are typical kinds of thin-walled structures that are widely used to store large quantities of granular solids in the industrial and agricultural sectors. In the present analyses, the buckling design of large steel silos subjected to wind pressure is demonstrated in accordance with Eurocode (EN1990, 1991, 1993) and proposed combinational Load Cases WE (wind and empty silo) and WF (wind and full silo). Six steel silos with capacities of 30,000-60,000 m3 with slenderness from 4.77 to 0.35 and thus representing very slender, slender, intermediate slender, squat and retaining silos are examined as examples. The finite element model is established using the commercial general purpose computer package ANSYS. Five types of buckling analyses are conducted on geometrically perfect and imperfect models with and without consideration of material plasticity. These models are designated as LBA, GNA, GMNA, GNIA, and GMNIA in EN 1993 Part 1-6. The concept of critical wind velocity vb,cr is put forward and defined for the first time in reference to our wind induced buckling analysis, according to which the silo structure obtains the equivalent buckling strength for Load Case WE and WF. The dominant loading conditions of Load Cases WE and WF can be determined by drawing comparisons between the critical wind velocity and designed wind velocity proposed by meteorological conditions. Nonlinear buckling deformations corresponding to the critical point in Load Case WE are governed by circumferential compression generated in the windward region of shells localized at the top of the silo wall. Nonlinear buckling modes of Load Case WF take the form of well-known elephant-foot deformations found at the base of the shell wall, which are induced by meridional compressive stress. Effects of geometrical and material nonlinearities and weld imperfection on the buckling behaviour of steel silos are very complex and are closely correlated with the slenderness of silo structures.