Stability of Open‐Top Cylindrical Steel Tanks with Primary Stiffening Ring under Wind Loading

Abstract

AbstractCylindrical steel tanks are very thin shell structures and vulnerable to buckling under external pressure due to wind or partial vacuum due to rapid emptying or blocked vents when they are either empty or partially emptied. A primary stiffening ring is commonly used at or near the top of the tank wall to increase its strength against external pressure instability. Most traditional design treatments largely ignore the non‐uniform circumferential variation of the wind and treat the tank as subject only to uniform external pressure when sizing the primary stiffening ring. Moreover, the interior of the tank also experiences suction pressures due to the leeward suction on the tank. Wind tunnel tests have shown that the magnitude of these suctions can be very significant compared with the external wind pressures. This study has investigated the buckling resistance of a range of cylindrical steel storage tanks with primary stiffening rings subjected to non‐uniform wind loading modeled as harmonic variations, including the suction, using finite element analyses. A criterion for the required primary stiffening ring stiffness is developed, which is found to depend on its value relative to the stiffness of the cylindrical shell under each harmonic of wind loading. The effects of the shell‐ring stiffness ratio on the buckling capacity are studied and it is found to be a powerful measure that is critical to the design of the ring. Improved design rules are directly obtainable from this new treatment.