Wind pressures and buckling of metal cantilever tanks.

摘要

This thesis reports work done to evaluate wind pressure distributions on aboveground tanks formed by a cylinder and a roof, and to assess shell buckling due to such pressures. First, wind tunnel experiments were performed to obtain wind pressure distributions developed on the wall and on the roof of circular short steel tanks, including different geometries and group configurations. The geometries considered were selected from typical cylindrical tanks located in the Caribbean Region (including Puerto Rico), with conical, shallow-dome, and deep-dome roofs. The pressure distributions measured on the cylinder of the isolated tanks were similar to pressure values on silos obtained by other authors. However, shielding arrays revealed increments in windward pressures on the cylinder, and group arrays generated changes to the pressure distributions with respect to the isolated tanks. Second, linear bifurcation and nonlinear step-by-step buckling analyses were performed on tanks using the pressure distributions measured from the wind tunnel experiments, in order to obtain buckling loads and their associated modes of deformation. Changes to the initial geometry of tanks using the first mode of deformation obtained from an eigenvalue analysis were investigated to compute the sensitivity due to imperfections. The magnitudes of the imperfections applied varied from 10% to 200% the thickness of the shell. From the results, it seems that bifurcation analyses represent adequately the buckling behavior of isolated tanks with conical roofs, but not of tanks with dome roofs based on the selected dimensions of short tanks. Results also showed that corrosion effects reduce the buckling capacity of steel tanks. On the other hand, ring stiffeners around the cylinder of the tanks provide additional buckling capacity that depends on the elevations at which they are located. About imperfections, it seems that tanks with roofs have higher buckling loads but at the same time are more sensitive to imperfections than open-top tanks.