Liquid storage steel tanks are vertical above-ground cylindrical shells and as typical thin-walled structures, they are very sensitive to buckling under wind load, especially when they are empty or at low liquid level. Previous studies revealed discrepancies in buckling resistance of empty tanks between the design method proposed by the American Standard API 650 and the analytical formulas recommended by the European Standard EN1993-1-6 and EN1993-4-2. This study presents a comparison between the provisions of current design codes by performing all types of numerical buckling analyses recommended by Eurocodes (i.e. LBA-linear elastic bifurcation analysis, GNAgeometrically nonlinear elastic analysis of the perfect tank and GNIA-geometrically nonlinear elastic analysis of the imperfect tank). Such analyses are performed in order to evaluate the buckling resistance of two existing thin-walled steel tanks, with large diameters and variable wall thickness. In addition, a discussion is unfolded about the differences between computational and analytical methods and the conservatism that the latter method imposes. A sensitivity study on the geometric imperfections and the boundary conditions is also conducted. Investigation on the boundary conditions at the foot of the tank highlights the sensitivity to the fixation of the vertical translational degree of freedom. Further, it is indicated that the imperfection magnitude recommended by the EN1993-1-6 is extremely unfavorable when applied to large diameter tanks. Comments and conclusions achieved could be helpful in order to evaluate the safety of the current design codes and shed more light towards the most accurate one.
In wind turbines, blades are critical design members because performance depends on blade material, shape, twist angle, etc. The problem of internal, mechanical design and material selection for a prototypical high-power horizontal axis wind turbine blade under static, flap-wise loading is investigated in this study. At first a materials selection methodology has been proposed. A very detailed computational analysis based on finite element modes is developed representing the load-carrying box girder of the blade with a given airfoil shape, size, and the type and position of the interior load-bearing longitudinal beams-shear webs. Results concerning displacements and stresses are generated using both plane and shell elements with linear and nonlinear analyses.
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