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This is Fig. 32a from the 2010 GENOPT paper. Shown here is the critical (lowest) general buckling mode from Thornburgh’s elaborate 120- degree STAGS model with T-stiffened weld lands at the symmetry planes at zero and at 120 degrees.
The buckling load factor is 2.0599, that is, the total buckling load from linear theory is 669235 x 2.0599 lb. in which 669235 lb is the design load used in the GENOPT/BIGBOSOR4 optimization and 2.0599 is the STAGS load factor, PA.
With optimized designs it is often a tedious chore to find the general buckling mode from STAGS because the critical (lowest) general buckling eigenvalue is hidden in a "thicket" of local buckling eigenvalues.
This is the 1147th eigenvector in Thornburgh’s model, which has 836514 degrees of freedom. The 1147th eigenmode is the first eigenmode that corresponds to general instability.
Notice that there is a significant component of local “pocket” buckling as part of this mode shape. This local buckling component gives rise to significant local stress concentrations, as seen from the STAGS nonlinear results plotted in Figs. 35a and 35b of the 2010 GENOPT paper.
In order to see figures referred to here but not shown here, please download the 2010 GENOPT paper from this website.
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