General buckling for same system as shown in the previous slide except that all stiffeners are smeared

This is Fig. 16 from the 2005 PANDA2 paper. Shown here is the STAGS prediction for a perfect shell previously optimized as imperfect by PANDA2. (Case name = testax4).

Here is the general buckling mode from a STAGS model of the optimized stiffened and sub-stiffened cylindrical shell under combined axial compression, external pressure, and in-plane shear.

In this model all stiffeners and sub-stiffeners are smeared, and the STAGS 480 finite element is used. This is bifurcation buckling mode 1, buckling load factor, Pcr = 1.8058.

Compare with the previous slide. Both this and the previous slide are for different STAGS models of the same shell.

Smearing the major rings and stringers leads to a significantly higher (unconservative) linear bifurcation buckling load factor, Pcr = 1.8058 here versus Pcr = 1.4468 in the previous slide for the same shell but with the major rings and stringers modeled as little flexible shell units rather than being smeared out.

Smearing stiffeners is often an unconservative practice. PANDA2 contains knockdown factors to compensate for this unconservativeness in PANDA2 models that involve smeared stiffeners.

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