4.5.1
[FSR 52] All structural items subjected to significant in-plane stresses (compression and/or shear) under any combination of ground loads, flight loads, or thermal loads shall be analyzed for buckling failure.
4.5.2
[FSR 53] Design loads for buckling shall be ultimate loads.
4.5.3
[FSR 54] If a loading condition tends to alleviate buckling, then the unfactored load shall be used in combination with other factored loading conditions.
4.5.4
[FSR 55] Buckling evaluation shall address general instability, local or panel instability, crippling, and creep.
4.5.5
[FSR 56] Analyses of thin-walled shell structures subject to buckling load conditions during the service life shall account for the differences between idealized model geometry and the physical structure, including boundary conditions.
Discrepancies between analytically and empirically derived buckling load capability are due in part to the differences between idealized model geometry and the physical structure. "Knockdown factors" (correlation coefficients) are used to adjust predicted values to account for these differences. Typical knockdown factors for thin-walled circular cylinders are listed in NASA-SP-8007, Buckling of Thin-Walled Circular Cylinders. Caution: If NASA-SP-8007 is used to calculate a knock-down factor (KDF) for composite cylinders, the original assumptions and limitations should be understood and care should be taken. As noted in the NASA Engineering and Safety Center (NESC) Technical Bulletin No. 16-01, the universal KDF of 0.65 for composite shells may be unconservative for certain designs that are outside the scope of the publication. See NESC Technical Bulletin No. 16-01 for additional guidance.