Issues regarding the calculation or lookup of the external pressure strain coefficient A
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Please refer to Clause 4.4.5 of GB150.1-2011: Allowable axial compressive stress of cylinders: a) The value of A is calculated using Equation (3) based on the outer radius Ro and effective thickness Re of the cylinder: A = 0.094δe/Ro. In other words, this formula is used to determine the value of A only when considering the axial compressive stress acting on the cylinder. For example: the calculations for a tower shell under axial forces, and those for the supports of horizontal vessels. In the case of thin-walled shells subjected to external pressure, the effect of axial compressive stress is much smaller compared to the circumferential compressive stress caused by the external pressure; therefore, this formula cannot be used to determine the value of A.
One is axial compression of the cylinder, and the other is circumferential compression.