CSiPlant offers P-Delta analysis, including P-Delta with large displacements. P-Delta analysis, also known as second-order geometric nonlinearity, involves the equilibrium and compatibility relationships of a structural system loaded about its deflected configuration. It also accounts for real world changes to element stiffness due to axial loads, as tension loads increase lateral stiffness of elements, while compression loads reduce lateral stiffness according to the laws of physics. The tightening of guitar strings is a good example of P-delta effects changing element stiffness. . With CSiPlant, considering P-delta effects is as easy as a mouse click requiring only a negligible amount of analysis time.
P-Delta analysis has been a near-mandatory requirement in structural design codes for many years due to the importance of its effects in design calculations. ASCE 7 has over 100 mentions of P-delta (P-Δ). However, piping stress models have traditionally ignored P-Delta effects since most older generation piping stress software programs are incapable of P-Delta analysis.
As this Ansys article says regarding large deflection analysis (aka P-delta): “geometric nonlinearity involves a few different concepts and it is not always easy to identify when it is required.” and “If you don’t know if you need large deflection (P-delta) or not, you should turn it on. There is really no way to know for certain if it’s needed or not unless you perform a comparison study with and without it.”
Although P-delta effects can have a significant effect on some plant piping layouts, P-Delta analysis with large displacements can be particularly important in analysis of buried and seabed pipelines where soil friction causes built-up compression forces that can make lateral or upheaval buckling a design concern. In the widely referenced paper, “About upheaval and lateral buckling of embedded pipelines”, author Dr. K. Peters emphasizes that rigorous analysis of upheaval and lateral buckling requires “second order solutions” (aka P-delta analysis), and he warns that “piping programs not able to produce second order solutions may not be used in solving upheaval or lateral buckling problems."
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