Internal Pressure of Pipe Members

In addition to bending, torsional, longitudinal, and strain loads, you can define and analyze the internal pressure of members with circular hollow cross‑sections in RFEM and RSTAB. The following perimeter and axial stresses resulting from the internal pressure load are analyzed using Barlow's formula and transferred to design modules in order to superimpose the remaining stresses due to internal forces.

The stresses due to internal pressure are calculated as follows:
Medium perimeter stress σ_u = (p × d_i) / (2 × s)
Longitudinal stress σ_x = (p × d_i²) / (4 × s × (d_i + s))

where
p = the internal pressure
d_i = the internal diameter
s = the wall thickness

Generally, these stresses due to internal pressure have no effect on the deformation. Only after you activate the "Bourdon" effect in the calculation parameters does the longitudinal strain apply (considering the transversal strain), depending on the axial stress, perimeter stress, and corresponding material stiffness. In this case, the positive internal pressure leads to an extension of the member element. If the member element is fixed elastically or rigidly on both sides, the extension leads from the internal pressure to a forced load, which induces additional internal forces.

Author

Mr. Niemeier is responsible for the development of RFEM, RSTAB, RWIND Simulation, and in the area of membrane structures. He is also responsible for quality assurance and customer support.

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