# Internal Pressure of Pipe Members

### Tips & Tricks

001102

7 September 2015

In addition to a bending, torsional, longitudinal and strain load, you can also define and analyse internal pressure of the 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 the 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 σu = (p × di) / (2 × s)
• Longitudinal stress σx = (p × di2) / (4 × s × (di + s))

Where:

• p = internal pressure
• di = internal diameter
• s = 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, the longitudinal strain applies (considering the transversal strain) depending on the axial stress, perimeter stress and the 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.