Membrane stress in ASME VIII Div 2

[rshayesteh]

ASME VIII Div II, 4.112 (f) states that Membrane Stress is a component of Normal Stress; While. FIG. 4-130.1 (Note 1) asserts “the symbols Pm, PL, Pb, Q, and F do not represent single quantities, but rather sets of six quantities representing the six stress components”
How could we explain this paradox?
Do Pm, PL and Pb include shear components? If yes, how could they be categorized?
thanks for your replies.

rshayesteh

 

[prex]

Don't forget that normal and shear stresses are relative to the reference coordinate system: in the system of the principal stresses there are no shear stresses.
In my opinion the statement in 4.112(f) is a bit confusing, as it references the normal situation of stresses in a vessel wall under pressure, where the principal directions are in the most common cases oriented as the geometry suggests (through thickness and along wall).
I personally always take all of the six stress components (expressed in the system used for the calculation) to determine relevant quantities.
Categorization instead is independent on the reference system, as you only need to know the principal stresses to calculate the various stress intensities of interest.

prex

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