NEW ASME VIII div2 2007 changes - Part 5 Design by Analysis 1

[cmore]

See 5.3.2 in the new code.

for "Protection Against Local Failure":

"The sum of the local primary membrane plus bending principal stresses" are compared to 4*S.

Whenever working with membrane stresses and ANSYS, I have used PLSECT to get the membrane stresses ACROSS A SECTION. Has anyone determined how to get the "membrane plus bending PRINCIPAL stresses" at every point in an FEA model (using ANSYS) so that the sum of these principals at the worst node can be compared to 4*S?

I look forward to discussions about this new Part 5.

 

[prex]

That rule was already in the old version (4-137). However the wording seems to be different in the new one (don't have it at the moment), as the old one referred to 'The algebraic sum of the three primary principal stresses'.
So a thing that's unclear to me is whether the new code refers to primary only, or to primary plus secondary stresses.
That said, a membrane plus bending stress is only defined via linearization (see faq794-982), so, if I'm not badly mistaken here, the maximum of the algebraic sum of the principals may only be at one of the two faces of a section, just like for stress intensities.
Hence the calculation is done with exactly the same methods.
Note also that I never found a situation where that rule was controlling: could be only where a state of very high compression is present, e.g. in a vessel wall highly pressurized from both sides.

prex

http://www.xcalcs.com

: Online tools for structural design

http://www.megamag.it

: Magnetic brakes for fun rides

http://www.levitans.com

: Air bearing pads