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Definition of bending & membrane stress..?

Definition of bending & membrane stress..?

Definition of bending & membrane stress..?

(OP)
Hi!

I am working with ASME section III  NF-3000, mainly with the plate and shell type supports.

When looking at the bending vs membrane stress do you look at the whole cross section? For example, consider a console (H-beam) with a moment load. The flanges will take most load but is this stress considered as bending or membrane? This stress is linearly varying over the whole cross-section but very uniform for the flanges. Should this stress be compared to Sm or 1.5*Sm?

Thanks!

Thomas

RE: Definition of bending & membrane stress..?

An I beam is not generally treated as plate and shell type, though you can do that.
The important point to account for is that, in the 1.5Sm limit for bending, the factor 1.5 is simply the ratio of the plastic modulus of a rectangular section to the elastic one. As it is a rectangular section, it applies only to unreinforced plates and shells.
To follow your example of an I beam, you can consider the flanges as plates, but then the stress is essentially membrane (=constant through thickness) so the limit is Sm. If you used a linear type approach instead of the plate and shell, then by using plastic collapse analysis, you would gain higher allowables, as the ratio plastic/elastic moduli is generally between 1.1 and 1.2 for I beams.

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