## DNV - Yield Check Allowable Values - How to include plate bending stress?

## DNV - Yield Check Allowable Values - How to include plate bending stress?

(OP)

Greetings Folks,

Important question. I am using general FEA software, now I have started work with DNV, and I am using DNV-OS-C201 with (page 41) yield check usin von Mises stress for plate finite elements in my model, but DNV states allowable stress for membrane stresses only, there is guide note, that one MAY use DNV-RP-C201 to account also for bending stress but it does not give transparent allowable check value.

To what compare my bending stresses, better, total stress (bending+membrane)?

Important question. I am using general FEA software, now I have started work with DNV, and I am using DNV-OS-C201 with (page 41) yield check usin von Mises stress for plate finite elements in my model, but DNV states allowable stress for membrane stresses only, there is guide note, that one MAY use DNV-RP-C201 to account also for bending stress but it does not give transparent allowable check value.

To what compare my bending stresses, better, total stress (bending+membrane)?

## RE: DNV - Yield Check Allowable Values - How to include plate bending stress?

I might be misunderstanding your problem but I would have thought the easiest answer would be to compare the FEA equivalent stress to the equivalent stress allowable?

I believe the check in RP-C201 is a localised yielding check for a plates structure. It's relevance will likely depend on the geometry and loading.

I would consider σ.x = σ.bending + σ.direct but I don't recall it that is what OS-C201 expects.

D

## RE: DNV - Yield Check Allowable Values - How to include plate bending stress?

Thanks for participation in discussion.

Well, what you have wrote "to compare the FEA equivalent stress to the equivalent stress allowable" it is under investigation by my query.

DNV define value of allowable stress only to be checked against von Mises build with membrane stresses.

There is no yield check defined to include also bending stresses in plate finite elements, hence my question still valid.

## RE: DNV - Yield Check Allowable Values - How to include plate bending stress?

Depending on the geometry your only concern would be if you had a localised bending issue with a lower allowable state.

D

## RE: DNV - Yield Check Allowable Values - How to include plate bending stress?

Globally considering the σ.j value as σ.e from the FEA would still be conservative (unless that poses a problem).

D

[edited to make more sense]

## RE: DNV - Yield Check Allowable Values - How to include plate bending stress?

But it is not confirmed that simply von Mises with all X Y Z components check against allowable will be safe assumption.

It might turned out that allowable stress which would include membrane and bending effects would be smaller value than just membrane requirement!

So you would compare grater stress value at the element against smaller then current allowable value... It is certainly not safe.

## RE: DNV - Yield Check Allowable Values - How to include plate bending stress?

So long as the sign for your stresses is the same then total equivalent stress (σ.membrane + σ.bending) will always exceed σ.membrane only equivalent stress? If you were very concerned with the a mis-matched loading, then you could always manually extract the membrane stress and the bending stress for the area of interest and ensure the combination of the two was additive.

But assistive loading (σ.tensile - σ.bending etc) is a genuine effect and it could be viewed as excessively conservative not to consider it, particularly if your design required capacity (and if the design is far from capacity you can afford to be overly conservative if it will save on analysis time)?

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As I say, I believe the DNV guidance note is referring to ignoring through-plate bending rather than globally induced bending stresses, they're checked individually.

D

## RE: DNV - Yield Check Allowable Values - How to include plate bending stress?

σ.x.Sd = σ.a.Sd + σ.m.Sd

Where:

σ.a.Sd = design membrane stress in the longitudinal direction due to uniform axial force

σ.m.Sd = design membrane stress in the longitudinal direction due to global bending

D

## RE: DNV - Yield Check Allowable Values - How to include plate bending stress?

What I am concerned about, is if hipothethical allowable stress which would include membrane stresses and bending stresses will be not smaller than actual allowable stress stated in DNV for membrane stresses only...

## RE: DNV - Yield Check Allowable Values - How to include plate bending stress?

I've never seen a specific allowable used for 'combined' equivalent stresses (over just regular equivalent stress) and cannot think of a logical reason there would be to have a higher allowable for direct than for combined axial stress - for a member, the difference of a stress from global axial loading and global axial bending is immaterial. I'm fairly sure that the membrane stress is inclusive of global bending.

If you are still concerned one could just email DNV direct and ask for clarification. My local contact is on vacation currently otherwise I'd be tempted to check myself.

D

## RE: DNV - Yield Check Allowable Values - How to include plate bending stress?

The issue is certainly addresed to problem where bending stresses in 3D shell/plate element are not imposed by global bending, but local loads or in vicinity of investigated elements to which geometry is enforcing local bending, still not being global.