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Load factors when conducting an elastic-plastic FEA in accordance with EN 1993-1-5

Load factors when conducting an elastic-plastic FEA in accordance with EN 1993-1-5

Load factors when conducting an elastic-plastic FEA in accordance with EN 1993-1-5

(OP)
Hi all,

I have begun to look into performing FEAs in accordance with EN 1993-1-5, and was a bit puzzled by Annex C of this standard which provides the rules. It allows the engineer to use any material model from linear elastic up to full elastic plastic, but does not mention any load factors associated with these models. My background is largely in the world of pressure vessel, and in that world there are distinct load factors associated with the material models one uses (e.g. ASME VIII Div. 2 etc).

Simply put, from what I can read from Cl. C.9 of EN 1993-1-5, we can use any material model, but the load factors and material factors have to be taken into consideration (here it is referred to EN 1990 Annex D which is for testing and has a strong emphasis on statistical approaches etc.).

JRC has released a document titled "COMMENTARY AND WORKED EXAMPLES TO EN 1993-1-5 'PLATED STRUCTURAL ELEMENTS'" (this is readily available on the web), but also here the guidelines are pretty diffuse.

Has anyone here had experience using elastic-plastic FEAs and EN 1993-1-5? What load factors do we use when performing an elastic-plastic analysis?



RE: Load factors when conducting an elastic-plastic FEA in accordance with EN 1993-1-5

Hi Julian

I am no expert in this field but reading the post you have presented it seems to me that the load factors have to be evaluated from actual physical tests however you don’t mention whether or not any information is available in this regard and I presume there isn’t any?
Also the EN specification points you to Annex D which you don't mention.

“Do not worry about your problems with mathematics, I assure you mine are far greater.” Albert Einstein

RE: Load factors when conducting an elastic-plastic FEA in accordance with EN 1993-1-5

(OP)
Hi,@desertfox, you are correct. I'm also no expert as you can gather. I'm struggling a bit since from reading the standards here there are no 'rigid' guidelines.

Annex D as you point is based on testing (see image below) from EN 1990. The basic premise is that the partial factors and load factors should basically be the same as for 'conventional' design methods, but the guidelines in Annex D also have to take into account the statistical uncertainties with regards to the number of tests carried out. Thus, my conclusion from this is that a calculation can be carried out either as elastic or plastic (or any in between), but the same partial factors are employed. This is what seems counterintuitive, as the capacity will often increase dramatically when considering hardening of the material.

RE: Load factors when conducting an elastic-plastic FEA in accordance with EN 1993-1-5

Hi Julian

Capacity may well increase but from memory I have never known hardening (work hardening) to be a benefit, in other words if the component increases in its capacity due to hardening then that increase would not alter the load factors in an analysis.

“Do not worry about your problems with mathematics, I assure you mine are far greater.” Albert Einstein

RE: Load factors when conducting an elastic-plastic FEA in accordance with EN 1993-1-5

(OP)
I find this confusing.. Maybe it's because my background is in pressure vessels..

But let's consider a plate in tension only. If the design tension (nominal tension load × load factor) is just slightly greater than the design stress (yield divided by partial factor), then the design is inadequate. But if we do the design with an FEA and include strain hardening (as above), then the design is considered to be OK by my interpretation, since the design load is the same and the collapse load much higher. What am I missing here?

RE: Load factors when conducting an elastic-plastic FEA in accordance with EN 1993-1-5

Hi Julian89

From my pressure vessel days and using the codes the yield stress divided by its partial factor gives the allowable stress. I which always perceived that to be an average stress over the vessel and that in certain small area’s of that vessel,the stresses locally maybe higher than the design stress but that was acceptable because it was confined to small area. It’s only when you use FEA that you can see area’s of the vessel that are stressed above the design limit.
I’m not sure that answers your question but I hope it might help😀

“Do not worry about your problems with mathematics, I assure you mine are far greater.” Albert Einstein

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