Plastic moment for composite sections with "get_mp()" function

[manjolosa]

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Issue

Hi Robbie,

I really enjoy you sectionproperties and concreteproperties modules. Congrats on your work.

I am developing a scrip to check composite concrete and steel sections following eurocode 4. I am using book examples to verify my results and I can't match my book example plastic moments to the ones from the "get_mp()" function.

I tried calculating by hand the plastic moment for the steel-timber section example in the sectionproperties documentation. The hand calculation resulted in 441.79kNm and the sectionproperties results in the documention return "mp_xx" = 485.81kNm.

The plastic neutral axis position from my book examples allways match the sectionproperties' plastic neutral axis position, which is a good sign.

I also tried the "get_mp()" function with a simple non composite steel section and the results match perfectly.

I don't know if I am missing something or if there is a bug on the "get_mp()" function.

Thanks for the help.

Best Regards,

[github-actions]

Thanks for opening your first issue in sectionproperties 🙌 Pull requests are always welcome 😉

[robbievanleeuwen]

Hi @manjolosa, if you post the example with working I'd be happy to have a look into it!

[manjolosa]

Hi Robbie,

Thank you for the quick reply.

Taking for example the composite section in the sectionproperties documentation. I attached a calculation of the plastic moment in excel and a comparission to the result in the sectionproperties documention.

The excel calculation results in 441.79kNm and the sectionproperties results in the documention return "mp_xx" = 485.81kNm.

I don't understand why there would be a difference between the two results.

Composite_doc_example.xlsx

[robbievanleeuwen]

Thanks @manjolosa for bringing this to my attention! It looks like there may be a bug affecting the calculation of plastic properties for composite sections only, which wasn't picked up in the current testing suite. I'll work to have a fix and release in the next few days 👍

[robbievanleeuwen]

Hi @manjolosa thanks again for highlighting this. The test suite now includes this example and another couple of composite plastic section examples. Note that the example reports mp_xx = 450 kN.m, which is slightly higher than your excel calculation due to the presence of root radii. The new example in the tests removes the root radius and gets the same result as your excel spreadsheet. A new release of sectionproperties is imminent.

[manjolosa]

Hi Robbie. Thanks for this. It´s a really life saver for me. You have developed a great tool for structural engineers. Looking forward for the new release.