Stress Analysis - Superpositions

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claudio_mend
Beiträge: 21
Registriert: Di 17. Sep 2013, 22:20

Stress Analysis - Superpositions

Beitrag von claudio_mend » Sa 9. Jun 2018, 19:50

Good afternoon,

I would like to know the meaning of the load case created automatically that is called "temp. loads". I highlighted it in red on the picture below. Why does it consider all the temperature load cases? What does LCGR on its type means? Is there any place in the manual where I can find more information on how to edit the load cases and its superpositons, equations and all?
Capturar.PNG

Thanks for the attention
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rohr2support
Beiträge: 390
Registriert: Mi 14. Sep 2011, 08:23

Re: Stress Analysis - Superpositions

Beitrag von rohr2support » Mo 11. Jun 2018, 07:02

Hi

In order to calculate the stress range equation, you need to calculate the stress difference between all load cases.
Historically that meant to calculate the moment range Mc of all thermal cases and then calculate stresses by sig=i*Mc/Z.
Since the stress indices (for bends) are also pressure dependant, it is required to calculate the stress range directly.
Therefore the automatic superposition will create a load-case group that is used to calculate the stress range including the load case dependant stress intensification factors:
SE.PNG
Best regards

ROHR2 Support
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claudio_mend
Beiträge: 21
Registriert: Di 17. Sep 2013, 22:20

Re: Stress Analysis - Superpositions

Beitrag von claudio_mend » Mo 11. Jun 2018, 22:59

Hi, thank you for the fast response.

But I didn't understood how this temp. loads case works, because seems to me that it is summin all the temperatura load cases. Maybe if you explain better what the "LCGR" type means I could have it more clear.
Normally on other softwares I analyze the stress with the equations indicated by you for the arithmetic subtraction of the operation - dead load case, for each operation case. I'm not understanding how this load case take into account every operation load case simultaneosly.

Thank you again.

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rohr2support
Beiträge: 390
Registriert: Mi 14. Sep 2011, 08:23

Re: Stress Analysis - Superpositions

Beitrag von rohr2support » Fr 15. Jun 2018, 13:40

Hi

The function of a LCGR , load case group, is to transfer a whole set of load cases into the stress analysis calculation.
This includes all sectional results of all elements (including all local bending moments) but also the internal pressure and temperature information.
Historically only the resulting bending moment range was calculated and transfered into the stress analysis function.
Nowadays the stress equation calculation takes the formula from the stress code (see post above) and uses all the load cases provided in the LCGR to calculate the correct stresses for the criteria. For a SE equation it will calculate the stress range including the different ii and io factors based in internal pressure of the load case.
Yes, it is complicated, but it is the only way to fullfill the requirements of the stress codes.

Best regards

ROHR2 Support

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