Allowable stress value for SOL in B31.1

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r2user
Beiträge: 144
Registriert: Mi 14. Sep 2011, 10:18

Allowable stress value for SOL in B31.1

Beitrag von r2user »

Dear Rohr2Support

I have a observation on the allowables stress in occasional cases (Code B31.1).

Let say there are two temperatures defined in the stress files.
1. Design
2. Operating

Obviously the design temperature in higher than operating temperature, so the SH value will be higher for operating.

Now as we combine the sustained case with occasional cases to check stresses (or occasional - normal operating), should we take the SH value for design case and multiple it by the occasional load factor (1.2*SH) ?

Or should we use the SH value based on operating case? I could not find anything related to this written in the code. This can create (theoretical) problems with some results, depending on which algorith we choose. What does Rohr2 do?

Best regards
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rohr2support
Beiträge: 455
Registriert: Mi 14. Sep 2011, 08:23

Re: Allowable stress value for SOL in B31.1

Beitrag von rohr2support »

Hi

My suggestion would be to consider design temperature allways for allowable stress calculation and operation temperature only for thermal expansion calculation.
Therefore you have one design temperature for any part of the system which does not change during your analysis and you calculate the allowable stresses for that temperature.
That is what happend in ROHR2 if you keep the default settings:
It calculates the allowable stresses for an operating case using the design temperature, but for the calculation of the thermal expansion we use the operation temperature.

For occasional loads you then use 1.2*Sh depending on the type of occasional load.

Of course this "standard" way of proceeding may be to conservativ in some special cases.

Best regards
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