Hi all,
I have analyzed a steam piping system and everything was working perfectly. After adding the wind loading in my static model in operating(case 3) and sustained case (case 4), somehow my expansion stresses (L3-L4) increased significantly (+/-60%)and now they are in excess of allowable. I expected that in this case the wind effects should be cancelled. Could anyone clarify for me why would wind loading have such a great effect in expansion case.

The first thing that comes to mind is that your system may be undergoing non-linear restraint changes between Sustained and Operating. Perhaps the wind load is causing a pivoting in the model that causes lift-off from a support?

(The other thing would be some type of input error, but I presume you have checked that out?)

Note that if you have a non-linear system, running a load case as W+P1+Wind1 (OCC) doesn't really satisfy the intent of the code. Your load cases need to be something like this:

1) W+T1+P1 (OPE) := standard operating case
2) W+T1+P1+WIND1 (OPE) := operating plus wind
3) W+P1 (SUS) := standard sustained case
4) L1-L3 (EXP) := standard expansion case
5) L2-L3 (OCC) := operating difference, gives wind effects
6) L5+L3 (OCC) := stress summation, SUS + OCC

Cases 3, 4, and 6 are your code compliance cases.

Thanks for your comments Richard,
I managed to find some recommendations in the COADE's Seminar Notes (page 2-53). It is advised that sustained +wind is checked against allowable, but not thermal +wind.
I assume your case 5. should have been L2-L1. Then case 6 is sus+wind and you confirmed the above (page 2-53).
I have updated my cases and they are as follows:
1. (HGR)
2. (HGR)
3. W+D1+T1+P1+F1
4. W+D1+T1+P1+F1+WIN1
5. W+P1+F1(SUS)
6. L3-L5(EXP)
7. L4-L3(OCC)-wind
8. L7+L5(OCC)-wind+sus.
(9. L7+L6(OCC)-wind+exp.)
If the stresses in cases 8. and 6. are acceptable, can we conclude that case 4. will be acceptable regarding stresses and ignore case 9. (even it shows excessive stresses)?

You said:


Yes you're correct - typo on my part.


Regarding your suggested load cases above:

• Cases 5, 6, and 8 are your code stress compliance cases
• Case 4 is not a stress case. This case should only be used for restraint loads, restraint design, and max deflection checks.
• Case 9 is not a valid combination. You are combining the effects of the occasional load (wind) with the expansion stress range. You don't want to add stresses to a "stress range".

[ November 09, 2001: Message edited by: rich_ay ]