Following are load cases I've defined for a model.

CASE 1 (HGR) W
CASE 2 (HGR) W+T1+P1
CASE 3 (OPE) W+T1+P1+H
CASE 4 (Alt-SUS) W+P1+H
CASE 5 (OPE) W+T1+P1+H+WIN1
CASE 6 (OPE) W+T1+P1+H+WIN2
CASE 7 (OPE) W+T1+P1+H+WIN3
CASE 8 (OPE) W+T1+P1+H+WIN4
CASE 9 (SUS) W+P1+H
CASE 10 (SUS) L10=L4,L9 MAX
CASE 11 (OCC) L11=L5-L3 ALG
CASE 12 (OCC) L12=L6-L3 ALG
CASE 13 (OCC) L13=L7-L3 ALG
CASE 14 (OCC) L14=L8-L3 ALG
CASE 15 (OCC) L15=L10+L11 SCALAR
CASE 16 (OCC) L16=L10+L12 SCALAR
CASE 17 (OCC) L17=L10+L13 SCALAR
CASE 18 (OCC) L18=L10+L14 SCALAR
CASE 19 (EXP) L19=L3-L9 ALG

There are three (3) cases defined as SUS stress type - a "normal" sustained case L9, an alternate sustained case L4, and a case that takes the maximum of the previous two, L10, which is then used to determine the OCC stresses for wind cases. CAESAR throws a warning worded as follows: "One of more load cases contain an Alternate SUS/OCC load case". I suspect it is in reference to one or more of the load cases L10 - L18. What if any load cases need to be corrected? Should I even be defining L10, or just using L9 to develop the occasional stresses?

B31.3 is silent on "if" or "how" the Sustained stresses from "all positions of the piping system" should be combined with the Occasional stresses. The warning message you site above is simply calling to your attention that you used an "Alt-Sustained" case in combination case.

Your use of L10 is perhaps the most conservative way to look at the requirement of SUS+OCC.

Thanks Richard.

Hello,

I have a question about these load case, why didn't you check your expansion case with max sustained load?

CASE 1 (HGR) W
CASE 2 (HGR) W+T1+P1
CASE 3 (OPE) W+T1+P1+H
CASE 4 (Alt-SUS) W+P1+H
CASE 5 (OPE) W+T1+P1+H+WIN1
CASE 6 (OPE) W+T1+P1+H+WIN2
CASE 7 (OPE) W+T1+P1+H+WIN3
CASE 8 (OPE) W+T1+P1+H+WIN4
CASE 9 (SUS) W+P1+H
CASE 10 (SUS) L10=L4,L9 MAX
CASE 11 (OCC) L11=L5-L3 ALG
CASE 12 (OCC) L12=L6-L3 ALG
CASE 13 (OCC) L13=L7-L3 ALG
CASE 14 (OCC) L14=L8-L3 ALG
CASE 15 (OCC) L15=L10+L11 SCALAR
CASE 16 (OCC) L16=L10+L12 SCALAR
CASE 17 (OCC) L17=L10+L13 SCALAR
CASE 18 (OCC) L18=L10+L14 SCALAR
CASE 19 (EXP) L19=L3-L10 ALG


I think it's the goal of the b31.3 to check the max Sl when you use liberal stress. I am wrong?
About the "max", why don't you use "ABS", because, you will not have the max "absolute" load in each point, no?

Sincerely

The B31.3 change that prompted the Alt-SUS addition to CAESAR II addresses the update to the allowable displacement stress range, SA, in equation (1b). There was no B31.3 change regarding the calculation of the expansion stress range. The 2014 edition of B31.3 further qualified the stress range in paragraph 319.2.3(b) by stating that calculated positions of the piping that define the range also include the sustained loads present in the system.
So, the Code wants true positions to set the range calculation (L3-L9), not (L3-L10). And, the Code wants the most severe SL used in determining SA using (1b). CAESAR II has always used the most severe SL in (1b); with the new version of CAESAR II, that Alt-SUS load case will add to the possible SLs in selecting the maximum SL.

Regarding MAX vs. ABS in load case 10 - MAX selects the maximum term from the defined set and ABS sums the absolutes from the defined set. ABS is not appropriate here.

Ok, Thanks a lot. I understand my mistake.

I just do not understand one point :
"with the new version of CAESAR II, that Alt-SUS load case will add to the possible SLs in selecting the maximum SL."

What do you mean by selecting the max SL?
How caesar select the max SL?

Thanks

Internally CAESAR II tracks the maximum Sustained stress at each node point, from all SUS load cases.

I just received the new Caesar and I'm considering how I can take advantage of the new ALT-SUS and ALT-OCC.
Say I have two operating modes, T1 and T2, and two occasional loads, U1 and U2. I would like to get some opinion on how I should evaluate the Occasional plus Sustained in accordance with B31.3 2014, using CII 2016. I've come up with these two sets of load cases to choose from (simplified to evaluate "hot sustained" plus occasional only).


SET 1
L1: W+P1+T1 (OPE)
L2: W+P1 (ALT-SUS)
L3: W+P2+T2 (OPE)
L4: W+P2 (ALT-SUS)
L5: W+P1+T1+U1 (OPE)
L6: W+P1+T1+U2 (OPE)
L7: W+P2+T2+U1 (OPE)
L8: W+P2+T2+U2 (OPE)
L9: L5-L1 (OCC) ALG
L10: L6-L1 (OCC) ALG
L11: L7-L3 (OCC) ALG
L12: L8-L3 (OCC) ALG
L13: L2+L9 (OCC) SCALAR
L14: L2+L10 (OCC) SCALAR
L15: L4+L11 (OCC) SCALAR
L16: L4+L12 (OCC) SCALAR


SET2
L1: W+P1+T1+U1 (OPE)
L2: W+P1+U1 (ALT-OCC)
L3: W+P1+T1+U2 (OPE)
L4: W+P1+U2 (ALT-OCC)
L5: W+P2+T2+U1 (OPE)
L6: W+P2+U2 (ALT-OCC)
L7: W+P2+T2+U2 (OPE)
L8: W+P2+U2 (ALT-OCC)

The simplicity of SET2 is definitely appealing, considering the fact that I'm trying to have T1 to T7 in my all-inclusive load case setup. Would SET2 be in compliance with 302.3.6(a) as stated below and not in violation of other parts of the code?


Or do I still have to go with SET1?

How about add normal sustained case at SET 1, and include Max sustained stress case with normal one, L2, L4.
This max SUS stress case may combine with your occ cases.

Also, you can combine SET 1 and SET 2 to check only the ALT-OCC cases.

Thank you for your input.
Yes, taking the max of L2 and L4 before combining with segregated occasional loads would be the most conservative approach. I'm still considering whether I want to do that or not. My argument for not doing it is that it's unnecessary, that I only need to add the occasional load calculated for one operating mode to the corresponding sustained load.

In any case, I'm wondering about the purpose of ALT-OCC. Do we have it now so that I don't have to do SET1 anymore? Richard/Dave, I would appreciate it if you shed some light on ALT-OCC. Thank you.

There is no B31.3 reference to what we are calling Alt-OCC in CAESAR II. It seemed appropriate that, since both SUS and OCC stresses are force-based, there may be use for a similar approach for OCC.
While Alt-SUS is used to properly set the expansion stress allowable limit in (1b), the Alt-OCC term would only affect the SUS+OCC evaluation. You may want to calculate the OCC stress using the (OPE+OCC) support configuration - this would then be Alt-OCC. [I lean towards using (OPE+OCC)-(OPE) instead.]

Thank you for the valuable explanation Dave.

Hi Richard/Dave,

I have a query regarding the ALT-SUS case.
If we use eqn 1a of 31.3, then in that case it would be ok to not use ALT-SUS case. I am correct to say that?
(I mean don't click "Liberal stress allowable" check box under special Execution parameters options)

Or it is still required to check the sustained stress under lift-off case?
(Since CAESAR II selects internally max of SL from all SUS cases)

Please advise.

Thanks,
SCJ

Yes, Alt-SUS is intended to satisfy the requirements of (1b) [what we call "Liberal Allowable"]. While you may be interested in a look at the redistribution of stress due to sustained loads based on the operating support configuration, there is no change to B31.3 which now requires this. But this added check on "operating" sustained stress may still be useful in its own right.