hi im working as a piping engineer in public sector,
Is it right to remove the lifting +y supports and check for sustained strees for any failure or can i allow the pipe to lift freely.

Give a word search and you will find lot of topics addressing this issue in this forum.

Regards

go to this thread you will get lot of information
http://www.eng-tips.com/viewthread.cfm?qid=229108&page=1

i think there should be warning messgae in error checking module
that this particular support is lifting in this particular operating case
so that will be great help for new user like me.



Regards
Stressed pinky

You can not change your model and "take out" the support that lifts off - this makes the Expansion case wrong. Review the discussion on "Hot Sustained" in the CAESAR II Technical Reference Manual.

Pinky - the Error Checker can't tell you that a support lifts off, since error checking happens "before" the analysis. The support lifts off during the analysis, so anything before that is unaware of the support behavior.

Dear Richard,

With reference to Caesar-II Technical Reference Manual, Chapter-6, Sustained stresses and nonlinear restraints, the following are the load cases for the hot-sustained,

W+P1+T1 (OPE)
W+P1 (SUS)
T1 (EXP)
L1-L2 (EXP)
L1-L3 (SUS)

My query is, why the load case 3 (T1 – EXP) shall not be operating (T1 – OPE) instead of expansion. Because there is more variation in stress due to change in the load case from expansion to operating. The following are the summary of stress variation from expansion to operating,

Sustained case – Normal (W+P1+H)

CODE STRESS %: 55.10 @NODE 20
STRESS: 87010.5 ALLOWABLE: 157911.5
BENDING STRESS: 74689.2 @NODE 20
TORSIONAL STRESS: 3466.4 @NODE 20
AXIAL STRESS: 12321.7 @NODE 20
HOOP STRESS: 22503.6 @NODE 20
3D MAX INTENSITY: 87286.3 @NODE 20

Hot Sustained Case – Considering load case T1 as Operating (i.e. W+T1+P1+H – T1) = W+P1+H (Hot sustained)

HIGHEST STRESSES: ( KPa )
CODE STRESS %: 94.94 @NODE 20
STRESS: 149928.2 ALLOWABLE: 157911.5
BENDING STRESS: 137797.8 @NODE 20
TORSIONAL STRESS: 13646.7 @NODE 20
AXIAL STRESS: 12130.8 @NODE 20
HOOP STRESS: 22503.6 @NODE 20
3D MAX INTENSITY: 152392.2 @NODE 20

Hot Sustained Case – Considering load case T1 as Expansion (i.e. W+T1+P1+H – T1) = W+P1+H (Hot sustained)

HIGHEST STRESSES: ( KPa )
CODE STRESS %: 62.52 @NODE 20
STRESS: 98732.5 ALLOWABLE: 157911.5
BENDING STRESS: 86578.8 @NODE 20
TORSIONAL STRESS: 2798.7 @NODE 160
AXIAL STRESS: 12153.7 @NODE 20
HOOP STRESS: 22503.6 @NODE 20
3D MAX INTENSITY: 98789.4 @NODE 20

From the above summary, it is seen that the variation in stress is mainly due to the bending stress and torsional stress.

My option on the above clarification is, operating case shall be used instead of expansion.

Please clarify, if I am wrong. The drawing is attached for reference.

Case 3 is a "construction case", you don't want to use the results of this case for anything, other than as a component in a subsequent case.

Dear Richard,

Yes, load case 3 is a construction case. But my query is whether the case3 shall be expansion or operating. Because as i mentioned in earlier query that there is variation in stress value considering the case 3 as operating or expansion.

In my case, when i consider case3 as operating the stress value is more when compared to considering the case3 as expansion. The stress summaries are already shown in the earlier query.

Also please note that, caesar reference manual mentions the case3 as a expansion case.

Please clarify whether expansion or operating shall be used for case-3 (T1).

But you're not going to use the stresses from Case 3. When you setup "L1-L3", you're subtracting the displacements of Case 3 from those of Case 1. Then from this difference forces and moments are computed, and from these the SUS stress.

Yes the stress computed in Case 3 will be different based on whether you specify the case as OPE or EXP; the stress equations are different. A temperature load by itself should be specified as EXP.

Dear Richard,

I agree your suggestion, but i just want to [b]know the reason, why case-3 shall be considered as expansion instead of operating.[/b] Since, as the case-3 shall only for a construction case, and normally for such case the condition shall be operating.

This query has raised due to large variation in stresses in considering case-3 as expansion or operating. In which operating is the dominant stress.

If you take Case 3, and compare it to how Flexibility Analysis was performed in the 1960's and 1970's, you'll find a corresponding case consisting of only "T1", or perhaps "T1 + D1". This was refered to as the "thermal case", and the Stress Type is Expansion.

Dear paldex

suppose if L1-L3(sus) is failing ,how to make it pass ?

Dear Friend,

If the sustained case is failing, then the support must be adjusted or relocated such that the allowable load must be within the limit. But making it to pass may be simple.