Hi everyone. I would like to post a question. I built the following load cases
1) W+P1+T1(OPE)
2) W+P1 (SUS)
3) T1 (OPE)
4) L1-L2 (EXP)
5) L1-L3 (SUS)
The load case five L1-L3 is my hot sustained case. The system i analysed was a piperack line of NPS 8 inch. There was lift at many places. When i checked the stresses in hot sustained it was under allowable but around 90%. I checked the displacement in hot sustained (which is usually not reqd) for my reference. The disp was around 1000 mm with negative sign. Then i modelled a pipe of same size (8 inch - STD), schedule, material as simply supported beam. The stress in sustained case was above the allowable with support span 20M. I checked the displacement at the middle i.e at 10M it was -290mm. My question is why the stress in hot sustained case is below allowable even when the displacement was -1000mm and above allowable with displacement -290mm when the allowable is same (Sh) in both cases.Please clarify.

Thanks in advance.

Check your setup and initial conditions: The 1000 mm displacement does not appear realistic for a pipe rack.

If the program is outputting an unrealistic displacement, then you're not advised to accept the resulting stresses coming from the same equations and mdoeling.

THINK!!!

Your "Hot Sustained" (just which paragraph of the Code discusses this load case, by the way?) load case is (W+P1+T1) - T1. Thus, the T1 case has no gravitational force associated with it. I would not at all be surprised to see that some displacements in this load case were very large uplifts. Then you are subtracting these displacements in the post-processor module from displacements generated by an analysis in which gravity is active, and which presumably has weight supports now and then.

HELLO!!!

ARE YOU THINKING YET???

Have you figured out the answer?

If YES - congratulations, you've learned something.

If NO - you are beyond hope and there's no point explaining.