Hi ,
How do we model the effect soil settlment on pipe supports in Caesar II.

what will be the load case to check the stress (B31.8 unrestrained)
Please dont mix it with tank settlement as there is no tank in this systtem.

There are a couple of ways:

1) You could remove the restraint and apply the displacement. (A restraint is the same as a displacement, but with zero magnitude.)

2) If you want to leave the restraints, then add a CNODE, and displace the CNODE.

3) If all of the restraints experience the same displacement, you can attach the same CNODE to all the restraints, then displace that one CNODE. If you do this, you need to change the (geometry) configuration directive CONNECT_GEOMITRY_THRU _CNODES to "false".

Thanks Mr.Ricahrd,
I have used option 2 , to model the supports.
At some location the support displacement through connecting node is more than the pipe displacemnt, means supports displces 350 mm while as pipe displaces only 250 mm in CAESAR II model while as onsite the pipe is touching the supports.
Does it indicate the pipe is already plastically deformed and CAESAR wont predict displcements after Elasctic limmit is exceeded.
Or Caesar II can predict the dislpacement after elastic limit (yeild limit is exceeded) and i need to add more node to my model.

Regards

Am I correct in assuming you have node B CNODE'd to node A with a +Y, where you displaced node A downward 350 mm? If so then it is possible that node B won't move down the entire 350 mm, due to the pipe stiffness and associated loads.

If you're trying to reproduce field behavior of an existing system, then your CAESAR II model doesn't match the field model.

Mr.Richard,
Yes your assumption of " node B CNODE'd to node A with a +Y, where you displaced node A downward 350 mm" is correct.
I think the behavoir of piping in CAESAR II should match the feild obsevation then only the results from CAESAR II will be correct.
For pipe stiffness, thickness and diameter are as per design and what has been observed on site with corrosion and mill tolerance taken into account.
My doubt is does CAESAR II give correct displacments after yeild stress is exceeded ....

Hello learner2011,

Here under, is a guideline from CAESAR II application guide page 40:

Use the following guidelines when modeling restraint settlement in CAESAR II:

- Model restraint settlement using a single-directional restraint with predefined displacements. The magnitude of the predefined displacement is the amount of anticipated settlement in the negative Y-direction.

- The operating load case is used to include the effect of settlement.

- The settlement displacements are prescribed for the connecting node at the single directional restraint. For more information, see Single-Directional Restraint with Predefined Displacement (on page 39).

- Settlement is considered to be an EXP load with a half-cycle.

Be careful, when the piping system cools down, these supports are not returned to their installation condition.

Dear Mr.Farhad,
Thanks for your valuable input and i will use the specified method to model support settlement.
Regarding the statement ,"Settlement is considered to be an EXP load with a half-cycle" .
As i am using B31.8
Allowable stress for cyclic loads is given as .
Sa=f(1.25(Sc+Sh)-Sl)) (Section 833.8 ASME 31.8)

-.02
f = 6 N <=1

So from above equation maximum value of f=1 ,irespective of the number of cycles weather 1 cylce, half cycle or 7000 cycles
Since you mention it as a half cycle load how is it going to change our allowables.

Regards