Hello all,

Could someone help me how to correctly model pipe supports for a static analysis in Caesar II?
The model in Caesar (restraints) should represent the following support characteristics:
1) The support clamps the pipe in one direction (Y) to the structure with a certain preload (lets say 6500N).
2) Movement in other directions (X,Z) is free, but limited by friction (normal load, causing friction: gravity plus preload)
3) The support structure under the support is not infinitiely stiff, but represented by stiffnesses in all three directions (X,Y,Z).

I have tried various options, but I can not get the combination of preload with friction and stiffnesses to work properly.

Any help is appreciated!
Regards,

Bart Singerling

Hello Bart.

(1) Mention the preload by checking the "forces and moments" option for that node and insert you preload as a vector in that direction.

(2)& (3) From what i can understand is that you have a restraint in the Y direction only and the pipe is free to move in the X and Z directions so define a restraint by manually inputting the "Stif" value when you define the Y restraint along with its "Mu". It will use this friction and stifness while moving in the X and Z-axis aswell.

I hope i've answered your query

BR
Umair

I tried this kind of supports some time ago for a compressor piping analysis. You only need to put +Y support at the support location and assign friction coefficient at the support, input the pre-load (as -6500N in your case) at the same support locations on the pipe.

Add the F load in your load case for the basic load cases(I do not want to go into details now).

Run the analysis.

To see the effect properly, make a small model with one anchor on aech side of the model which has a 90 degree elbow in the middle, and one or two supports (with preload condition) on each side of the elbow. You will see it is working.
You need to organise the load cases for your need (do not forget to put F pre-load case into your loads cases).

You can verify the by introducing a node on each side of the support location which are, let us say, half the pipe diameter apart from the support and add the half preload on each node instead of support node and run the same analysis and see the difference. Use the same friction coefficient at support locations.

These analyses will give you the displacements and the loading in X, Y, Z directions. Some cases in the different models, you may get uplift at the support location in case the load on the support location exceed the pre-load + sustain loads.

Hope it helps.

Ibrahim Demir

I forgot to mention that you need to input thermal and/or occasional loads cases into analysis to see the effects I described above.

Regards,

Ibrahim Demir

I have missed the stiffnesses in X, Y and Z direction you mentioned. You need to alocate those stiffnesses to the supports in case you are running analysis for an ordinary piping.
I guess modeling the structure will give you better picture rather than the assigning the stiffnesses.
In my analyses, for the compressor piping we needed to comply with the stiffness requirement of API 618 for the structural support members.
If you are running analysis for the compressor piping read this code carefully.

Regards,

Ibrahim Demir

Thank you both for your help!

However I see some problems with the solution described. When I enter a load vector F (for the preload) in y-direction, on a support where a stiffness is also specified in y-direction:
1)Will this not cause a displacement in y-direction? In reality this displacement will not be there.
2)Pre-Load on support will decrease due to deformation of pipe (other pipe supports will take part of the entered load vector)?

Regards,

Bart Singerling

If you have stiffnes in +/-Y direction there will be a Y displacement depending on the direction of the acting resultant loads.

If the loads are acting in -Y direction so there will be a displacement in -Y direction.

In case the resultant acting load in +Y direction this will show you the displacement in +Y direction and the neigbour/other supports will take large loads.

These are expected. However, I can not exactly visualise what you are trying to do. Therefore, my earlier comments are still valid. If you can provide more information about your project I guess you will find more comments from others experienced in that field.

Regards,

Ibrahim Demir