Hello,

I'm calculating an existant installation with many spring supports my probleme is that I have some doubt obout my spring support model:
in the spring support data sheet there is:
Stiffness 166.3 N/mm and max vertical displacement is 2 mm (down)

My vertical Axis is Z,

in my model I puted on the concidered node +Z with 1663 N/Cm stif
and 2 mm gap but in the results I got more then -8.568 mm displacement on the same node.
Normally it must not pass the 2 mm gap that I introduced in the restraint!!!!!
Can someone tell me where is my mistake?

Regards,

Hi,

First of all, if you want to use Z as your vertical axis, make sure you have the "Z axis vertical" field value listed as TRUE in the configuration. If not, gravity will act in the Y- direction.

Also, by modeling the spring support with the Z+ restraint, Caesar understands the following. At the node :
- Z+ movement is UNRESTRAINED
- Z- movement is restrained by a 1663 N/cm stiff spring or rod
- There is 2 mm of UNRESTRAINED movement in the Z- direction the node can travel BEFORE being restrained.

If you want to model a spring hanger/support at a node, you check the "HANGERS" checkbox at that node instead of "RESTRAINTS". In your case, you have a predefined spring support so you will need to fill out the "Predefined hanger data" fields. Also, if you spring support BOTTOMS-OUT after 2mm of downwards travel, you could add a Z+ restraint with MAXIMAL STIFFNESS and a 2mm GAP at that same node.

I'm not an expert with Caesar II (anyone, feel free to correct me) but this is so far what I came to understand by reading the TECHNICAL REFERENCE. I HIGHLY recommend you do the same.

P.S.: Dis-moi si tu veux des explications en français.

Hi,

Thank you for your advices, My Z axis is listed as true.
I used predefined hanger support and I puted a negative value in the available space cause my support is a Can (spring support not hanger) and a maximum allowed travel limit 2 mm but still have the same probleme; the displacement in the same node is -4 mm on Z axis,
How to fixe the spring travel to 2mm ????
If I use the predefined hanger is that mean Caesar II don't consider the input entered in the maximum allowed traval???

P.S: j'aimerais bien parler français mais si quelqu'un aura le même problème que moi il ne comprendra rien à ce qu'on raconte dans ce topic

Correct.

hi abdelkader


peut être votre cas de charge source de ce déplacement .c'est à dire -8.568mm est le résultat de mouvement de restraint pour le ope+occ (exple: ope donne déplacement Z1, occ Z2 , donc z=z1+z2)

I see no mention of your spring preload. Defining that value may give you the number you seek.

And what of this 2mm displacement? You state that this is your maximum vertical displacement. Does that mean the support point will move 2mm from installation to operation? Or, are you saying that support is limited to move no more than 2mm? These are two different concepts and neither is represented by a 2mm gap on your spring. A 2mm gap on an unloaded spring will require that the pipe must move vertically 2mm before the stiffness engages.

If there's no preload and a 2mm gap, it kind of makes sense that your results show a greater drop at this support.

Hi,

I already defined the spring preload (7500 N) but still have the same problem.
The 2 mm is the maximum allowed travel: it mean that my support is only allowing 2 mm displacement.
But now it's clear, as per Mr Richard answer Caesar II is calculating a new value of displacement considering my predefined input.
So I have to find an other way to model this existing can support with only 2 mm displacement allowed.
I will let you know if I fix this issue.

Thank you all for your answers.

PS: @Taoufik: the result is from a simple operating case (W+P+T+H) not for a combined case