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.