Dear Friends
I met some questions when i model a pipe system,hope you can help me.
1. when the loads on the restrain is zero,the constant hanger is still chosen. why?
2. how to model damper?
3. how to consider the monitoring point?

thanks in advance!

1) A variable spring hanger has a defined travel range and a defined load range. If you exceed these ranges - on either end - you can't use a variable hanger. When this happens the only thing the software can do is suggest a constant effort support with the appropriate load.

2) You can't in statics. Damping is a dynamic phenomenon. At the moment, CAESAR II does not address dampers.

3) Can you be more specific here, or provide details?

You can read this:

http://www.anvilintl.com/db/datasheets/Pipe_Hanger_Design-05.pdf