I try to model a support (structure) which is fabricated by different size of pipe material in CAESAR_II.
First of all, is it possible to use pipe in structural modeling?
I know with selecting user define, section Id can be defined but when I try to save the model, there is an error shows SECID is not defined.
How can I solve this problem?

Normally structures should comply to some specific regulations. This is why there are some specific softwares that can perform analysis of stuctures and check their code compliance to the main structure codes.
With these softwares you can make model made by pipes as well, you can check the effect of wind, snows, additional weight acting on surfaces, and so on.

Yes it is possible to use pipe in structural modeling for pipe supports. If you're using pipe, you don't really need to use the Structural Modeler, you can build your support structure in the Piping Input.

To resolve the specific error you're getting, please send your model file in to TechSupport so we can review it.

It was so helpful.
Thanks for your reply.