Hello neshghi,
if you are using 1-D bars with perfect bond, you can typically simply omit the hooks in your model.

If you are using a bond law, the simplest way to represent a hook is by activating the corresponding "no slip at start/end" option (=assuming the hook as a perfect anchor).

If the above show not good enough, please send us your model + skteches explaining what you are modelling such that we can recommend a way (ATENA Troubleshooting, 2.1.1).

Regards.