Currently, there is no option which can help provide stirrups in the Curved Beam.
When applied varying rebar, it shows incorrect placement of stirrups
This type of reinforcement can be created using the Free Form Rebar Aligned Distribution, released with Revit 2019.1:
https://knowledge.autodesk.com/support/revit-products/learn-explore/caas/CloudHelp/cloudhelp/2019/EN...