Hi Josep,
Really the only way to get them into Tekla as true rebars is to find their centerlines (+diameters) and use that as input for the Rebar components from the live link. This info isn’t trivial to extract from surfaces - there’s some discussion about it elsewhere on the forum, but not sure if the proposals would do anything on polysurfaces.
I assume these bars have been modelled using centerlines in whatever tool they were authored with, so it would be much better if you could get hold of that data instead.
Cheers,
-b