... like this https://steamproxy-script.pipiskins.com/sharedfiles/filedetails/?id=3314345561

It is easiest if the bridge disappears underground. Then you have the normal ground surface on which you can place your decorations.
But sometimes you can also hook in a decoration if the blueprint is very close to the ground. I have several pictures of this in my artworks xD Just don't tell the devs.

very cool job ! So bridges have to be semi on the ground ? or ground level ?