The research should appear in the research tab even when the prerequisites aren't researched yet. I guess there is a compatibility problem but hard to say more.

And I also recommend you to buy the game when you already have so much fun with it to play modded. Remember there are people who work their asses of to get this game running. It's not some highly funded AAA ♥♥♥♥.

So you have a priated copy of Rimworld. That's pretty lame, Given that Rimworld dev is one guy & a driven community of modders.

But on this particular subject I think maybe he is asking if the research is within the Medieval tech classification? Which from what I can tell it is not.
He seems to be looking for a Bridge mod of this sort, or like RF's Advanced Bridges that would work with say Medieval Time's or Lord of the Rim's.
I personally would also love to see this. As many cultures built substantial stone bridges during the pre industrial age.

I've been playing the beta (an open beta) at the time i posted, so, I think its a different matter particularly when the game is not in its full glory at that time.
I would gladly buy the game but maybe after I finish my post-grad thesis and sorts which are kinda expensive. Priorities first dude.
Also, you can edit some lines along the code to suit the medieval/tribal run at your own risk(like what I did).

That's a really ♥♥♥♥♥♥ argument. You play this game and probably for a lot of time and not just testing a few hours. I guess you also don't want to work in a job and your boss says "I maybe pay you next year. Just work for free for now, we need to buy a new machine which is expensive".

Anyway, I don't really remember what tech levels I used here, but like DarkArtistry said, it makes sense to at least build stone bridges in medieval times. I'll fix that when I have time to work on this mods again.