I am going to be honest here, first of all. This is a problem for me too, because I play with a bunch of people who are really into STEM stuff. I’ve been on both sides of the player/GM line around this issue, so as a player, I can say this: it is *really* hard to turn off a part of your brain that thinks about problem-solving, especially if that’s part of your job. Honestly, I would try to avoid blaming  your players for thinking about what they would do if *they*, not their characters, were in this situation. 

The way I see it, you have a couple of things you have to do here.  

One, **talk to the players in question**. I think there might be a difference in opinion. To me, it seems like your players want to do semi-realistic stuff using OOC knowledge. You seem to want that to be justified in character (please correct me if I’m wrong). When I was in this situation, I talked to the player in question and tried to figure out a couple of things. One, is creative problem solving a part of the game they like? Two, is it a part of the game you like? Three, you say they don’t have skills appropriate to the task. How would *they* (this needs to come from them, preferably after a discussion about the first two things) work it out in character? Where have they heard about the idea, tried something like it, read a schematic? This can be great for worldbuilding. My suggestion  for this is that you be open to ideas from the player, but veto something if it’s all the way out of left field, like a hermit-like character who’s never been in a city coming up with a plan to build a ten-story apartment building. 

The second thing to do is pretty much the same as the other answers. If there isn’t a logical reason for a character to make that plan work, make them roll for it or veto it. Maybe the INT-dumping barbarian actually has a really great idea once in a while (no insult meant here, I thought of the logical extreme as an example). 

Finally, I have an example from one of my games where this worked. I sort-of-kind-of co-GMed back in middle school with a friend for a world we built together. One of our players, playing a noble, said she wanted to make a shelter for the wilderness adventure they were on according to plans she’d drawn up before the game. The player, call her A, had a good bit of wilderness and engineering experience but the character really didn’t. I talked to A about it between sessions (this was back in middle school, so it was at our next break), and she said she liked creative solutions, we talked to my co-GM and he was not really sure what he thought about it, then A decided that the character had read some schematics but didn’t know how to do it. At the next session, A rolled to see whether she could remember how to build it, then a different check to see whether it worked right (which failed, but she didn’t know that until it crashed in the middle of a long rest). Another player, who IC had helped with planning did the actual building, and they used it for a while. 

In my case, the talking it out plan worked, but if it doesn’t, this might be time for a session 0 to discuss it. In general, for your next campaign you might want to include a discussion about OOC knowledge and justifying it in game to stop this from happening again.