Materials for Structures - Wood - Part 5

So there's a lot we could keep talking about with light-frame construction, but let's move on to timber. I'm not gonna talk that much about timber because I think there's just a few terms you really need to know, and beyond that, it seems unlikely that you would spend a lot of time looking at specific examples. But let's just mention a few different elements. One of the big issues with timber is gonna be those connections. Remember I said earlier that light-frame construction the great part about it is I have a whole bunch of redundancy built into the system. With the timbers, I don't have that redundancy.

I have very few of these bigger and much more important pieces, and so the specific way that each one is actually connected becomes very important. One of the nails isn't quite nailed in right in the light-frame construction, it really doesn't matter. If one of the connections in a timber frame situation isn't done right, well that means that corner of the building just fell down. So really thinking through how those things work becomes actually really quite important. So imagine you have say an eight by eight column, and you're gonna have a beam coming into that column.

You know how would you make that connection? Well typically the way you'd make that connection would be with a steel angle maybe and some steel plates, and you would tie the whole thing together. You'd sort of put it near each other, and then you'd bolt it the whole thing together. But from a timber standpoint, it might be that you would actually create something like that, and then you'd create a hole in the column, and you would stick the beam into the column and have it be sort of solidly connected.

Well that would be a very good way to deal with the sort of straightforward gravity loads going up and down, but what if something was pulling it out of the hole? How would you deal with that? Well, I might have a hole that I would drill all the way through, including through there, and then when I stuck that thing in I would then take a peg and hammer that peg right through, and that would go through both the column and this little tooth of the beam and it would hold it all together.

So I might actually have multiple pegs, it would depend on what the structural system was needing to withstand. It could be a very beautiful and complicated thing, it could be hidden.

There's a bunch of different ways that this thing could go, but you're looking for these very carefully thought through systems that allow for the movement of each of the individual pieces but also that it can't pull itself apart, it can't expand a little bit every year and just sort of pull itself out of that slot. There's a lot of different ways this thing could be. It could be a half lap, it could be a single tooth in like the one I've shown here.

But it could also be something that's more where I have that steel that I was talking about, lag bolting that in, placing the beam on top, taking some steel bolting it into place, on the side maybe a steel plate.

You know so this can be done in a sort of dramatic way where we're adding all of these different things, but we have to find a way to make these big connections be solid connections and have easy to assemble. So there's gotta be a place where it can bear while we are kind of getting everything sort of put together, and believable in terms of how it's being put together that it's actually something that could be done up in the air, as well as has some beauty and interest to it.

You wouldn't do timber construction if there wasn't some desire for that special quality that the timbers have, something about wood and especially big pieces of wood that are very desirable, people enjoy quite a bit. So once we start thinking about how this beam and this column start going together, well clearly this could become much more complicated if I have beams coming in the other direction. I have a much more complicated set of interactions, but I think you sort of get the idea of how these things need to be thought through in order to stop them from pulling away, but also provide a sort of logical way of connection that can actually be done out in the field.

Under the light-frame construction, I then have joists every 16 inches, and that's certainly possible. I could have joists that sit up on top of something like this, and then put a floor up on top of that. And that happens sometimes, but that would be a little unusual. And so I'm gonna try a different version.

That different version is I'm gonna take decking material, which is three inches thick, and it's tongue-and-groove, and it's often made out of three different pieces of wood. Not always, sometimes it's actually sort of carved out of one solid piece, but often it's made out of three different pieces of wood, and that makes it easier to make that tongue-and-groove.

And then that allows us to just have this wood decking. That wood decking can span pretty far, especially because it's tongue-and-groove, so it's not acting alone. It's actually working with all of the other ones together to make this very very solid floor. The reason they're three inches thick is because that's giving us a fire protection that it's gonna take a long time to burn through three solid inches of wood.

So having that three inches of solid wood is going to make very hard for fire to get up from the lower level up through that floor. It will eventually, but it'll delay that process. If we just had a regular wood floor, well first of all, regular wood floor would need joists at that regular interval because that you know 3/4 inch of wood needs to be able to span maybe it can span 24 inches, but it's certainly not gonna span anything longer than that.

So I get these much chunkier three inches of wood, that's gonna be able to span a much farther distance, so I can have these beams maybe at every six feet, every 10 feet, something like that, but also I'm not gonna have a fire be able to get easily get through from one floor to the other. So the decking, when we soon as we start talking about timber systems, we're also talking about decking systems. It could also go with steel decking with a concrete topping, something like that. That would have a similar effect, but then you're mixing and matching different systems, and you'd have to decide from an aesthetic standpoint whether that was something you were really wanting.

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