Saturday, April 7, 2007

Detail of the Week: Expansion Joints 2, Electric Boogaloo

Oh, like you didn't see that '80s throwback joke coming a mile away.

I found some more shots of the building I used for the exterior expansion joints DoW, so I'm milking this concept for all it's worth. See, the big expansion joint running along the outside of the building also has to come inside, too. When you build walls in a building, you have to anchor the framing of those walls to the structure, right? And if the structure likes to move, and the wall you build is running across that expansion joint, then the expansion joint goes through the interior walls too.

Now, I tried to annotate these photos a bit on my clunky photo-editing software at home, so let's see how well it publishes...

Ha! It works! You can see the gap left in the drywall where the joint will go. What will fill this joint? Something that looks like this:

Several companies make expansion joint covers; this one happens to be by Watson-Bowman. You can kind of see inside it on top how it looks like a "W" in plan, which allows it to expand and contract in place while being attached to both sides of the joint.

But this is below the ceiling. What's happening above the ceiling?

Since no one's gonne see it, the contractor here has chosen to simply cover the joint with a piece of drywall. This is okay, I guess, as long as the wall isn't rated. If the wall is required to have some kind of fire or smoke resistance, then the contractor would have to put the expansion joint cover shown above all the way up to the underside of the structure above. Speaking of structure, what happens when these vertical and horizontal joints come together?
In this case, they just kinda come together. Again, if this joint isn't in a rated wall, then the drywall-over-the-gap should suffice. If it is rated, then we need the cover piece all the way up here. The light stuff you see in the joint is insulation. What's going on on the roof, on the other side of this gap? I think you've seen the photo before....

The leg on the left of this joint is what we're seeing the underside of in the photo before it (if that makes any sense on a Saturday afternoon).

Okay, I think I've beat this topic up quite enough. Next week's DoW will tie in with something that BaxterWatch has explained on her website. Blogging in Stereo: can you stand it? Only one way to find out...!


The Wandering Author said...

It's interesting, because I like to think I'm not a stupid person, and I know all about expansion and contraction, but I never thought about the need for special joints in large buildings.

I do have a question, though, if you happen to know the answer. I'm a freak for medieval architecture, and I know there are tithe barns and such that would seem to be large enough to need expansion joints, if I read your posts correctly. But as far as I know, they don't include anything like that. So why have they stood up so well over so many years?

BaxterWatch said...

OOO! I can answer that one - medival architecture (depending on what country you are in) utilized a technique of using logs in the stone wall to stand on as they built the stone walls. Think about it - they didn't have man lifts or elevators, and its a pain to move ladders.

So they would build a log into the wall, poking out side ways. They would put these in periodically and use them to stand on as they built the walls higher.

They could take the force of a man towards the ground. Then they would either pull them out, or more likely, burn them. In many castles in ireland and england you can see the holes in the stone walls where these logs would have been.

and there you have built in "expansion" spaces. Which allows the stone to swell and contract without messing up the structure.

At least that is what the tour guides told us.

And YEA! Pixie is pimpin' my site. Excellent!

faded said...

Expansion joints are your friends.

Many years ago (45+) when I was a kid growing up in Philadelphia there was a spectacular road way failure due to a bound expnasion joint. The Schuylkill express way had been badly maintianed and unbeknowst to the city fathers most of the expansion joints in the road and some of the bridges had bound. On a hot summers day this had the effect of causing a section of the road to pop up. Except that it was an entire slab and it poped up with such force that it stood straight up on end. It stood up just long enough for a car to fall in the hole were the slab was. The the slab fell back down crushed the car and killed the driver.

Expansion joints are you friends.

Anonymous said...

The answer to The Wondering Author's question about expansion ans contraction of midevil architecture is - These structures were built of natural stone and they do not expand and contract like clay or concrete building materials.