CJ location in CMU wall

[Gopher13]

All,

The contractor I have is suggesting locating cmu control joints on both sides of door/window openings and extending vertically straight up to the top of the wall as show on the attached detail 2/A-301? Has anyone ever done this before? I have detailed them as stepping around the lintel at bearing and then extending straight up, but never as he is suggesting.

He is saying this is the weakest point in the wall and a crack will form here regardless. While I agree that this is the weakest point, isn't the face of the support the last location I want a full width crack to form? I have read NCMA TEK 10-2C and 10-3, and each seem to indicated the CJ's should be located just outside the vertical reinforcing around the openings.

The said walls are shear walls and they only take 2 feet tributary width of roof gravity load. They are reinforced as indicated on the attached detail 1/A301.

Thanks!!!

 

[Guastavino]

I'm assuming a CMU lintel, so I argue no joints there. If you put a joint there, what exactly holds this lintel up?

I've got to run out of the office, but I might be able to wax more poetically later.

Also, #6 bars at 24" o/c???? for a one story? really? Not being negative, but that is a lot of reinforcing.

 

[jike]

I have done it both ways. The argument against putting the joint at the face is that the lintel or bond beam tends to keep the CJ from working fully. Your wall appears to be relatively short and I personally think it looks better at the face of the opening. In your particular case, I would opt to put the joints at the face of the opening.

 

[Gopher13]

njlutzwe: It is a lot of reinforcing, and I have heard that same statement from every construction worker at the site, but it is the first building I have designed since a tornado came through the area and badly damaged a handful of our buildings. I am a little gun shy....check that, a lot gun shy.

 

[XR250]

Might want to make sure you have a heck of a ceiling diaphragm if you are worried about this building. It does not look like anything braces the top of the CMU.