CMU control joint detail new openings

[bnickeson]

It seems to be common practice for CMU control joints to occur at larger openings starting at the top corners under the lintel, going outward 8", then continuing up to the top of the wall (see attached upper right detail). That's the way NCMA shows to construct it. However, doesn't this cause an instability for out-of-plane wind loads? If there is no horizontal joint reinforcing or rebar crossing the control joint, and the slip plane under the lintel is assumed to not have any out-of-plane shear capacity, then what prevents the wall from just pushing inward? It seems that without any additional detailing to transfer shear through the control joint into the adjacent wall that this is not a structurally adequate detail.

Does anyone have experience with additional detailing on these control joints? I assume you can place smooth dowels in bond beams every few feet vertically across the joint, but that seems like quite a bit of work and cost. I am thinking about just showing that the joints have to be a minimum distance (say, 40" or so) away from the edge of an opening. The corner of the opening may crack a little, but I have vertical rebar at 16" o.c. and horizontal joint reinforcing at 16" o.c. so I'm not too concerned about the cracking being a problem.

Any thoughts on this? Thanks.

 

[a2mfk]

I have not detailed it that way before. A lot of the buildings I have designed are in Florida and there was already a challenge in lateral loading combined with bending from the floor beams. I would place the expansion joint maybe one or two filled cells off the jamb, then put another filled cell on the other side of the joint. This was necessary to make the wall work out in bending. I also have my doubts about masons installing everything correctly to get this detail to work, but that is my experience in this area...

 

[hokie66]

I never detail control joints at the opening, for the reasons you gave. The option at the bottom of your referenced page shows in concept the method which I think is best.

 

[bnickeson]

Thanks for reinforcing my thoughts (no pun intended) on this. I'll place the CJ's away from the openings.

It just really surprises me that NCMA publishes a control joint technique that clearly doesn't work structurally without additional detailing.

 

[yudkib]

I realize this is a little old now, but I'm doing some reading on that particular TEK right now.
NMCA DOES note that you need to account for out-of-plane loading and transmit shear via keying or other actions such as preformed or special masonry units. Bars with one side in sleeves helps with this too as you mentioned. Vendors do sell drop-in items with either rebar or helical ties which makes installation faster.

NMCA also suggests not using this detail unless the wall is not reinforced at the openings, which is silly for a bevvy of reasons.

I used to do a lot of CompSci work, the saying those guys would use for this is "RTFM"

 

[haynewp]

I use figure 2c in your link, architects often incorrectly show the joint right at the opening edge and aligned with the brick joint. Brick expansion joint locations are addressed in BIA Note 18A.

 

[NinerStruct]

My firm has a typical detail that places the CJ at the corners of the opening similar to 2a and 2b in the link above. We have another detail for bond beam reinforcing to stop each side of the CJ and a single bar, with one end taped to prevent bond, extending across the joint. We call for horiz. joint reinforcing at the first two bed joints above the opening and 16" o.c. elsewhere.

How are others treating this issue when using steel lintels? I'm an in-house structural engineer at an architectural firm that typically has used WF lintels with a bottom plate due to the width of the window frames we have always used. This is obviously a problem when trying to provide a detail similar to 2c and 2d, because it interrupts the vertical reinforcing on either side of the opening and doesn't provide any horizontal reinforcing that I could extend past the openings. Aside from trying to convince the architects to use a different window that would allow me to use reinforced masonry lintels with a brick angle, is there anything I can change to allow me to move the CJ off the corner of the openings?

What if I provide the required full height verticals at the first cores past the end of lintel bearing, and run a bond beam across the top of the lintel, essentially assuming an opening roughly 8" wider on all sides?