CMU Wall Corners...

[walterbrennan]

Good morning.

I have a general question about masonry load-bearing wall construction. Considering a typical exterior building wall corner, constructed of load-bearing CMU in running bond. Assume that no control joint was indicated to be located precisely at the corner; neither by the structural drawings, nor the architectural drawings.

With only these facts in mind, and under conventions of construction typical in the masonry industry of today, would I be more likely to end up with a wall corner that was constructed integrally (i.e. one wall “tied” to the other by “toothing in” of units), or rather should I expect these walls to be constructed structurally separate from one another?

Any insight, from your unique perspectives in the industry, would be greatly appreciated.

Respectfully,

Walterbrennan

 

[jike]

I would expect the corner to be fully bonded. We don't expect control joints to be added at locations not shown on the drawings, especially when it may affect the integrity. Do the walls span vertically or horizontally?

I would hope that you could point to some statement in your structural notes or specifications regarding bonding at intersecting walls. If the project is small and perhaps does not have notes or specifications, you should still be able to require the contractor to follow the governing code requirements. For instance, the section in IBC 2000 that you need to refer to is 2109.7.2, Intersecting walls. If the governing code references ACI 530-99, then check out 5.8.2.

I hope this helps!

 

[SacreBleu]

The wall corner should be constructd in running bond as jike mentions. Corner "Dur-O-Wal" reinforcement shoulkd be used, or at least corner bars to lap with the bond beam reinforcement. For lighter construction, one vertical should be at corner, but most offices use 3 verticals (one each adjacent cell in addition to corner).

 

[walterbrennan]

jike,

The walls I was thinking of were reinforced to span vertically to a roof or floor diaphragm. Which means, since ACI 530 section 5.8.2 talks about masonry walls, “… depending upon one another for lateral support…”, it's not really a concern, here. And, looking at section 1.9.4.1 (b) (also ACI 530), as long as the transfer of shear is completely avoided at intersecting walls (i.e. control joint right at the corner/intersection, and no bars, joint reinforcing, etc. from wall to wall), then the code has been satisfied there, as well.

For a wall designed to span vertically, and resist in-plane shear adequately, it shouldn’t be a big concern, analytically. But from a redundancy standpoint… well, solid corners just make a guy feel better than corners that are built up to one another.

Anyway, I’m really just wondering, from a state of the industry standpoint, whether masons are still (generally) building FROM the corner (solid, interlocked), as opposed to building TO the corners (control joint at the corner); in the absence of any other direction… (like most things in building construction, used to be a time when it was just taken for granted...!)

Let me know what you're seeing, out there.

Thanks,

Walterbrennan

 

[bylar]

I dont know what they do in the rest of the country but everywhere I have lived teh corners are construted as per Jike.

 

[jike]

There are some buildings that we have done where the architect wants a full height window at the corner. Obviously, in this case the masonry is not tied together at the corner. It does not present a problem if the wall is continuously supported at the floor and roof.

The only drawback that I can see about not tying the corner together is that when the sun hits one side and not the other, one wall will bow and the other will not. Maintaining a caulk joint and prevent water infiltration may become a problem. Appearance may also be a problem.

 

[haynewp]

I have put in the general notes that wall intersections shall be toothed. With the wall corners locked together, I feel it helps with in plane overturning for short shearwalls. I wouldn't want a control joint here.

 

[SacreBleu]

haynewp,
Speaking of short shearwalls, is there anything in the IBC or ACI-530 that shows how to take advantage of the "return" around the wall corner to increase shear capacity (actually overturn resisting and reduction of tension/compression at each end)?
Does any one have a spreadsheet solution to this?

 

[miecz]

Asked a contractor here in Connecticut. He said they never put a control joint at the corner, unless it's specified on the drawings.

 

[haynewp]

I know 530-99 has section 1.9.4 that addresses intersections and in the commentary CC-13.

The Reinforced Masonry Eng. Handbook has examples on p. 125 of this.