Large Round Openings in Masonry Walls (Greater than 30" Diameter)

[MrEngineerUS]

I am looking for some information on typical lintel designs for post-installed, large round openings in masonry walls. My particular wall is an exterior cavity wall of 12" stacked CMU with standard face brick. The opening is for ductwork for HVAC improvements. The architect wants me to design a "curved lintel" that would be welded together from plates. This sounds like a lot of hassle to go through so I wanted to check with you all to see if you have any information on what is typically done in these cases? Are curved lintels used? I would think it would be easier to just put a strait, typical lintel above the opening but I'm not sure how to detail the masonry work below this for such a large opening.

Any ideas? Thanks!

 

[jike]

Why would the Architect want to waste money on a curved lintel, when one is not needed?

The typical way is to use a straight lintel over the opening and a square opening below. The remaining opening can then be closed off with sheet metal or filled in with masonry around the duct depending on the final appearance that the Architect wants to achieve.

 

[MrEngineerUS]

...the remaining opening can then be closed off with sheet metal or filled in with masonry...

Thanks jike. You wouldn't happen to have a detail showing the above would you? It would be nice to have something to show the architect when I explain why a curved lintel is unnecessary and I haven't been able to find anything as of yet.

 

[jayrod12]

It's unnecessary because the fabrication cost would far outweigh the cost of jike's solution not because the curved lintel can't be done.

 

[MrEngineerUS]

I was thinking the same thing, jayrod12. Seems like a lot of hassle = expense. I'd still like to have something in-hand as to how round openings are handled per code but, as far I can tell, all the details I've found show rectangular openings only.

 

[jike]

I retired 2 years ago so I no longer have any of my details. It is relatively simple process to sketch up something. You might even be able to find a photo or two on line.
Make sure straight lintel spans beyond the required opening for the round duct with 8" minimum bearing provided at each end. Sheet metal closure would be two pieces with a round cutout to match duct. Fasten sheet metal to masonry and duct all around. If the wall has a fire rating or needs block to provide sound deadening, then fill in the opening around the duct with cut block, doweled to adjacent block as you can. If wall is exposed to seismic or wind, then doweling can be very important for integrity.

 

[MrEngineerUS]

Thanks, jike. I've started sketching up something after finding a cut sheet for "cinch plates" that basically seem to show what you've described. Would you mind elaborating on the method for doweling cut block to adjacent masonry?

 

[jike]

You can provide truss type joint reinforcement in each horizontal joint (8" oc) around the opening. Bend down before duct installation. Bend back up after duct installation, cut to length as needed and place into joint as you fill in the additional masonry around the duct.

Alternately, you can add 1/4" dowels, drilled into grouted masonry around opening or into 3/8" horizontal joints before dowel installation. Dowels extending beyond the square opening then need to be built into the masonry fill in.

 

[dhengr]

MrEngineerUS:
If you have a good competent wall, at both wythes, you should/could certainly consider some arching action in the masonry wythes. Then all you are really trying to do is hold up conc. blk. 3 or 4 courses high immediately over the opening, keeping them from fall into the opening, and giving the mason something to finish his work to. Essentially the same thinking for the brick veneer, but 10-12 courses high, depending upon the opening size. Then, in its simplest form why couldn’t the lintel piece just be a .25" thk. by 11" wide (at the conc. blk.) or .25" thk. by 3" wide (at the brick veneer) piece of bar stock rolled to the proper radius. Then, at the mid-height of the opening +/- (at a mortar joint) weld .25" thk. by 11" or 3" wide by 4-6" long horiz. feet (bearing pls.) to the arch/lintel piece. You might put a small triangular stiffener btwn. the foot and the rolled bar piece. This all slides into the wall, leave space for a 3/8" + mortar joint atop the stl. bar stock, and the mason cuts some masonry to fit, to fill in.

 

[thaidavid40]

@MrEngineerUS,
For retrofit dowels and anchors to reattach brick to masonry backup walls, look at the link here:

http://www.helifix.com/products/retrofit-products/helibar/

Good luck,
Dave

Thaidavid