Another Lintel in Existing CMU Question
Another Lintel in Existing CMU Question
(OP)
New opening in existing cmu wall (about 5.5' in lightly loaded bearing wall suppt roof), I want to use the commonly used detail of sawcutting a slot and insterting an angle and then repeating this on the other side. After the block is removed we'll stitch weld a closure plate on the bottom. This procedure seems fairly common but I have a few questions:
- Do the sawcut corner need to be chamfered to get the angle to fit in (i.e. to fit the radius of the angle toe)
- What is the end condition? Bearing plates? Grout?
- How do you ensure that the angle is actually tight to the underside of block? It seems like the sawcut cut won't be straight and a good portion of the block won't actually sit on the block. Any way to remedy this?
Thanks for the input in advance.
- Do the sawcut corner need to be chamfered to get the angle to fit in (i.e. to fit the radius of the angle toe)
- What is the end condition? Bearing plates? Grout?
- How do you ensure that the angle is actually tight to the underside of block? It seems like the sawcut cut won't be straight and a good portion of the block won't actually sit on the block. Any way to remedy this?
Thanks for the input in advance.






RE: Another Lintel in Existing CMU Question
The bearing condition is probably just steel against block unless the stress becomes too high...then you might want to grout.
I don't think you would know whether or not the block is bearing tight to the angle because you cannot see it. Again, grout is probably the answer, possibly requiring a few holes through the face shell of the masonry.
BA
RE: Another Lintel in Existing CMU Question
I just extend the angle and additional 16" past the opening and provide a chemical anchor at the end of the angle through the face of the CMU wall.
The builder should be able to perform a very straight cut, particularly if they cut along the bed joint. The CMU wall will crack in an arching pattern over the opening and will bear on the angle as the angle deforms.
RE: Another Lintel in Existing CMU Question
RE: Another Lintel in Existing CMU Question
Just go around to some masonry construction projects and look at what the masons do for openings of this type. You will learn a lot.
Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask
RE: Another Lintel in Existing CMU Question
Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask
RE: Another Lintel in Existing CMU Question
RE: Another Lintel in Existing CMU Question
BA
RE: Another Lintel in Existing CMU Question
Yes... and No...
The angles are temporary supports, yes, and more...
And No... With the Nelson Studs welded to the top of the flat plate and inserted between the horizontal legs of the angles, with the plate welded to the bottom leg of the angles, the grout is ABOVE the angles and plate, with the Nelson Studs providing the composite action so that the angles serve as the lintel beam steel.
This is probably an overkill for such a short lintel, but would be very applicable for a longer, more highly loaded span.
As BA says though, there are other ways. For example, if there is suffficient arching action over the lintel, if the upper cut is made at the bottom of an existing bond beam, and if there is sufficient steel and deop[th of the bond beam for the load, no additional reinforcing would be needed to remove the block and install the window.
Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask
RE: Another Lintel in Existing CMU Question
Msquared - got it, I don't think that's necessary on such a short span, but I like the idea. thanks.
I can't count on arching action, the opening is only a couple of courses below the roof and is close to a corner.
RE: Another Lintel in Existing CMU Question
2. Provide needle beams normal to wall just above opening supported on temporary shoring. Remove masonry in opening. Grout cores in jamb blocks. Place W8x10 with 1/4" x 7" plate bottom (assuming 8" wall). Shim between beam and masonry. Add 2" x 8" solid block each side flush with wall to finish.
For an opening as small as 5'-6", many contractors would omit the needle beams and take a chance that the wall would hang together, particularly if the clear height above the opening was adequate to permit arching action.
BA
RE: Another Lintel in Existing CMU Question
The original question was - assuming that double angles are used do people typically see problems with cracking above the lintel until the angles are fully engaged.
RE: Another Lintel in Existing CMU Question
BA
RE: Another Lintel in Existing CMU Question
That being said, there must be a bond beam at one of those courses for shear transfer from the roof diaphragm.
Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask
RE: Another Lintel in Existing CMU Question
The loading is relatively light, I'm not worried about the final condition for strength/serviceability, almost anything will work - I'm just trying to minimze collateral disruption with the installation. This is an existing apartment and I'd like to minimize cracking above/around the new opening.
I wanted to do a concrete lintel but they are steering me towards steel. The double angles seem cheapest/easiest I was just wondering what people do about the end conditions and grouting between the angle/block (see original post).
RE: Another Lintel in Existing CMU Question
Use (2) 8" channels as the lintels.
To install them, you identify the area just above were the new opening will be. You then break the face shells of the block on one side. So for this example you would break out an 8" high by 6'-6" +- area. Continue with the removal to include a portion of the webs, to the point were you can slide the channel in. Install a bearing plate and shims under the channel at the new jambs to assume some of the load of the wall. Repeat procedure on the opposite side.
Create the new opening. If appearnece is a concren, weld a plate to the bottom of the channels and fill with soaps.
We always did this without any shoring. Obviously you would want to make sure there is no heavy concentrated load directly above you.
RE: Another Lintel in Existing CMU Question
BA
RE: Another Lintel in Existing CMU Question
When I was working for the construction company, I was just entering into my engineering education. I wish that I would have had more technical knowledge when I was exposed to things like this. These guys knew about arching action and took full and sometimes more advantage of it.
So, I agree with you in terms of shoring. As a design professional I would never do half the things that I saw them do.
RE: Another Lintel in Existing CMU Question
- do you do any grouting to ensure the angles are in full contact with the cmu and how do you get good access to grout?
- what do you do with the end conditions, just grout under the angles at the bearing location?
RE: Another Lintel in Existing CMU Question
BA