Opening in existing cmu - concrete lintel?
Opening in existing cmu - concrete lintel?
(OP)
I have an existing 8" cmu load bearing wall, I need to put a new opening ~6' wide. Typically I would use the detail with channels and squeeze the wall (or angles) but I need the finished product to be as close to flush as possible, the walls are not built out very much architecturally. The lintels would also need to be fireproofed.
I've been thinking about using a concrete beam instead of steel but have never done this, does anyone have experience with this? My thought is to place two channels above the future concrete beam w/through bolts frequently and squeeze the wall. I can then remove one course of block (or two if reqd.) below the channels, drop in bars, form up and pour. You wouldn't be able to completely pour it due to the channels/wall above but this could be grouted up with non-shrink after. The other option is to drop a precast beam in there and grout the gap on top. Once the concrete beam is set I can take out the channels and the wall below.
I also plan on inserting bars and grouting the cells adjacent to the new opening so I like the continuity of the rebar/grout on top of the opening as well as the sides.
This seems ok to me - it solves the fireproofing issue and leaves a flush/clean final product. Does anyone see any problems with it?
Thanks for your help
I've been thinking about using a concrete beam instead of steel but have never done this, does anyone have experience with this? My thought is to place two channels above the future concrete beam w/through bolts frequently and squeeze the wall. I can then remove one course of block (or two if reqd.) below the channels, drop in bars, form up and pour. You wouldn't be able to completely pour it due to the channels/wall above but this could be grouted up with non-shrink after. The other option is to drop a precast beam in there and grout the gap on top. Once the concrete beam is set I can take out the channels and the wall below.
I also plan on inserting bars and grouting the cells adjacent to the new opening so I like the continuity of the rebar/grout on top of the opening as well as the sides.
This seems ok to me - it solves the fireproofing issue and leaves a flush/clean final product. Does anyone see any problems with it?
Thanks for your help






RE: Opening in existing cmu - concrete lintel?
It also depends on loads and ensuring you get adequate bearing at supports.
RE: Opening in existing cmu - concrete lintel?
Then we knock out pockets in the brick work to install the props before we knock out the rest of the beam volume. Use plastic sheet between the soffit of your beam and the brick work that must be removed - otherwise it will stick. Once your beam volume is opened up install your rebar in the void. Place the form work and cast from the top, do the anti-shrink grouting to fill the gaps the next day. Do not remove your brick work under before the concrete is set (he he he).
We also used horizontal gum poles to bridge brick work and then remove everything before we install the RC beam.
However, sometime steel beams just work better.
RE: Opening in existing cmu - concrete lintel?
STATICPH - I like the sound of your method, it sounds essentially similar to what I am proposing. What is a 'gumpole', I haven't heard this term before. Also, I'm assuming that the timber props get cast into the beam is that correct?
RE: Opening in existing cmu - concrete lintel?
RE: Opening in existing cmu - concrete lintel?
RE: Opening in existing cmu - concrete lintel?
RE: Opening in existing cmu - concrete lintel?
RE: Opening in existing cmu - concrete lintel?
RE: Opening in existing cmu - concrete lintel?
Other than that, seems workable to me.
Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask
RE: Opening in existing cmu - concrete lintel?
Gum pole - trunk that was debarked and treated ready for stuctural use, otherwise not cut in planks
Yes, the "short props" remain in place, but it is thick rebar (25mm) that is wedged in with timber wedges on both heads (hold in place with nails)
RE: Opening in existing cmu - concrete lintel?
I think your proposal has merit, I would install the channel to act as a temporary lintel and knock out an additional 16" either side of the opening for the lintel to bear-on. I would grout fill the lintel and adjacent cores from the top of the wall. I would specify a high slump, small aggregate size to help to grout self consolidate.
Because this is only one story and roof, does uplift become a consideration?
RE: Opening in existing cmu - concrete lintel?
I'd go up a few courses and use an angle grinder and remove the mortar joint to a depth of about 3" on each side and a foot past the opening and slip in one leg of an angle on both sides. I never through bolted or "squeezed" anything. Then I just pulled one angle out at a time and grouted after putting the new beam in. I usually used precast lintels that you can pick up at most masonry supplies.
I would not recommend this method on large openings.
RE: Opening in existing cmu - concrete lintel?
kikflip - Thanks for the sketch, it is basically what I was proposing. I haven't established the grouting/reinforcing of the wall yet, I don't currently have access as this is just a feasibility study. I think I'll be ok with uplift, if I go w/concrete it will be tied to the wall.
msquared48 - The opening is too close to the roof to count on arching (although I'm sure it still exists to some degree).