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Opening in masonry wall
6

Opening in masonry wall

Opening in masonry wall

(OP)
My client bought two bays in a commercial building and wants to connect them by creating an opening in the demising CMU wall. The wall is non-loadbearing but it is ±24 feet high. He wants an opening of 8'-0"H x 10-'0"W opening. I am thinking of adding two channels on each side of the wall, connect them tight with bolts and then cut the opening. Does this should feasible? I can ask them to weld a plate below channels after opening is made.

RE: Opening in masonry wall

Done that often... also a couple of temp channels and cut out the wall and install a W6 steel beam below the channels... and remove the channels when it's installed.

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

RE: Opening in masonry wall

Some acrows with strongboys?

Much easier to install.

Then fit a lintel / beam underneath?

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

RE: Opening in masonry wall

Rather than channels, you can use angles - cut out half the bed joint, insert angle. Cut out the other half from the other side, insert angle. Cut out wall, weld your plate (if required/desired). Or insert a couple of needle beams above and install a wide flange lintel and then patch the CMU.

RE: Opening in masonry wall

It's borderline for me but I like the channels for a 10' span. Some things to consider:

1) Most folks do weld a plate to the bottom flanges for masonry containment and some measure of load sharing and composite action (laterally).

2) Keep in mind that all of the vertical load that you accumulate in the bolts over the opening needs to exist through the bolts at the sides of the opening. You may need more bolts at the sides or even vertical reinforcing channels beneath the bearing points. pham's angle solution has a leg up in this regard.

3) If this is a building likely to have large exterior doors open during wind events, give some consideration to whether or not that may cause problems for the jamb elements that will exist on either side of the opening.

RE: Opening in masonry wall

Also, if you're going channels, I'd go with deeper ones. C12/C15. Reasons:

1) Stiffness is your friend with masonry.

2) You're showing an awful lot of bolts in a single course of block.

3) The cost of this will be all about labor. Material saving will likely be immaterial.

RE: Opening in masonry wall

Quote (Littleinch)

Some acrows with strongboys?

Those acrows look awful noodly to resist the eccentric loading...

I typically do a few needle beams and a WF underneath.

RE: Opening in masonry wall

(OP)
Thank you all for your valuable inputs!

RE: Opening in masonry wall

Juat curious, what span/deflection ratio do y'all design for when installing a beam under old masonry? Seems it would have to be stiff AF for it to actually keep the masonry from cracking. My suspicion is that the beams end up being there as a safety measure and the masonry just spans the distance in most cases.

RE: Opening in masonry wall

XR - I usually shoot for L/600...but I agree. Considering the number of openings I've seen cut in masonry with no perceptible problems in the first 10-15 years, over modest sized openings the masonry will arch over and then the stuff below the "arch" hangs from the mortar. The beam ends up acting as catch when the mortar does final start to fail in tension. at 10' clear opening I'd start to get a little more cautious with it, though.

RE: Opening in masonry wall

I'm in the L/600 camp as well with a maximum of 3/4"

RE: Opening in masonry wall

(OP)
I agree with L/600 approach. As KootK suggested, the channels should be stiffer than required which shall make the deflection negligible. Considering 60° load triangle over the 10 feet opening, the dead load from self weight of wall is not that high. 2-C300 (C12) should take care of it.

RE: Opening in masonry wall

I have also provided a detailed procedure before when doing this so the support sequence is known. I included needle beams the last time I did this but it may not be necessary with the double channels, unless you want the bottom plate installed prior to loading the channels.

RE: Opening in masonry wall

I typically go L/1200 on old masonry and L/600 on green masonry.

RE: Opening in masonry wall

I've been doing L/600 with a 3/8" absolute limit. It's tough because it feels like any deflection would likely cause cracking. In this sense, pham's take on it is probably the pragmatic reality.

Per the sketch below, I've also had some heretical thoughts regarding what the real loading on such a beam really is in these situations. Any takers??



RE: Opening in masonry wall

I just wrote out a response to refute you, but I can't do it. I think you may be on to something. As long as the masonry is in good condition, it does seem logical. The beam can only deflect if you have cracks in the masonry - otherwise the masonry is just holding itself up. Once it cracks, the load will distribute based on the characteristics of the masonry (arching action) and the stiffness of the lintel (stiffer toward bearing).

I think this is limited to forensics and answering "why hasn't that collapsed yet?" sort of questions. Unless it makes the design really stupid, I usually design for the full rectangular load - what if your nice new opening begets a vertical crack? If it's new construction, what if the architect throws in an expansion joint at that door without saying anything?

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