Steel beam supporting existing CMU

[JStructsteel]

When adding a steel beam to header off a large opening in a CMU wall, do you folks add any mechanical connections to the beam to "capture" the CMU, or do you just rely on grout/friction or horizontal span to resist any lateral load?

I was thinking dowels or studs on top of the beam, but that could get in the way of the installation. I also thought angles welded to the underside of the top flange to capture the CMU. Lastly I was thinking holes in the to flange to install expansion anchors or epoxy dowels at the grouted cells un into the wall.

Thoughts?

 

[milkshakelake]

I put channels on two sides to sandwich the wall and thru-bolt it. Otherwise, I'd only be relying on friction between the mortar and steel. It's okay I guess, but I don't like to do sketchy connections. It's good that you're thinking about this.

Furthermore, this method eliminates any need for shoring.

 

[JStructsteel]

My issue is that once side I have bar joists that need supported, then wall above and a high roof supported. Im at a W18x50 right now.

 

[milkshakelake]

You can add two L6x4x1/4 LLV welded to the top to make a "cup" to receive the CMU with the W18. Pack with grout to make it tight. Gets rid of any concerns about sliding.

But anyway, my solution can also work with some deep C or MC channels or something. There are two of them.

 

[BAretired]

Projecting the flanges into the CMU wall does not seem particularly easy to do; and it messes up the continuity of the wall at the top of the channels. If the flanges project outward, it would be much easier, although the architect might not like it.

 

[milkshakelake]

@BAretired Agreed, it's easier to project it inward for brick because you can slot it into the mortar joints. Facing it outward will achieve easier installation for CMU, although I agree that it might not be architecturally good.

 

[JStructsteel]

I was thinking something like this into the cells that had rebar.

[URL unfurl="true"]https://res.cloudinary.com/engineering-com/image/upload/v1708382349/tips/Flange_Pinned_rkzohu.pdf[/url]

 

[jerseyshore]

What a pain this will be to shore the existing wall bearing bar joists and get the new beam in.

 

[JStructsteel]

Jerseyshore, yes it will be. On the high side there is more joists too. Im going to look at some channels, and perhaps some channels as jambs too.

I dont think the contractor has looked at it too much yet, I was directed to use W beams.

 

[BAretired]

That is an entirely different situation than the thread title suggests. I was imagining a new beam in an existing CMU wall with no brick veneer and no OWSJ bearing on it. I don't think the contractor will like this detail very much.

Not only that, but the beam needs to be laterally braced, possibly by extending the bottom chord of each OWSJ and the beam should have stiffeners over the column.

I would be tempted to raise the top of beam above top of OWSJ, with a wide enough top plate to support both brick and block, then after the beam is secured, support the joists on a seat welded to the beam web, bracing the top of beam and web as required.

 

[milkshakelake]

How would you get the W beam under the CMU? The CMU would be floating, and would have to be shored somehow. I'm not sure how that shoring would work.

 

[jerseyshore]

I didn't even realize the brick at first glance, just the idea that the CMU shoring would get in the way of the beam installation.

Why is there brick on the inside of a building that has wall bearing joists? And what's supporting it now?

Not sure how they would shore this without using a ton of needle beams above (outside?).

I think you'd have to go with the channel detail here because you can't afford to remove the wall beforehand without some intense shoring setup.

Maybe you leave the first course below the joist seats and start your channels below that. Brutal.

 

[BAretired]

How would you get the W beam under the CMU? The CMU would be floating, and would have to be shored somehow. I'm not sure how that shoring would work.

Needle beams supported by posts each side of the wall is the usual way if a single steel beam is to be used.

 

[JStructsteel]

This is a low/high roof condition. CMU wall to the high joists, lower roof framing in to the CMU (pockets) Outside brick supported down to the lower joists. New opening will be at the low joists.

The contractor would need to shore, that has not been discussed yet. I have sent review set of drawings for them to review.

I like the idea of channels, but the one end is a inside corner, so channel would stop at the edge of the opening, and need support there too. .

 

[milkshakelake]

You put channels at the ends, too.

For W beam condition, I'd probably put columns. Columns are also okay for the channel thing, using cap plate and possibly stiffener gussets as "knee braces."

I don't really like the idea of needle beams in general. It's quite expensive, a lot of detailing and sequencing, and you rely on arching action of the CMU unless you find a way to support it at the bottom face of the beams...which might end up being channels anyway. You'd also presumably need temporary footings under the columns for needle beams, which come with their own details and inspections.

If W is required, as jerseyshore said, you could temporarily shore it with the channel idea instead of using it as permanent structure. Then install W shape below it, install upward facing angles to prevent sliding, and pack it with grout.

If you use the channels permanently, you can find a way to attach joists and brick support those to the channels. Seems feasible to me. It's just steel, after all.