CMU Wall Opening with W Shape Lintel

[IlliniPE]

I have a client that is wanting to open up a CMU wall for as long of a span as I'll allow. Typically, I would just use angles for a lintel for the opening, but this wall is a combination of one 8" block wall and a 6" block wall, leading to an overall wall thickness of 14-15". I know I can find W shapes with this flange width, but I have major reservations against using the flange to support a wall instead of aligning with the web due to flange buckling and torsion. I have thought to add a plate to the outside faces of the steel to essentially make a steel section resembling a hollow CMU block.

Has anyone done design for eccentric loading on a W-shape or know of a design guide for it?

 

[IlliniPE]

these two walls loaded separately?

Yes. The 8" supports 38' span steel beams going to the "left" and the 6" supports 20' span LVL beams going to the "right". Both interior. Not entirely sure how they ended up with that configuration but here we are.

 

[BridgeSmith]

IlliniPE, adding the plates as you proposed doesn't preclude bend of the flanges of the beam (although it does engage the bottom flange, as well as the top, if you weld it to both). It's also alot of steel, which would make the bending capacity huge - the span would probably be limited the support available for the concentrated vertical loads at the ends of the span. Welding the bottom flange to the plates is not an easy weld, either.

I suggest a pair of angles, welded to the top flange of a WF, similar to what haynewp suggested. With and adequate weld, it makes for a very stable and strong built-up section. You may still need to add some vertical stiffeners transverse to the web to support the top flange at intermediate locations, depending on the load, span, and the size of angles you use.

 

[IlliniPE]

You could also use a smaller flange WF beam and have a welded plate along the top in your detail above.

I am going to check this with a W shape and with an HSS member, for the sake of torsion. We will see how big of a member I end up with and if which the contractor wants to weld.

Welding the bottom flange to the plates is not an easy weld, either.

This is a great point to consider. I had the thought of making the plates intermediate to allow for easier fabrication, but I agree that some angles on a W shape or HSS member would be easier. My primary concern that I will have to check is rotation/torsion with this configuration. That was the goal of the plates, to reduce rotation and aid in reducing flange bending.

 

[BridgeSmith]

As driftLimiter pointed out, if the beam is centered under wall there should be no torsion on the beam. With angles, or some other means of bracing the top flange to the wall above, LTB is prevented, so the beam should be stable.

If flange bending is a concern, transverse stiffeners are the more efficient and economical solution, if you even need them. Have you checked the flange thickness required for the load from the masonry? I suspect you'll find you don't need that much. If you do, you may want to consider an S shape.

 

[IlliniPE]

As driftLimiter pointed out, if the beam is centered under wall there should be no torsion on the beam

It won't be centered under the load. See my response to jerseyshore. I believe I can attain the required strength with angles and a Wshape. Just need to ensure no rotation about the web. Two beams may be the way to go.

 

[jerseyshore]

A significant difference in loading means I would probably lean to using two separate pieces as well. It's almost always easier to get 2 beams off the shelf then it is to do a lot of welding for a built-up section.

 

[masonrygeek]

I'm probably too late to this discussion, but where is the recommendation to use a masonry lintel (beam) in place of steel. Just reading the discussion above makes me think that a masonry lintel would avoid all of the detailing issues above. CMU comes in 16" thick versions (sometimes called Ivany block depending on where you are) although not common in al areas. Masonry lintels can easily span 12' and there have been examples of deep masonry lintels/beams spanning 48'. Of course, these are multi-course lintels, but they work. And no messy steel beam detailing.

Here's a publication on masonry vs steel lintels:

https://website.forsei.com/wp-content/uploads/2024/01/Lintel-MASONRY-VS-STEEL_v6_2024.pdf.

And one on the design of masonry lintels:

https://website.forsei.com/wp-content/uploads/2024/01/LINTELS_Efficient_v1_2024_copy.pdf.

NCMA also has a design manual on masonry lintel design:

https://ncma.org/wp-content/uploads/2019/02/TR91B-Lintel-2004-2012-UPDATED.pdf.

Hopefully, I am simplifying your life....

 

[IlliniPE]

where is the recommendation to use a masonry lintel (beam) in place of steel

Really just boils down to construction. That would likely be too difficult to build while shoring the wall.

I think we are set on an HSS beam and HSS columns. My question is the connection. I cannot find any details of a bearing connection between an HSS beam and column. All of the details and design guides fix angles to the outside face of the column, and the beam bears on those angles. Are there any real concerns with allowing the beam to bear directly on top of the column? See attached image.