Torsion or Not

[BouncedPod]

I'm currently working with a (3) wythe existing brick wall that will require new window opening support. Because of some constraints I am not able to center the new lintel beneath the wall, and am concerned that the load distribution of the wythes will cause torsion in the new lintel. Below is a sketch of what I am dealing with.

[URL unfurl="true"]https://res.cloudinary.com/engineering-com/image/upload/v1665592810/tips/20221012113015237_x7lsaa.pdf[/url]
Questions:
1) Is the addition of the transverse stiffeners enough to "drag" the load from the outer wythe into the web of the W section?
2) I am leaning towards using an HSS section sized to resist the torsion, but I have no good way to resolve it at the ends of the lintel. Any ideas?

 

[driftLimiter]

1) Even if you did 'drag' the load to the web, it still is a force acting with a lever from the centroid (its torsion).
2) HSS is a good idea here. Would need to see the detail your coming up with to help resolve the torsion better. Usually want to try to resolve this into a couple that can be resisted well. Perhaps a couple over the face the masonry wall and get bolts to act in shear.

You can always try to find a detail that eliminates torsion (this is the #1 recommendation by AISC).

 

[milkshakelake]

2) In case there's a column at both sides, a moment connection can be good for torsion too, or a modification of that. If it's into a brick wall, I agree with driftLimiter. I'm thinking some kind of large plate with bolts. Or pocket the beam and use some angles welded to top and bottom and some bolts to handle torsion. Another way is to separate the gravity and torsion forces (kind of like the pocket) by doing the angle thing and also adding a long WT support with bolts under the beam reaction, like a long stiffener; some problem solving will be needed for the detailing of this.

 

[KootK]

1) Is the addition of the transverse stiffeners enough to "drag" the load from the outer wythe into the web of the W section?

I agree with dL, the stiffeners will "drag" the shear over to the web but they'll drag the torsion along with it.

2) I am leaning towards using an HSS section sized to resist the torsion, but I have no good way to resolve it at the ends of the lintel. Any ideas?

My recommendation would be to study the beam considering how the points of load delivery will likely shift laterally under that rotation. Often, this can make it so that the torsion does not collect along the span of the beam and, therefore, does not accrue awkwardly at the support. I'm not a big fan of the HSS here. If the method that I just described works, then there's no real benefit to it. If the method that I just described doesn't work, you'll have a heck of a time delivering the beam end torsion to the supports and would likely need a more invasive solution anyhow.

 

[driftLimiter]

My recommendation would be to study the beam considering how the points of load delivery will likely shift laterally under that rotation. Often, this can make it so that the torsion does not collect along the span of the beam and, therefore, does not accrue awkwardly at the support.

This is like pin-pin for torsion from AISC design guide I think. Can you elaborate on this a little I have a hard time understanding how this works.

 

[KootK]

Let's see if we can do this sans sketch...

1) I imagine that OP has set his loads out specifically to coincide with the centers of the wythes.

2) When the beam twists, the centers of reaction of the wythes will tend to shift in a fashion that reduces the tendency to twist.

3) This implies some moment in the masonry wythes. At the same time, I suspect it's this mechanism that makes a lot of loose brick lintels survivable in the wild.

How that?

 

[driftLimiter]

Yes that helps thanks KootK. Its somewhat analogous to so called self-limiting rotation.

 

[KootK]

Yes, just so. Or, at the least, one hopes that it will be self limiting. I try to demonstrate that a rotated center of load lands on top of a horrendously eccentric center of beam reaction without Armageddon ensuing. If it doesn't, on to other solutions.

 

[BouncedPod]

Update:
I am looking at making some modifications to the foundation wall/brick ledge that will allow me to center the lintel on the brick wall and eliminate, or at least greatly reduce, the torsion on the w section.

 

[Greenalleycat]

We deal with a fair few funky details

If this thing is a free-spanning lintel (i.e. no good framing coming in the side) I'd be proposing using a rectangular section with a 10mm (3/8") angle welded off the side
Stack the bricks on the angle and then let the torsion accumulate to the ends - will be a bit tricky getting the moment out but could weld a flat plate off the end with a bolt above-below into studs
Could probably make the numbers work into timber but I'd use steel to prevent creep

Alternatively use a PFC (A C-Channel, not sure what your notation is) with the web out and weld the angle to that, I would think it's cheaper than the stiffened I-beam?
This has rubbish torsional stiffness though so you'll need intermediary framing to restrain this
If you go for that option, following the load path in minute detail as I did this exercise recently and found some critical junctions that aren't obvious at first look

 

[phamENG]

Is this new or existing? Since you're in the US, and it's triple wythe brick, I'm guessing it's not only existing but also historic.

How big is the opening? Is it a new or existing opening? For typical window widths (and even some larger up to about 8'), this is usually overkill. Most old buildings have sufficient brick to arch over the windows, and the lintel is really just there to hold up the brick while the mortar sets. If you don't believe me, look at the brick above as a deep masonry beam using the modulus of rupture for head joint mortar perpendicular to the joint. Of course, if you're opening up a 20' storefront opening on a downtown main street, your solution is likely more appropriate.

Also, if it's historic, the architect is probably planning an arch in the face brick. If so...use it. You're not going to want some two bit hack of a mason messing with a building like this; they should be capable of building an arch to support the face brick while your beam supports a concentric load above. And, bonus, the arch looks better when it doesn't have steel under it.

 

[BouncedPod]

phamENG

This will be a new 10' opening in an existing historical main street type building but will not have an arch. Because of floor joists knifed into the wall and window openings in the level above, I am not able to develop arching action over the lintel.