Loose Lintel with Channel

[T_Bat]

Hey everyone,

I've got a project where the architect wants to provide a steel channel above the windows. We discussed welding this channel to the bottom of the loose lintel angles (see below arch section). From a vertical support standpoint, the channel actually helps my angle. I think there would be some waterproofing issues to thing through - particularly at each end of the channel.

See any major issues with this approach?

 

[JAE]

The channel's shear center is inside of the brick's inside surface. The weight of the brick will tend to rotate the channel counter-clockwise in your section.

If the angle and channel are welded together, the shear center of the combined section may be further "out" but I'd want to check it.
The entire shape needs to have some measure of rotational restraint I would think.



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[BridgeSmith]

I agree with JAE, the channel will at least need to be restrained from kicking out at the top and in at the bottom.

I would think you'll also need a drip edge at the lintel and at the bottom of the channel, to divert water away from the channel and the window frame.

 

[T_Bat]

Thanks - the drip edge is per the arch's drawings. As far as rotation is concerned, I was going to check and see just how much rotation we are looking at. The windows are not very wide. I would compare the "naked" angle rotation to the built-up section's. If they were close I would just treat this like a standard loose lintel.

 

[BridgeSmith]

I (and JAE, I think) were just concerned about the moment due to the eccentricity between the center of the load (the bricks above) and the support for the channel, causing the channel to rotate out at the top, taking the lintel and brick with it. The channel needs to be restrained so that it remains vertical. If the channel could move out, so that the channel web was more centered under brick veneer that it's supporting, then those concerns would mostly be alleviated.

Edit: Actually, if the channel was turned around, I think it would be better structurally, aesthetically, and functionally (no bottom flange sticking out to catch water).

 

[T_Bat]

That's what I thought you meant. I guess to me it's a similar rotation as the eccentrically loaded angle on it's own. The loose lintel would also want to rotate with or without the channel right? Does the addition of the channel make it significantly worse?

I agree the flipped channel would be best structurally, but the current orientation is what the architect wants, otherwise we could just use a flat plate instead of messing with the channel.

[edit] I've already talked to the architect about moving the channel out some more. That would help get the shear center closer...

 

[BridgeSmith]

As far as the rotation of the lintel, it's only gets significantly better if the channel is moved out or the lintel angle itself is secured, unless you can somehow get to the back of it to weld the angle to the channel on the back side.

If the channel rotates, the lintel would move with the top of the channel, and it would likely allow it to tip forward also, both of which would increase the eccentricity. If the channel is secured so it stays vertical, then it's just a matter of whether the edge of the top flange of the channel is far enough out to keep the lintel from tipping when any out-of-plane forces are applied to the bricks above.

 

[dik]

as noted... not good it's a bad detail... can you use a W8x18? or move the toe of the channel out to the leg of the angle? Improve shear centre issue, and a matter of checking. Channels and angles are not great for torsion. What is the span? Can you use an L6x4?

or a note, "LOOSE LINTEL, SEE ARCH DWGS"?

Dik

 

[T_Bat]

Comments are appreciated! Loose lintels generally fall into the SE's scope in my area so I can't punt this back on the architect. Span is 6 feet. For this span I would normally use an L5x3-1/2 or L6x3-1/2 angle (LLV of course). The channel will be welded to the angle on both sides. I can see about using the W8 or moving the channel out even more (not sure that's doable given the channel's relationship to the head of the window). I guess I just have a hard time seeing how this is any worse that just a plain loose lintel. Admittedly I haven't had time to sit down and run any numbers yet so I'm not throwing out your concerns - it just seems this isn't way off from standard procedures for loose lintels.

 

[dik]

OP: for that span, why do you need the channel? A couple of BAR 1/4x1/2 stoppers at each end to ensure arching action and ql^2/12 moment based on a 45deg or more conservatively 60deg included brick.

Dik

 

[T_Bat]

The channel is purely for an aesthetic look. I don't need it structurally. I'm telling the architect we can just attach it to our lintel angle.

 

[BAretired]

A loose lintel would normally bear on brick each side of the opening. The sloping flanges of the channel messes up the brick coursing for the length of bearing. Maybe a light gauge cold formed steel channel would be better.

BA

 

[dik]

Maybe channel not needed; see attached.

I'll check it and add wind loading for bi-axial bending.

Dik

 

[BAretired]

Dik,
The architect wants the channel for an aesthetic look.

BA

 

[hokie66]

It's an architectural adornment. I would weld it to the lintel angle, but not carry the channel into the jamb. Think of the poor mason who has to make it happen. Hot dip galvanize the assembly. Then he can paint it whatever colour he likes.

 

[T_Bat]

That’s what I was thinking. Stop it short and let the angle bear on the brick. I’m thinking about having the weld plates on the end of the channel (like an end plate) to assist with flashing.

 

[BAretired]

I like that idea, hokie.

BA

 

[dik]

Missed that... if the channel is for show only, it can be attached to the shelf angle with a couple of slotted connections in the shelf angle and some welded threaded studs to the channel? The entire assembly can be HDGed. Would have to be assembled in place prior to placing the brick. The opening could be flashed as a normal shelf angle detail with a couple of holes. For movement issues, I'm not sure you want to incorporate the channel into the flashing detail.

Dik