Multi-wythe masonry wall again

[JStructsteel]

Looking at a building tomorrow that the client wants to open up a wall with a window. He's reported its 2 wythe outside, air gap, then inner wythe wall. Was wondering a few options to open it up.

First option is cut in a groove for an angle, and slide in. Question on this is what stops the wall dropping when they cut the groove? I get arching action, but locally could bricks slide down?

Other is to do a clamping type beam each side, but with the air gap, could cause failure if tightened too much.

I guess option one is the best, what is worry some is the inside wythe, what collects that load? The header bricks? Cut the groove below those?

The client is looking for me to be the expert, but in reality, isnt this the contractors issue, I am just giving suggested construction methods?

 

[phamENG]

Assuming there's sufficient masonry above, I'd start by drawing a 45degree angle up from each of the corners of the opening you'll be making (including the added width to get bearing for the lintel). Everything above that will arch over to the jambs. Then, draw vertical lines between the needle beams - those will be the tributary areas for each beam. Unless you have them remove the triangle between each needle beam, it'll still be hanging and need to be supported on the beams. If the mortar is in good shape (can be difficult to assess for the inner wythe - moisture intrusion into a cavity wall can do some crazy stuff), you can get away with just dividing total weight of the brick to be supported by the needle beams as the wall is generally stiff enough to make that safe. But I'd only do that for short term work and using steel needle beams. Wood needle beams....I'd be a bit more hesitant.

 

[RPGs]

phamENG's load analysis is how I approach it.

Another consideration: I usually design the needle beams with a long enough span to leave at least 12" on either side of the wall for access--24" for larger openings with huge new lintels. Keeping deflection of the needle beams to less than L/600 of the new opening width tends to control the design. Others have indicated stricter deflection limits.

It might work in the right situation but I have never used wood for needle beams. The temporary shoring contractors I work with all prefer W6x12 needle beams on single or double W6x12 transfer beams bearing on premanufactured steel shoring towers with screw jack legs.

 

[XR250]

Keeping deflection to L/600 max tends to control the design.

Seems to me L/600 is fine for new masonry as the mortar still has some plasticity. Existing masonry is not as tolerant.

 

[phamENG]

L/600 is not applicable to needle beams. L/600 is a limitation on curvature for in plane supports of masonry above. As XR alluded to, it's about keeping plastic, uncured mortar joints from stretching too far and throwing the coursing visibly out of line.

The curvature of the needle beam doesn't matter as it's only supporting the plane of the wall at a single point. You could use the L as the width of the opening and limit the deflection of the middle needle beam to that L/600, I suppose. But I'd be setting a hard limit of 1/16" or so to needle beam deflection.

 

[dik]

I've used them... you are not pulling the interior and exterior wythes together, you are using the C sections to provide the lateral restraint. Likely less effect than the wind loading on the exterior wythe... your choice. If concerned, you could put some solid blocking in the air space (I've not done that)... for deflections, I typically use L/720...

-----*****-----
So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

 

[JStructsteel]

Thanks dik. So you just look at the bolts going thru as a "beam" that is holding up the masonry? I guess they are only 14" long

 

[dik]

yup

-----*****-----
So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

 

[jerseyshore]

I'm a big fan of the double channels. I think it's by far the easiest for bigger openings. Eliminating the need for shoring of a masonry wall is the best thing for a builder.

 

[phamENG]

I've used double channels with CMU, but never for multi-wythe brick. I don't like the idea of drilling through the brick, which it seems you'd have to do. Drilling the mortar would 1) still damage the brick's shell and 2) you'd be left with the brick above 'teetering' on the bolt. I realize it would do that exactly, but any faults in the adjacent mortar joints and that's essentially what you'd have.

 

[masonrygeek]

JStruct, you don't mention the span of the opening or the quality of the brickwork. Have you considered something like Prosoco's helical beam technique:

https://prosoco.com/a-better-way-to-restabilize-brick-walls/?

This might be appropriate for shorter spans and where you have access on both sides of the wall when you have a multi-wythe wall.

 

[phamENG]

masonrygeek - very nice. I could see that working on the single wythe, but do you have any examples of it being used for a multiwythe cavity wall? Seems like ensuring the inner wythe is adequately supported would be challenging.

 

[dik]

masonrygeek... Prosoco has had a couple of webinar on their helical beam product.

-----*****-----
So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

 

[dik]

pham... you generally have replacement bricks from the opening, if you need them.

-----*****-----
So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

 

[phamENG]

dik - my point is getting the ties into that inner wythe. The beauty of this method is that the brick can remain in place. But to get to the inner wythe, it seems you'd need to deconstruct one of the wythes to get at it. Granted, that's better than having to deconstruct the entire header to rebuild, but I was curious if anyone had found a better way to get at it.

 

[dik]

It's good if you don't have to and a lot of work if you do... Those red dots represent the helical reinforcing? Prosoco's webinars show that approach.

-----*****-----
So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

 

[phamENG]

Right. I'm wondering how Prosoco's method applies to this kind of cavity wall and what sort of best practices they've found for it. Most of the brick structures I work with are three wythe.

 

[dik]

...same here, but solid, not 'rain screen' veneer. Most of the ones I've dealt with are historic... not modern construction.

-----*****-----
So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

 

[JStructsteel]

Circling back to this, I am doing needle beams (4x4's) at 2'-0" for the 7'-0" Opening. Then install 3x3 angles. Once all 3 angles are installed, screw a 2x12 on the bottom to allow window installation.

Thoughts?