Anchoring To Freshly Grouted CMU Wall

[zurch1818]

I'm in the process of designing a wall mount to an old unreinforced hollow masonry wall. It was built in the early 60's, so I'm not surprised about the wall construction.

Anyways, my calculations are showing it needs to be grouted solid to support the needed loads. We also don't have have enough space on the inside of the wall to do a through bolt and a backing channel, so I'm trying to figure out what anchorage would be the best solution. I usually like adhesive anchors, but it seems odd to use that in wet grout. I also think a mechanical anchor probably doesn't really work in fresh grout either. I'm leaning towards a cast-in anchor, but I would prefer to not put a huge hole in the wall. Thoughts everyone?

 

[milkshakelake]

You could try modifying the detail to get in more bolts so it can work without grouting.

If you're set on grouting the cells, I prefer an epoxy like Hilti HY-270 after the grout hardens. If you use cast-in-place, you're engaging the whole thing for shear but only the newly poured wet part for tension. I'd rather engage the whole thing. Also for cast-in-place, you'd also need to poke the holes and then find a way for the new grout to not flow through those holes, which seems infeasible.

I don't really like mechanical anchors for high loading in old CMU. At least Hilti doesn't have a solution for it. Maybe there's a different manufacturer, like Powers or Simpson, that has an appropriate one.

 

[dik]

Can you use Hilti 'screens' with Hit-Hy 270?

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

-Dik

 

[zurch1818]

Thanks for the suggestions. The screen tubes don't really provide the capacity that is really needed. Even if it did, I'm struggling to get the global wall to check out (especially since it probably never checked out to current code in the first place). My issue is the penthouse has virtually no compression in it, so it doesn't take much to exceed the allowable flexure capacity of unreinforced masonry.

My client wants to hang about 500-800lbs of dead load and maybe 500lbs wind load (ASD) off two brackets that are about 4 feet to maybe 6 feet apart. The loading may have a little cantilever in it but I'll try to talk them out of it. Adding a WT or channel is actually not a bad idea. Essentially arguing the wall doesn't need to carry the flexure load and it only needs to carry the shear (which probably will check out. It's just a matter of getting the wall to act compositely. I completely agree Milkshakelake that it would be very difficult to cast the anchors in and not have the grout come out of the holes.

I have started using a mechanical Powers product for older two-wythe brick structures as their load tables are rated for that and Hilti's are not. I also prefer adhesive anchors to mechanical ones for older structures.

 

[milkshakelake]

I think regardless of which connection you use, the wall will need to be checked for axial+flexure because of the eccentricity of the load. There's no way to remove the eccentricity completely unless you make a pocket in the CMU. The WT might reduce tension in the anchor bolts and spread the shear to more anchors, but doesn't help with the global flexure.

 

[zurch1818]

True true. I was thinking of just saying the CMU wall didn't need to carry any of the flexure if the WT or channel (which is probably the shape I would lean towards) could carry the flexure alone. I do have a concrete pan and joist penthouse and main roof, so I feel as long as I can get the shear load from the flexure into these diaphragms, I should be OK. My hunch says these CMU unreinforced walls should have the shear capacity at the top and bottom to carry the load I need it to. But yea, it's not technically correct because there is still an eccentricity the channel would be putting on the wall that I'm not really accounting for.

The channel has worked for me in the past when I had clay tile and a concrete diaphragms. In those cases, I just bypassed the wall altogether and connected directly to the floor/ceiling and didn't rely on the wall to carry the shear at all. Clay tile is just a material that I don't understand why it was as popular as it was. It's a truly awful material. For every "fair" (being generous) condition clay tile wall I've seen, I've encountered about 5 "poor" condition clay tile wall where the tile has literally crumbled. I don't even know if grouting those walls even makes sense as it could actually make it worse. Additionally, the voids run horizontally and there are so many cracks/holes from poor historic performance that it just seems completely infeasible.

 

[milkshakelake]

Clay tiles are the worst. They're so brittle and look weird. I don't think I've ever seen it in good condition. I've seen shafts made of them and they just keep falling down the shaft, creating a hazard. It's not really feasible to repair them in some cases, because they'll just crack again. /end rant