Grouting top course of CMU wall with

[Nythius]

This feels like a stupid question, but after extensive googling and searching these forums I still don't have an answer...

New nonloadbearing CMU wall going to underside of existing slab (or any structure for that matter). Slight gap for deflection of course. Partially grouted with bond beams and verts. My question is what is the best detail at the top... how do you get grout into the top course?

Below is what I've come up with:
-bond beam at second course from top
-verts stop at top of second course (so you can "drop the blocks over rebar")
-grout fill with top course not in place
-wet-set little 16" dowels so you have at least something extending to top course
-then install top course (need to cut slots in face to slide it in with rebar already there...)
-drypack the cells with verts in the top course
-install "retainer angles" for out-of-plane restraint

see attached screenshot.

Alright...fire away...prove I'm an idiot.

Thanks in advance,

 

[jerseyshore]

If I asked one of the masons I usually work with they'd probably say they'll just cut a slot in face of the block and push the blocks on that way.

 

[gte447f]

They make open ended blocks for these purposes (i.e., so you don't have to lower every block from the top of the vertical rebars). In this case the correct blocks to use are open ended bond beam blocks (i.e., with a short web at the center of the 2 cells), but masons, can get creative with saws/chisels/hammers to use regular blocks if that is all they have access to.

As far as grouting, face shells will be removed and formed up with wood/etc. as needed to get grout into the top course.

 

[XR250]

If you are going to remove the face shells, why buy an open end bond beam block?

 

[gte447f]

If you are going to remove the face shells, why buy an open end bond beam block?

Good question. I guess you might as well not. Then again, if you had a stack of them laying there you might use them and only knock out face shells where you thought you needed to. As I think about the referenced detail more, the most troublesome part seems to me like it would be getting the bond beam horizontal rebar into the top course below an existing elevated slab. How would this typically be done? Removing face shells? All of them? I think you could form and pour the entire bond beam instead of using CMU. I have seen the referenced detail on drawings often. There must be a typical procedure used by masons, or is it always modified/substituted via RFI or without asking. Maybe a CMU guru will chime in.

 

[XR250]

I suppose you could install the bond beam one course down if you even need one

 

[dik]

I suppose you could install the bond beam one course down if you even need one

That would be my choice...

 

[Nythius]

Thanks all. Good to know about the open ended blocks.

Without them, I guess it's not such a big deal to knock them out on site...it's only 10'x13' tall wall. I had instinctively tried to avoid the need for widespread manual modifications to the blocks, but maybe that is easier than dropping the blocks over the bar for the top ~4'.

I still think I am missing something....people build miles of these walls in their parkades to enclose service rooms etc. I have seen details that show the bond beam at the top with no explanation as to it works... and they are not coring/sleeving the slab, as I would have noticed that.

Guess I'll just have to swallow my pride and ask a mason next time I see one....

 

[jerseyshore]

Thanks all. Good to know about the open ended blocks.

Without them, I guess it's not such a big deal to knock them out on site...it's only 10'x13' tall wall. I had instinctively tried to avoid the need for widespread manual modifications to the blocks, but maybe that is easier than dropping the blocks over the bar for the top ~4'.

I still think I am missing something....people build miles of these walls in their parkades to enclose service rooms etc. I have seen details that show the bond beam at the top with no explanation as to it works... and they are not coring/sleeving the slab, as I would have noticed that.

Guess I'll just have to swallow my pride and ask a mason next time I see one....

My guess is some combination of knockout blocks and them making enough openings in the faces to get it all in place. Definitely best to ask a mason tho.

 

[PEinc]

I don't see any way of "drypacking" the top course of blocks. There is not any room to ram a damp sand/cement (drypack) mixture inside the top blocks. Why not just fill with grout?

 

[gte447f]

I think the grouting would be the easy part (relatively speaking, compared to placing the bond beam reinforcing). I think grouting can be accomplished by knocking out face shells and forming as needed. Personally, I do wonder how they get the horizontal bond beam reinforcing in place in the top course under an existing slab. I need to make it a point to try to witness that the next time I get a chance.

 

[phamENG]

why is there grout/bond beam, anyway?

 

[Just Some Nerd]

I can't for the life of me figure out why there's a beam at the top of this non-loadbearing wall. Ordinary masonry ties don't just work for restraining this?

 

[gte447f]

I was taught that all CMU walls are to have a bond beam at the bottom and the top at a minimum for load distribution and continuity. I have at times questioned whether they are really always necessary, but I typically default to requiring them top and bottom.

 

[phamENG]

@gte447f - for a bearing wall, I absolutely agree with the top. The bottom...I've seen it, but don't do it myself. I specify joint reinforcement starting at the first course and every 16" on center throughout the wall, so no bond beams below the top unless absolutely required for attachments, etc. For a non bearing infill wall? Nah. I would design it as unreinforced masonry unless there's a compelling reason not to (too tall, abnormal loading requirements, etc.). Then just trap it between two angles to pin the top but allow live load deflection in the beam above.

 

[jerseyshore]

Bond beam use and placement has to be one of the most variable things from firm-to-firm and engineer-to-engineer. It seems like every place does something different. We always do the same as you do pham.

 

[ANE91]

TMS 402-22: Chapter 15 governs Masonry Partition Walls, which are defined as walls (1) that are limited to vertical loads not greater than 200 plf, (2) that can span vertically or horizontally, and (3) were not part of the lateral-force-resisting system. (Source: Masonry Designer's Guide 2022)

Nonparticipating Elements requirements in 7.3.1 are to be used for partition walls designed using the prescriptive requirements of Chapter 15. Isolate the wall and detail it to accommodate story drift. Seismic analysis may be waived for SDC A and B.

I don't see any bond-beam requirements for your situation. Typically, these would come up for shear strength and crack control. If it's an indoor partition wall, and unsightly cracks will be an issue, then I could see needing them or using bed-joint reinforcement, instead.