Calculations to determine reinforced CMU wall dowels into concrete slab

[oengineer]

I am looking for information to calculate what is my required dowel rebar size and embedment length to dowel into a reinforced concrete slab?

I know ACI has provisions for doweling a concrete column/pedestal into a footing, but I am trying to find something regarding doweling CMU rebar into a concrete slab.

Any suggestions/comments are appreciated.

 

[phamENG]

There's a magical dividing line between the wall and the slab. The steel is the same in both (A615 or A706), just the material it's embedded in is different at each end. So embedding the rebar in the concrete slab follows ACI 318. The part of the bar in the CMU follows ACI 530.

You have to pay attention to both.

 

[oengineer]

There's a magical dividing line between the wall and the slab. The steel is the same in both (A615 or A706), just the material it's embedded in is different at each end. So embedding the rebar in the concrete slab follows ACI 318. The part of the bar in the CMU follows ACI 530.

You have to pay attention to both.

So are you saying for embedding into the concrete i just need to follow ACI Code, Section 16.3.4.1 requirements? I am not sure what section of the TMS or MSJC covers anchorage of Reinforced CMU walls to reinforced concrete slabs.

 

[phamENG]

It doesn't. It covers embedment of bars into CMU. That's my point.

Your bar has two ends: One of them is in concrete, and must follow the requirements of ACI 318 for embedding rebar in concrete. The other end is in CMU, and must the follow the requirements for embedding rebar in CMU.

If you're using ACI 318-14, then no - the minimum reinforcing requirements for a cast in place column do not apply to a CMU column/wall. But you do have to use the rebar detailing rules in chapter 25 to accomplish what you're trying to do.

So I guess the question should be asked: what are you trying to do? Are you trying to develop a moment connected base? If so, you'll need to develop your bars into the concrete such that the moment is transferred. Are you doing a pin connection between the wall and the footing and need bars for shear? Then you can do some searching on the forum and find no shortage of discussions on the topic. I'm a fan of specifying rebar to meet requirements for shear friction if they're needed.

 

[oengineer]

It doesn't. It covers embedment of bars into CMU. That's my point.

Your bar has two ends: One of them is in concrete, and must follow the requirements of ACI 318 for embedding rebar in concrete. The other end is in CMU, and must the follow the requirements for embedding rebar in CMU.

If you're using ACI 318-14, then no - the minimum reinforcing requirements for a cast in place column do not apply to a CMU column/wall. But you do have to use the rebar detailing rules in chapter 25 to accomplish what you're trying to do.

So I guess the question should be asked: what are you trying to do? Are you trying to develop a moment connected base? If so, you'll need to develop your bars into the concrete such that the moment is transferred. Are you doing a pin connection between the wall and the footing and need bars for shear? Then you can do some searching on the forum and find no shortage of discussions on the topic. I'm a fan of specifying rebar to meet requirements for shear friction if they're needed.

I am doing both, actually. I have four walls to consider. All of the walls, except one, are pin connected. Only one is a cantilever wall.

 

[oengineer]

@phamENG

What section in ACI 318-14 of Chapter 25 are you referring to regarding this situation?

 

[phamENG]

Several of them. Hooked bar dimensions and development are the most important. I suggest you read through it and familiarize yourself with the whole chapter. Just remember to keep following the load path - especially for the cantilever wall. You'll need to make sure the footing is detailed such that the tension from the bars coming down from the wall is transferred into the footing and resisting by the reinforced concrete there through bending, etc.

 

[oengineer]

Several of them. Hooked bar dimensions and development are the most important. I suggest you read through it and familiarize yourself with the whole chapter. Just remember to keep following the load path - especially for the cantilever wall. You'll need to make sure the footing is detailed such that the tension from the bars coming down from the wall is transferred into the footing and resisting by the reinforced concrete there through bending, etc.

For this project I am actually anchoring into an existing concrete slab. It's an existing reinforced concrete slab. I am trying to find some information about how to go about it. I am looking to find information on drill & grout design checks for the rebar from the CMU extending into the existing reinforced concrete slab.

I bring this up cause it seems like to me, based on the THE REINFORCED CONCRETE DESIGN HANDBOOK - A Companion to ACI 318-14, Chapter 25 is mainly useful for if the dowels are going into a newly constructed slab (i.e. like retaining wall stem reinforcing going into the footing).

 

[phamENG]

Gotcha - sorry if I missed the existing part.

How thick is the slab? You may have some difficulty with fixity if the loads are very high. You may also have issues with development. Best thing to do is get a Hilti or Dewalt-Powers or Simpson anchoring catalog/design manual and take a look there. Most of the factors that you'd need to use for post installed anchors are going to come out of the manufacturer's literature anyway.

Simpson has a software package to help with anchor design - I'm not certain if it does rebar. Hilti Profis does, but they've recently switched to a pay-to-play format instead of their old freeware.

 

[oengineer]

Gotcha - sorry if I missed the existing part.

How thick is the slab? You may have some difficulty with fixity if the loads are very high. You may also have issues with development. Best thing to do is get a Hilti or Dewalt-Powers or Simpson anchoring catalog/design manual and take a look there. Most of the factors that you'd need to use for post installed anchors are going to come out of the manufacturer's literature anyway.

Simpson has a software package to help with anchor design - I'm not certain if it does rebar. Hilti Profis does, but they've recently switched to a pay-to-play format instead of their old freeware.

It was my mistake, I didn't mention it was an existing slab in the initial post. I was think about using Hilit Profis, but I didn't think it would calculate for just rebars. I will check. Thank you for the suggestion.

 

[phamENG]

Another thought - sorry I can't develop it any further, don't have a copy of the book at my desk - one of the Hilti products was developed specifically for developing rebar and the table gives minimum embedment to achieve a bond equal to or exceeding the yield strength of the bar. That's not the end all, be all, of course, since the load has to go somewhere, but it's a good first check.

Might be there 500 series? Haven't spec'd it in a while.

 

[JLNJ]

If there is no moment, then maybe you don't need the dowels. With no moment the degree and manner of anchorage is not important.

For CMU walls on slabs, I often give them some starter bars just to provide the wall some nominal overturning strength beyond what the mortared face shells provide.