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PEMB Slab Control Joints

PEMB Slab Control Joints

PEMB Slab Control Joints

(OP)
Hi All,

So I spent some time to research the forums but didn't find exactly what I needed question-wise, but forgive me if you find a similar post.

Two things:

1. I've got an 8" concrete slab #4 at 12" o/c (middle of slab) each way for an exterior (but roofed, just no walls) PEMB shelter structure. I'm using hairpins so I need the slab structurally. But, I also don't want #4@12 crossing control joints because of cracking potential. Has anyone encountered something similar with success? I'm thinking I should use only enough #4 bars that I need for horizontal thrust pass through the control joint and cut the rest. There will be some vehicular loading too so I'll likely use smooth dowels where I cut the bars. Thoughts or other ideas?

2. There is a structural apron slab leading up to this PEMB. There will be vehicular traffic on this apron as well. I'd like to keep it separate from the building footings etc. I don't like the idea of dowels because it's a sloped slab (1/4" per foot) and my guess is that the dowels won't be installed at the right angle and thus render them pointless. So I was thinking provide a 3" wide shelf at the building slab turndown(little bit of a forming nightmare but I can live with that) to rest the apron on and put a bond breaker between the apron slab and the shelf and 1/2" expansion joint material on the vertical face. That way it can grow but not differentially settle. Thoughts or other ideas?

Thanks much, I appreciate you all.

Nick

RE: PEMB Slab Control Joints

Installing the dowels on a sloped traffic slab is not an issue...they will still perform with the slope you noted.

As for the other control joints, even with reinforced slabs that you are tieing together for lateral thrust, keep the control joints the same as used in non-reinforced slabs....24 to 36 times thickness.

Consider using plate dowels instead of dowel rods.

RE: PEMB Slab Control Joints

(OP)
Thanks Ron. I plan to space the control joints at between 15'-20' on center (based on plan layout and max spacing per unreinforced tables). I just don't like the idea of continuing a lot of reinforcing through the joint because random cracking is more likely to control since the joint will not be weakened as much as if all the bars were cut. Meanwhile, I don't like the idea of not continuing some reinforcing through the joints. I am sure other engineers have encountered this before and just want to see what they have done as well.

RE: PEMB Slab Control Joints

Smooth, greased dowels have been used in the past.

Mike McCann, PE, SE (WA)


RE: PEMB Slab Control Joints

Smooth, greased dowels have been used in the past. Also, cutting every other bar crossing the joints.

Mike McCann, PE, SE (WA)


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