Dowels from CMU wall to slab

[300redbeard]

I'm performing a plan review.

Example: 8" slab w/#3 bars @ 18" oc ea way & #4 dowels (from CMU wall) @ 24" oc. (obviously different spacing)

Does this fly?

I've typically always required/designed my slab steel and dowels to the same spacing for lapping together.

I've always had the impression that dowels from CMU wall to slab were for out of plane forces, thus lapping to slab steel instead of relying on development length.

 

[hawkaz]

It depends on what the dowels are doing. In my area, we rarely use slab dowels for masonry construction.

You need to find out if these dowels are doing anything structurally. Are they intended to limit slab movement only, are they providing a horizontal support point for the masonry wall...

You should be able to tell from the EOR's calcs what these dowels are intended for.

 

[a2mfk]

There is also likely a concrete tie beam or bond beam that ties everything together. Unless you are doing something funky like putting moment at the slab edges into the walls not sure why it would matter to have them align. Maybe for some seismic regions that I am not familiar with...

 

[msquared48]

If the CMU wall needs to develop a moment at the base of the wall, I would align them.

However, if no moment is needed, the only design consideration would be shear in nature, and this has nothing to do with the slab steel spacing.

Look to the EOR's calculations for the wall to determine what to do.

Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask

 

[300redbeard]

I'll have to contact the EOR, the calculations are not addressing the dowels.

Thanks for the remarks.

 

[hokie66]

A detail would help. We don't even know if this is a ground supported or suspended slab. The spacing of the reinforcement which goes into the wall is probably influenced by the block core spacing.

 

[dik]

#3@18 is a little light for an 8" slab...

The bars don't have to be syncronised for spacing, but it is better and to achieve the same strength, the bars should be a tad longer than usual. Is it possible to construct the CMU wall with a wider block underneath the slab and support the slab on it?

Dik

 

[300redbeard]

The structure has both 8" & 12" cmu block (2000psi) x 24 to 34 feet high. Footing is 24" & 30" wide x 16" deep. Adjacent mat slab is 8" or 18" thick with #5 @ 12" OC or #3 bars @ 16" OC ea way top & btm. Seismic design category 'D'.

My thoughts are that the dowels are for out of plane forces, so in this case the 24" length is for development into the slab with no lapping to slab steel.

The provided calculations are supposed to be 100%, but I would rate them at 50%. Easy to make assumptions when information is lacking.

I'm waiting for a response from EOR regarding dowel design. It will probably be a few weeks before I get a response.

I appreciate all the input.

 

[slickdeals]

#3@18 is wimpy. It does not even meet Temp/shrinkage requirements of 0.0018 Ag.

#4 @ 24" is shy as well. You need a bare minimum of #4 @ 12"