Joint in Concrete Slab

[j19]

I am working on an 80' wide by +/- 200' long metal building with a concrete slab. The owner is adding on to the 80' end of the building with an 80' x 150' addition. The existing wall will be removed so that the completed building will be 80' x +/-350' with an open floor plan and no surrounding pavement or walls. The building use will be light storage with some small forklift traffic. The new slab will butt against the existing slab so I am showing greased, smooth dowels at 32" o.c. drilled into the existing slab. I don’t think a compressible filler is required between the existing slab and the new slab because there is nothing from preventing the slab from expanding outward, but another engineer in my office says to always put it in. What do you think? By the way, the slab will be poured in the next week at what will probably be the coldest temperatures that we see on an annual basis.

 

[steellion]

I agree with the dowels. I don't see a need for a PJF where there will already be a natural construction joint between new and existing slab-on-grade.

 

[a2mfk]

A filler/compressible strip would be one way of providing a bond break as the new slab shrinks. Shrinkage is what you need to be worried about, this will likely be more than any post-curing expansion. With forklift wheels the joints can become a maintenance issue (as well as your CJs throughout the slab), there are several different details that can be used...

I have a project that I need to think about joint protection for light forklift traffic on CJs too, I'd like to hear other posters experiences and suggestions.

 

[Ron]

You didn't give the slab thickness....let's assume 6". If so, be careful of the dowel thickness. I would space the dowels closer together than 32" (typically 18-24"), and I would limit the dowel thickness to 5/8". As noted, grease the dowel that will be inserted into drilled holes in the existing slab, and cast the new slab against it. In my opinion, you do not need a separator or filler. Let the slabs abut each other but use plastic sheet or felt to break bond.

Leave at least 1/4" space past the end of the inserted dowel to allow for dowel expansion. Probably won't ever occur, but good to have a little space in there.

Consider using flat plate dowels. Those are good for thin slabs.

 

[rscassar]

Being a slab on ground the free shrinkage will be restrained so I don't think there will be a large shrinkage component away from the existing slab (~1/2" maybe) and this would negate any thermal expansion that would occur in a protected environment (even if it is an industrial building). I would have the dowels closer than 32" (16-20").

 

[MiketheEngineer]

BTW - has someone re-checked the end walls for shear capacity if that comes into play for the overall design of the building??

Going from 200' long to 350' long will definitely change things!!

 

[rscassar]

If it where braced were cross bracing it would be an issue. I am imaging the structure is stabilized by rigid frames (portal frames) in the 80' direction so the contributing shear on each portal frame will be the same.

 

[j19]

Kikflip is correct. It's a metal building with rigid frames in the 80' direction and rod x-bracing in the 350' direction.