Replies

1. 
   SamT | Feb 03, 2006 06:00pm | #1

   Gregor,

   I'm not sure that I understand you.

   By "beams" do you mean the footers? By "trench" do you mean you're forming the footings straight in the ground? The slab will sit on top of the footers? Having a cold joint at or under grade?

   If your footings need #5, that is one big shop. If your shop is that big, why are you only using #3 in the slab.

   You said you're using a "Cage" in the footers. Those must be some stout footings.

   You want to turn the slab mat "down" into the footings. Aren't you using a stemwall of any heigth under the sills?

   SamT

1. 
   gregor | Feb 03, 2006 06:55pm | #2

   Let me clarify,
   I'm in Texas where we have little or no issue with frost so the normal way to build a thickened edge slab here is you grade the site and fill with crushed limestone to ~5" below the finished height of the slab. Then you trench beams around the edge ~12" into undisterbed soil. Normally the slab is formed to come out ~9" above grade at the lowest point. A slab of this size will normally have 3 additional beams across the 30' dimension and one up the center on the 50' dimension.The entire slab is poured as a monolithic structure. Does that make the situation more clear?

1. 
   brownbagg | Feb 03, 2006 07:23pm | #3

   tied to beam is fine, as far as #5. our bldg code will not allow anything smaller than #5 on anything. #4 and #3 are not allowed no more.. 2+3=7

2. 
   SamT | Feb 03, 2006 10:09pm | #5

   Gregor,

   Yeah, mo cents, thanks.

   That's what I would call a slab on beam. My "slab on grade" has no beams.

   IMHO, you definately want to turn the mat down into the beams around the edges. I've seen "Zee" bars used in the inner beams. The Zee runs in the beam a ways, turns up into the slab zone, turns and runs in the slab a ways. I've also seen "Cee" bars. They hook under a beam rod and over a slab rod. Chairs work, but, IMO, best if one slab rod runs inside the top loop.

   Just about any way you can get iron truely stuck in both slab and beam. Watched an OOPS get fixed in a hurry once. Stuck straight pieces at an angle from the bottom of the 'beam' up into the slab.  At many angles. Short pieces at near vert, long sticks at near level. BI said, "Gotta have connecting sticks 2'OC."

   The best practice, again, just IMO, is saddles. Look like a waaaaay swaybacked old nag. Horizontal legs in the slab, middle drops to form the cross pieces of the beam. Easy assembly. Lay a couple grid rods next to the trench setting on adobes, drop the saddles across them into the trench and drop the #5 in the saddles. The saddles can be specc'ed to tie to the parallel grid rods or to fall in between.

   SamT

1. 
   gregor | Feb 04, 2006 07:31pm | #6

   Thanks for the input. That all sounds like pretty sound engineering to me. I think I'll go build me one...Greg

1. 
   atrident | Feb 05, 2006 04:45am | #7

    If you are going to have electricity ther you might as well incorporate a Ufer . A piece of rebar sticking up out of the concrete for a ground. There are some other specs as well

2. 
   MJLonigro | Feb 03, 2006 07:32pm | #4

   You used the term "cages"..That would imply a set of #5 with #3 stirrups around them..(or some other similar combination of bars)...Correct?

   Well, I would then tie the #3 mat bars to the stirrups. However, the ACI standard is that wire tied rebar should lap 40 times the diameter of the bar or, in the case of a #3, 15"...You obviously don't have 15" of flat stirrup space..so the mat bar should bend around the cage...

    

    

   
   

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   Edited 2/3/2006 12:54 pm ET by MJLonigro