Reinforcing bar or wire for small equipment pads?
Reinforcing bar or wire for small equipment pads?
(OP)
We’re placing 4in thick equipment pads on an existing 6in thick slab on grade. The pads are small and range from 15-26ft^2 and the building will experience an interior temperature swing of 40°F-120°F. Which is more prudent choice in regards of longevity: placing #4s @ 16in (in some cases only two bars are placed in direction) or placing welded wire (D5) at a much closer interval?






RE: Reinforcing bar or wire for small equipment pads?
If in doubt, add another piece of rebar since it is cheap.
You should develop some way to bond/adhere the 4" slab to the existing slab.
Dick
Engineer and international traveler interested in construction techniques, problems and proper design.
RE: Reinforcing bar or wire for small equipment pads?
RE: Reinforcing bar or wire for small equipment pads?
TLHS: Thanks, none of the equipment has a large rotating mass and the equipment ranges in weight from 500 to 4000lbf. Knocking out the existing slab I believe will be too costly.
RE: Reinforcing bar or wire for small equipment pads?
RE: Reinforcing bar or wire for small equipment pads?
You'll have them at a pretty close spacing, relatively speaking. Say you're putting them at a 12" grid or something, each bar will only lift something in the ballpark of 12"x12"x6" of concrete. That's almost no weight. If you want to put a better number to it, figure out the moment capacity of your slab as plain concrete, figure out how far past the edge of your pad your slab would survive in moment if you were to hang it from the pad, and then use that to come up with a maximum load one of your pieces of rebar can see before the slab fails first.
Embed them in 4" of so, see what that capacity is and whether it's enough given the above information.
Note that you'll presumably have to justify any shear capacity using something other than shear friction, since you don't have full development. You'll normally have enough bars, though, that this isn't an issue.
RE: Reinforcing bar or wire for small equipment pads?
I was considering only adding dowels at the edge of the new equipment pad making the concrete per dowel much greater than 12"x12"x4". These edge dowels would then lap with the pad reinforcement grid. Still, it will likely be 12"x12"x6' so it's still not that much?
The existing slab is reinforced with #4@12" and the new slab reinforcement is undetermined.
RE: Reinforcing bar or wire for small equipment pads?
I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.
RE: Reinforcing bar or wire for small equipment pads?
Options:
1. You need the weight of the lower slab for overturning or something similar - do generally what I said above. You can increase spacing if you are comfortable using the bending capacity of plain concrete.
2. Your housekeeping pad doesn't transfer significant shear or uplift/overturning - in this case, your dowels don't do anything. Throw a few in to make sure your housekeeping stays tight with your slab on grade in curing and operation
3. You have a large amount of shear somehow... but no overturning - Do the same as number 2, but double check that your dowels have sufficient breakout capacity. I've never had this govern if I have at least a handful of bars around the perimeter of the pad.
RE: Reinforcing bar or wire for small equipment pads?