In many instances a concrete slab may be connected to a concrete footer rather than the slab "floating" on top of the footer. Construction where free movement of the slab is not desired (for seismic or elevation reasons) will require the two to be "tied" together. You can construct and pour your concrete footings separately from your slab or as a monolithic pour (everything at the same time).
Things You'll Need
- Rebar installation drawings
- Site construction drawings
- Tie wire
- Wire pliers
Install your footings as designed on your rebar installation drawings and/or site construction drawings. Often you will have to use both sets of drawings to install the footing correctly. The rebar drawings will detail what type and shape of rebar has been made to build the footing but the construction drawings will have all the engineer's specific requirements for spacing and placement.
Add the slab tie-in bars to your footing. These may be provided in one of two basic forms. The first is a "slab dowel." This dowel is a piece of rebar bent at a 90-degree angle that is designed to rise vertically out of the footing or footing stem wall and bend into the slab so it can be tied directly to the slab rebar mat. The second type of tie-in is a "pass-through beam." The footing may be designed as a beam made of rebar stirrups. The top of this beam will be slightly higher than the height of your slab rebar so the slab rebar may run through the beam.
Install your slab bars as designed on your rebar and construction drawings. Make sure each intersection of the bar is tied with tie wire (use wire pliers to make the ties). If your footing is a "pass through" make sure that your slab bars pass through and under the top continuous bars of the beam.
Connect the slab rebar to the footing rebar. Tie the splices of the dowels to the slab mat using three ties: one at each end and one in the middle. For pass-through beams, make sure the slab bars are tied at each intersection with the bar in the footing.
Tips & Warnings
- Read your drawings carefully; some designs call for a mix of the two basic types of slab to footing connections. A pass-through beam may also need slab dowels and often they are placed at a different, and offset, spacing to the spacing in the slab rebar.
- Double-check that the rebar that you have placed to connect a concrete slab to a concrete footing does not rise above the height of the pour. If you do not check this as you progress (and keep checking every 10 feet) you could wind up having to cancel the pour as you will need time to dismantle and rebuild a slab that is tied together but has high spots that will stick out of your concrete pour.
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