So, you're pouring a reinforced concrete pier foundation. The "concrete" part is easy, but you're a bit stumped as to how you can accurately place the steel reinforcement to match the design...
The pro's would just fabricate a rebar "spiral" with their fancy million-dollar rebar coiling machine. (see the video) And then attach the vertical reinforcement to the rebar coil.
Obviously you don't have one of those, so you'll need another way to build your rebar cages, preferably on-site. This instructable will show you how to do just that, and you'll only need these things: zip-ties and some large diameter plastic pipe. (along with basic measuring tools and a drill)
We'll also be substituting welded steel mesh for coiled rebar. This is OK for small diameter footings like this one.
Step 1: Measure and Mark the Jig
Your exact measurements will vary depending on your design. (but you can follow this one to make a cage for a very strong 10 inch diameter cylindrical footing. Generally speaking you want 0.75"-1.5" inches of "cover" (this means concrete between the reinforcement and the edge of the footing) so choose a pipe roughly 4 inches in diameter smaller than the diameter of your footing.
Our cage will include two types of steel reinforcement:
- Vertical Rebar reinforcement to develop a bending moment resistance
- Steel welded mesh reinforcement to develop "confinement" to improve resistance to vertical loads (this in place of coiled rebar)
Now lets set up the jig:
- Trace out the circumfrence of the pipe, and mark the radial arrangement of the vertical rebar pieces. (I have 6, so I used a protractor to mark 60 degree increments (see image)
- Transfer those marks onto both sides of the pipe, and then use a ruler and a sharpie to draw and label the alignment lines.
Step 2: Prepare the Jig
The last thing we need to do before we can start building our first cage is to prepare the jig.
- Since we're going to temporarily attach the vertical re bar segments to the jig with zip-ties, we need to drill holes on each side of the alignment lines on each end of the pipe. (see the image)
- Now, lets pre-thread those holes with zip-ties, and leave them loose. (again see image)
Step 3: Affix Rebar to Jig
Now we can attach the vertical rebar segments to the jig using the zip-ties. Use a board to make sure the ends of the rebar are aligned. Slide the bars in, align them ,and then tighten the zip-ties. See, that was easy.
Step 4: Roll-On and Connect the Re-Mesh
Now, we need to tie everything to the welded steel mesh using steel wire.
- Attach one vertical rebar segment to the end of the wire mesh sheet using steel wire-twisted with pliers.
- roll the jig and vertical bars onto the wire mesh, and methodically wire each vertical bar neatly to the vertical bars.
- When you reach the end, make sure to wire each potential joint on end the steel mesh
- Trim the extra wire mesh away.
Step 5: Slide Off the Finished Rebar Cage
Now, we have finished our cage! Simply clip the zip-ties with your pliers and slide out the jig, and get started on the next one!