In concrete construction, a stirrup is used in concrete beams or columns to hold the main longitudinal rebar in place. They typically are square or rectangular in shape and consist of five 90 degree bends. The bends on the ends of the bar overlap. A variation is the seismic stirrup which has 135 degree bends on the ends instead of 90 degrees.
Because stirrups are usually made from smaller diameter bars, it is easy enough to bend one or two of these by hand using just a ruler and a marker. But what if you need to make 100 of them and they all need to be the same?
Whether you are bending by hand or using some type of powered rebar bender you will need to set up some kind of jig or reference to accurately give you the dimensions you need and keep the stirrup flat. You don’t want it spiraling like a corkscrew. You also need to determine exactly how long the bar needs to be so you can use your rebar cutter to cut all the lengths before you start bending the stirrups.
The diameter of bar being used and the radius of the bending die on the rebar bender will have an effect on the length needed. An easy way to figure this out is to make a trial piece. First add up all the sides of your stirrup. For example if you are making a 12 inch by 18 inch rectangle with 5 inch long overlapping ends add 5 + 12 + 18 + 12 + 18 + 5 = 70 inches. We know this is going to be longer than needed because it takes less bar to make a radius corner than a square one. Cut a bar 70 inches long anyway and make the stirrup. The last leg of this stirrup is going to be longer than it should be. Deduct that extra amount from 70 inches and you now know exactly how long to cut your bars so the stirrup comes out perfectly.
Using a rebar bender that has an accurate angle control really speeds up the job and assures consistent results. To make seismic stirrups you need to set two angles and switch between them as you are bending the shape. If your rebar bender can only set one angle just make your stirrups in two batches. First set the angle at 135 degrees and bend the two ends of your bar. Do this on all of your precut bars. Now reset the angle to 90 degrees and complete the rest of your bends to finish the job.