How do you Calculate Rebar Overlap for Splicing

Over the past ten years or working with concrete customers, I have seen at least three different ways to calculate rebar overlap length for splicing, and I wanted to share them with you, get your opinions and possibly learn some new ways.

Which do you like or dislike? let me know as I think we all could learn something new from the talent pool of amazing users at zzTakeoff.

Also let us know if you have a different way that you would like to share.

Method one- Common denominator x rebar diameter

The specifications will sometimes require a multiplier between 30 and 50 times the diameter of the rebar for overlap splicing.

                  a).           40 times  .67 for #4 rebar would give you 26” to overlap for splicing

                  b).           40 times  .875 for #7 rebar would give you 35” to overlap for splicing

So basically, this is easy to use in a formula in zzTakeoff, if your rebar list has the diameter in the product list as well as the weight per foot.

Method two- Standard Length

There is no denominator or factor, just overlap 24-36” as needed. 

                  a).           #4 rebar the splice would be to use a 24” 

                  b).           #7 rebar the splice would be to use a 36”

So the math is easier to understand in zzTakeoff, and if you put the splice length in your rebar product list it becomes very versatile. I suspect that this formula may not meet some of the more difficult specifications that you could see in structural concrete.

Method three- Common denominator by rebar number

I learned this one last week from a very successful structural concrete contractor, and I really like it and it basically multiples .625 times the rebar number, not by the rebar diameter

                  a).           #4 rebar the splice would be 4 x .625 and the splice would be 2.5 feet

                  b).           #7 rebar the splice would be 7 x .625 and the splice would be 4.375 feet

As a side note, I am curious if our rebar users, deduct the splice from the length of the rebar, then calculate the total length of rebar by the new length? 

See below:

Let’s say I have a 200 foot linear run of rebar that needs only one strand of #4 and we are using 20’ lengths. 

a). would you just find out the total number of 20’ rebar  (10 in this case) then multiply that times the rebar overlap (will use 2’) and get 220 feet of rebar.

b). would you deduct the 2 foot rebar splice from the 20’ and then divide the total length needed by 18 feet, which gives you 11.11 pieces of rebar or 222.22 feet?

I have always calculate the above a). method and the Rebar times diameter times a factor, but the math can really get messy in the formula section. I kind of like the B method as well.

Your thoughts are very welcome on this as we have so many talented users in zzTakeoff and I think the responses here would really help our community.