Rebar bending question

[lukeiamyofatha]

I am looking for either a formula or a table showing the amount of "creepage" or stretch rebar has while it is being fabricated in the rebar shop.
Obviously the main things to know would be the angle of the bend, the bender pin diameter and the rebar diameter.
From memory it is not an absolute length but generally good enough for fabrication.
An example of what Im looking for is: I want a length of rebar to be 2m long with a 1m 90 degree bend. The diameter is 35mm and the bender pin size is 360mm.
How much will the rebar stretch during bending ? This amount would be deducted from the bar cutting length.

Any help appreciated

 

[JStephen]

Well, I'm not a rebar fabricator- but I would think that centerline length would remain pretty much the same, with allowance for the radius. (Just having a radius in the bend will make it seem as if the bar is stretching- sum of lengths will be more than unbent length). If it doesn't, you could just bend one sample bar, measure it before and after, and that should give you an idea.

 

[lukeiamyofatha]

Thanks JStephen, I suppose your suggestion would be possible however, when given a shape code that has many bends of differing angles it becomes a bit much to try samples !
Obviously the radius has a great effect on the amount the bar stretches and is dependant on the diameter of the mandrel used on the bender.
Its been a few years since I have had a need to know about "creepage", I used it on the Hibernia GBS in Eastern Canada and wanted to re-familiarize myself with the basics before I start a new job on monday in Australia.
The basic formula without the use of anything absolute was something simple like 1/2 of the angle plus 1/2 the rebar diameter = the amount to be deducted from the shearline cut length, therefore to get a 35mm dia bar @ 2m with a 1m 90 degree bend the cut length would be 2000+1000-45-17=2938
Like I said, its not absolute but usually within tolerances.
If anyone else can refresh my memory I'd appreciate it.

 

[unclesyd]

Here is some information on bending conduit that I found from information in a handbook I have.

http://www.electrician.com/electa1/offset.html

Try this search on “developed length of bending rebar". Lots of good leads to information.

http://www.google.com/search?hl=en&...developed+length+of+bending+rebar&btnG=Search

 

[metman]

I think a fairly safe approach would be to use the inside design radius plus .44 X dia as the nuetral axis. so then (angle/360) X pi X 2 X (nuetral axis radius) + straght sections = origianl length before bend.

You cannot use the pin dia because of springback (elastic recovery) but then I suppose it is not necessary to be so precise for a rebar bend.