Rebar lap splice lenght

[11echo]

Is there a "rule of thumb" for determining the lap splice length of certain size rebar in foundations? ...Just to prime the pump here, I've heard 30 diameters, but I'd like to confirm this. Any help would greatly be appreciated!!

 

[JAE]

It varies depending on concrete strength, reinforcing yield strength, concrete cover over the bars, whether any horizontal bars have concrete below it more than 12", rebar diameter, whether the bars are stressed beyond a certain level, Whether all the bars are spliced at once or staggered, etc.

There is no real valid rule of thumb such as X bar diameters.

 

[msucog]

depends on the type of splice plus several other factors. see aci 318. 30 bar diameters is on the low end of the scale...most i see are much larger (44 to 60 bar diameters)...but again, it depends on several things. search the structural engineering threads or google if you don't have a copy of aci318.

 

[oneintheeye]

does vary but on UK codes if you use 38 X diameter you wont be far wrong as an estimate. (it usually is for normal strength concrete).

 

[Dinosaur]

ACI 318 and AASHTO codes once had values such as these, but I think they went out in the 70s. Now we have to know the strength of the concrete, the size of the bar, is it placed as a top bar, is it epoxy coated, ...

No more rules of thumb.

However, you can prepare a table of the most frequently occurring situations and use that to speed your work.

 

[11echo]

The rebar size is either #6 or #8 in size ASTM A615 GR60, its in a footed transformer foundation(s), approx. 3" from the surface all the way around, and at 15" O/C-T/B-EW. It's not epoxy coated. These are all contact splices that are wrap-snap tied.

 

[Dinosaur]

I guess you are asking us to give you the length of the lap splice. In 3000 psi concrete, a Class A splice for a number 6 bar is about 27 inches and 48 inches for a number 8. A Class B splice would require about 35 inches for the #6 and about 63" for a #8. A Class C splice would be around 46 inches for a #6 and about 82 inches for the #8. In 4000 psi concrete, the lap splice lengths are reduced a small amount. For example, the Class C splice values in my notebook show 43 inches for the #6 bar and 71 inches for the #8. Close bar spacing requires more length than wide bar spacing. I would rather you contact a structural engineer and have him look at your case to give you specific values. If the lengths are longer than you had planned, rebar couplers are available that will reduce the length possible to a few inches, but are a more expensive alternative. Good luck.

 

[11echo]

I appreciate all the input here! …To explain, my discipline is process piping. I've been doing it a lot of years. During that time I've had to "bump" up against other disciplines and got to get a "feel" for what they do and how. Now I’m the first one to point out I am not expert in these other disciplines! ...BUT I'm better then a "monkey see monkey do draftsman". I now work for a small engineering firm where I'm pressed to cover other bases ...material procurement, estimating, Xerox machine repair, AND civil and structural design. I take my best shot at it, BUT I point out to my bosses that my work needs to be checked by someone that KNOWS WHAT THEY ARE DOING!!! ...And I'm sure you'll agree it's easier to change something that is existing rather then start something from scratch.
My question here is for my own education, the work I've done is already out the door (where I used the 30x dia.s). The closer I can get to a "correct" design and call-out the least amount of time and effort it'll take the experts to change …or bill my company to do so. So I wasn’t fishing for “free engineering” …just some general knowledge (which I have discovered isn’t so general!) …AGAIN thanks to all for the input!