A36 Anchor Rod Embed length
A36 Anchor Rod Embed length
(OP)
I have (4) 1" dia. A36 anchor rods, each carrying 22k tension. I am trying to determine their embedment length into a 3' dia concrete pier. I cannot use the ACI development length equations because they are smooth, not deformed, bars. I referred to the AISC LRFD manual table 8-26 (p. 8-90 of the connections manual)and it requires a minimum of 12d, or 12" which I cannot believe is adequate (just my engineering judgement). Others have suggested to calculate the embedment length based on a bond stress of 100 to 120 psi. Using 120 psi, this gives a length of about 58" which seems excessive. I cannot use headed anchors because the failure cones interfere since the concrete pier is only 3' dia.
Suggestions?
Suggestions?






RE: A36 Anchor Rod Embed length
Try using vertical rebar and determine the embedment length of the rebar, which will be the embedment depth of the bolt (plus cover and shear cone from center of bolt to rebar, see ref below). The rebar has to be extended/detailed below the bolt enough to develop the rebar's strength.
Use Fisher's AISC manual for Industrial Buildings.
Just used this for bigger bolts (3" to 6") in Chile and it really saved depth and width of foundation.
If you need more info just post again.
RE: A36 Anchor Rod Embed length
RE: A36 Anchor Rod Embed length
RE: A36 Anchor Rod Embed length
RE: A36 Anchor Rod Embed length
However, if the area of your pier is sufficiently large, the concrete alone will be strong enough to resist the tension.
But the fact that you are using smooth, unheaded rods is something that may control, and I don't know what the bond to a smooth rod would be. Can't you use "all-thread", where the entire rod is threaded?
DaveAtkins
RE: A36 Anchor Rod Embed length
Unfortunately, I'm not a member of AISC so I don't have access to any of their member resources.
I did consider the reduction in strength from overlap of the failure cones, but as I spaced the bolts further apart to minimize the overlap, the size of the baseplate became excessive.
I also thought of using threaded rods, however I'm not sure if you could consider these to be "deformed bars" and follow the ACI development length calculation. (Although they are "more deformed" than smooth rods.)
I am leaning toward lapping the anchor rods with the vertical steel as DaveAtkins suggested. Right now I only have a steel cage around the pier (minimum steel). As a rule, I always neglect any tension resistance offered by the concrete. If I understand the suggestion correctly, I would add one rebar per anchor rod and lap them.
RE: A36 Anchor Rod Embed length
You should check the design equations for development length also. It seems like there was a factor in there to take smooth bars into account. I would not rely on the threads to necessarily act the same way as a deformed bar. You're making an unnecessary guess. Bar deformations are larger and stronger than are the threads, they aren't likely to behave the same way.
RE: A36 Anchor Rod Embed length
RE: A36 Anchor Rod Embed length