Treating J anchor as rebar?

[Serhiy2]

Good day,

I'm dealing with a moment frame design where I have large tensile forces at column base. Column base is anchored with 4 j anchors embedded in grade beam pilaster. I analyzed j anchor capacity using the standard CSA A23.3 procedure and the resultant tensile strength is way less than I need. The tensile strength I got is approximately 0.45 of the tensile strength of steel. My question is: can I treat j-anchor as a rebar so I would be able to use its full tensile strength as long as my embedment length equals to development length of a rebar? I would probably need to treat is as a smooth rebar and find the development length calculation approach for it but this is secondary.

 

[jayrod12]

Why not change to double nuts and a plate washer? Significant increase in capacity

 

[KootK]

Probably no:

1) plain bars lack the knurls of rebar and thus develop differentlrpy from rebar. As you noted.

2) it is critical to recognize that even if your J bolts actually were developed rebar, that alone still doesn't guarantee successful anchorage. The bar tension would either need to be passed to pier verts or react against a concrete strut.

3) Anecdotally, if it were this easy, we'd all be doing this. And we're not.

 

[TehMightyEngineer]

Agreed with all of the above. Bad idea.

Ian Riley, PE, SE
Professional Engineer (ME, NH, VT, CT, MA, FL) Structural Engineer (IL, HI)

 

[Serhiy2]

jayrod12, thanks for this hint, I will try it.

KootK: agree, I would have to check development length and ensure that there is a proper load transfer mechanism down into piles.

 

[jayrod12]

I should clarify, Appendix D calcs for J-bolts have a serious reduction on capacity to account for localized crushing in the corner of the J and the straightening of the anchor bolt as failure mechanisms.

Plate washers with double nuts are considered the same as headed studs/bolts. Therefore you would use D.6.3.4 instead of D.6.3.5 for maximum capacity.

For example, a standard 19mm diameter J-bolt with a 75mm bend versus a 19mm diameter anchor rod with a 75x75 plate washer. Taking the common terms out of the equation, fc', FIEc, and R.
J-bolt = 1283
Washer= 42732

Therefore you have the potential to have a 3300% increase. The other failure modes don't have as drastic of a difference, but that was the easiest quickest one to show.