High Strength J-Bolts 7

[GSigma]

I need to design several surface mounted base plates to resist relatively large pull-out and shear forces. Due to spacing and edge distance limitations we are running out of options with regular expansion and epoxy anchors plus the contractor would like to use some type of embeded anchor. Any recommendations on J-Bolts, or L-Bolts(MNFR, TYPE, STRENGTH, CAPACITY, etc) would be appreciated.

Thank yuo

 

[JedClampett]

Since ACI discourages the use of J or L bolts by reducing their capacities, why not just stick with hex head bolts?

 

[GSigma]

Is there anything else besides ACI 318 Apendix D that I can use for tips or recommendations? The bolts will be in direct tension and shear and the pedestall edge distances are very limited.

TY

 

[paddingtongreen]

They use "hairpins" in some slabs to hold against column lateral breakouts. For tension, if a hex head doesn't cut it, then you need an anchor plate.

Michael.
Timing has a lot to do with the outcome of a rain dance.

 

[sandman21]

A j-bolt does not get the same loads as a hex. If breakout is the issue, design reinforcement to take the load, this applies to shear or tension loads.

 

[connectegr]

Several years ago I attended a lecture given by Jim Fisher, the author of Design Guide 1. He had several slides and examples where bend anchor rods straightened and pulled out from tension load. I suggest reviewing DG 1 for other options.

http://www.FerrellEngineering.com

 

[hokie66]

You could also use U-bolts. They can't pull out by straightening.

 

[ToadJones]

DG1 has tables for pull out strength.
I think for 36 ksi rods with a nut, concrete pull out never controls.
You'll still need to check everything else in APP D

 

[charliealphabravo]

Working around the assumptions and limitations of Appendix D was just discussed in a recent thread. It basically requires a more rigorous consideration of stirrups, supplemental reinforcement, welded base plates, and use of the strut and tie model.

There is a link to some related papers as well.

Also I second or third the recommendation to use heavy hex head rather than hooked rod ends.

http://www.eng-tips.com/viewthread.cfm?qid=310997

 

[Once20036]

I thought the the failure mode for L & J anchors was crushing of the concrete at the corner prior to any significant bond stresses developing between the straight portion of the rod and the adjacent concrete.
Thus - wouldn't a U-bolt fail in the same manner - crushing of the concrete? Sure there's some prying action present in the J anchors not present in the U anchors, but is the effect that significant?

 

[hokie66]

Don't know about the failure mode being concrete crushing. I thought some of the US guys had reported that the bar just yielded and pulled out around the corner, which would not be possible with a U-bolt. Maybe someone can advise for sure, as some of us prefer U-bolts.

 

[jt83]

Are these post installed or new construction?

 

[Lion06]

How do you post-install a J-bolt? WHY would you post-install a threaded rod with a heavy hex nut?

 

[jt83]

I just briefed at his posting- was going to suggest possibly considering MaxiBolt undercut anchors. They have field test results (failure loads) for various anchor sizes, concrete strengths and anchor patterns etc. You can then use your judgement in regards to a safety factor depending on the type of structure. You can core drill an oversize hole and (epoxy)grout an embed plate with headed stud(s) to weld to. If cast-in-place (I assumed) he could add hairpins, ties, stirrups, forged head rebar or other restraining reinforcing.

 

[Once20036]

Hokie -
I was just looking at this for a project this AM. Refer to ACI 318`05 RD5.3.5,
"...neglecting any frictional component because crushing inside the hook will greatly reduce stiffness..."

 

[hokie66]

The type U-bolts I am talking about are bent about one big pin, not like reinforcing bar fitments. Thus the stress on the concrete is more or less constant around the half circumference of the bent bar.