"J" anchor bolt vs headed anchor 2

[delagina]

Any link when to use either. I almost always use headed anchor. Also any link regarding "J" bolt embedment calculation.

 

[KootK]

For the most part, I don't bother with J-bolts anymore unless they crop up in vestigial detail someplace. Mechanically, it basically comes down to this: J-bolts tend to straighten and crush the concrete so they suck for serious tension. Doesn't ACI 318 Appendix D cover J-bolts explicitly now? The Canadian concrete code does and, to my knowledge, it's pretty much a straight copy of 318.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[delagina]

Client has a point why he wanted "J or L" bolt. He said in the future they maybe be loosening the nut. Headed anchor bolt may fail (rotate), J or L bolt have more resistance. Since there is very minimal tension in this case, I just used J bolt.

Question though, do we even have calculation for headed and L bolt capacity against rotation if they loosen the nut in the future?

 

[KootK]

Question though, do we even have calculation for headed and L bolt capacity against rotation if they loosen the nut in the future?

Not that I know of. It's not an issue that I've considered. Frankly, I'd be surprised if straight steel rod would even rotate. You get some bond on the shaft. When we drill and epoxy straight hilti bolts into concrete, we don't normally hear of issues with bolt rotation. At least, not with properly installed Hilti bolts.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[delagina]

yes, first time I heard of this. they may have issues in the past where the nut was tightened too much. this inside a plant, they move equipments around often. I'm talking cast-in-place not hilti.

 

[JStephen]

I've wondered about that where using just a nut as the anchor plate. I can see after 20 years of paint and corrosion on the top side, that trying to remove the nut could turn the bolt in the embedded nut. But not aware of any case of that actually happening.

 

[KootK]

I realize that you're talking CIP rather than Hilti. I was just using the Hilti example as the nearest analogous situation that I could think of.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[thaidavid40]

Anchor rods with sufficient pre-tension could rotate when you try to loosen the nuts, especially when they are debonded from the surrounding concrete along their lengths. We always specify that the bottom nuts on anchor rods be tack welded so that this precludes their rotating when loosened. If they are set with embedded steel templates, we tack them to those instead, even when clamped with a nut on top of the template plates.
Dave

Thaidavid

 

[Ron]

Tack weld the nut, plate washer and bolt together before installation....solves the twisting issue

 

[delagina]

I'm using headed bolt in the concrete, nut and washer above concrete. How do I explain this. Headed bolt shouldn't rotate, only pre-tensioned bolt where nut was not tack weld?

 

[BUGGAR]

The head of an anchor bolt will fit within a right-sized piece of HSS and the bolt will not rotate within the HSS. You figure out the rest.

 

[EngineeringEric]

Don't tack weld (Ron!) because the contractor will tack weld the wrong side. Specify mechanical deformation of the threads below the nut.

This is what Miller just told me the other day in a webinar.

 

[Ron]

Eric! There is no wrong side! You can tack weld the shaft of the bolt to either side of a plate washer. Makes no difference. Mechanically deforming the threads will keep the nut from coming off but won't keep the bolt from spinning in the plate washer hole.

 

[EngineeringEric]

Ron! i think all names need exclamation points. The reason i think the logic on the wrong side was the whole idea of heating the tension side of the rod. I honestly don't care but since i know you deal with a good number of forensics (from post history) and i literally just watched the webinar this week where Miller mentioned this issue and cited AISC document something-something.

The mechanical deformation results in the rod spinning some but can only spin up so far before engaging the deformed threads, at least that's how it works in my head...

Edit: [Just so my horrible sense of sarcasm is not misconstrued as being a jerk or cocky, i meant the "!" as a joke (a bad case of type sarcasm), i actually do hold your opinion pretty high based on my readings of your past posts]

 

[Ron]

Eric!

The whole anchor bolt is in tension at its point of fixity, so there is no "tension side". I would agree with Miller if you were only using a nut on the end of a threaded rod, but most times there is a plate washer above the nut. The nut itself will turn because of localized crushing of the concrete at the points on the hex head. The plate washer is not threaded and is free to turn on the bolt. If you tack weld the plate to the bolt, the bolt can no longer turn relative to the plate and the plate is large enough that it will not locally crush the concrete and spin.

If you come across the AISC reference you noted, post it. I'd like to look at that.

 

[KootK]

Often, we use a double nut and washer assembly for anchor rods (nut/washer/nut). If the weld occurs on the top of the upper nut, where the rod is still carrying its full tension load, then I believe that you're subject to localized embrittlement issues similar to what we deal with when welding rebar. Different steels are susceptible to varying degrees of course.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[BUGGAR]

So make an anchor bolt that can be gripped and prevented from turning at the top. Does anybody remember adjusting their valves?

 

[Ron]

KootK....that's a good point; however, most anchor bolts are relatively mild steel and weldable. If for some reason you are using a steel that is subject to embrittlement then I would be cautious of welding or even tack welding.

See attached sketch for illustration.....

 

[KootK]

This is a response that I got from Portland bolt in 2010 supporting the notion that nut welding is no big deal.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[Ron]

KootK....yes! Well stated from Portland Bolt. ps....they are a wealth of techy info!