Curious as to why people are still using J-bolts 1

[Leftwow]

Is there scenarios where J-bolts are stronger? Even though mathematically headed bolts are stronger in breakout and pullout than J-bolts?

 

[BAretired]

Now I remember! There is one reason to like J-bolts that may have some validity. Some feel that they are more resistant to twisting in the concrete when torqued. Not sure how true it is that rods with nuts and washers will spin but that's what I've heard on occasion.

This is the criticism I have heard from one contractor when I changed L shaped anchor bolts to nut and washer. Welding the nut to the bolt or using a double nut would help but adds to the cost. I don't recall ever hearing about the anchor bolt spinning when tightening the nut above the column base plate, but unless one of the above measures is taken, the only thing resisting spinning is the bond between the concrete and the anchor bolt.

Following the Edmonton tornado of July 31, 1987 which flattened many buildings, I inspected several steel framed buildings where columns had pulled 3/4" diameter J-bolts out from the foundation. The vertical hole left in the concrete foundation appeared to be almost a perfect 3/4" circle with little evidence of concrete cracking, splitting or spalling.


BA

 

[msquared48]

I still use them for residential projects...

In fact,

I use H series open web steel joists

I also use I joists...

I use J Bolts, and

I use K series open web steel Joists.

Just thought you'd like to know.

Mike McCann, PE, SE (WA)

 

[KootK]

How did anyone ever think these WOULDN'T pull out? This looks like Kootk's wet dream for an argument as to tension forces running around a corner bar detail! lol...

I hadn't though of it that way but yeah, definitely. Basically the pulley where you're only pulling on one end of the rope. Obviously, the real mechanism at play with J-bolts is very similar to the nut and washer approach. You've got a blob at the end engaging the concrete. Presumably, the J-bolts don't straighten out as easily as the L-bolts because, just like 135 seismic hooks, the tail is wedged in there pretty good for bearing against the concrete.

This is the criticism I have heard from one contractor when I changed L shaped anchor bolts to nut and washer. Welding the nut to the bolt or using a double nut would help but adds to the cost. I don't recall ever hearing about the anchor bolt spinning when tightening the nut above the column base plate, but unless one of the above measures is taken, the only thing resisting spinning is the bond between the concrete and the anchor bolt.

The anecdote relayed to me was this:

1) Modest bolt size and modest embedment in and industrial application.
2) Smooth shaft most of the way.
3) Lower nuts not welded in place.
4) Worker trying to remove rusted out upper bolts.

I'm not sure if this exact scenario has been tested but, intuitively, spin seems plausible.

Around here they're popular only because all of the steel suppliers have literally thousands of 3/4" diameter 18" long anchors bolts with a 3" bend sitting in boxes.

Supply begets demand begets supply... viscous.

Archie doesn't that operate on the same principle? Can you say Lshapebolt is a jbolt?

That's how I see it. I'd originally thought that we were talking L-bolts too. 9" + 3" dominates my market.

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.

 

[WARose]

Following the Edmonton tornado of July 31, 1987 which flattened many buildings, I inspected several steel framed buildings where columns had pulled 3/4" diameter J-bolts out from the foundation. The vertical hole left in the concrete foundation appeared to be almost a perfect 3/4" circle with little evidence of concrete cracking, splitting or spalling.

Thanks for the info BA. I think I've heard that elsewhere as well.

 

[JoshPlumSE]

I've seem them spin before. I think we just got an installer with a longer wrench and bigger biceps than normal. And, poof, the anchor rod was spinning.

t was a fairly large project and I think only the one bolt had that problem. At first we thought we just broke the tack weld, but then we kept spinning it and the rod never moved vertically. So, we figured that we broke the concrete.

I was a junior engineer at the time and I was only in the field for a week or so. I don't remember what was done to fix the problem. But, it was odd to me that something so simple could cause such a big problem.

 

[CELinOttawa]

CEliOttawa...your fifth point listed above about the influence of the threads on pullout is interesting...I would assume that it would also apply to threaded rods....

Yup, I would bet it would apply to any fine-and-regular-deformation (ie: Threaded rod), but I have never seen any testing on plain threaded rod pull-out. Everyone always seems to use at least one nut and one washer. If properly attached (or torqued together) I have a hard time believing that even the most beasty of workers is going to be able to turn that bolt, as the nuts give a really effective twist-resist bearing shape. I can certainly see it happening, it just means the Contractor didn't prep the threaded rod anchors properly.

That's a point I would like to hear about people's preferences on as well: When specifying threaded rod anchors, I always specify two nuts and two washers, as I don't like how thin some of the HDG washers seem to be... The Contractors' are often unhappy with that setup, until I point out that it eliminates the need to tack weld. Somehow I am suddenly their best friend. lol

So: One washer or two? One nut or two?

For absolute clarity, here's what I spec:

 

[sandman21]

L-bolt are just as poor performing as J-bolts. I dont know why you would use two washers, spec a plate washer if washer fails. I dont tack weld as they can never seem to do it right and HS bolts dont like welds.

 

[JoshPlumSE]

There could be lots of other issues that led to the problem in my case.... Poor concrete placement, with air pockets. Contractor overly eager to tighten bolts and doing so before the concrete fully cured.

I only mentioned it because someone said they had never seen it. I'm not saying that the behavior is common. Just that I've seen it happen.

 

[CELinOttawa]

I dont know why you would use two washers

I don't like how thin some of the HDG washers seem to be...

Call it a paranoid reaction from years of testing materials...

 

[dik]

CEL... I"ve been using the detail on the left for over 20 years and no problems... including the little tack weld. My General Notes have a comment about letting the concrete gain a little strength before torquing... Also often spec ASTM 1554 in Grade 55 S1, that's weldable and Grade 105 (not weldable, but peened).

Bottom nut goes right to the top of the lower thread.

Dik

 

[hokie66]

Does no one else use "U" bolts? You can't pull them out by straightening, and they won't spin. Crushing the concrete is one mode, I suppose. Where I am, contractors don't mind them.

 

[BAretired]

I never considered using U-bolts, but that sounds like a good idea. Two U-bolts instead of four anchor bolts for a typical column anchorage. If concrete crushing is a concern, a nut could still be welded to each branch of the U-bolt.

BA

 

[KootK]

Do U-bolts make anchor bolt placement any more difficult? Perhaps not if a template is being used anyhow.

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.

 

[hokie66]

To the contrary, they make it simpler. The spacing is fixed in one direction. If used in a suspended slab, they require coordination with the reinforcement. In that case, I prefer bolts welded to a plate which sits on the form.

 

[KootK]

I see it. Does AU code provide a method for evaluating U-bolt capacity?

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.

 

[hokie66]

Not to my knowledge. But then, we don't have that complicated Appendix thing to deal with which you folks are always talking about. First principles are good enough for me.

 

[sandman21]

Call it a paranoid reaction from years of testing materials...

Then provide an actual washer, intended for the application.

 

[dvd]

Pic below is from an OSHA investigation of a fatal accident (

https://www.osha.gov/doc/engineering/2012_r_04.html)

 

[hokie66]

dvd,

While the anchor bolts in the collapsed building which you referenced may not have been ideal, that was not what caused the failure. The structure collapsed during erection due to inadequate temporary bracing.

 

[Leftwow]

yea the baseplate wasn't designed to support a heavy moment, that's why the beams are haunched