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?

 

[FoxSE14]

We went away from J-bolts as a company standard a few years ago. I believe it to be good practice to avoid them (I think ACI weighed in on this in the 318 commentary somewhere? Local crushing occurs at the radius, leading to a 'wobbly' bolt)

Contractors will request them from time to time...unfortunately, this tends to happen the residential world. We try to steer them toward the various 'quick drive' anchors (Titen HD, Kwik-HUS, and similar), but you can't always teach an old dog new tricks - even if they're easier tricks.

 

[Archie264]

J-bolts *look* stronger (even though tests have proven otherwise). It could be as simple as that.

 

[BUGGAR]

Excellent example of how slowly the industry moves.

 

[CANPRO]

but you can't always teach an old dog new tricks - even if they're easier tricks.

This has been my experience. I like to use threaded rod with a plate washer...the contractor doesn't really care if they're stronger I suppose, but they hang plumb from the templates and all the contractor needs is a length of threaded rod and a bucket full of nuts/plates and he can make up any length anchor he needs...for those reasons I would have thought they would prefer that detail. I've tried to sell a few regular clients on this concept, but they never bite. The guys on site always wonder "where are my J-bolts??"

 

[Leftwow]

HAHA that's very interesting CANPRO.

One engineer told me that plates on an anchor bolt can cause cracking to the horizontal of the plate, and he refused to use them. Have you heard anything about this?

 

[MotorCity]

J-bolts went out with the dinosaurs in my neck of the woods. Have not seen engineers or contractors use them in 10+ years, although I can't speak to the residential side. It has always been my understanding that one of the major concerns with using J-bolts is that they tend to straighten out. I have a hard time trying to imagine the bolt straightening out and being pulled cleanly from the hole and being straight or semi-straight. My gut tells me the bolt or the concrete would break first. Anybody ever witness this phenomenon in the field or lab?

 

[KootK]

J-bolts are still popular in my area. I feel the same way though, I wish that they would just be discontinued. I think that they persist because:

1) There is this pervasive sense that anything different from typical must be more expensive, no matter what.

2) Appendix D actually gave J-bolts modest design values so, on that merit, they're still a viable thing.



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.

 

[Leftwow]

Yea I get that flak from designers, them saying "oh that's more expensive". I would be surprised if they knew the prices on bolts. It's like the whole A307 bolt, old guys want to use that everywhere even though we've been using F1557

 

[CELinOttawa]

I have been involved in a lot of testing over the years. I have actually seen an all-thread J-bolt pull out, but it tends to require a few things to actually happen:

1. Crap concrete.
2. Poor placement.
3. Little/Poor/No vibration.
4. Greased Bolts (this was done on purpose, and was surprisingly ineffective).
5. Perfect threads.

Note that the fifth one is listed because I had a hunch that you could make the pull out stop happening if you deformed/cut/marred some of the threads. That tended to work, and actually caused the J-bolts to perform better.

As best as I can tell from my exposure to these "bad boys", the threads tend to capture and hold air. Even once actually surrounded by concrete with little air, they tend to have paste flow into the grove between the threads, rather than a good mix including fine aggregate.

Best avoided, but you can get good capacity if they are done right. They are just too damn sensitive to changes and poor practice.

 

[CELinOttawa]

Like MotorCity, the old smooth shaft J-bolt went out around here before I started to practice. I was shocked to see them still available from a large supplier, honestly not having realized these existed other than in the existing and heritage buildings I work on.

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...

 

[KootK]

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.

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.

 

[CELinOttawa]

Ha! The amount of torque you'd be talking about to need that j-shape would be very effective at breaking, or at least lessening, the bond and maximize the chance of getting pull-out!

Silly people... Testing, testing, testing. Anything else is to ASS U ME.

 

[Archie264]

Shoot, I didn't realize that's what we were talking about. I thought we were discussing bent "L"-shaped anchor bolts vs. anchor bolts with nuts and washers.

 

[Leftwow]

Perhaps it's cheaper because you need to tack weld the Nut onto the bolt?

 

[Leftwow]

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

 

[CELinOttawa]

No. L-shape and J-shape behave differently, particularly if you consider the old cast L-bolts. They perform really quite well... J bolts have a pre-cast pull-out path...

 

[moltenmetal]

We use LOTS of them- but for bolting things to bar grating, not for embedding in concrete.

 

[SAIL3]

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.....

 

[jayrod12]

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. So if we can use them, they'd prefer that over plate washers and nuts.