Curious as to why people are still using J-bolts
Curious as to why people are still using J-bolts
(OP)
Is there scenarios where J-bolts are stronger? Even though mathematically headed bolts are stronger in breakout and pullout than J-bolts?
When was the last time you drove down the highway without seeing a commercial truck hauling goods?
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Curious as to why people are still using J-bolts
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RE: Curious as to why people are still using J-bolts
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.
RE: Curious as to why people are still using J-bolts
RE: Curious as to why people are still using J-bolts
RE: Curious as to why people are still using J-bolts
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??"
RE: Curious as to why people are still using J-bolts
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?
RE: Curious as to why people are still using J-bolts
RE: Curious as to why people are still using J-bolts
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.
RE: Curious as to why people are still using J-bolts
RE: Curious as to why people are still using J-bolts
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.
RE: Curious as to why people are still using J-bolts
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...
RE: Curious as to why people are still using J-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.
RE: Curious as to why people are still using J-bolts
Silly people... Testing, testing, testing. Anything else is to ASS U ME.
RE: Curious as to why people are still using J-bolts
RE: Curious as to why people are still using J-bolts
RE: Curious as to why people are still using J-bolts
RE: Curious as to why people are still using J-bolts
RE: Curious as to why people are still using J-bolts
RE: Curious as to why people are still using J-bolts
RE: Curious as to why people are still using J-bolts
RE: Curious as to why people are still using J-bolts
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
RE: Curious as to why people are still using J-bolts
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)
RE: Curious as to why people are still using J-bolts
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.
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.
Supply begets demand begets supply... viscous.
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.
RE: Curious as to why people are still using J-bolts
Thanks for the info BA. I think I've heard that elsewhere as well.
RE: Curious as to why people are still using J-bolts
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.
RE: Curious as to why people are still using J-bolts
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:
RE: Curious as to why people are still using J-bolts
RE: Curious as to why people are still using J-bolts
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.
RE: Curious as to why people are still using J-bolts
Call it a paranoid reaction from years of testing materials...
RE: Curious as to why people are still using J-bolts
Bottom nut goes right to the top of the lower thread.
Dik
RE: Curious as to why people are still using J-bolts
RE: Curious as to why people are still using J-bolts
BA
RE: Curious as to why people are still using J-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.
RE: Curious as to why people are still using J-bolts
RE: Curious as to why people are still using J-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.
RE: Curious as to why people are still using J-bolts
RE: Curious as to why people are still using J-bolts
RE: Curious as to why people are still using J-bolts
RE: Curious as to why people are still using J-bolts
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.
RE: Curious as to why people are still using J-bolts
RE: Curious as to why people are still using J-bolts