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Curious as to why people are still using J-bolts

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?

RE: Curious as to why people are still using J-bolts

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.

RE: Curious as to why people are still using J-bolts

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

RE: Curious as to why people are still using J-bolts

Excellent example of how slowly the industry moves.

RE: Curious as to why people are still using J-bolts

Quote (FoxSE14)

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??"

RE: Curious as to why people are still using J-bolts

(OP)
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?

RE: Curious as to why people are still using J-bolts

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?

RE: Curious as to why people are still using J-bolts

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.

RE: Curious as to why people are still using J-bolts

(OP)
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

RE: Curious as to why people are still using J-bolts

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.

RE: Curious as to why people are still using J-bolts

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...

RE: Curious as to why people are still using J-bolts

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.

RE: Curious as to why people are still using J-bolts

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.

RE: Curious as to why people are still using J-bolts

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.

RE: Curious as to why people are still using J-bolts

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

RE: Curious as to why people are still using J-bolts

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

RE: Curious as to why people are still using J-bolts

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...

RE: Curious as to why people are still using J-bolts

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

RE: Curious as to why people are still using J-bolts

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.....

RE: Curious as to why people are still using J-bolts

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.

RE: Curious as to why people are still using J-bolts

Quote (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.

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

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)


RE: Curious as to why people are still using J-bolts

Quote (CEL)

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.

Quote (BAretired)

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.

Quote (jayrod)

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.

Quote (Leftwow)

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.

RE: Curious as to why people are still using J-bolts

Quote:

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.

RE: Curious as to why people are still using J-bolts

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.

RE: Curious as to why people are still using J-bolts

Quote (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....

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

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.

RE: Curious as to why people are still using J-bolts

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.

RE: Curious as to why people are still using J-bolts

Quote (sandman21)

I dont know why you would use two washers

Quote (CELinOttawa)

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

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

RE: Curious as to why people are still using J-bolts

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

RE: Curious as to why people are still using J-bolts

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.

RE: Curious as to why people are still using J-bolts

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

RE: Curious as to why people are still using J-bolts

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.

RE: Curious as to why people are still using J-bolts

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.

RE: Curious as to why people are still using J-bolts

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.

RE: Curious as to why people are still using J-bolts

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.

RE: Curious as to why people are still using J-bolts

Quote (CELinOttawa)

Call it a paranoid reaction from years of testing materials...
Then provide an actual washer, intended for the application.

RE: Curious as to why people are still using J-bolts

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.

RE: Curious as to why people are still using J-bolts

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

RE: Curious as to why people are still using J-bolts

hokie66 - I read the report and agree that the cause of failure was due to improper erection practices. I found that photo a while back and thought that it was a good illustration of pullout on anchor bolts versus breakout cone.



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