"Killing" of a nut on an anchor bolt

[pattimelt]

I have 20 or so (out of 7,000) anchor bolts (1" X 13" allthread) set in epoxy grout (17,000 psi avg strength) whose nuts are not fully engaged (about 1 to 2 threads below flush) Rather than bring in the core drillers to pull these out I would like to be able to have a welder come in and "kill" the nut - fill the opening of the nut with a puddle weld The nuts are 2H and they are in a horizontal plane splice connection They are spaced intermittently throughout a run of approximately 1600 feet AWS D1.1 allows the welding repair of anchor studs, but doesn't address this RCSC talks about load and welding with respect to rivets, but not this My PE has provided numbers indicating that there is little load involved (in fact, a jam nut could have been used instead of a full nut) Suggestions? Comments?

 

[MikeHalloran]

If your PE says a jam nut is good enough, then buy 20 jam nuts and install them.



Mike Halloran
Pembroke Pines, FL, USA

 

[DennisP]

If there are no threads exposed as the OP stated, a jam nut will not work.

 

[Duwe6]

First, recheck with the engineer and make sure that 'soft' nuts are acceptable. Your 2H's will be 'soft' after welding.

Second, retighten those connections. Anchor bolts are notorious for loosening up after the first tightening.

Then 'puddle' weld the nuts using E-7018. Have the welder run the rod around the ID of the nut, until a puddle of weld metal [not weldmetal plus slag] fills the nut. Slag will be dripping out of the nut when he finishes.

This is a standard 'fix' for short anchor bolts, but is usually applied to 'soft' Grade 2 nuts. 2H's are readily weldable, but will be 'soft' when done.

 

[pattimelt]

Well, if I have them install the jam nut, I will have enough threads exposed BUT I have a GC to answer to, as well as the client and knowing them from past experience they are going to shoot down the jam nut even though there is documentation from the PE (it just looks out of place-like a sore thumb so to speak)

 

[dhengr]

Remind the client and the GC who it was who set the ABs improperly. You have a fix method from the PE which he approves, it will show some exposed bolt thread and probably raise fewer questions in the future. While I generally agree with Duwe6's last post and his analysis of the issue, it may raise more questions because of the metallurgical issues. The engineer looked at the number of threads engaged btwn. the nuts and the bolt vs. the load on the bolt to make his judgement, that’s the important design consideration. And, most people walking buy will see exposed threads and think no more of it. Is replacing the nuts appreciably more costly than dragging welding equipment all over the property? Don’t epoxied Abs have a long term creep problem when continuously loaded?

 

[connectegr]

I know that I have commented on this in previous posts. Are the anchors, quenched and tempered material?

AISC specifically states that quenched and tempered anchors should not be welded or heated.

If the EOR will state that there is no shear or tension on the anchors, the argument for plug welding the nuts is purely academic. But, plug welding generally creates a lot of heat. Which would not be recommended within the area of the engaged threads.

Am I missing something?

http://www.FerrellEngineering.com

 

[connectegr]

If the anchor rods and nuts are weldable material. AISC does not consider plug welding of partially engaged nuts an effective means of attachment.

http://www.FerrellEngineering.com

 

[connectegr]

Where the attachment?

Here...

http://www.FerrellEngineering.com

 

[pattimelt]

If I am reading the information from the P.E. correctly, the engagement (so to speak) is provided by the placement of the anchor bolts into the high strength epoxy grout - the bond of the grout is what is holding them in place. These connections are at a splice bar with the anchor bolts holding the bar down, but the torque/tension being supplied at another point on the bar in the horizontal plane. My other option with this is to have the offending shorties core drilled out and replaced with the anchor bolt to the correct depth.

 

[MikeHalloran]

Is the epoxy manufacturer going to stand behind the stuff after the ABs have been heated enough to melt the ends?



Mike Halloran
Pembroke Pines, FL, USA

 

[ricklts]

You might want to remind the client that in most thread(assuming something like an -8UNC thread profile) designs, that approximately 80% of the load is carried by the first three threads. Why weld? If cosmetics are the primary issue, fill the top of the nut with epoxy.

 

[pattimelt]

Thanks to all We were able to present the client with the calcs and they accepted the jam nuts We replaced with same, making all connections uniform, and got it bought off