Why don't you just specify that the threads be defaced above the bolt?
Personally I prefer to have my bolts embedded in the finished concrete, or to add a lock nut (second nut). I don't trust any of the chemical products to be 50 year plus reliable.
I'll be very keen to see what others post!
Cheers,
YS
B.Eng (Carleton)
Working in New Zealand, thinking of my snow covered home...
Usually just wrecking the threads above the nut works (as well as the secondary nut-already mentioned)...I've also seen the nut tack-welded to the anchor rod.
the contractor does not leave enough projection as shown on the drawing. top of the nut is the same as top of anchor. i dont think we should weld the nut as the heat will damage the material. i found loctite. has anyone use it before?
The temperature required for a tack weld is minor. You just need to be confident that your contractor/fabricator will understand that very low heat and the smallest of tack is what is really required.
If you're in a seismic area, I can understand your hesitation. Crimping the threads is the best way to go, as long as a permanent solution is desirable. In french we would call it "defacing" the thread, but no matter what it is called, if you deform, destroy or otherwise marr the thread your bolt isn't going anywhere.
I have often thought that if I had nearly no thread, I would ask for the interface between the top of the bolt and the top of the nut to be v-punched to cause a defacing. I'll post a sketch of what I'm thinking if I get the chance.
Cheers,
YS
B.Eng (Carleton)
Working in New Zealand, thinking of my snow covered home...
Don't use a tack weld. Even though the bolts are relatively mild steel (A307, likely), the nuts are likely hardened. Tack welds can be a source of cracks.
Gall? That's a new one to me... Are you simply saying "change" the threads so that the nut cannot back off? That would be yet another term for marring, defacing, crimping, etc, etc, etc, a nut.
I think we need a dictionary of standard structural terms to be put out by the ISO.
Cheers,
YS
B.Eng (Carleton)
Working in New Zealand, thinking of my snow covered home...
DNBEA had followed up his original comment with the statement that the end of the anchor was flush with the top of the nut. Suggesting to booger the threads (new word) or use a lock nut, no longer fit the situation.
DNBEA, if by Loctite you mean the adhesive, it looks like it is just for sealing the threads. You can still remove the nut with a tool.
A tack weld is best. Don't worry about hardened nuts and all that other stuff. The little bit of heat generated by a tack weld will not change the metallurgy to any significant degree. All you need is a little bead at the inside rim of the nut to the edge/end of the anchor.
Loctite makes a range of excellent products for thread locking, not just one. There are strengths that range from temporary to essentially permanent. These products are used extensively in the electric utility business, including some very heavy duty applications.
Your can check the Loctite website or with their representatives to get a recommendation for your specific application.
There has been a previous thread on this subject. Everybody seems to have a prefered method, tackweld, damage threads, loctite or locknut.
My personal preference is for locknuts
- I do not like loctite (being a structural engineer I trust physical methods over chemical ones)
- tackwelds make possible future replacement difficult. Having worked in two retrofit projects I tend to be a bit more sensitive to it.
- Damaged threads will prevent the nut from falling off but they will not prevent the bolt from becoming loose.
I prefer to "gall", "spike", "mar" or "burr" the threads at the nut using a punch where the threads enter the top of the nut.
this is on the AISC Solutions Center:
6.5.1. What can be done to prevent the nut from loosening?
In general, when properly installed, the high-strength bolt-nut assembly will not loosen. When snug-tight bolts are used, the loading will be such that loosening of a nut will not occur. When fully tensioned bolts are required, as for slip-critical connections subjected to vibratory or fatigue loading, the installed tension and the attendant friction on the threads will prevent the nut from loosening.
In some other cases, such as nuts on anchor rods (for which full-tensioning is generally inappropriate), further consideration may be required. In such cases, an additional jamb-nut or second nut may be provided. Alternatively, the threads can be spiked or marred or the nut can be tack-welded to the base metal to prevent it from turning. Note that the latter two solutions are permanent actions. There also exist proprietary nut devices with locking features to prevent the nut from backing off.
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![[r2d2]](/data/assets/smilies/r2d2.gif "[r2d2] [r2d2]")
