A325 bolts

[DNBEA]

I have a situation in which i totally rely on the tension capacity of some a325 bolts. and the failure of the connection would be fatal. does anyone see it is a problem to weld the nut and bolts to the steel plates. although the bolts would be tightened to full pretensin force, as time goes by i worry about it will get loose especially if we get some kind of dynamic loads. thanks.

 

[Lion06]

Put a note on the detail that after it is properly tightened to damage the expose threads. Also, if it is that critical, why not consider using the same diameter bolts, but A490?

 

[JStephen]

There are also various retainers you can use to keep nuts from loosening, where the metal is bent up around the nut.

High strength nuts and bolts aren't intended to be welded, and you don't really know what kind of strength you have left after you weld them, so I would avoid that on a critical application.

 

[DNBEA]

Jstepthen

You mean to bent it after it is installed?

 

[csd72]

Use redundancy, more bolts than you need so that if one fails it doesnt matter.

You should never use a single bolt in a critical connection for this reason. I have seen slip critical bolts come loose on a portal frame, though unlikely, it can happen.

 

[DNBEA]

of course i did use more and stronger bolts than I need. it is really not about the strength of the bolts. since nuts can always be turned off from the bolts which make me feel that it is not as secure as a welded connection or a bolted shear connection. i doubled the nuts. Thank you all.

 

[dik]

If tensioned for slip critical, they should not work their way loose. You can use Loctite Red... and then they can only be removed by applying a torch.

Dik

 

[vincentpa]

You could always damage the threads on the bolt. This way the nut can't be backed off. It is very common to do this especially for anchor bolts. Welding will create a stress notch and will weaken the bolt. Adding another nut will probably act like a lock washer. In any case, make sure your inspector knows that this is a critical item or whatever method you call for might get overlooked.

 

[Taro]

High strength bolts are heat-treated and are not weldable. You could actually damage the bolts by welding them.

Pretensioned bolts will not loosen under service loads because the tensioning imparts a large static friction force on the threads. For extra peace-of-mind, you could spike the threads or add a jam nut. If it's that critical, you could use the bolts just for erection purposes and use welds for the permanent connection.

 

[registeredpe]

Greetings:

Welding the nut to an A325 grade bolt is a definite "no-no". The use of locking nuts,double jam nuts, lok-tite are all good options, but I would agree with Taro's post regarding the welding.

As a footnote, I personally avoid(fatal as you put it)tension only connections wherever possible. I go for the gravity type connection where the bolts simply are for erection and or to avoid displacement.

Best regards, registeredpe in AZ

 

[271828]

Taro wrote: "High strength bolts are heat-treated and are not weldable. You could actually damage the bolts by welding them."

This is what I was thinking. Ironically, welding is being considered to make it safer?!

More bolts, double nut, booger the threads, etc. are better IMO.

 

[registeredpe]

Greetings:

271828, the welding Taro was referring to was to weld the structural member to the supporting member, not welding the nut to the bolts! This redundancy would indeed make the connection safer!

Best regards, registeredpe in AZ

 

[271828]

registeredpe, maybe I'm losing my mind, but I think Taro first referred to welding the nut and then threw in a statement about welding the members. I was referring to the former. Then again, it's been a long day--already...

 

[nutte]

Welding the nut is a bad idea. Even if you're just welding the nut, the heat from the welding operation could alter the properties of the bolt as well. Do the jamb nut methods mentioned above.

 

[HgTX]

I'd like to pile on with Taro. If you fully tension the bolt as if it were a slip-critical connection, the nut will not back off. The force in your connection feeds into the friction force that keeps the nut from turning; it's not going to work loose on its own.

I'd also like to pile on with everyone who said not to weld the nut. Don't weld the nut.

I would vote against the A 490 option. They're more brittle and can't be retightened.

Whether you should make this a welded or bolted connection depends on which you feel more paranoid about and which you think the workers are more likely to accomplish in accordance with design assumptions. There are ways to screw up both.

Hg

Eng-Tips policies: faq731-376

 

[slickdeals]

Just out of curiosity, could you describe your connection? maybe there is a way that you can get it to work with bolts being in shear.

 

[hokie66]

DNBEA,

To answer your section post, he didn't mean to bend the bolt. He just meant to foul the threads beyond the nuts by taking a big hammer and cole chisel to them.

 

[DNBEA]

Yeah we can get it work with bolts being in shear, but it would look different from what the client wanted. I didnt think about it too much until I got sign and seal it. thank you all.