How to lengthen short anchor bolts 2

[denniskostrzewski]

I am installing several exhaust systems, each weighing 15,000 pounds on existing pads with existing threaded anchor studs. 1.25 dia x 6.
Some of the studs are short preventing full nut engagement.
What are the best practices to extend the length of the bolts?

 

[CoryPad]

You can use a flanged nut with a long length (sometimes called a T nut) to make up the length difference. Look at the top image here:

http://www.sigmatool.com/t-nuts/2way-t-nuts.html

You would need appropriate clearance holes in the clamped parts.

Or, you can use a turnbuckle style long nut:

http://www.midwestcontrol.com/catdisplay_short.php?pg=192

You probably don't need the long middle section shown here, so just use view it as a conceptual diagram.

Regards,

Cory

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[unclesyd]

I would give these people a call about a coupling nut covering your problem.

http://www.cns-sales.com/product.html

 

[CoryPad]

Yeah, a coupling nut is essentially the same thing I was saying with a turnbuckle. You likely will find a suitable product using unclesyd's link.

Regards,

Cory

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[RARWOOD]

I'm not sure how a coupling nut solves denniskostrzewski's problem.

If I understand the question correctly, I believe dennis problem is that he has equipment that has holes in the base for 1 1/4" diameter anchor studs. What he needs to do is extend the 1 1/4" diameter rod.

I am assuming that he doesn't want to enlarge the holes in his equipment base. It appears to me that to use coupling nuts or turnbuckles you would need to enlarge the holes. The T-nut looks like it may work if the holes in the equipment base are oversized to allow for field adjustment.

I believe dennis is looking for a method to extend the studs by welding or other means.

I have heard of people welding additional rod length on to existing anchor bolts. My experience is of the use of full penetration welds to make rebar splices. I would think dennis' problem would be similair.

 

[CoryPad]

RARSWC,

The idea with the coupling nut is that you would then position your part with its hole over the coupling nut, then use a bolt to clamp the part to the coupling nut/anchor stud combination.

Or, if that doesn't work, a T nut could be used.

Usually threaded fasteners are heat treated to relatively high strength. Also, they have closely controlled dimensions. Welding ruins both of these, so it usually isn't recommended for fasteners.

Regards,

Cory

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[dik]

Can you provide a 1/4" backing plate with a hole 1/16" larger than the anchor rod and CJP weld an extension. It may be necessary to chip out some concrete to clear the baseplate.

Any chance the anchor rod can punch throught the concrete because embedment is too great?

Dik

 

[VeryPicky]

Well, I am not sure I understand the problem in full and the practices offered to the originator. When it comes to anchor bolts I see no other option than redesign, cut if necessary and weld new, longer bolts.

Putting Human Factor Back in Engineering

 

[dimjim]

How thick are the nuts and how many
threads are engaged?
I assume this is strictly a tension
application. You might have enough
threads in contact anyhow.

 

[denniskostrzewski]

This is for dimjim

Yes, the anchoring puts the bolts in tension.
Most nuts engage all the treads so the threads are even with the top of the nut.

A few bolts are short and their nuts engage about 50% of the nut height.

The bolts are 1.25dia x 6 coarse. There are 8 per unit.

I wish I knew how to write you directly.

Also I have two conflicting answers -- one says weld, another says don't weld.

 

[unclesyd]

What is the code or specificion that these bolts fall under?

 

[UcfSE]

dennis, the conflicting answers are the nature of this site, from a certain point of view. Everything you get here is just advice and opinions. While after time you will understand who knows their stuff and who is probably really an engineer, in the end anyone can register and claim to be an engineer, so you need to take some of what you get from this site with a grain of salt so to speak. In the end, in "the real world", the decision is left up to you and your judgment alone.

Have you thought of drilling new holes in the base plate and using post-installed anchors? No weld problems, no extending nuts or worrying about having enough room for this or that, just cut off the bolts that are too short and put in some new ones. The question then becomes is drilling a new hole OK, will the new configuration of bolts be impractical, is the area accessible, and so on.

 

[denniskostrzewski]

TO UcfSE

(The new units are in design so we can add more holes to the base rings so new anchors can be installed.

We will do a wind load and seismic analysis even though the pads are in place to test our customer's assumption that the old pads are adequate since the weights are about the same as the old units. We may add bolts regardless.
Thank you.

 

[dik]

part of my standard notes is that anchor rods be weldable... just because of all the problems I've encountered in past... if the material is weldable, then you can weld an extension as noted. For A36 material and F1554 matl, they are generally weldable, but check first.

Dik

 

[dimjim]

You should check the specifications that governs
your particular situation to see if welding can
be used. If it is low carbon like A36 material,
I would think that welding would be ok. If it were
high strength studs or anchor bolts, you would have to degrade them because of the welding drawing out some of
the apparent hardness. I would be greatly troubled if
two of these were side by side or on the same side of
the bolting pattern.

 

[DRC1]

If your base plate is thick enough, you may be able to turn down the material at the bolt penetration. This would give you sufficent engagement. But be sure that thinning the base plate is ok.

 

[VeryPicky]

Dennis,
Conflicting answers may come from lack of information and datails and different experience of people involved. I want to apologize for short answer last time, but I was pressured by time and just wanted to caution against any technical half solutions to extend the anchor bolts.
What I was intending to point out is:
1. Do proper design of any solution you implement: welding or no welding, irrespective.
2. Know the materials involved, do not take shortcuts there.
3. Consider new anchor bolts, avoid extensions, they tend to be weaker than monolythic bolt.
4. If you find new bolts weldable and it is the feasible option, weld, but, again, make sure your weld is designed properly.
5. Don't assume, check all calcs again.
6. I can give you complete solution but I need details, drawings and charge number.
7. In the meanwhile you are an engineer and responsibility for due diligence in resolving the problem lies with you, no matter what advise is given on the forum.
And thank you, UcfSE, for doubting. Doubt is a basis of good, responsible engineering.

Putting Human Factor Back in Engineering

 

[Sciscoe]

Dennis, not sure about the material or thickness of your pad. If it is a concrete pad, you may want to consider removing the old bolt and replacing it with threaded rod using an epoxy anchor system for embedment into the concrete. Powers fasteners has some products we like, including fast setting epoxy. We use this approach for some structural connections. You can find threaded rod in a variety of strengths, I think B17 is around 125K. Just a thought. Welding on an extension is a bit of a bear if you have to include matched threading. You will also have to stay on top of rust with an inhibitor (paint or cold galvanize) or rust could weaken capacity.

 

[RARWOOD]

Assuming the anchor bolts are weldable material, with 50% nut engagement would plug welding the nuts to the anchor bolts be an option?

I have heard of the above being down with steel column base shoes. I'm not sure I would consider plug welding the nut when the bolt is subjected to tension. However with a four anchor bolt base shoe for a column loaded only with gravity loads I might give it some though.

 

[dik]

I try to avoid welding nuts and washers... Dik