Reuse Lifting Bolts

[iv63]

I am designing lifting lugs bolted to skid base with four 1” dia ASTM A490 bolts. After skid is loaded onto truck, the lifting lugs need to be removed due to shipping width restrictions. Can these bolts be reused at the job site to lift the skid again, if the bolts are just snug-tight previously? Also since nuts are not accessible can they be welded to inside of skid beam and tight bolts from outside?
Thank you very much,
IV

 

[kelowna]

I would not see a problem with re-using them as long as they are visually inspected prior to re-use.

Welding nuts is something I have done on ocasions too, but only for temporary works and it should be done with care and proper procedures.

It also depends on the specific circunstances. Are you talking about 2,20 o 200 re-uses? Maybe you should allow re-use but replace regularly 'just in case'. What is the load on the bolts vs. capacity. If it is 20% probably not a problem, if it is 95% maybe not so good an idea.

 

[desertfox]

Hi iv63

Depends on what the bolts have been tightened to in the first instance, a rule of thumb, bolts are reusable if they have not been tightened above 75% of the yield stress.
Also you have not indicated how the bolts are loaded during the lift of the skid.
Personally if there is any doubt I would send new bolts to site its much cheaper then having an accident.

desertfox

 

[iv63]

kelowna and desertfox thank you both for quick responses. Attached is my preliminary layout. Bolts will be reused 2 or 3 times only and load on the bolts is very high. My main concern is if reusing bolts and welding nuts are code prohibited.

 

[jenDL]

Here are some references that I have found regarding reusing bolts. Generally, desertfox has the right idea...order a few more bolts.

If you have the 13th Edition of the Steel Manual, flip to the back..they've reprinted the Specification for Structural Joints Using ASTM A325 or A490 Bolts. Section 2.3.3 discuss reuse (pages 16.2-7 through 16.2-11). Per the text only black ASTM A325 bolts are permitted to be reused. You can also access the text at boltcouncil.org

I've also found a little info. from the AISC website (link below to Engineering FAQ 16.11.2) with a little more discussion about reusing bolts. If the bolts were only installed "snug tight" they are OK to reuse. Otherwise, if they've been fully pre-tensioned they are NOT OK to reuse.

 

[desertfox]

Hi iv63

Thanks for the diagram, according to my calculations the bolt diametrically opposite your 40kips load at (60 degrees)
see's the most load which I calculate to be 16.182kips direct tensile and a resultant shear load of 3.2307kips which when put into the formula:-

Fr= 0.5(F+(F^2+4Q^2)^0.5) where Fr= resultant load
F= tensile load
Q=shear load

to give a resultant tensile load of 16.8 kips approx 17kips per bolt.
A quick glance at 1" bolts of thr grade your using suggests that you have a good margin of safety.
I don't know what code your working to however I don't like
welding nuts onto plates when there carrying heavy loads especially in your case because you can't see them once the plates been welded in but thats just my personal opinion. Welding the nuts can alter the nut strength due to the heat from the weld which I assume your concerned about and I would be too other than that I wouldn't like to say.

desertfox

 

[kelowna]

There is very good reference information about bolts on

http://www.boltcouncil.org

This document:

http://www.boltcouncil.org/files/2ndEditionGuide.pdf

has a discussion on bolt re-use.

If the load is very high I would be doubtful about re-use more than once or twice. the document comments on it.

The welding will change properties on the nut, for sure, that is the reason it has to be done properly. Tackwelding would have a negligible effect on its performance and it will help holding it in place. It is true it is not allowed by code, that is the reason I only do it for temporary conditions, but I have seen it done many times on different places and without any trouble.

 

[desertfox]

Hi iv63

I don't know how your calculations compare to mine however I made the assumption that: the lifting points tip at the edges of the plate their mounted on so all 4 bolts take some load, also I haven't counted on any friction taking the shear after the lifting lugs are bolted up, I just assumed all the bolts in the joint shared the shear which will probably not be true in practice.
I assume you may have done your calcs assuming that not all the bolts in the joint are taking load in which case your figures would be higher.

desertfox

 

[DWHA]

High strenght bolts & nuts are not to be welded. These bolts are quenched and hardened. Welding to them causes brittleness.