Bolts Loosening and Coming Off

[StructSEZ]

Hi guys,
I've got a situation where an aircraft hangar (trusses on concrete columns) is experiencing bolts falling out.

Some of the guys reckon the builder/rigger did a poor job of tightening them. However, I find that a bit hard to believe.
In your experience, what would cause snug-tight (not fully tensioned) bolts to come loose to the point of falling off? Three of them have actually dropped to the ground and when I went up there to inspect, about 40% of them were loose to the point of being able to twist the nut by hand with very little physical strength required.

I should also mention that it's an aircraft hangar, and the guys over there reckon when the wind blows it shakes a fair bit. From that, I'm thinking there's a harmonic being setup which is pushing the nut off along the threading.
That does sound a bit fantastic though, so if I could get some ideas thrown in maybe I could have more angles to work to finding the cause and remedying it.

Thanks in advance,

 

[MiketheEngineer]

Loctite them, re-torque and put a dab of paint on them to monitor. Then check every month or so


Good Luck

 

[Bobber1]

If they are A325 or A490 bolts and they have loosened, I don't believe you can pretension them because they have likely lost their required factory applied coating. They will have to be replaced with new bolts in sealed containers if they are to be pretensioned.

 

[paddingtongreen]

I say they were never torqued. "Snug tight is achieved with the full effort of a man using a normal spud wrench" according to a number of codes. This amounts to a serious torque, structural bolts do not come undone when snugged except in extraordinary circumstances. Such circumstances are not described here.

The fix would be to snug the bolts and monitor them.

Michael.
Timing has a lot to do with the outcome of a rain dance.

 

[bridgebuster]

Ungalvanized A325 bolts can be re-used if the threads aren't damaged.