Bolts Loosening and Coming Off
Bolts Loosening and Coming Off
(OP)
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,
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,






RE: Bolts Loosening and Coming Off
RE: Bolts Loosening and Coming Off
I have seen loosened bolts on a portal frame once, no way to determine the extent except the hard way one bolt at a time.
How old is the hangar? Where are the bolts located?
RE: Bolts Loosening and Coming Off
Firstly, let's just point out, this structure is not 'mine'. I was not the designer for this thing. I'm consulting on how to fix it.
Secondly, the whole tack weld this is a bit of a band aid solution and as you say yourself, it is prone to fatigue. Clearly, this thing is cycling/moving a lot. More than a tack will take.
Thanks for your input, although I'm trying to figure out a more holistic proposal as to what's going on. If you will, find the root cause...
RE: Bolts Loosening and Coming Off
The hangar was handed over about 3 months ago only. (brand new!)
Most of the bolts that are loose are on the fly-braces and in splice plates on the primary trusses. Also, some of the bolts on the roller door hangers as well.
So, pretensioned bolts might be the way to go then...
I'm not familiar with the American codes, but I'll take a look see.
RE: Bolts Loosening and Coming Off
A relative of mine that heads the maintenance of national roads here says that on signs on the roads they are continuously repairing fatigued boled joints, particularly at baseplates, either the plates break, the nuts get loose, and things alike. That I remember, for bolts fatigued by wind, pretensioned bolts are also mandatory.
It is worth to mention also that: the bolts you are mentioning may have not been considered part of the lateral resisting system, nor contributing to the resistance to wind, nor have been (if just for bracing) been included in the structural model. This is another reason why I am a fan of including bracing members in the structural analysis, you start to see what they take and not. Then the structure may have been dimensioned too flexible for lateral forces, but economy asks so many times.
RE: Bolts Loosening and Coming Off
RE: Bolts Loosening and Coming Off
I've seen a lot of "finger tight" bolts. You can tell from the paint marks if they've ever been tightened before. This more often occurs in lighter structures (PEMB's in particular), but happens in structures where the erector does mostly lighter framing, not heavy beams/moment connections.
Yes, bolts can loosen, but that isn't common and usually occurs under high cycle fatigue and/or at relatively high bolt stresses.
RE: Bolts Loosening and Coming Off
Poor or no inspection can inspire the erector to take all kinds of short cuts.
I had an erector tell the owner and me, "at any one time he is working on ten different projects. You can't inspect all of them. The one or two jobs that you do inspect, I can afford the rework."
The owner fired the erector on the spot, but it was telling of the mindset of the erector. The cost of getting caught and having to do the rework was simply a cost of doing business. If he got away with substandard work on 9 out of every 10 jobs, he made money.
Best regards - Al
RE: Bolts Loosening and Coming Off
I suppose I'll have to really take a look at the option of poor worksmanship.
Detective work's afoot!
Thanks again,
RE: Bolts Loosening and Coming Off
If these are structural bolts, A325 or A490, I do not recommend damaging threads by welding. Quenched and tempered material should not be welded.
http://www.FerrellEngineering.com
RE: Bolts Loosening and Coming Off
RE: Bolts Loosening and Coming Off
Yeah, we've done that. The issue is the Contractor is in Africa and we're a tropical island in the indian ocean.
They were flown in and the steel was shipped in.
The argument to get them back here is ongoing, however, in the mean time we're going up there ourselves to tighten the things up on the short term.
Of course their standpoint is 'It's not our fault' hence why I'm trying to consider any plausible explanation for the phenomenon.
RE: Bolts Loosening and Coming Off
http://www.FerrellEngineering.com
RE: Bolts Loosening and Coming Off
If you can, I would retighten all the loose bolts, and check with a wrench the others.
I would moniter the situation by putting a small stripe of paint over the bolt to the bearing surface and see if any move over time. Would not have to do this on all the bolts, but certainly the ones that were the loosest. Periodically check the selected bolts for any rotation.
Primitive, but it works.
Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask
RE: Bolts Loosening and Coming Off
I doubt they even had a properly sized torque-wrench available on-site, much less used it for every bolt.
Get the bolts re-tightened firmly fast - before they rust out and can't be turned at all. Then TORQUE them. And charge the contractor.
RE: Bolts Loosening and Coming Off
What kind of bolts are used? A307, A325? makes a difference... and, if A325 were spec'd, are they the ones that were used? May have substituted something else.
Dik
RE: Bolts Loosening and Coming Off
RE: Bolts Loosening and Coming Off
As for what to do about it. Follow msquared48's advice and check/tighten every bolt in the building, then monitor the situation. If the problem reappears, you have a vibration problem (I doubt this will happen). If not, you have a claim against the contractor.
RE: Bolts Loosening and Coming Off
seems like you have vibration/movement from what you are saying.
RE: Bolts Loosening and Coming Off
Good Luck
RE: Bolts Loosening and Coming Off
RE: Bolts Loosening and Coming Off
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.
RE: Bolts Loosening and Coming Off