Help - A490 Bolts Loosening all by themselves
Help - A490 Bolts Loosening all by themselves
(OP)
We have a job where the contractor and testing agency is telling us that the A490 bolts are loosening all by themselves. The bolts in question are 7/8" diameter x 2-3" long, and are being used in top & bottom plate moment connections on floor beams, so loaded primarily in shear. (non-seismic zone) We only are requiring snug tight connection.
They are telling us that within a few hours of tightening them to (supposedly) snug tight, that they can go back and run the nut off by hand.
None of us here have ever seen this before. There is only three things that I cna think of that would cause this:
1. Flange and moment plate are not in full contact, so the plate is relaxing under the load, and thus the tension on the bolts is also relaxing.
2. Tightening method is not reliable, in that they are not going back over the bolts after they have brought the plies together to ensure that they are all still tight.
3. the bolts are poor quality steel, and are relaxing under the tension from the initial tightening.
Has anyone seen this before? Do you have any suggestions for what the problem is, or how to solve it?
I am ready to tell them to test a random sampling of the bolts for ultimate strength and for creep/relaxation properties. Does anyone know if there is an ASTM test method for this? I have not found one yet in my web searching.
Thanks very much.
They are telling us that within a few hours of tightening them to (supposedly) snug tight, that they can go back and run the nut off by hand.
None of us here have ever seen this before. There is only three things that I cna think of that would cause this:
1. Flange and moment plate are not in full contact, so the plate is relaxing under the load, and thus the tension on the bolts is also relaxing.
2. Tightening method is not reliable, in that they are not going back over the bolts after they have brought the plies together to ensure that they are all still tight.
3. the bolts are poor quality steel, and are relaxing under the tension from the initial tightening.
Has anyone seen this before? Do you have any suggestions for what the problem is, or how to solve it?
I am ready to tell them to test a random sampling of the bolts for ultimate strength and for creep/relaxation properties. Does anyone know if there is an ASTM test method for this? I have not found one yet in my web searching.
Thanks very much.






RE: Help - A490 Bolts Loosening all by themselves
I have always used slip critical bolts in oversized holes for this application. See ASD 9th Edition, pg. 4-110 and 111, toward the bottom of each page.
RE: Help - A490 Bolts Loosening all by themselves
RC
All that is necessary for the triumph of evil is that good men do nothing.
Edmund Burke
RE: Help - A490 Bolts Loosening all by themselves
We have asked them that, and they claim to be doing it right. This has been happening for a while now, some areas have been inspected and failed 4 times now.
I would too, but in this case, the engineer that designed the connection specified standard holes with bolts in bearing. Also, we just found out that they are using A490 bolts instead of the A325 bolts that were specified.
All of this is just coming to our attention, even though the contractor and testing agency have been dealing with it for some time. Now that it is affecting their schedule (they were supposed to start fireproofing this week), they are getting us involved.
RE: Help - A490 Bolts Loosening all by themselves
In this case, clip critical is not required. These are wind frames with no seismic requirement. The code generally recognizes that MWFRS components are not subject to "significant load reversal", as the wind is generally considered quasi-static loading, so typically slip critical is not required.
Also, they are not sharing load with welds, so no requirement in that case for slip critical.
RE: Help - A490 Bolts Loosening all by themselves
RE: Help - A490 Bolts Loosening all by themselves
RE: Help - A490 Bolts Loosening all by themselves
The flange plates tend not to sit flat against the beam flange; they often tilt upward from welding.
Can you make these connections work with slip critical values since they provided A490's in lieu of A325's and you already have an acceptable faying surface since you are fireproofing. If so, have them fully torque the bolts. If not, you may have to weld.
RE: Help - A490 Bolts Loosening all by themselves
RE: Help - A490 Bolts Loosening all by themselves
I don't know about bolt extension right now. I have one of my junior engineers down at the job site now to look at some of these things, including holes sizes and alignment issues. And yes there are shims in place, but I am not aware of requirement for slip critical with shim. Can you point out a reference please?
I think we could definitely make them fully tighten the bolts, though I don't know yet (have not yet run the numbers) if the bolts would be adequate in slip ciritcal. But in reality, they are still in bearing, as they would probably have slipped into bearing condition now, since the slabs have been cast. Pockets in the slab were made at the bolts, to allow the bolts to be installed after the dead load of the slab was in place. So we may make them fully tighten them, in hopes that they won't loosen once fully pretensioned.
Thanks for your help.
RE: Help - A490 Bolts Loosening all by themselves
There are a few reasons why this may happen.
1)Are faying surfaces in intimate contact?
2)Are bolts being systematically tightened, from the most rigid point out?
3)Are washers hardend steel?
4)Is there any welding being performed on the connection after snugging the bolts? Thermal expansion will almost always cause snugged bolts to loosen. Although you state that your issues are occurring within 4 hours of snugging. Normal temp differences should not cause problems within 4 hours. But if welding is performed, then this can happen quickly.
A pre installation verification test may be of some help. Snugged bolt do not require this. But it may help determine if there are in fact issues with the material. Have the bolt snugged in a skidmore and held for a few hours.
RE: Help - A490 Bolts Loosening all by themselves
I may be wrong, but wouldn't you want the clamping force of slip critical bolts to prevent an unwelded shim from slipping? If it is welded, that is a different situation.
Perhaps the newer AISC codes cover this more expicitly.
RE: Help - A490 Bolts Loosening all by themselves
RE: Help - A490 Bolts Loosening all by themselves
The later AISC specifications do go into this a little more.
RE: Help - A490 Bolts Loosening all by themselves
Turn of nut? Torquing?
RE: Help - A490 Bolts Loosening all by themselves
I've heard of something kinda like this happening with stainless steel, but not so much that they could be removed with just fingers.
RE: Help - A490 Bolts Loosening all by themselves
Are they using enough wrench to properly snug tighten the bolts.
I was privy to a similar situation where the iron workers were using very short handled wrenches to tighten some 1" bolts and were coming up short in the required clamp load.
RE: Help - A490 Bolts Loosening all by themselves
That said, I would be surprised if an ironworker using an ordinary spud wrench could snug up all of these bolts effectively. Typically a spud wrench and "cheater bar" are required to get the job done. The 'cheater bar' is simply an extension added to the spud wrench to increase the moment arm.
Are the bolts coated or are they "black" bolts with no protective coating? Sometimes on precoated bolts and nuts the coating will fail and clog the threads between the nut and bolt. This is enough to prevent tightening even when you have a power wrench.
Regards,
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Qshake
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RE: Help - A490 Bolts Loosening all by themselves
Thanks everyone for your help on this. Hopefully this will no longer be an issue now.
RE: Help - A490 Bolts Loosening all by themselves
... by the way, does the AISC definition explicitly specify use of a wrench?
Mike Halloran
Pembroke Pines, FL, USA
RE: Help - A490 Bolts Loosening all by themselves
RE: Help - A490 Bolts Loosening all by themselves
1/3 after snug tight and see if they still loosen after
4 hours?
RE: Help - A490 Bolts Loosening all by themselves
I can't believe that they went around and around with the testing agency, who kept failing the bolts, and no one figured out that they didn't have the shims in place. Makes me really question both the erector and the testing agency. I really hate the quality of the labor here in Florida. I swear, the guys erecting steel today must have been washing dishes yesterday, or whatever other job the labor finder place put them in that day.
RE: Help - A490 Bolts Loosening all by themselves
RE: Help - A490 Bolts Loosening all by themselves
RE: Help - A490 Bolts Loosening all by themselves
Depending on the amount of tightening... it may not be possible to re-use the A490 bolts. A490's should be able to be tensioned sufficiently that they will not work their way loose.
Dik
RE: Help - A490 Bolts Loosening all by themselves
Reference AISC Steel Construction Manual, 13th Edition, Commentary 16.2-25
"With this edition of this Specification, snug-tightened joints are also permitted for statically loaded applications involving ASTM A325 bolts and ASTM F1852 twist-off-type tension-controlled bolt assemblies in direct tension. However, snug-tightened installation is not permitted for these fastener in applications involving non-static loads, nor for applications involving ASTM A490 bolts."
My understanding of the above paragraph is that the A490 bolts are not to be used in the "snug-tight" connections.
Am I misinterpreting the paragraph?
Best regards - Al
RE: Help - A490 Bolts Loosening all by themselves
RE: Help - A490 Bolts Loosening all by themselves
After carefully reading that section I see my mistake. It makes sense now.
Thanks again.
Best regards - Al
RE: Help - A490 Bolts Loosening all by themselves
They ought to have a summary table identifying exactly what is required for different kinds of bolts in various situations.
RE: Help - A490 Bolts Loosening all by themselves
I believe this is the little handbook I used for information about structural steel bolting and it's use. If I recall it detailed the use of each spec fastener.
h
RE: Help - A490 Bolts Loosening all by themselves
Best regards - Al
RE: Help - A490 Bolts Loosening all by themselves
RE: Help - A490 Bolts Loosening all by themselves
I had both the bolts and the welding references and both have walked away. The one on bolting is in Alabama and is supposed to be returned while the one on welding is in NYC with an inspector for the Port authority.