Help - A490 Bolts Loosening all by themselves 1

[structuresguy]

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.

 

[structuresguy]

Yes, AISC defines snug tight (paraphrasing) as when all plies have been brought together by the full effort of an iron worker using a spud wrench. So "snug tight" is an actual term for us in the structural world.

 

[dinjin]

What is wrong with tensioning these bolts ie turn them
1/3 after snug tight and see if they still loosen after
4 hours?

 

[structuresguy]

Nothing at all. Now that we have learned that they were not installing the shims, we are going to make them put the shims in place. This should solve the problem. But at this point, they want to be sure, so we will have them tighten the bolts beyond snug.

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.

 

[Bagman2524]

See previous thread about staked threads. Can the bolts be staked or tack welded on to prevent them from backing off?

 

[bridgebuster]

A490 bolts shouldn't be welded because the material is brittle.

 

[dik]

Structureguy...

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

 

[gtaw]

I was under the impression that A490 bolts were required to be fully tensioned regardless of the connection type.

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

 

[nutte]

Al, that applies to A490 bolts in tension; those must be fully tensioned. A490 bolts in the bearing condition, with just shear applied, can be snug-tight. See page 16.1-103, which says, "Bolts are permitted to be installed to only the snug-tight condition when used in (a) bearing-type connections ..."

 

[gtaw]

I appreciate your help.

After carefully reading that section I see my mistake. It makes sense now.

Thanks again.

Best regards - Al

 

[structuresguy]

Ya, that spec can be difficult to read, and its easy to miss things.

They ought to have a summary table identifying exactly what is required for different kinds of bolts in various situations.

 

[unclesyd]

structuresguy,

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.

http://www.steelstructures.com/Publications/SSTC_publications_home.html

 

[gtaw]

Thanks for the link.

Best regards - Al

 

[structuresguy]

syd: Thanks for the link. Those look like great references. I am going to order a set (bolts, weld, strucutral steel) for all our junior engineers to take out to the field with them when they do inspections.

 

[unclesyd]

i use the both when I was a little more active and able to climb around. I used the a lot and like the literature says to help settle disagreements and I'm not a real structural guy.

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.