HSS column tolerance

[dbriant]

We have an exterior stair column (HSS 3x3x1/4) with a K-brace that was field-welded mid-height. The 2 diagonal brace members are L3x3x1/4, welded to the column with 1/4" fillet welds all-around. The column is 11.5 ft tall. The owner noted that it appeared the column had been hit and was deflected. Contractor verified that column is deflected 7/16" (l/315) but states that it is due to the field-welded brace connection. The deflection is perpendicular to the plane of the brace. A couple of basic questions come to mind:
- Is the erection tolerance of l/1000 what controls? If so, then this column is out of tolerance.
- The column is relatively lightly loaded (4,000 lb max) so being out-of-plumb by 7/16" isn't as much of a structural concern. However the owner's a bit annoyed that the contractor didn't point it out first.
- Could field-welding braces on cause this type of deflection? Thoughts on how to prevent it in the future? Is this up to the erector to provide adequate temporary bracing if needed to counteract effects of welding deformation?

Thanks for any insight.

 

[JAE]

- Is the erection tolerance of l/1000 what controls? If so, then this column is out of tolerance.
[blue]From AISC criteria (Code of Std. Practice section 7.13) it appears that L/1000 is correct.[/blue]
- The column is relatively lightly loaded (4,000 lb max) so being out-of-plumb by 7/16" isn't as much of a structural concern. However the owner's a bit annoyed that the contractor didn't point it out first.
[blue]With the out-of-plumbness, you could check the column under the lighter load for second order effects and see if the deflection is a real concern or not.[/blue]
- Could field-welding braces on cause this type of deflection? Thoughts on how to prevent it in the future? Is this up to the erector to provide adequate temporary bracing if needed to counteract effects of welding deformation?[blue]I'm not sure field welding on the one face could - but if one leg of the angle was welded along a side, and the other side of the column just had the angle tip weld, then there possibly would be a much higher heat applied to one side of the column vs. the other. You'd have to see if the column bend matches the higher weld size or not.[/blue]

I might add that welding "all around" on an angle like that probably isn't the best weld detail. The leg of the angle is exactly 3" and the flat face of the tube is only 2" or so....so your angle isn't in full contact with the tube face "all around" and thus portions of the fillet weld would not be qualified, or correct.




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