Allowable stress in deformed column
Allowable stress in deformed column
(OP)
We have an existing 14 x14 HSS square tube column (about 45' long) that was filled with water that froze. This acton caused the four walls of the HSS section to bulge outward and have a permenant deformation of about 1/8". The ice/water has since been removed an now the owner is asking us to determine the load carrying capacity of this column.
How would you determine the allowable stress of the deformed section?
Thanks
How would you determine the allowable stress of the deformed section?
Thanks






RE: Allowable stress in deformed column
RE: Allowable stress in deformed column
RE: Allowable stress in deformed column
RE: Allowable stress in deformed column
RE: Allowable stress in deformed column
RE: Allowable stress in deformed column
civilperson - Your assumption is correct, the bulging occurs on the 4 faces for the height stated above. Strain hardening most likely is not a factor here due to the amount of deformation (this amount of deformation would be in the plactic range)
I agree that the yield stress of the steel would not change, however I'm not sure what other effects this deformation may have on the columns' load capacity.
RE: Allowable stress in deformed column
RE: Allowable stress in deformed column
What load is this member designed to take? At 14 X 14, it is a primary member, and should be checked for microcracks in the vicinity of the bulge.
Did this happen during construction prior to sealing the section, or did it come to the jobsite that way?
Mike McCann
McCann Engineering
RE: Allowable stress in deformed column
Even though you may have an apparently 'larger' section and a greater load carrying capacity, you will have residual stresses in the material though as yield has been exceeded either in tension or compression. The residual stresses should be considered in combination with the nominal stresses you'd expect to see to determine if localised failure would occur either through buckling or by exceeding the allowable stress (some factor of yield).
corus
RE: Allowable stress in deformed column
If the deformation has caused a curvature in the longitudinal axis of the column then there would be an adverse effect on the capacity of the column, with regards to overall buckling. If the column remains 'straight' from top to bottom then the 'bulging' should increase the overall resistance to buckling. By how much? Not sure - I'll see if I can dig up my old notes on beams, but it's been a while.
RE: Allowable stress in deformed column
Somewhere along the length of the member it changes from the standard shape to the bulged shape, this creates a local buckling tendency that cannot be ignored.
look at any cold formed steel text and it will give you the general ides
RE: Allowable stress in deformed column
RE: Allowable stress in deformed column
If you "heard" it on the internet, it's guilty until proven innocent. - DCS
RE: Allowable stress in deformed column
I do not know the utility of the column, but if it is a wind column, then you are dealing with a subjection to a fatigue type situation. It is true that microcracks are present everywhere in steel structures, but what I am concerned are those specifically induced by the bulge that would be larger, and consequently more than the normally accepted number, size and length.
It is also way outside the alowable milled tolerances for tube shapes if you will compare the description in this string to the AISC manual standards for the shape - see page 1-123.
Mike McCann
McCann Engineering
RE: Allowable stress in deformed column
RE: Allowable stress in deformed column
Either way, this , IMO, creates a localized region of weakness. I don't know how to account for it, but I am hoping someone does. I don't see how you can neglect it for the reasons I stated early in the post and other ones that others have echoed and different concerns of others.
RE: Allowable stress in deformed column
Even if this weren't the case, I'd still agree with StructuralEIT. I don't think it's that clear-cut that this is not an issue- especially due to localized p-delta effects.
RE: Allowable stress in deformed column
Is there also a transition section near the base plate? There would have been a very large force on the welds to the base plate, so that area should be looked at.
How did the water get into the column? Let me guess, the architect insisted on putting plumbing inside the column.