huangyhg

allowable stress in deformed column
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
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no loss of capacity, in fact there is a small gain if using the new deformed shape.
i also agree with civilperson, the axial load will directly follow the deformed route to transmit to the base.
i don't know. it seems like this is a localized condition and not along the entire height of the column (is this true grover1?). that being said, wouldn't this be a point for a localized buckling to occur? if it is permanently deformed, it's obviously reached its yield stress locally.
my assumption was that the deformation was exterior face bulging due to ice swelling the interior volume. the fact of previous yieding does not lower the capacity of the steel, in fact strain hardening usually gives higher capacity of area of steel times yield. the bulged section is stronger than the original shape.
doesn't this localized "buckled" shape create a weak spot for local buckling to occur? especially if you consider some localized p-delta effects?
structuraleit - the bulge covers for about 1/2 the height of the column (+/-22').
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.
agree with civilperson. nothing to worry about.
this is a high strength steel that has, in effect, been cold worked. i do not think that this is a slam dunk here. due to the temperature, there could be local, microscopic brittle fracture. the presence of such would affect the capacity.
what load is this member designed to take? at 14 x 14, it is a primary
microcracks are present in all structures, particularly fabricated/welded strauctures and aren't of concern unless you're considereing fatigue loading.
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
it appears that the column is no longer prismatic. i've tried working out the overall capacity of non-prismatic beams like this before, but it's difficult without a great deal of patience or a software package. professor nick trahair did some work on this.
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.

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