HSS 4x4 column-splitting
HSS 4x4 column-splitting
(OP)
We got the call from the homeowner saying that the exterior column supporting deck was splitting. I thought he was talking about a wood post but its actually HSS supporting 3 decks (multistory). The total load is no more then 25 kips, so the column is not failing because of inadequate capacity.
However, the column is not fabricated very well. It appears that fabricator used two pieces for the bottom story, a 2’ long top piece and then another piece to make up the height. The weld between the two pieces is fairly easy to see (see attached picture). The column also seems to be not galvanized and only painted on the outside. So the inside of the column is not protected against corrosion.
I believe that water has been infiltrating from the top of the column, through the joint between the two tube sections and possibly creeping up from below. I couldn’t see any vent holes in the column and thus this creates perfect conditions for corrosion, resulting in material expanding in volume and this may have resulted in the split in the column.
As to why the split happened where it did (near the base), I think there could be three major reasons 1) that’s where the load is maximum 2) most of the water flows down/creeps up near this location 3) the column at the base is restrained by the base plate and possibly the surrounding concrete slab and thus doesn’t have room to expand.
I have asked for the column to be replaced and I think I have a good handle on the cause of the problem but I do have a curious questions:
Could the forces from corrosion-expansion be that strong to split the column at the joint? Or was there possible an inherent fault in the column fabrication. I also think that the weld between the two pieces of column is not good, this may have made the bottom piece to act like a cantilever resulting in k=2.0.
However, the column is not fabricated very well. It appears that fabricator used two pieces for the bottom story, a 2’ long top piece and then another piece to make up the height. The weld between the two pieces is fairly easy to see (see attached picture). The column also seems to be not galvanized and only painted on the outside. So the inside of the column is not protected against corrosion.
I believe that water has been infiltrating from the top of the column, through the joint between the two tube sections and possibly creeping up from below. I couldn’t see any vent holes in the column and thus this creates perfect conditions for corrosion, resulting in material expanding in volume and this may have resulted in the split in the column.
As to why the split happened where it did (near the base), I think there could be three major reasons 1) that’s where the load is maximum 2) most of the water flows down/creeps up near this location 3) the column at the base is restrained by the base plate and possibly the surrounding concrete slab and thus doesn’t have room to expand.
I have asked for the column to be replaced and I think I have a good handle on the cause of the problem but I do have a curious questions:
Could the forces from corrosion-expansion be that strong to split the column at the joint? Or was there possible an inherent fault in the column fabrication. I also think that the weld between the two pieces of column is not good, this may have made the bottom piece to act like a cantilever resulting in k=2.0.






RE: HSS 4x4 column-splitting
RE: HSS 4x4 column-splitting
BA
RE: HSS 4x4 column-splitting
RE: HSS 4x4 column-splitting
RE: HSS 4x4 column-splitting
Link
RE: HSS 4x4 column-splitting
Corrosion shouldn't cause that kind of failure as far as I know, any surface corrosion would just expand inward inside the tube. There could have been a preexisting crack but there's no way I know of to check that.
You could avoid replacement of the tube if it's still in good shape by drilling the ends of the crack and welding it shut. Grinding and rewelding that joint would make sense, too. Weep holes will obviously be a useful addition.
Maine EIT, Civil/Structural. Going to take the 1st part of the 16-hour SE test in October, wish me luck!
RE: HSS 4x4 column-splitting
RE: HSS 4x4 column-splitting
Mike McCann
MMC Engineering
http://mmcengineering.tripod.com
RE: HSS 4x4 column-splitting
RE: HSS 4x4 column-splitting
Mike McCann
MMC Engineering
http://mmcengineering.tripod.com
RE: HSS 4x4 column-splitting
If the column is loafing under the load, why go to all the trouble of replacing it? Just fix up the weld, gouge the crack and re-weld.
BA
RE: HSS 4x4 column-splitting
As for the weld...it sucks. Based on the staining, there is obviously water on the inside of the HSS.
Agree that if the loads are light, just weld the crack, reweld the poor weld joint, provide drainage and move on.
RE: HSS 4x4 column-splitting
RE: HSS 4x4 column-splitting
And thats why I am recommending remove and replace.
RE: HSS 4x4 column-splitting
RE: HSS 4x4 column-splitting
RE: HSS 4x4 column-splitting
RE: HSS 4x4 column-splitting
I agree, just take it out and replace it.
RE: HSS 4x4 column-splitting
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