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Hole in HSS 1

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SteelPE

SteelPE

Structural
Mar 9, 2006
2,759
Maybe this isn't a good question to ask because I know absolutely nothing about the project, but I received a question from a fabricator client recently and I am wondering the answer myself. Attached you will find a picture of some painted HSS columns. The column has a hole drilled in the base of the column. He said that all of the columns have this hole at the base.

IMG-1463_qa0syb.jpg

IMG-1462_xgvcqv.jpg


I know you would typically provide a hole for vending during galvanizing, however, these columns appear to be painted. I was wondering if it was for drainage during erection. I am now wondering if I am suppose to be providing holes in the bottom of my HSS columns (not really).
 
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It could provide drainage during erection. It's also possible that the columns were galvanized and painted afterwards, though I've never seen that.

 
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Those are exactly my thoughts as well, however, the anchor bolts are not galvanized, so I was thinking galvanizing was not the cause.
 
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I have known a few folks that like to have a hole in pretty much all otherwise closed HSS. Theory being that, even if it's sealed, there may be moisture laden air in there that might produce condensation and corrosion with ambient temperature variation. I'm honestly not sure whether or not that's a legitimate concern. You know how we structural guys are though. Once we latch on to some detailing issue perceived to be clever, it stays. The alternative to looking smart is, of course, looking stupid. Can't have that.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.
 
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I usually provide drainage holes in HSS columns exposed to freezing conditions... even if they are sealed.

Dik
 
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Agree with Dik

I've actually seen it specced a few times to add drainage/weep holes for closed sections, especially if theyre outside.
 
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SteelPE:
I’ve seen plenty of hollow sections, supposedly seal welded shut, which ended up with water in them. Who knows why and how, but it happens; at the very least, they seem to breath, draw in moist air and then condense it. Freezing, sometimes rupture, or continuous internal rusted seem to be the result. I think it is good practice to provide a real drain hole at the low spot, while you can control its location as relates to design, stresses and welding, as apposed to a more critical location due to a rupture.

 
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Voids in anything tend to fill with water for a number of reasons. Completely sealed voids will not, but even a tiny pin-hole anywhere means it is not sealed. Voids breathe due to temperature fluctuations causing air to expand and contract. This carries humidity into the void. When temperature drops below dewpoint (inside the column) condensation occurs, which drains to the bottom. It takes a great number of breathing cycles with no condensation occurring to dry the void. But if condensation occurs on one cycle, it is likely to occur on subsequent cycles. In which case the voids will fill with water. Standing water will rapidly corrode the column from the inside. If a few feet of standing water freezes, it will split the column. So drains are generally a good idea.
 
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With the increase in steel prices, we are going to see a lot more weep holes.

Mike McCann, PE, SE (WA)


 
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msquared48,

My fabricator clients state otherwise in regards to tubes vs wf. They have end user clients that I design structures for. I have been told to switch to WF as the cost difference is now in favor of WF and with the WF being less to fabricate with their automation.
 
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The holes allow water to drain out of closed sections. The holes also prevent build-up of internal pressure. (I’ve seen several instances where closed sections burst open.) Vent holes are also required when closed sections are galvanized (to prevent bursting).
 
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sandman21, my guess is that it is a capacity based design - connection has to be good for the full strength of the brace multiplied by an overstrength factor. That means once you slot the HSS for the connection, you lose some section and it has to be replaced with the cover plates.
 
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Not needed for OCBF the requirement is for SCBF, its also not full strength of brace times overstrength. If they are using SCBF and need the cover plate then they have additional issues.
 
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