XR250 said:
For a situation that the OP is referring to, the 1/4" seems to work fine as well as 3/16" wall columns.
I don't doubt that it does. Everything under the sun has some capacity and, therefore, some suitable application. What I do doubt, under certain contractual models, is whether or not the effort expended in refining the design is justified. Cui bono? The design of a thin base plate is no herculean effort but, for me, involves:
1) 10 minutes to run/re-run a spreadsheet.
2) 10 minutes to add a row to my column design schedule.
3) 5 minutes on site to remind myself what those thin base plates where supposed to be.
Depending on who does the work, that's maybe $50 worth of billable time. Hopefully, it's being expended on behalf of half a dozen columns in stead of just one. So maybe a unit cost of $10/column. $50 is not a huge some but, then, it's
my money. And what I would prefer here is a column base design that I really don't bother to design at all. Seriously. So, if I'm to expend the effort, I want someone who would fall under the heading of "client" for me to experience a tangible benefit. Let's say, for the sake of argument, that this is the difference between a 1/2" 12 x 12 plate and a 1/4" one. So that's what, 10 lbs of steel and $25 per base plate on a column? Ish.
1) Is a $15 net savings per column worth pursuing if you're the PEMB guy and it's all your $$$. Yup. Just business economics.
2) Is a $15 net savings worth pursuing if your client is the contractor AND the savings will actually get passed along from his good buddy the steel fabricator to him? Probably.
3) Is a $15 net savings worth pursuing if your client is the owner/architect and any steel fabrication savings will likely just go to the steel fabricator and
maybe the contractor without ever actually being passed along to my client, the owner? Nope. In this case, I'm just throwing away money and increasing potential liability a bit. I guess I'm reducing waste which has environmental benefits but I'd be lying through my teeth if I pretended that had any real impact on my decision making process.
For most of my projects, I'm working under #3. When fabricators estimate the cost of the post for my projects, they price the connections as just a generic % add without even really looking at what I've done unless it's highly atypical in some way. Yeah, over time, fabricators might give me a better deal on that percentage if I've got a reputation for doing things lighter than everybody else. But that's a long slog and of no real benefit to today's project.
Perhaps the economics are different if this kind of steel is your "usual" steel and skinny base plates are the norm rather than the exception.
XR250 said:
Lets face it, for most residential loads in which a 6x6 would be used, it likely does not matter.
Agreed. Unless lateral loads are involved, I'd say that a 6x6 HSS is likely to have
grossly more capacity than generally required for most residential applications. That's why I'll usually try to lighten up my columns by using a smaller size at 1/4" thickness. Something in the 3"-5" range.
For steel used outside the building envelope -- particularly steel that will be hidden from view and/or in a coastal environment -- I like to have a bit of sacrificial wall thickness available in case my post sees some unanticipated corrosion over the course of it's lifetime. The Canadian steel code limits steel used outdoors to 3/16" for just this reason. So that's one entity's opinion of where that line ought to be.
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.
