W-section base plates for a small Metal Building

[Leftwow]

A few questions in my base plate analysis. I know that you can design a structure with a pinned reaction in a structural modeling software. However, does an engineer test to see how much moment COULD be transferred to the base plate, or does he just assume if fully braced, use an inside four bolt plate reaction? I originally started my design with a large moment resisting baseplate, then found out that my 16 inch grade isn't large enough to support a large moment baseplate. So do they not typically design small metal buildings with a large moment baseplate on a W-section column?

 

[KootK]

Standard practice for columns not part of lateral frames is to just call them pinned. In a properly braced building, you don't usually get enough drift at the column tops to generate problem moments at the bases. I'm not a fan on the inside anchor bolt / fake pin thing. I think that results in nearly identical base moments but a greatly reduced ability to handle those moments without brittle anchor failure. In Europe, they've been developing a "component" design method allowing designers to give some account of base plate partial fixity.

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.

 

[Leftwow]

I am kind of cautious to use the inside fake pinned connection configuration myself, however, I do believe that If the anchor bolts can resist the Max factored moment that staad gives me for my reactions in that configuration... the only thing holding me back from using that design, is fear =P

 

[Klitor]

The example of component method... Stumbled on this today when I was looking for article to help on another thread here.

The article itself smells a bit fishy to me (wondering what you opinion is Kootk?) but you get the gist of the method which I think is good.

I myself dont use it yet, for now its just nice to know it exists, as an ace up the sleeve, if I find myself cornered-in...

 

[Leftwow]

I assume that the baseplate will not bend even though it has to bend slightly. Interesting enough though, seems as an engineer could perhaps design counter moments using base plate thickness, or counter moments using a anchor/concrete strength.

 

[thaidavid40]

Another problem with using inside-aligned anchor rods (narrow-pattern) is sometimes meeting the OSHA safety requirement for erection stability (300lbs at 18" out from column face) before completing the overhead, stabilizing connections. For many small to moderate-sized PEMBs, this becomes a problem issue, even when the minimum required four anchor rods are used.

Thaidavid

 

[KootK]

The article itself smells a bit fishy to me (wondering what you opinion is Kootk?)

Just got around to reading this article. Thanks for sharing it. Two interesting takeaways:

1) Base plate stiffenening seems to not greatly affect base connection flexibilty.

2) Apparently a two bolt pattern does reduce base connection stiffness to the point that a pinned assumption makes sense. That's contrary to a long held view of mine.

At least, these are the analytical conclusions of the author. I'm not really in a position to comment on any potential "fishy-ness".

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.