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PEMB 'Basic' Column Reactions

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JoelTXCive

JoelTXCive

Civil/Environmental
Jul 24, 2016
919
US
We are designing the foundations for a carport-like canopy for equipment storage.

I'm having difficulty understanding the column reaction tables provided by the pre-engineered building company.

Please see below. They provide one table purporting to show the 'Maximum (& Minimum) Reactions, Anchor Bolts & Base Plates'. It's my understanding that this table has factored loads.

Additionally, they provide a 'Basic Column Reaction' Table. It's my understanding that this table contains raw un-factored loads.

It seems to me that a lot of the unfactored loads are larger than the factored loads?

Maybe I'm not understanding the tables correctly? This looks like canned software. Is anyone familiar with these tables? (the redlines are made by me and not the PEMB company)

PEMB_Column_Reactions_jvkaic.jpg


Thank you!
 
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My guess is the load combinations being used are ASD, not LRFD. I'll also go out on a limb and say that the wind loads are being derived based on ultimate wind speeds, which means a 0.6 LF for ASD load combinations.

For frame line 2, column A:

DL = 1.0k
WL = -10.6k (For the Wind_Left1 condition)

0.6*D + 0.6*WL = 0.6*1.0k + 0.6*-10.6 = 0.6k - 6.36k = 5.76k ~= 5.8kip of uplift (Vmin value for column 2A)

These sheets usually have a table showing the load combination that corresponds to the Load ID given for each max/min, which would show directly what kind of load combos were used.


 
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The first two tables are factored-load combinations; the last table lists the unfactored (base) loads. You should follow the load ID# (in the 3rd column of the first two tables) to find out the case of the combination and the loads included in that case (ie, ld 2 - 1.2 dead + 1.6 live), then plug in the base load reactions listed in the last table. Suggest first to try a few simpler cases to get a better feel/handle of it.
 
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