So, let's say that the column for the example we looked at in class ... instead of being short, or fully braced, is non-short, and un-braced. An example might be a column that is framed into a wall ... the wall braces it in one direction, and not the other. Let's consider the 6-3/4 by 6 ... and since it is nearly square ... we will, for conservative sake, assume it is NOT braced in the weak (thinner) dimension. (Actually, assuming the beam frames perp. to wall, to align the sides of the column with the 6-3/4 in. width of the beam - the 6-3/4 in. width will be braced and the weaker 6 in. width will not. So our conservative assumption is good.)
... let's assume the length (height) of the column is 8'-0".
... now let's go to the AITC Column Capacity Table ... DF, Load Duration 1.0 ...
(website: http://aitc-glulam.org/column.asp)
The Table gives us a value of ... 31,510 lb.
The Table says `Capacity' ... more technically this is an `Allowable' (axial) load.
The axial load in our situation is/was 15,000 lb.
So, is the applied load = 15k less than or equal to the Allowable load of 31.5k? Yes, GOOD!
Still plenty of capacity.
Look at the footnotes ... slightly different design value used ... 1900, instead of 1950 from class today. (Something is out of date.)
Note the blurb on eccentricity. The capacities in this Table allow for b/6 or d/6 off-centered-ness.
Note as you go down the 6-3/4 by 6 `column' (no pun intended) how the numbers are getting smaller ... that's what `Cp' is doing.
Functionally Cp is reducing the Allowable stress to account for (prevent) buckling.
Other things equal, going from a 4 ft unbraced length to an 8 ft unbraced length dropped our capacity by 25%.
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