Applies To
	Product(s):	STAAD.Pro
	Version(s):	All
	Environment:	N/A
	Area:	Design
	Subarea:	American Steel Design
	Original Author:	Bentley Technical Support Group

The KL/r value that STAAD reports for a single angle member does not match my hand calculation. Design is per the AISC ASD 9th edition code.

A single angle is subjected to 2 buckling modes :

1. Column buckling. This is determined using the simple expressions (Ky.Ly/ry) and (Kz.Lz/rz), where ry and rz are the radii of gyration about the principal axes.
2. Flexural torsional buckling : This mode of buckling uses an equivalent KL/r, which is computed on the basis of equation (4-4) on page 5-311 of the AISC ASD 9th edition code. Generally, this mode of failure produces a higher KL/r than the ones from the column buckling mode.

You should check whether the flexural torsional buckling mode governs in your case. The KL/r calculated for the flexural torsional mode, if it happens to the largest of the 3 values, is reported only with a TRACK 1.0 detail of output. It does not get reported for TRACK 0 or TRACK 2 level of detail of output. In other words, if you want to see the KL/r in the flexural torsional buckling mode, use the parameter TRACK 1.0.