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Despite the fact that CSA O86 6.5.3.2.3 and 7.5.6.3.1 say that members with a depth to width ration greater than 2.5:1 must be laterally supported at points of bearing, users have indicated that they would like to design beams that are either not laterally braced at interior points of bearing or that are insufficiently laterally supported, in their engineering judgment, and therefore consider the full beam length as the unsupported length Lu for the calculation of the KL factor.
Noting that mechanics of the buckling equations used to derive the KL factor require only that the beam be fixed against rotation at two points, and that the American Wood Council Technical Report 14 includes a multi-span beam example with unsupported length as the entire length of the beam, Sizer allows the choice of whether a beam with a depth to width ratio greater than 2.5:1 is or is not laterally supported at interior supports. This is specified for each support via a check box in the Supports for bearing and notch design data group.
The Beam Stability factor KLmust be calculated for such members with depth-to-width ratios greater than 2.5:1.