EWPAA Structural Plywood and LVL Design Manual - Engineered ...

A8Chapter 8 AppendixBending / Compressive Strength Stability Factor k 12The stability factor k 12 reduces the allowable compressive or bending stresses for slenderbeams that are subject to torsional buckling due to lateral instability of compression flanges.The beam capacity can be increased by providing lateral restraint to compression flanges, fullrestraint to the tension flange or by using a mores stocky beam.Calculation of k 12 for strength reductions for buckling of plywood diaphragms is covered inAppendix E of AS1720.1-1997. A more thorough examination of lateral torsional buckling,slenderness co-efficients and critical elastic buckling moment can be found in Appendix E ofAS1720.1-1997 and the EWPAA Design Guide for Plywood Webbed Beams. The approachused in this Manual is to approximate the slenderness co-efficient for box beams using theformula:0.5where:⎛ 5 . 3.Lay.(EI) x ⎞S1= ⎜⎟⎜ h1.d.(EI) ⎟⎝y ⎠L ay = distance between effectively rigid buckling restraintsh1 = constant from AS1720.1-1997 Table E6 reproduced belowMoment parameter βSlenderness factor h1(see diagram below) Free restraint condition* Fixed restraint condition*1.0 3.1 6.30.5 4.1 8.20.0 5.5 11.1-0.5 7.3 14.0-1.0 8.0 14.0*The buckling restrains must prevent rotation of the beam about the z-axis. The terms ‘free’ and ‘fixed’restraint condition refer to the possibility for rotation of the beam about the y-y axis at the restraintlocations, as shown in Figure A8.1.TABLE A8.1 : Reproduced from Table E6, AS 1720.1-1997(A8.E1)83