Design of Laterally Unsupported Timber Beams

Timber specifications now recognize a rational procedure for the design of laterally unsupported beams, and design aids have been developed to simplify selection of members. Three categories of flexural members are recognized based upon the potential mode of failure. The allowable stress for beams subject to lateral instability is a function of the beam slenderness factor and modulus of elasticity. The slenderness factor is a dimensionless constant relating the effective unbraced length, width, and depth. Beam properties and lateral stability constants are furnished for a wide range of laminated beam sections. Allowable stress curves for the full range of permissible slenderness factors are presented for three grades of laminated timber. Design examples illustrate the design procedure and the use of the design aids.