Design of Wood Columns for Flexural and Axial Loading

Present design practice of wood columns is reviewed. The derivation of the design expression adopted by National Design Specifications for wood structures is given and its limitations and range of applications are analyzed. Two methods of design are given: (1) Hand calculations, which is based on successive approximations; (2) a general computer program, for which the coding is also given. The latter renders all possible solutions in stress graded lumber of laminated wood for a given case. The sections are listed in ascending order of cost, least weight sections being listed first. The design of braced and unbraced columns with various end restraints is examined using the concept of effective length to determine actual slenderness. Present design practice renders conservative results for braced columns. However, in the case of unbraced columns, unless the actual slenderness is used, unsafe sections may result. Therefore, adoption of design provisions calling for use of actual slenderness and a minimum eccentricity of the load about both axes of bending are strongly recommended.