Wood Column Design with Variable Parameters Using Computers and Plotters

A computer program, properly implemented for accuracy and flexibility, can provide preciseness with considerable saving in time. A simple punchcard program has been prepared to solve an elementary column problem involving from only three to a dozen significant variables. The HP 9820A program is available without cost from the authors. It is prepared for use in the metric system (S.I.) as well as in the U.S. customary system of measurement, and the automatically-plotted curves show both types of units. A modernized column formula is the basis of the program. The systematic approach to the problem involves such variable parameters as the type and extent of loading, grade of lumber, compressive strength, modulus of elasticity, size of column, slenderness ratio, factor of safety, end conditions, fixity, eccentricity, duration of loading, and sill material (wood, concrete, or steel). Any of these factors may be critical or limiting. A safe as well as economical design requires careful consideration and accurate computations. Column end conditions are shown to cause strength to vary as much as sixteen to one. Sill strength can vary up to 500 percent, duration factors by more than 200 percent. Four examples indicate how a column may be designed to carry a specific load, by different structural assemblies, resulting in size and cost ratios of nearly three to one. The process shows how a safe as well as efficient design can result from using suitable parameters, rather than an ultra-conservative approach.

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