Minimum Weight Proportion for Steel Girders

Formulas are derived for the optimum proportions for minimum weight for laterally supported plate girders without web stiffeners designed under the working stress provisions of the specifications of the American Institute of Steel Construction. The results are presented in dimensionless form, and apply to any type of steel and any transverse loading. Example designs illustrate the use of the formulas. It is shown that for very short deep girders compact sections are lighter, while noncompact sections are lighter for girders of more usual proportions. The use of higher strength steels reduces the optimum weight of a girder more than in inverse proportion to the square root of the yield stress. Standard rolled sections are shallower and heavier than optimum sections. Girders of conventional proportions are usually shallower than optimum girders. In some cases, however, an optimum section is not only lighter, but also shallower than a conventional section.