Design Method for Optimum Unstiffened Girders

The minimum weight design of constant height unstiffened plate girders has been formulated as a nonlinear optimization problem using the American Institute of Steel Construction specification. The girders are assumed to be symmetrical and fully restrained against lateral buckling. A two-stage minimization procedure is then employed to obtain minimum weight solutions. The results of the study are in the form of simple design curves and formulas which can be used for any loading condition. A rapid and accurate design method for plate girders with constant cross section is then proposed. It is also shown how this design can be extended to allow for limitation on girder height, flange curtailment, and discrete values of plate thickness. The study indicates that significant savings in material can be achieved when optimum girder proportions are employed instead of the widely used hot rolled steel sections.