Interactive Optimization of Multispan Plate Girders

Abstract

An efficient and robust optimization algorithm is presented for minimum weight disign of continous multispan steel plate girders using the general geometric programming technique. The loading on the girder can consist of any number of concentrated and uniformly distributed loads. The nonlinear programming problem is formulated on the basis of the last edition of the American Institue of Steel Construction (AISC) specification. The desing variables are the flange width and thickness, teh web depth and thickness, and the dimensions and spacings of the transverse stiffeners for stiffened plate girders. In the optimization algorithm, the nonlinear primal problem is transformed to and via double condesation. The algorithm is quite general and can be applied to stiffened of unstiffened, homogeneous or hybird plate girders. The girder may be fully restrained agained lateral torsional buckling or may haae lateral supports only at selected locations along the length ofthe girder. The algorithm id implemented in FORTRAN 77 in an interactive computing environment with graphic capabilities. The grogram can display the plate girder elevtion, various cross sections, and loading on the girder. Three examples are presented, a two‐span homogeneous, a three‐span hybird, and a five‐span homogeneous plate girder.