Optimum Design of Mixed Steel Composite Girders

Steels having a variety of yield points are now available to the construction industry, allowing the designer to choose strength as well as size to meet design requirements. This work is concerned with the use of a variety of steel strengths in continuous, welded, composite plate girder bridges to produce minimum cost structures. The solution which is reported obtains the optimum design of a girder subject to the standard specifications of the American Association of State Highway Officials. Span lengths, material properties, concrete deck dimensions, and cost information on steel types and on splicing operations must be given. The capability selects the optimum combination of web height, flange width, plate thicknesses, and the arrangement of steel types for a continuous girder of constant depth. An iterative scheme is used between the material and splice location selection and the determination of the best web depth and flange width. Results are given for example problems considering seven available steels for the design of a composite plate girder.