Optimum Design System for Steel Cable-Stayed Bridges Dealing with Shape, Sizing Variables and Cable Prestresses

: A general-purpose, rigorous and efficient optimum design system for steel cable-stayed bridges is developed, in which not only can the cable anchor positions on the main girder and pylon, and the crosssectional dimensions of the member elements be dealt with as design variables, but also the pseudo-loads applied to the cables. A powerful two-stage optimum design method is proposed to determine the optimum values of design variables for the cost minimization problem under stress constraints. At the first-stage optimization process, the cable arrangement and sizing variables are optimized by using the approximate concept and dual method with mixed direct/inverse design variables. Then the optimum values of pseudoloads, which induce the optimum prestresses into the cables, and the optimum sizing variables are determined so as to minimize the total cost of the bridge further by utilizing the sensitivities with respect to the pseudo-loads and a modified linear programming algorithm. The rigorousness, eficiency and practical usefulness of the proposed optimum design system are demonstrated by giving numerical design examples and the investigations of the optimum solutions at various design conditions. The significances of dealing with cable anchor positions and pseudo-loads as design variables are also emphasized.