OPTIMAL-DESIGN OF STRUCTURAL CONCRETE BRIDGE SYSTEMS

Superstructure design of short- and medium-span highway bridge systems may be conceived as a process of multilevel and multiobjective optimi zation. Three optimization levels are identified: (1) Level 1-componen t optimization: (2) level 2-structural configuration optimization: and (3) level 3-overall system optimization. Designs nay be optimized by separately or simultaneously considering one, two, or more of the foll owing objectives: cost, prestressing steel or concrete consumption, an d superstructure depth. The optimal solution may be found by a sequenc e of nonlinear programming and sieve-search techniques. Levels 1 and 2 optimizations identify the best solutions for specific components (pr ecast I-girders, voided and solid slabs, single- and two-cell box gird ers) and layouts (for precast I-girder: one, two, and three; simple or continuous spans). Level 3 optimization selects the overall best syst em for given bridge lengths. widths, and traffic loadings. The present study results in: (1) A systematic procedure for bridge design (2) a rational approach to optimization of standard precast sections; (3) di rect design aids for selection of optimized bridge systems; and (4) si mplified optimality criteria for preliminary design.