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 optimization. Three optimization levels are identified: (1) Level 1 - component optimization; (2) level 2 - structural configuration optimization; and (3) level 3 - overall system optimization. Designs may be optimized by separately or simultaneously considering one, two, or more of the following objectives: cost, prestressing steel or concrete consumption, and superstructure depth. The optimal solution may be found by a sequence of nonlinear programming and sieve-search techniques. Levels 1 and 2 optimizations identify the best solutions for specific components (precast I-girders, voided and solid slabs, single- and two-cell box girders) and layouts (for precast I-girder: one, two, and three; simple or continuous spans). Level 3 optimization selects the overall best system 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) direct design aids for selection of optimized bridge systems; and (4) simplified optimality criteria for preliminary design.