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This paper presents a study of the parametric variability of post-tensioned concrete box-girder pedestrian bridges. SAMO2 algorithm is used for the parametric study. This algorithm combines SA with a mutation operator, to find the economic solutions. A span-length parametric study analyzes the characteristics for the best design of a three-span deck in which the main span ranges from 30 to 60 m. The depth and the number of strands were adjusted according to span length, while the thickness of the slabs presented the same optimum values in all cases. Results show that the amount of steel and volume of concrete per square meter of deck shows a good correlation with the main span length. This study demonstrates that by increasing the main span length by one meter, the total cost per square meter of the deck increases by 6.38 euros on average. Thus, this paper shows the relationship between the span length and geometrical and steel variables to produce and build a cost-efficient pedestrian bridge.

This paper deals with the economic optimization of high-performance post-tensioned concrete boxgirder pedestrian bridges. To this end, a program analyzes and evaluates the structural restrictions following Spanish codes for structural concrete and bridge design loads. This problem includes 33 discrete design variables that define the geometry, the concrete, the reinforcing steel bars and the post-tensioned steel. Various acceptance criteria are proposed to modify a variant of the simulated annealing algorithm with a neighborhood move based on the mutation operator from the genetic algorithms (SAMO). An objective methodology based on the extreme value theory is used to determine the number of experimental tests required to provide a solution with user-defined accuracy as compared to a global optimum solution. Results indicate that the local optima found by SAMO2 fits a threeparameter Weibull distribution and improves the cost results for this structural problem. The minimum value obtained by SAMO2 differed just 0.34% compared to the theoretical minimum value so that, from the structural engineering perspective, the divergence was small enough to be accepted. Highstrength concrete performance was further studied in a concrete strength parametric study to acquire more evidence-based knowledge on its implications for economic efficiency. Finally, the study showed that high-strength concrete decreases the cost by 4.5% and the amount of concrete by 26%.