ABSTRACT
ABSTRACT: This paper describes a methodology for an optimized preliminary bridge deck design when the span-by-span construction method is used. The formulation assumes that the deck has an infinite number of spans of equal length. Therefore, only two structural systems have to be considered. The first simulates all constructive stages, where the actions of one stage are applied in a semi-infinite continuous beam. In the second model, all the actions applied after the deck execution are considered in an infinite continuous beam. These assumptions lead to a simplification of the problem, being nonetheless the results quite close to those that would be obtained in continuous decks with five or more spans. This is also the case that commonly occurs when the use of a Moveable Scaffolding System (MSS) is economically justified. A Genetic Algorithm basedAugmented Lagrangian method (GAAL) is used to search for the optimal solution. In this algorithm, each individual represents a solution, which is defined by a set of variables that characterize the various degrees of freedom of the deck geometry, prestress layout and quantity. The objective function is the materials’ total cost. In order to minimize it, the unitary costs for concrete, prestressing and reinforcing steels have to be assigned. During the algorithm, the best individual evolves towards security and economy. Solutions that do not check for security are penalized in their cost using an Augmented Lagrangian function. Genetic operators used in the algorithm, such as selection, crossover and mutation, are explained in the paper. Finally, an example of a 70.00 m span, with a box section deck designed for a highway bridge is presented. In this example the considered variables are described, and some solutions obtained during the evolutionary process are shown.
