# Cost analysis on the optimum design of prestressed doubly-symmetric steel beams

## Palavras-chave:

prestressed, steel beams, optimization, genetic algorithm## Resumo

In the last few years, the utilization of steel beams has shown great growth in civil construction.

Although steel has a higher cost, its use is justified when wanting to overcome large spans. This aspect motivates

the development of more economical alternatives as well as the implementation of prestressing tendons. The

objective of this paper is to present the optimization problem aimed to reduce the total cost of prestressing doubly-

symmetric I-sections of steel beams. MATLAB’s native Genetic Algorithm technique was implemented in the

mixed integer programming optimization problem, focusing to optimize the cross-section’s geometrical properties

(i.e., depth of cross-section, flange widths and thicknesses, and web thicknesses) and the number of tendons. The

evaluation and validation steps used two examples from the literature. The design method, through constrained

functions, verifies the Ultimate and Serviceability Limit States from the standard NBR 8800:2008. Therefore,

results showed an efficient alternative for the structural engineering practice, giving a reduction in the total cost of

24.43 and 25.62% for the studied cases.