A strategy for the optimal design of steel portal frames

Resumo

This article presents a strategy for the optimal design of single-span steel portal frames used in the
primary framework of single-story buildings. A methodology that integrates a structural analysis program and a
heuristic optimization algorithm for the design process is developed and evaluated. The methodology is applied to
the design of single-span symmetric pitched roof portal frames fabricated from built-up welded I-shaped sections
with rigid connections. Geometric properties of beams and columns cross-sections are optimized for the
minimization of the weight of the portal frame. The flange width and the total section depth are taken as continuous
design variables, while web and flange thicknesses are limited to the discrete standard values. The portal frame is
subjected to self-weight, the secondary elements weight, the service load and wind load. The optimization
constraint functions include checks of serviceability and ultimate limit states given by Brazilian standards.
Numerical experiments indicated that the proposed strategy produce high quality design with reasonable
computational cost. Additional tests showed that increasing the number of iterations of the optimization algorithms
or reducing the range of the design variables based on engineering judgment may improve the efficiency of the
design strategy.