The study looked at different types of steel-concrete bridges to see which one is the most cost-effective and structurally sound. They analyzed three types of bridges: normal steel-concrete bridges, prestressed steel-concrete bridges, and steel-concrete bridges with box-girders. The research found that steel-concrete bridges with parallel girders perform well under stress and deformation, and the most economical design may have a height-to-span ratio greater than 1/20.