Vertical brace sizes

[VinuCG]

There is a mutli storied steel building with 4 sides vertical braces. V bracings and chevron bracings. All the single angle braces sizes are L6*6*3/8 and all double angle braces are L6*6*5/16. What may be the reason the design engineer has choosen different sizes for braces than choosing the same size everywhere?

 

[human909]

Probably weight savings. Though unless it is an extremely large building the weight saving a probably not worth the trouble for the fabricator.