Why is the steel shape circular or round?

Xaini

Apprentice
Why is the steel shape circular or round? Why isn't rectangular or triangular? Kindly describe with the technical points.
 
Since there is stress concentration at edges, due to sudden change in geometry these shapes are avoided. Now, we have two options left one is a circular shape and the other is oval. In Oval cross-section, there will not be a uniform distribution of stress due to its oval geometry.