Hi currently a first year student working towards a HNC in Civil Egnineering.

Doing a lab report on tensile testing of a steel test piece (S275) have pretty much finished the report apart from one question that the answer to has gone straight over my head during class and was hoping someone could possible help me out or point me in the generally direction of an answer.

The question is :

Explain the significance of the bar's diameter chosen towards application in design?

If anyone could help would be amazing if not thank you anyway. Small Bio