Is it permissible to reuse existing rolled structural shapes? If so what specification applies?

Yes, existing rolled structural shapes shall meet the requirement of ASTM A-20 as a minimum

Yes, existing rolled structural shapes shall meet the requirement of ASTM A-370 as a minimum

Yes, existing rolled structural shapes shall meet the requirement of ASTM A-6 as a minimum

Yes, existing rolled structural shapes shall meet the requirement of ASTM A-7 as a minimum