It seems that you are one of the many users who do not read the user manual ! There is a way to input the concrete f'c instead letting the program calculate it.
Dannyo :
Its seems that your equations came from O.W. Blodgett's book "Design of Welded Structures" p.3.3-10 eqn (13)
The book is available from Lincoln Arc Company.
KRH
I had been Structural Engieer for the last 16 years. I had worked for large engineering company and also small consulting engineering company.<br><br>You have an unusual opportunity. My experience is that it is always good to work for small company first and then large company...