In the RAM Steel verification document, I noticed that you're using two different equations for the concrete modulus of elasticity Ec. On page 2, you use the AISC Chapter I equation for stud strength, and on page 5 you use ACI Eqn. 19.2.2.1a for I,effective calculations. Should you not choose just 1 equation for compatibility? It appears that the program is doing this as well.
Thanks,
Drew
RAM Steel Beam AISC Verification - document in question
This is a quote from a very old AISC code, but I think this language is still somewhere in the current with regard to lightweight concrete.
For stress computations, the compression area of light-weight or normal weight concrete shall be treated as an equivalent area of steel by dividing it by the modular ratio n for normal weight concrete of the strength specified when determining the section properties. For deflection calculations, the transformed section properties shall be based on the appropriate modular ratio n for the strength and weight concrete specified, where n = E/Ec
I guess my point is that both equations are using the weight of concrete in the equation. The main difference the AISC equation uses f'c in ksi, and the ACI equation uses units of psi. The 33 factor on the ACI equation more or less handles this conversion, since the square root of 1000 is 31.6, but it results in a slightly different Ec (multiple of 31.6 vs 33). The ACI equation states that is is used for weights of concrete between 90 and 160 pcf. Is there a reason to use two equations that are so similar?