Effective Moment of Inertia
For mildly reinforced members, deflections are computed using the effective member of inertia from Equation 24.2.3.5.1. The loading is split into the portion supported by the non-composite cross-section and the portion supported by the composite cross-section. For each of these loading stages, the effective moment of inertia is calculated independently.
Sustained Load Multiplier
Additional time-dependent effects are accounted for by following Section 24.2.4.1.1. This provision provides a deflection multiplier to use on all sustained loads. The compression reinforcement ratio used in Equation 24.2.4.1.1 is computed either at midspan or over the support. The program will check the supports if the cantilever exceeds more than 10% of the beams total length.
The multiplier computed is an additional multiplier, therefore the program uses one plus the value computed as a final deflection multiplier.
Codes
ACI 318-14