References
ACI 318-14
Effective Moment of Inertia
Mildly For mildly reinforced members compute , deflections are computed using the effective member of inertia from equation Equation 24.2.3.5.1 in ACI 318-14. The loading is split into the portion on supported by the non-composite cross-section and the portion on supported by the composite cross-section. Each For each of these loading stages calculate , the effective moment of inertia independently. The difference between these two stages is the gross section properties as we always use the final applied load. This prevents rare cases where the cracked composite section is a stiffer section than the gross precast sectionis calculated independently.
Sustained Load Multiplier
Additional time-dependent deflections effects are accounted for by following section Section 24.2.4.1.1 of ACI 318-14. This provision provides a deflection multiplier to use on all sustained loads. The compression reinforcement ratio used in equation Equation 24.2.4.1.1 is computed as the average ratio over the length of the member. This is typically can be a conservative assumption as it typically results in a higher deflection multiplier.
Codes
ACI 318-14
Hand Calculation
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