Page Comparison

...

Codes

ACI 318-14

ACI 318-19

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 the non-composite section and the portion on the composite section. 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 section.Depending on the member being designed, up the three different effective moment of inertias can be used based on three different loading levels. These three loading levels are:

• All loads

  • Computed based on the composite section properties (cracked and gross)

  • Used to compute the instantaneous deflection due to all loads applied to the composite section

• All sustained loads

  • Computed based on the composite section properties (cracked and gross)

  • Used to compute the additional deflections due to long term creep and shrinkage effects.

  • The composite section properties were chosen since all long term effects will take place when the section is composite

• All loads applied to the non-composite section

  • Computed based on the non-composite section properties (cracked and gross)

  • Used to compute the instantaneous deflection due to all loads applied to the non-composite section

  • If the section is not a composite section, this effective moment of inertia is not used

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 a conservative assumption as it results in a higher deflection multipliereither 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 additional deflection multiplier is used in combination with the deflections caused by all sustained loading using the corresponding effective moment of inertia. The final deflections are the sum of the instantaneous deflections and the additional deflections.

Hand Calculation

...