Code References
ACI 318-14
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Here, only the red part of the moment curve will be applied to the cracked section
Beam uses a bi-linear deflection curveapproach (Ig/Icr) to calculate deflections at sections where the applied M is greater than Mcr during a loading stage. Only that portion (or %) of M which is greater than Mcr is applied to Icr, while the remainder of M is applied to Ig. In the spirit of ACI E24.2.3.7 when the midspan cracks, the program computes Icr at every section where the member is NOT Class U, using the procedure outlined in Robert Masts’ “Analysis of Cracked Prestressed Concrete Sections: A Practical Approach,”. The program then calculates the % of load that is applied to Icr at the first section that cracks (typically at or near midspan) and applies this % of load to every section where Icr was just calculated.
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Mild deflection multipliers are calculated using Eq. 24.2.4.1.1 (shown below). For this method, each load combination computes its’ own reinforcement ratio. In addition, the time-dependent factor is set to 2 for final loading and all other stages.
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where λ is the deflection multiplier
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This deflection multiplier is applied to all sustained loads on the members.
Hand Calculation
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