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Calculation of Time-Dependent Deflections per ACI 318-19 with ideCAD

How does ideCAD calculate time-dependent deflections according to ACI 318-19?

  • Time-Dependent Deflection is calculated automatically.


As' = area of the compression reinforcement, in2
b = width of compression face of member, in.
d = distance from extreme compression fiber to centroid of longitudinal tension reinforcement, in.
ρ' = ratio of As' to bd
ξ = time-dependent factor for sustained load
λΔ = multiplier used for additional deflection due to long-term effects

According to ACI, additional time-dependent deflection resulting from creep and shrinkage of flexural members can be calculated as the product of immediate deflection caused by sustained load and the factor λΔ.

ρ' is the ratio of the As' , area of the compression reinforcement, to bd

Time-dependent factor ξ is 2.0 in accordance with ACI Table

Sustained load duration, months

Time-dependent factor, ξ







60 or more


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