# Calculation of Immediate Deflections per ACI 318-19 with ideCAD

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

• Immediate Deflection is calculated automatically

Notation

Ec = modulus of elasticity of concrete, psi
fr = modulus of rupture of concrete, psi
fc' = specified compressive strength of concrete, psi
Icr = moment of inertia of cracked section transformed to concrete, in4
Ie = effective moment of inertia for calculation of deflection, in4
Ig = moment of inertia of gross concrete section about controidal axis, neglecting reinforcement, in4
Ma = maximum moment in member due to service loads at stage deflection is calculated, in.-lb
Mcr = cracking moment, in.-lb
yt = distance from centroidal axis of gross section, neglecting reinforcement, to tension surface, in.
wc = density, unit weight, of normalweight concrete, lb/ft3

According to ACI 24.2.3.1, Immediate deflection is calculated using elastic deflection formulas, considering the effects of cracking and reinforcement on member stiffness.

According to ACI 24.2.3.4 Modulüs of elasticity, Ec is calculated in accordance with the following equation.

According to ACI 24.2.3.5, the effective moment of inertia Ie is calculated in accordance with the following equation and ACI Table 24.2.3.5.

Service moment

Ie , mm4

Ig

According to ACI 24.2.3.6, continuous one-way slabs and beams, Ie can be taken as the average of values obtained from ACI Table 24.2.3.5. For the critical positive and negative moment sections.

According to ACI 24.2.3.7 for prismatic one-way slabs and beams, Ie can be taken as the average of values obtained from ACI Table 24.2.3.5. At midspan for simple and continuous spans and at support for cantilevers.

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