Calculation of Immediate Deflections per ACI 31819 with ideCAD
How does ideCAD calculate immediate deflections according to ACI 31819?
Immediate Deflection is calculated automatically
Download ideCAD for ACI 31819
Notation
E_{c }= modulus of elasticity of concrete, psi
f_{r }= modulus of rupture of concrete, psi
f_{c}^{'}_{ }= specified compressive strength of concrete, psi
I_{cr}_{ } = moment of inertia of cracked section transformed to concrete, in^{4}
I_{e }= effective moment of inertia for calculation of deflection, in^{4}
I_{g }= moment of inertia of gross concrete section about controidal axis, neglecting reinforcement, in^{4}
M_{a }= maximum moment in member due to service loads at stage deflection is calculated, in.lb
M_{cr }= cracking moment, in.lb
y_{t } = distance from centroidal axis of gross section, neglecting reinforcement, to tension surface, in.
w_{c} =_{ }density, unit weight, of normalweight concrete, lb/ft^{3}
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, E_{c} is calculated in accordance with the following equation.
According to ACI 24.2.3.5, the effective moment of inertia I_{e}_{ }is calculated in accordance with the following equation and ACI Table 24.2.3.5.
Service moment  I_{e} , mm^{4} 

 I_{g} 


According to ACI 24.2.3.6, continuous oneway slabs and beams, I_{e} 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 oneway slabs and beams, I_{e} 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.
Download ideCAD for ACI 31819