How does ideCAD define effective section stiffness factors for reinforced concrete members according to ACI 318-19?
The multiplier values given in Table 18.104.22.168.1(a) are automatically applied for the calculation of earthquake effects.
Ag = gross area of concrete section
bw = web width of section
h = overall thickness, height, or depth of member, in.
Ig = moment of inertia of gross concrete section about the centroidal axis, neglecting reinforcement
The effective section stiffness of the reinforced concrete structural elements is accounted for by using the effective section stiffness factors given in Table 22.214.171.124.1(a) in ACI 318-19. Effective cross-section stiffness factors are applied only in the calculations under the loads included in earthquake effects. Effective cross-section stiffness multipliers are not used in calculating loads included in load combinations that do not have earthquake effects.
Member and Condition
Moment of inertia
Cross-sectional area for axial deformations
Cross-sectional area for shear deformations
Flat plates and flat slabs
Vertical loads indicated by G 'and Q' in earthquake combinations are again calculated with cracked section stiffness. Moreover, these loads are used in earthquake combinations.