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Effective Section Properties per ACI 318-19 with ideCAD

How does ideCAD define effective section stiffness factors for reinforced concrete members according to ACI 318-19?


  • The multiplier values ​​given in Table 6.6.3.1.1(a) are automatically applied for the calculation of earthquake effects.


Notation

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 6.6.3.1.1(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

Columns

0.70Ig

1.0Ag

bwh

Walls

Uncracked

0.70Ig

Cracked

0.35Ig

Beams

0.35Ig

Flat plates and flat slabs

0.25Ig

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.


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