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 centroidal axis, neglecting reinforcement
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The mathematical model is created with cracked sections to determine seismic design forces and displacements according to 12.7.3.
The effective section stiffness of the reinforced concrete structural system elements is taken into account elements is accounted by using the the effective section stiffness factors given in Table 4.2 , as described in Section 4.5.8 of TBDY 6.6.3.1.1(a) in ACI 318-19. Effective cross-section stiffness factors are applied only in only in the calculations under the loads included in earthquake effect Load Combinations (Combinations) and that fall into these load combinations according to Article 4.5.8.3 of TBDY . effects. Effective cross-section stiffness multipliers are not used in the calculation under loads included in load combinations that do not contain earthquake effect.
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The constant 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 | |||
Dead load and live load effects, from which internal forces and displacements are obtained, calculated using the effective cross-section stiffness factors, are represented by symbols G ' and and Q' in combinations combinations. Effective cross-section stiffness multipliers are not used in load combinations without seismic effects. In this case, the constant dead load and live load effects, from which internal forces and displacements are obtained, calculated without using the effective cross-section stiffness multipliers, are shown with symbols G and Q in combinations combinations. Earthquake effects are taken into account using effective cross-section stiffness factors and the results of the analysis made using these factors in load combinations are taken into account.
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