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# 6.6.3 *Section Properties*

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Moment of inertia and cross-sectional area of members shall be calculated in accordance with Tables 6.6.3.1.1(a) or 6.6.3.1.1(b), unless a more rigorous analysis is used. If sustained lateral loads are present,

**for columns and walls shall be divided by (***I***1 + β**), where_{ds}**β**is the ratio of maximum factored sustained shear within a story to the maximum factored shear in that story associated with the same load combination._{ds}**Table 6.6.3.1.1(a)—Moment of inertia and crosssectional area permitted for elastic analysis at factored load level**

Member and condition | Moment of Inertia | Cross-sectional area | |
---|---|---|---|

Columns | 0.70I_{g} | 1.0A_{g} | |

Walls | Uncracked | 0.70I_{g} | |

Cracked | 0.35I_{g} | ||

Beams | 0.35I_{g} | ||

Flat plates and flat slabs | 0.25I_{g} |

**Table 6.6.3.1.1(b)—Alternative moments of inertia for elastic analysis at factored load**

Member | Alternative value of I for elastic analysis | ||
---|---|---|---|

Minimum | I | Maximum | |

Columns and walls | 0.35I_{g} | 0.875I_{g} | |

Beams, flat plates, and flat slabs | 0.25I_{g} | 0.5I_{g} |

Notes: For continuous flexural members, *I* shall be permitted to be taken as the average of values obtained for the critical positive and negative moment sections. *P _{u}* and

*M*shall be calculated from the load combination under consideration, or the combination of

_{u}*P*and

_{u}*M*that produces the least value of

_{u}*I*.

For factored lateral load analysis, it shall be permitted to assume

**for all members or to calculate***I*= 0.5*I*_{g}**by a more detailed analysis, considering the reduced stiffness of all members under the loading conditions.***I*For factored lateral load analysis of two-way slab systems without beams, which are designated as part of the seismic-force-resisting system,

**for slab members shall be defined by a model that is in substantial agreement with results of comprehensive tests and analysis and***I***of other frame members shall be in accordance with 6.6.3.1.1 and 6.6.3.1.2.***I*It shall be permitted to calculate immediate lateral deflections using a moment of inertia of 1.4 times

**defined in 6.6.3.1, or using a more detailed analysis, but the value shall not exceed***I***.***I*_{g}### Related Code Sections

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