The rules regarding the modeling of structural systems to be used in the linear calculation to be made within the scope of Strength Based Design are as follows:
12.7.1 Foundation Modeling: For purposes of determining seismic loads, it is permitted to consider the structure to be fixed at the base.
12.7.2 Effective Seismic Weight: The effective seismic weight, W, of a structure shall include the dead load, as defined in Section 3.1.
12.7.3 Structural Modeling: A mathematical model of the structure shall be constructed for the purpose of determining member forces and structure displacements resulting from applied loads and any imposed displacements or P-delta effects.
Structures that have horizontal structural irregularity Type 1a, 1b, 4, or 5 of Table 12.3-1 shall be analyzed using a 3D representation. Where a 3D model is used, a minimum of three degrees of freedom consisting of translation in two orthogonal plan directions and rotation about the vertical axis shall be included at each level of the structure.
12.7.4 Interaction Effects: Moment-resisting frames that are enclosed or adjoined by elements that are more rigid and not considered to be part of the seismic force-resisting system shall be designed so that the action or failure of those elements will not impair the vertical load and seismic force-resisting capability of the frame.
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