The stiffness and strength of elements that are important to the distribution of deformations and forces are included in the analysis.
The model includes ‘stiffness properties of cracked concrete sections’ and the contribution of panel zone deformations for steel moment frames.
For building structural systems, a 3D analysis model is created automatically. Structures with horizontal structural irregularity Type 1a, 1b, 4, or 5 of Table 12.3-1 must be analyzed using a 3D representation. A minimum of three degrees of freedom consisting of translation in two orthogonal plan directions and rotation about the vertical axis are included, and the designer can interfere with the freedoms from the modal analysis section in the structure tree.
If the diaphragms have been classified as semi-rigid, the model includes a representation of the diaphragm’s stiffness characteristics, and the diaphragm’s degrees of freedom and stiffness are included in dynamic analysis.