Form: Active Degrees of Freedom
Use the Analyze menu > Set Active Degrees of Freedom command to specify the active degrees of freedom.
Click the Analyze menu > Set Active Degrees of Freedom command to access the Active Degrees of Freedom form.
Use the form to specify the Building Active Degrees of Freedom. The possible degrees of freedom for a building are UX, UY, UZ, RX, RY and RZ. When a degree of freedom check box is checked, that degree of freedom is active for the model. Alternatively, the following four buttons can be used to quickly set the degrees of freedom for the typical cases that might arise.
Full 3D button. Sets all six degrees of freedom active. The vast majority of building models should be run using this option.
XZ Plane button. Sets the UX, UZ and RY degrees of freedom active. It is intended for two-dimensional frames that are modeled in the global XZ plane.
YZ Plane button. Sets the UY, UZ and RX degrees of freedom active. It is intended for two-dimensional frames that are modeled in the global YZ plane.
No Z Rotation button. Sets all degrees of freedom active except for RZ. Oftentimes, to satisfy building code requirements, engineers run lateral force analyses of their structures using various positive and negative eccentricities of mass (lateral load) from the calculated center of mass of the building and with all six degrees of freedom active. In addition, they run analyses with the mass (lateral load) located at the calculated center of mass of the building and the Z-rotations locked. The design is then based on the worst case of all of those analyses. This No Z Rotation feature sets the degrees of freedom of a model appropriately to run an analysis with Z-rotations locked.