Form: Frame Assignment - Release/Partial Fixity
Any of the three translational and three rotational degrees of freedom can be released at either end of a frame object. However, the releases are meaningful only if a frame section property has been assigned to the frame object. It is possible to specify partial fixity at the ends of the frame object. This is accomplished by specifying a spring stiffness when the member end release is assigned as described herein.
The releases are always specified in the frame object (frame section) grid system. End releases are always assumed to occur at the support faces, that is, at the inside end of the end offset.
Select the frame object(s) to which end releases or partial fixity are to be assigned.
Click the Assign menu > Frame > Releases and Partial Fixity command to open the Frame Assignment - Release/Partial Fixity form.
On the Frame Assignment - Release/Partial Fixity form:
Specify the required end releases by checking the appropriate check boxes.
Alternatively, specify partial fixity by entering a spring stiffness value for the frame partial fixity springs.
To remove all of the currently specified end releases from a selected member, including partial fixity, check the No Releases check box at the bottom of the form.
Click the Apply button. Any previously assigned end release or partial fixity will be replaced by this assignment.
When the Apply button is used, the Frame Assignment - Release/Partial Fixity form will remain open until it is closed by clicking the Close button. This allows selection of another frame object(s), to which a different assignments can be made.
If only one assignment is being made to only one set of selected objects, the OK button can be used to both apply the assignment and close the form.
Unstable End Releases
Any combination of end releases may be specified for a frame element provided that the element remains stable. This ensures that all load applied to the element is transferred to the rest of the structure. The following sets of releases are unstable, either alone or in combination, and are not permitted.
Releasing U1 (axial) at both ends.
Releasing U2 (shear force 2, major) at both ends.
Releasing U3 (shear force 3, minor) at both ends.
Releasing R1 (torsion) at both ends.
Releasing R2 (moment 22, minor) at both ends and U3 (shear force 3, minor) at either end.
Releasing R3 (moment 33, major) at both ends and U2 (shear force 3, major) at either end.
See Also