Form: Frame Assignment - Moment Frame Beam Type
ETABS allows moment beam sections to be assigned to any beams in a model. When a beam is modeled as one of the special moment beams, ETABS creates a special, nonprismatic analysis section for the beam. This special section is used internally only in the analysis model, not in the object-based model. In addition ETABS adds several special output stations to the beams so that forces are reported at relevant locations in the beam.
Select the beam to which the assignment is to be made.
Click the Assign menu > Frame > Moment Frame Beam Type command to access the Frame Assignment - Moment Frame Beam Type form.
Note: This form also displays when the Special Moment Beams check box is checked and the Specify Type button is clicked on the Structural Geometry and Properties for Steel Deck form. When the form is displayed in this way, the assignment steps listed below (Steps 1, 2 and 4) are unnecessary.
Choose one of the following assignments.
Standard Moment Connection option. This option is assumed to be self-explanatory.
Reduced Beam Section options. For the reduced beam section (sometimes called the ”dog bone section”), specify dimensions a, b and c that define the size and location of the reduced section. These dimensions are illustrated in a sketch on the form.
The reduced beam section is modeled using a variable (nonprismatic) section with seven segments. The beam cross-sections used at each end of each segment are the full beam cross-section or the reduced beam cross-section, that is, the cross-section at the center of the reduced beam section. The segments from beam left end to beam right end are as follows:
Face of left-end column to start of left-end reduced section.
a. Full cross-section at each end of segment.
Start of left-end reduced section to center of left-end reduced section.
a. Full cross-section at segment left end; reduced cross-section at right end.
b. Cubic variation of EI33 and EI22.
Center of left-end reduced section to end of left-end reduced section.
a. Reduced cross-section at segment left end; full cross-section at right end.
b. Cubic variation of El 33 and EI22.
End of left-end reduced section to start of right-end reduced section.
a. Full cross-section at each end of segment.
Start of right-end reduced section to center of right-end reduced section.
a. Full cross-section at segment left end; reduced cross-section at right end.
b. Cubic variation of El 33 and EI22.
Center of right-end reduced section to end of right-end reduced section.
a. Reduced cross-section at segment left end; full cross-section at right end.
End of right-end reduced section to face of right-end column.
a. Full cross-section at each end of segment.
Side Plate Section option. The side plate section is a proprietary system developed by SidePlate Systems, Inc., Cypress, California. It consists of a series of plates welded to the beam end and the column to strengthen the beam-column connection and force hinging to occur in the beam away from the connection.
Click the Apply button to make the assignment. Any previously assigned moment frame beam will be replaced by this assignment.
When the Apply button is used, the Frame Assignment - Moment Frame Beam Type 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.
See Also