Form: Frame Assignment - Additional Mass
Every object contributes mass to the structure from the mass density of its material. Use the Assign menu > Frame > Additional Mass command to assign additional mass to a frame. Any additional mass assigned to a frame object is added to the object mass to give the total mass of the building. The additional mass might be used to account for partitions, cladding, and the like.
Note: The additional frame mass is considered by ETABS only if the mass source is to be based on object masses and additional masses, not from a specified load combination. Also, the additional frame mass is applied only in the three translational degrees of freedom.
Select the frame to be assigned frame mass.
Click the Assign menu > Frame > Additional Mass command to access the Frame Assignment - Additional Mass form. Use the options on the form to specify the frame mass and how the mass should be applied.
Frame Mass/Length: Specify the translational mass per unit length. The masses are entered in Force-Second2/Length2 units.
Options: Specify how the frame mass will be assigned.
Add to Existing Masses: Adds the specified frame mass to the frame. If one or more frame mass assignments have already been made, this option increases the existing frame mass.
Replace Existing Masses: Replaces the currently specified frame mass, if any, with the new frame mass. If no assignment exists, the new assignment is still made. This is the default option.
Delete Existing Masses: Deletes any and all frame mass assignments made to the selected frame(s). When this option is selected, the items in the Frame Mass/Length area of the form are ignored when the Apply button is clicked.
Note that the default option is Replace and that the program defaults to this every time the form is opened.
Click the Apply button to complete the assignment.
When the Apply button is used, the Frame Assignment - Additional Mass 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