Form: Joint Assignment - Additional Mass
Use the Joint Assignment - Additional Mass form to assign additional mass to a joint object. Note that the additional mass is considered by ETABS only if the mass source has been specified as being based on defined mass.
Select the joint objects to which additional mass is to be assigned.
Click the Assign menu > Joint > Additional Mass command to access the Joint Assignment - Additional Mass form.
Use the defaults or enter the required parameters for the following:
Masses in Global Directions edit boxes. Specify the translational masses in the global coordinate system direction in Force-Second2/Length units.
Mass Moment of Inertia in Global Directions edit boxes. Specify the rotational mass moments of inertia about the global axes in Force-Length-Second2 units.
Options. Specify how the mass is to be applied.
Add to Existing Masses option. Adds the specified mass to the joint object. If one or more mass assignments have already been made, this option increases the existing mass, assuming a positive mass is being specified.
Replace Existing Masses option. Replaces the currently specified mass, if any, with the new mass assignment. If no assignment exists, the new assignment is still made.
Delete Existing Masses option. Deletes any and all mass assignments made to the selected joint object(s). When this option is selected, the items in the Masses in Global Directions and Moment of Inertia in Global Directions areas of the form are ignored when the Apply or OK button is clicked.
Note that the default option is Replace and the program defaults to it every time the form is opened.
When the Apply button is used, the Joint Assignments - Additional Mass form will remain open until it is closed by clicking the Close button. This allows selection of another joint 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.
Note that if the Include Lateral Mass Only option is selected when defining mass source, only the Direction X mass, Direction Y mass and the Rotation about Z moment of inertia are considered in the analysis.
Important Note: It is possible to assign negative mass to a joint object as long as the total mass tributary to the joint object still remains positive (or zero). If some negative mass is assigned to a joint object, do it with great care because it can cause trouble. If ETABS detects negative mass at a point during the analysis, it will terminate the analysis and provide an error message about negative mass. ETABS does not check for negative mass before running the analysis.
See Also