Form: Joint Masses
Every object contributes mass to the structure from the mass density of its material. Use the Advanced > Assign > Joints > Masses command to assign additional joint mass to a joint. Note that the additional joint mass is considered by CSiBridge only if the mass source has been specified to be based on element masses and additional masses, not from a specified load combination.
Select one or more joints to be assigned additional joint mass. Other types of objects may be selected because they will not be affected by this assignment.
Click the Advanced > Assign > Joints > Masses command to access the Assign Masses form.
As Mass, As Weight, and As Volume and Material Property options Choose to make the assignment in terms of mass, weight, or volume and material property.
Material drop-down list. If the As Volume and Material Property option is selected, use this drop-down list to select the Material property, or click the + (plus symbol) beside the drop-down list to access the Define Materials form and create a new material property definition.
Mass Direction Coordinate System drop-down list. Choose the coordinate system within which the mass is being assigned.
Masses/Weight/Volume edit boxes: Specify the translational masses in the Local coordinate system direction. The masses are entered in Force-Second2/Length units. Type in the Mass values in the local Direction 1, Direction 2 and Direction 3 edit boxes.
Mass/Weight/Volume Moment of Inertia edit boxes: Specify the rotational mass moments of inertia about the Local axes. The rotational mass moments of inertia are entered in Force-Length-Second2 units. Type in the Mass Moment of Inertia values in the Rotation about 1, Rotation about 2 and Rotation about 3 edit boxes.
Options: Specify how the mass will be applied:
Add to Existing Masses: Adds the specified mass to the joint. If one or more mass assignments have already been made, this option increases the existing mass, assuming, of course, that a positive mass is being specified.
Replace Existing Masses: Replaces the currently specified mass, if any, with the new joint mass assignment. If no assignment exists, the new assignment is still made. This is the default option.
Delete Existing Masses: Deletes any and all mass assignments made to the selected joint(s). When this option is selected, the items in the Masses in Local Directions and Mom. of Inertia in Local Directions areas of the form are ignored when the OK button is clicked.
Note that the default option is Replace and that the program defaults to this every time the form is opened.
Important Note: It is possible to assign negative mass to a joint as long as the total mass tributary to the joint remains positive (or zero). If negative mass is assigned to a joint, do it with great care. If CSiBridge detects negative mass at a joint during the analysis, CSiBridge will set the joint to zero with a warning. CSiBridge does not check for negative mass before running the analysis.
See Also