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Mass Source
Form: Define Mass Source

Use the Define menu > Mass Source command to access the Define Mass Source form and specify how SAP2000 should calculate mass for the model. In SAP2000 mass and weight serve different functions. Mass is used for the inertia in dynamic analyses, and for calculating the built-in acceleration loads. Weight is a load that you define and assign in one or more load cases (see the topics in the Assign - Area Loads, Frame Loads, Cable Loads, Tendon Loads, Joint Loads, Link Loads, and Solid Loads books of this Help), which can then be applied in one or more analysis cases.

Mass Definition. Choose how to define the mass of the structure using one of the following options:

From Element and Additional Masses option. This is the default. With this option, the program uses the following mass specifications:

Mass density specified for materials

Additional line mass assigned to frame or cable objects

Additional area mass assigned to area objects

Mass specified for link properties

Mass assigned directly to the joints

From Loads option. With this option, mass may be calculated from a scaled combination of load cases (see Define Mass Multiplier for Loads, below). The absolute value of the net load acting in the global Z direction is divided by the acceleration due to gravity, in the current units, and is used for the mass in the three translational directions.

From Element and Additional Masses and Loads option. This option is a combination of the other two options wherein mass is defined from mass specifications and from scaled combinations of load cases.

Define Mass Multiplier for Loads. If the From Loads or From Element and Additional Masses and Loads option was selected for Mass Definition, enter a combination of one or more load cases in the table using the Add, Modify, and Delete buttons. Those load cases will be scaled by the specified factors and then are added together to determine the mass. Do not include the acceleration as a result of gravity in the scale factors; the program will do that automatically.