Mass data is used by RAM Frame in generating seismic load cases and in performing P-delta and dynamic analyses. RAM Frame automatically calculates Mass, Center of Mass, and Mass Moment of Inertia for each rigid diaphragm, using information obtained from the RAM Modeler. A value indicating the eccentricity between the center of mass and the point of application of the mass is calculated; the default value for eccentricity is taken as 5% of the over-all building dimensions, slab edge to slab edge. This value is used only when the user specifies that eccentricity is to be considered in the generated seismic load cases. The calculated mass values can be overridden with user-specified values using the Loads > Masses command.

Diaphragm Masses dialog tabulates story/diaphragm masses according to their diaphragm numbers. It should be noted that any mass associated with diaphragms are shown with respect to the story name and diaphragm number. If there is any mass that is not associated with any diaphragm (such as the mass components of point or line loads placed outside of any diaphragm, or self-masses from members not connected to any diaphragms, etc.), it is listed separately, with the Diaphragm Number specified as None ; it is part of no diaphragm.

The column Combine To is used to combine (lump) mass from one diaphragm to another diaphragm. The user can select a diaphragm number and a story (diaphragm – story name) from the drop-down list to indicate the diaphragm to which the mass is to be combined. Similarly, the None mass component of a story (if applicable) can be combined to any diaphragm at either the same story or another story. Note that a None mass component of a story cannot be combined to a None mass component of another story.

For models for which no floor masses were modeled and assigned in the Modeler, the user must input the mass data in order to have seismic story forces generated or dynamic analyses performed. This is done using the Loads > Masses command.

Occasionally there are small partial levels that do not contribute significantly to the lateral force resisting system or to which it is not desirable to have a generated seismic story force assigned. In such a situation the mass of that level can be combined to another diaphragm by also using Combine To command. The same command can also be used to lump masses from levels with no diaphragm to levels with a diaphragm.

The mass is calculated from the Mass Dead Load values specified for the Surface, Line and Point loads in the RAM Modeler as well as the member self-masses. Refer to Self-Mass Calculations for more information on the calculation of the self-mass.

As explained above, if any mass corresponding to any members or loads are not associated with any rigid diaphragm (either from loads outside the diaphragm, or members disconnected from diaphragm), it is still accounted for by the program and labeled as story None mass component in the Diaphragm Masses dialog. If they are not combined by the user to any rigid diaphragms, they are ignored during analysis.

Regarding diaphragm lumping (combining) assignments, RAM Frame checks whether lumping assignments are valid or not and gives a warning if an invalid lumping assignment is detected. For example, if the mass in Diaphragm A is lumped to Diaphragm B, and if Diaphragm B is later deleted in the Modeler, RAM Frame gives a warning for Diaphragm A and clears the lumping assignment. It is the user’s responsibility to re-assign the lumping for Diaphragm A again, if desired. Also note that, diaphragm lumping is only applicable for Rigid diaphragms.