RAM Concept calculates information for each mode that can be viewed in the mode data text table. This includes the vibration frequency as well as modal mass information for each mode. Calculated modal mass is dependent upon the normalization method used for the mode shapes. In seismic calculations, a mass normalization technique is often used which results in the sum of the modal masses equal to the total system mass. In RAM Concept , the modal masses are calculated using mode shapes that are normalized such that the maximum displacement on the mode has a value of 1.0. The modal masses reported can be thought of as the amount of mass participating in a given mode, or as the mass of an equivalent single degree of freedom system. The modal mass fraction is the modal mass of a mode divided by the total mass in the structure. The sum of the modal masses reported in RAM Concept will not equal the total mass in the structure.