The mass details report calculates and presents the center of mass for each mass load case together with the total translational and rotational masses about the center of mass. It is useful for a dynamic analysis if you need to lump the masses at the center of mass of each floor of a building or perform calculations that are relative to the center of mass such as would be required if you wish to take into account the extra torsion due to accidental eccentricity.
Note that if you wish to obtain the mass details for each floor of your structure then you should create a filter for each floor and then obtain a mass details report for each filter.
The total rotational masses include the sum of the individual rotational masses plus the sum of the translational masses multiplied by their distance to the centre of mass squared. For example, the total rotational mass at the center of mass about the Y axis is calculated as follows:
Ry = (R1y + R2y + ... + Rny) + (T1x*d1z2 + T2x*d2z2 + ... + Tnx*dnz2) + (T1z*d1x2 + T2z*d2x2 + ... + Tnz*dnx2),
where for mass n, Rny is its Y rotational mass, Tnx & Tnz are its X and Z translational masses, and dnx & dnz are the X and Z distances from mass n to the centre of mass.
If self-weight is included in a mass case then the self-mass of the structure will also be included in the mass details report and will affect the centre of mass and other calculations shown in the report.