Mass of a story, Center of mass, Center of Gravity

Staad does calculate the mass of the structure to be used in the detemination of the seismic base shear.That is if you mean the seismic mass. But this mass is dependent on the seismic weights which you will input after you define the seismic load parameters. After you define the parameters you will be prompted to specify the seismic weights.You can do this in this sequence. Go to Commands>Loading>Define Load>Seismic Load then choose code. Note that Staad will not use the any dead load which you input in the "Load" tab under the "General" page. You can have Staad print the location of the Cg by adding "Print CG" command after the "Perform analysis" command in the staad editor. After analysis, staad will give you the location of the Cg.

Staad does calculate the mass of the structure to be used in the detemination of the seismic base shear.That is if you mean the seismic mass. But this mass is dependent on the seismic weights which you will input after you define the seismic load parameters. After you define the parameters you will be prompted to specify the seismic weights.You can do this in this sequence. Go to Commands>Loading>Define Load>Seismic Load then choose code. Note that Staad will not use the any dead load which you input in the "Load" tab under the "General" page. You can have Staad print the location of the Cg by adding "Print CG" command after the "Perform analysis" command in the staad editor. After analysis, staad will give you the location of the Cg.