This option adds bar masses to bars for structure dynamic analysis or for static calculations, when forces are generated for body loads (body forces as well as centrifugal and angular acceleration forces) and self-weight. Open the Bar Mass dialog by clicking 
in the Load Definition dialog.
You can define bar masses distributed along the length of a bar in this dialog. The value of the mass is determined using its weight (acceleration of gravity is applied). Also, you can define the angle at which the mass acts.
The coordinates of the beginning and end point along the bar's length at which the bar mass is applied can be defined at the bottom of the dialog. The coordinates can be specified as relative or absolute values. If Apply to All Cases is selected, the defined mass is added to all dynamic cases defined for the structure.