Introduction to masses

Masses represent a kind of load that is used with dynamic analysis. The mass then models the effect of some real load. The real load is idealised and introduced in the form of a material point, i.e. mass.

Mass characteristics must be input in order to describe fully the inertial properties of a model. Properties must be defined for on-structure masses and for masses that are connected to the structure. Self-weight of the individual structural members is determined automatically from the shape, dimensions and material used. The user must only specify masses of other structure parts and of additional devices attached to the structure. Masses may be introduced into geometrical nodes, or defined on members. The latter may be either concentrated in one point or distributed along a given interval.

To facilitate the calculation, masses are sorted into groups (analogy to standard load cases). Each group is independent on others and may contain both nodal and member masses, concentrated or distributed. Each group has got its name used mainly for easy identification in printed document. It is therefore advisable to include all masses present on the structure at the same time into one group. (e.g. group 1: additional equipment of water tank, group 2: water in tank, etc.).

Each group may be re-edited any time later. New data (masses) may be added to the group, the existing ones may be modified, no-longer-necessary data may be deleted. Also the whole group can be removed, if required.

To some extent, the masses are analogous to loads and mass groups are analogous to load cases.