If you want to model a surface entity like a wall, a roof, or a slab—where the load is distributed in more than one direction—you must use a surface entity to carry that kind of loading. The kind of entity that is used to model a beam or a column cannot be used to model a slab. A different entity referred to as a finite element is required. In a finite element analysis, a wall or a slab is subdivided into smaller parts consisting of triangles or quadrilaterals.

The difference between a beam and a plate is a load that is applied to the beam must pass to one or both ends (supports).

Beam model load distribution

In a plate, load is distributed through the elements to the edges, resulting in multiple load paths.

Plate model load distribution

STAAD Foundation Advanced uses plate elements in the modeling of mat foundations.