Beam refers to a structural element that primarily resists loads applied laterally to the beam's axis. They are the Horizontal members of the structure. It's mode of deflection is primarily by bending. Struts are short members in an assembly of members that get compressed, as opposed to ties which are stretched. They are the Horizontal or Inclined member of the structure. It's mode of deflection is primarily by Tension.
struts are the element which are compressed under axial load and fail due to buckling...where as beams are the element which fails under bending due to shear load..
Columns are the vertical members of the frame structures and can be provided both as long and short columns. Whereas Struts can be inclined or horizontal, and are generally short in length as compared to columns....A member of structure carries an axial compressive load is called Strut.
beams undergo bending due to shear force which is predictable....and ....struts are subjected to axial compressive loads always and undergo unpredictable buckling..