A study is presented of the dynamics of a beam-like structures having a range of aspect ratios. It is shown that for a slender structure the dynamics is well represented using Euler theory whilst as the aspect ratio becomes smaller, it becomes necessary to use Timoshenko representations of the constituent members. However, this model constrains cross sections to remain planar and as the beams are made thicker, this will not be satisfied particularly in the corner regions and hence it becomes necessary to use a two-dimensional representation for the framework. The method of achieving this is described and the resulting structural eigenvalues are compared with those from the beam representation. Two examples are given which are representative of a wide range of practical structures. The first is a non-uniform beam which clearly relates to many rotor problems, whilst the second case is that of a portal frame.