Finite element procedures based on Mindlin's theory are computationally advantageous and also have the capability of accounting for transverse shear deformation in plates. Complementary to Mindlin's theory is Timoshenko's theory that accounts for transverse shear deformation in beams. In the present work, both of these shear distortion theories have been applied to the finite element analysis of stiffened plates subjected to lateral loading. Discrete plate-beam formulations, termed FEM(Ml) and FEM(M2), have been set up illustrating two major approaches in the finite element analysis of stiffened plate structures. A third orthotropic formulation, named ORTHO, has been presented based on the smeared plate approach, and is applicable to the case of closely spaced torsionally soft stiffeners. The performance of the discrete plate-beam formulations, especially of the second viz. FEM(M2), has been found to be quite satisfactory based on a comparison with a number of the available results. For the first time an attempt has been made to estimate theoretically the errors that are likely to result from the use of an orthotropic formulation. This has been accomplished by comparison between ORTHO and FEM(M2) in the form of a parametric study. Additionally, the orthotropic formulation has been extended to include geometrically non-linear behaviour. It is recognised that under less demanding conditions this latter formulation may be preferable for the reasons of economy of CPU time and simplicity of input data
