Modified Constrained FSM

Unconstrained FSM provides the most rigorous solution, but does not allow decomposition nor identification of the buckling modes. Constrained FSM is clearly defined, but its lack of agreement with classical analytical solutions (the beam model) makes its practical use limited. Exact agreement between the beam model and constrained FSM is impossible. However, if we artificially assume that Poisson’s ratio is zero, the constitutive equation for the constrained FSM model, Eq. (16) reduces to that of the beam model, Eq. (14). The two models are not identical, since transverse strains are zero in constrained FSM and non-zero in the beam model, but this difference has little effect, as Figure 7b shows.

Figure 7. Comparison of global mode calculations for example (a)