Retrieving the GBT modal decomposition from large displacement shell finite element results

This paper proposes an efficient procedure to post-process non-linear shell finite element analysis results, in order to recover the unique modal decomposition features of Generalised Beam Theory (GBT). This procedure extends, to the large displacement range, a previous one developed for first-order elastoplastic, bifurcation and vibration analyses of thin-walled members (Manta et al., 2021). This means that the structural insight typically obtained through GBT analyses can be quite straightforwardly recovered from shell finite element collapse analysis results. The proposed procedure retrieves modal strains rather than modal displacements, since the GBT kinematic description is not suited to describe cross-section finite rotations. To show the capabilities and potential of the proposed procedure, two validation examples, in which a comparison with analytical solutions is made, and two application examples, involving large displacements and plasticity, are presented and discussed.