Nonlinear normal modes of planar frames discretised by the finite element method

This article describes the implementation of a computer program to calculate nonlinear normal modes of structural systems. The procedure follows the invariant manifold approach, adapted to handle equations of motion of systems discretised by finite element techniques. In its current version, it generates individual modes of planar framed structures exhibiting geometrically nonlinear behaviour. The program was tested in simple examples available in the literature, and showed very good results. Because finite element discretisations are not restrictive to the geometry of the structural system, it was also possible to generate, for the first time, nonlinear modes of framed structures.