A numerical method for the nonlinear analysis of thin-walled composite structures is presented within the finite element method. In addition to the static analysis, onset and propagation of delaminations are considered. The variational formulation is described by a multi-director approach with piecewise polynomial functions of the displacements. Initiation of delamination is controlled by a stress based fracture criterion. For its propagation the energy release rate is calculated as a further criterion. An isoparametric quadrilateral multilayer shell element is used for the numerical calculations. It leads to a comparable number of degrees of freedom as by using brick elements but additionally has some main advantages, as 2D-mesh generation is possible, coupling with conventional 2D-shell elements is easier, bending behavior is better, description of interlaminar interfaces is simple. For the kinematic expansion of delaminated zones, additional degrees of freedom are introduced. They are not adjoined to a distinct interface in advance of the delamination analysis. The theory holds for a complete 3D-stress state. Applications to glulam beams are given.
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