Force-based FE for large displacement inelastic analysis of two-layer Timoshenko beams with interlayer slips

This paper presents a novel finite element model for the fully material and geometrical nonlinear analysis of shear-deformable two-layer composite planar beam/column members with interlayer slips. We adopt the co-rotational approach where the motion of the element is decomposed into two parts: a rigid body motion which defines a local co-ordinate system and a small deformational motion of the element relative to this local co-ordinate system. The main advantage of this approach is that the transformation matrices relating local and global quantities are independent from the choice of the geometrical linear local element. The effect of transverse shear deformation of the layers is taken into account by assuming that each layer behaves as a Timoshenko beam element. The layers are assumed to be continuously connected and partial interaction is considered by adopting a continuous relationship between the interface shear flow and the corresponding slip. In order to avoid curvature and the shear locking phenomena, the local linear element is derived from the force-based formulation. The present model provides an efficient tool for the elastoplastic buckling analysis of two-layer shear deformable beam/column with arbitrary support and loading conditions. Finally, two numerical applications are presented in order to assess the performance of the proposed formulation.