Mixed-mode buckling of shear-deformable composite laminated I-beams.

• A new method for the determination of mixed-mode buckling loads of composite beams. • Results are of excellent accuracy when compared to finite element simulations. • Negligible computational effort in comparison with finite element simulations. • Ready-to-use efficient analysis method for practical engineering purposes. This paper presents a novel semi-analytical approach for the determination of the local buckling loads of moderately thick-walled composite laminated doubly-symmetric I-beams under uniaxial compression. The composite laminates that make up the flanges and webs of the I-beam are assumed to exhibit symmetric orthotropic layups and are further assumed to be moderately thick so that a higher order laminate theory, namely Reddy's Third Order Shear Deformation Theory, is employed. Contrary to the commonly used approach of discrete plate analysis for local beam buckling calculations, i.e. the separate consideration of flanges and webs, the analysis method that is presented in this paper considers the interaction between webs and flanges by using series expansions for all buckling degrees of freedom and a subsequent assembly by employing adequate continuity conditions at those locations where adjacent segments of the cross-sections intersect. Such a coupled analysis will be called mixed-mode buckling in the course of this paper. The current analysis method uses the Ritz method in conjunction with the principle of minimum elastic potential of the buckled beam, and it will be shown that the method converges rapidly with a very low number of shape functions in the employed series expansions so that it works with superior numerical efficiency when compared to full-scale finite element computations, however with a comparable results accuracy which makes the present approach especially attractive for any practical application purpose where the local buckling behavior of moderately thick-walled composite laminated beams needs to be considered. Image, graphical abstract [ABSTRACT FROM AUTHOR]