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Z.S. Chen, H.A. Mang:
"Buckling of Multi-Lamellae Compression Flanges of Welded I-Beams: A Unilateral Elasto-Plastic Plate-Stability Problem";
International Journal for Numerical Methods in Engineering, 26 (1988), 1403 - 1431.

Buckling of compression flanges of welded I-beams consisting of more than one lamella is charcterized by partial loss of contact between the lamella welded to the web and the neighbouring lamella. The boundaries of the contact regions of the buckling modes of the two lamellae are originally unknown. Thus, the present elasto-plastic plate-stability problem is coupled with a contact problem. It presents a unilateral problem because eigenforms with penetrations of lamellae are physically impossible. This problem is solved first for the elastic material domain. The Rayleigh-Ritz method is used for determining symmetric eigenforms. A finite-strip technique is employed for determining unsymmetric eigenforms. The solution of the unilateral elastic plate-buckling problems serves as the starting point for the iterative solution of the corresponding elasto-plastic plate-stability problem. The buckling pressures are compared with corresponding buckling stresses resulting from a classical design procedure disregarding the interaction of the lamellae at buckling.