Keywords: thin-walled beams, local buckling, cold-formed, FEM.

Cold-formed thin-walled beams have many advantages that are important from the engineering point of view, for example the high ratio of their load capacity to weight. Materials that are used for building modern structures make it possible to reduce their weight for heavier loads. Cold-formed thin-walled beams with open cross sections are widely used in contemporary constructions.

The directions of current research on the stability of cold-formed thin-walled beams are presented in the work of Hancock [1]. He proposed the method for determining the critical bending moment of lipped flanges of channel and Z-section beams. The methods of modelling the mechanics, strength and stability of cold-formed thin-walled beams are described in many monographs, for example [2,6].

The subject of the paper are two cold-formed thin-walled channel beams with sandwich and double bend flanges. The beams are simply supported and subject to a pure bending state. Critical stresses of local and global buckling are defined for the beams. Theoretical solutions of elastic buckling problems for these beams are numerically found using the finite element method and experimentally verified [3]. Similar investigations has been carried out by Schafer [4] who proposed formulas for global and local buckling and their interactions. Stasiewicz et al. [5] proposed a simple expression that make it possible to determine the critical load of a bent flange of thin-walled beams.

The proposed subject of investigations is the continuation of previous research that has been carried out in The Unit of Strength of Materials and Structures of Poznan University of Technology. Finally, the results of the investigation for thin-walled beams with sandwich and double bend flanges are compared in paper. The results of the calculation are presented in tables and figures.

1

Hancock G.J., "Design for Distortional Buckling of Flexural Members", Thin-Walled Structures, 27(1):3-12, 1997. doi:10.1016/0263-8231(96)00020-1

2

Magnucki K., Ostwald M., "Optimal design of selected open cross sections of cold-formed thin-walled beams", Publishing House of Poznan University of Technology, Poznan, 2005.

3

Paczos P., Wasilewicz P., Magnacki K., "Experimental investigations of local-elastic buckling of cold-formed thin walled beams", Proceedings of Fifth International Conference on Advances in Steel Structures, Singapore, Volume III, p. 473-478, 5-7 December 2007.

4

Schafer B.W., "Local, Distortional, and Euler Buckling of Thin-Walled Columns", Journal of Structural Engineering, 128(3):289-299, 2002. doi:10.1061/(ASCE)0733-9445(2002)128:3(289)

5

Stasiewicz P., Magnucki K., Lewiski J., Kasprzak J., "Local Buckling of a Bent Flange of a Thin Walled Beam", PAMM, 4:554-555, 2004. doi:10.1002/pamm.200410258

6

Timoshenko S.P., Gere J.M., "Theory of elastic stability", McGraw-Hill, New York, 1961.

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