Selected problems concerning determination of the buckling load of channel section beams and columns

• We examine a few methods for buckling load determination.
• Perform experimental test of channel section columns subjected to compression and beams under pure bending.
• Compare buckling loads obtained using different methods and way of determinations.
• The rules for each methods of buckling load determination have been proposed.

The issue of buckling load determination in composite channel section beams subjected to pure bending and channel section columns subjected to uniform compression is considered. Some selected problems with determination of buckling load on the basis of the collected and processed experimental data are discussed. The data necessary to determine buckling load (applied load and the corresponding displacement, strains at chosen points of beam-columns and displacements in three perpendicular directions of all visible points of the considered beam-columns) were collected with a strain gauge system, an Aramis® 3D optical system and a universal testing machine. Buckling load was determined by means of the following well-known methods: the mean strain method, the method of straight-lines intersection on the graph of load vs. mean strains, the curve inflection point method, the load-square of deflection curve method and Koiter’s method. All results were obtained during the experimental investigations and the numerical FEM analysis of the channel section profile made of a GFRP laminate with the symmetrical eight-layer arrangement [45/-45/90/0]s. The profiles under consideration were subjected to compression or pure bending (four-point bending test). The rules for each methods of buckling load determination are proposed on the basis of the obtained results.