Thin-walled composite columns with a closed rectangular cross-section are the subject of this study. The test specimens were made using the autoclave technique and were characterized by constant geometric parameters. Experimental tests were carried out using interdisciplinary techniques within the framework of experimental testing, which enabled an in-depth analysis of the bending behavior of the composite structures. The research analyzed the effect of varying boundary conditions (support spacing) on the load carrying capacity of the structure and the damage state of the composite. In the course of the research, the damage phenomenon was evaluated both quantitatively and qualitatively.