The experimental and analytical investigations of torsion phenomenon of thin-walled cold formed channel beams subjected to four-point bending

• The analytical investigation of two open section thin-walled beams shows that only about 0.5% of total beam load is capable to destroy the real inaccurate made and set beams. Most important conclusions are as follows.
• The shape of beam cross section has a very high influence for torsion stiffness coefficient.
• Very important relation exists between torsion rotation of beam cross section and residual shear force in the beam.
• Very small change of boundary conditions (in range of supporting and geometry) indicates the observable torsion angle.

Thin-walled beams have many practical applications. This stimulates practical and scientific researches on them. The recent developments in metal cold forming makes it possible to produce more complicated shapes to reduce the mass of structural members. However, vast variety of cross-section of such beams make their analysis difficult. In the paper the authors have investigated thin-walled cold formed steel beams with open section loaded subjected to pure bending. Experimental results were compared with analytical ones. This gave the answer why the actual tested beams rotated around the shear centre though they were subjected to pure bending. The authors described the factors which are responsible for the torsion moment in the investigated thin-walled steel beams with open sections subjected to pure bending. Two different cross-sections of thin-walled beams were investigated and the more resistant to torsion phenomena was indicated.