The aim of this research programme was to provide evidence for the moment-rotation characteristics (moment capacity, rotation capacity) of hollow section beams on the basis of 4-point-bending tests. The present code requirements for plastic and elastic design, which are given by b/t-ratios, were checked. The research programme included 4-point-bending-tests for rectangular hollow structure (RHS), circular hollow structure (CHS) and concrete filled RHS and CHS profiles. The results of these tests were used for the calibration of a computer simulation program and to identify the influence of the different parameters on the moment and rotation capacity. The overall objective of this research project is to check whether the classification of hollow sections according to the b/t or d/t-ratios in Eurocode 3 is acceptable or could be improved.