Lateral-torsional buckling behaviour of welded Q690 steel I-beams with double lateral restraints along the length

This paper presents experimental and numerical investigations of lateral-torsional buckling behaviour of welded Q690 steel I-beams with double lateral restraints along the length. In the experimental programme, 11 steel beams with different beam depths, load ratios and span ratios were tested under two concentrated point loads. Lateral-torsional buckling resistance of beams was obtained through experimental tests. Comparisons between experimental bending moments and calculated values suggest that existing design methods in different national codes cannot accurately predict the critical moments of beams in the selected range of slenderness. Besides, numerical models were also established and verified against test data. Parametric studies showed that the buckling factor of beams increased with increasing ratio of the middle span over the clear span and with increasing ratio of concentrated point loads on beams. It was also concluded from numerical results that the Chinese code and the American code are not safe when used for calculating the buckling factor of beams with intermediate slenderness, whereas Eurocode 3 is rather conservative. Comparisons between buckling factors of continuous and single beams also indicate that the buckling factor of beams can be substantially underestimated if only the beam segment in the middle span is considered by neglecting the restraints provided by adjacent beams. Finally, a modification factor was proposed for welded Q690 steel beams with unequal bending moments at the two ends, which can predict the buckling factor of beams with fairly good accuracy.