Influence of torsion on carrying capacity of steel girders analysed as shell assemblies

Few experimental investigations described in the literature of steel thin-walled girders with very slender webs under bending and torsion clearly proved that in the post-buckling state their torsional rigidity considerably decreases and the torsional stresses have substantial influence on the behaviour and the capacity of the tested models. A series of thin-walled box and double-tee beams with webs of slenderness ratios 200, 250, 300 was analysed in the way of numerical simulations carried out with use of the programme ABAQUS 6.4. Paths of equilibrium were determined for those models with and without imperfections. As a consequence of the introduction of a torsional moment due to eccentric placement of the transverse force a reduction of the carrying-capacity of the box girders up to 50% their bending resistance occurred. Calculations of the capacity of the models according to standard recommendations were also carried out.