Flange vertical buckling of I-shaped steel girders

•Flange vertical buckling of an I-shaped steel girder is studied.•Flange vertical buckling occurs with larger flange thickness.•Web plate scarcely affects vertical buckling behaviour.•Timoshenko's model of a bar on the elastic foundation is appropriate to estimate the vertical buckling strength.•Spring constant of Timoshenko's model for vertical buckling varies almost linearly to flange thickness.

This paper deals with flange vertical buckling of an I-shaped steel girder having the practical section dimension. On flange vertical buckling, Basler et al. presented a formula to verify the occurrence of flange vertical buckling of an I-shaped steel girder by using the width-thickness ratio of the web plate. Two authors of the current paper carried out an experimental test on the hybrid steel girders, and in the test, unexpected vertical buckling was observed in the experimental test. With above background, the authors conducted the numerical studies on flange vertical buckling of the I-shaped hybrid steel girders having smaller section dimensions than practical based on the experimental model. Through these studies, the authors pointed out that occurrence of flange vertical buckling is owing to the thickness of flange and web plate and not to the width-thickness ratio. This fact suggests that a new collapse model is required to establish the procedure for verification of flange vertical buckling. In the current paper, the spring constant should have the new collapse model, the value determined by the Timoshenko's model. This paper shows the points that should be considered when creating the new collapse model.