Interaction behaviour of steel I-girders Part I: Longitudinally unstiffened girders

•M-V-F interaction behaviour of longitudinally unstiffened steel I-girders is investigated.•Previous design proposals are studied and compared.•Structural behaviour under the combined loading situation is analysed.•New design interaction equation is proposed for interaction behaviour.

If steel structures are subjected to the combination of bending, shear and patch loading, the interacting stability behaviour in the design should be taken into consideration. The combined loading situation can often occur in case of bridge girders during launching, therefore the determination of the load carrying capacity under the combined loading situation is an important aspect of the bridge design. In the current version of EN1993-1-5 [1] there is no standard design method to take the interaction of these three effects into account and there are a very small number of previous investigations in the literature about this topic. The current paper focuses on the investigation of the interaction behaviour of longitudinally unstiffened steel I-girders under the combination of bending, shear and patch loading. The companion paper (Part II) Kövesdi et al., 2014 [25] deals with the M–V–F interaction behaviour of girders with longitudinal stiffeners. Based on a verified numerical model, the load carrying capacities are determined on various girder geometries for various loading situations, and the applicable interaction equation is investigated in the current paper.