Abstract Sinusoidal corrugated web girders, which are in the focus of the current paper, have been increasingly used in the past years in civil engineering applications due to economical design. Recently, a number of experiments dealing with the particular behaviour of this girder type have been carried out at room temperature, while the structural behaviour at elevated temperature has not been widely analysed and requires further investigation and clarification. The current paper deals with the improved geometrically and materially nonlinear analysis with imperfections (GMNIA) of sinusoidal corrugated web girders under fire conditions. The developed finite element model, which is validated based on previous measurements during fire tests found in the international literature, is capable of modelling the specialties, e.g., the so‐called ‘accordion effect’, of corrugated web girders. The applicability of design formulae is also illustrated in the paper while an extensive numerical parametric study is also carried out to demonstrate the impact of different parameters on the stability behaviour and failure mode of corrugated web girders at elevated temperature.