On the use of Bernstain-Bézier functions for modelling the post-fire stress-strain relationship of ultra-high strength steel (Grade 1200)

•Bernstain-Bézier functions are used to develop a material model for UHSS cooled from fire.•The model considers the effect of fire temperature and sustained axial load ratio.•The model is calibrated and validated against experimental tests results.•The model is capable of extrapolating the results out of the range of tests data.•The creep strain of UHSS under a transient fire and a constant stress is derived.