Stress-strain-temperature response of grade 1200 ultra-high strength steel (UHSS) tube under creep and high temperature loadings

This paper studies the mechanical response of Grade 1200 ultra-high strength steel (UHSS) tube under a multi-phase loading scenario including fire and creep. Two sets of experiments are performed on standard dog-bone specimens taken from UHSS tubes. In these tests, the effect of creep on mechanical behaviour of UHSS at elevated temperatures of up to 700°C and after cooling to room temperature is discussed. The variation in the stress-strain curves obtained from the tensile tests and the residual strength of the UHSS specimens after different tests are evaluated. The Bernstain-Bézier functions are employed to present the relationship between the stress, strain, the maximum fire temperature and the sustained axial load ratio for UHSS cooled from fire temperatures to room temperature. Also, the instantaneous stress-induced strain and consequently the creep strain of UHSS subjected to different constant sustained load values during transient fire are obtained.