Experimental study on the post-fire cyclic behavior of Q960E ultra-high-strength structural steel

This paper presents an experimental study on the cyclic behavior of Q960E ultra-high-strength steel (UHSS) after exposure to elevated temperatures and subsequent cooling down by water. The test program comprised six temperature levels ranging from room temperature to 900 °C, along with four cyclic loading protocols. A total of 46 tests were conducted in this study, and the failure mode, hysteretic curve, springback behavior, Young’s modulus, and fracture strain were discussed in detail. Subsequently, a method was proposed to calibrate the equivalent strain–stress data and true strain–stress data based on the reversion method with axisymmetric model. Based on the calibrated data, the stress–strain relationship and strain hardening behavior were examined, and the corresponding parameters were also calibrated. Finally, comparisons of the numerical simulation results and experimental data demonstrated that the suggested constitutive model accurately described the cyclic behavior of Q960E UHSS after elevated temperatures. The findings of this study have potential applications in evaluating the seismic performance of UHSS structures following exposure to fire.