Sensitivity study of time delay coefficient of heat transfer formulations for insulated steel members exposed to fire

Heat transfer analysis for an insulated steel member exposed to fire conditions, in general, involves solving a 2D transient conduction equation with well-posed conditions. For design purpose, the current Eurocode 3 provisions adopt a closed-form solution from the SP approach which employs a simplified 1D characteristic heat transfer model. A virtual "time delay" has been incorporated in the analytical solution based on the assumption that the heat capacitance of insulation material is small compared to that of steel section. A sensitivity study is presented in this paper to assess the validity of the time delay coefficient. Results of the study indicate that for insulation with large heat capacitance, the time delay estimation in the SP approach yields significant discrepancy compared against exact solution. An exact formulation of time delay is recommended, which gives accurate results for insulation material with either small or large heat capacitance.