Numerical Modeling and Design of CFRP-Strengthened Short Steel Tubular Columns in Fire

This paper presents the details of a numerical study aimed at investigating the fire performance of carbon-fiber-reinforced polymer (CFRP)-strengthened short square hollow section (SHS) steel columns with and without an insulation system. Steady- and transient-state finite-element (FE) models were developed to simulate the behavior of CFRP-strengthened columns exposed to uniform elevated temperatures and CFRP-strengthened and insulated columns exposed to standard fire conditions, respectively. They were validated using the results of the authors' experimental study. A detailed parametric study was then conducted using the validated steady-state FE model to determine the influence of SHS steel grade and dimensions and CFRP strengthening configuration on the axial compression capacity deterioration at elevated temperatures, based on which suitable design equations were proposed to predict the elevated-temperature axial compression capacity of CFRP-strengthened columns. Fire resistance ratings (FRRs) of CFRP-strengthened and insulated SHS columns were determined based on the time-temperature profiles from heat-transfer analyses and the load ratio versus critical temperature profiles developed from steady-state FE analyses. In this study, two types of insulation materials (spray-applied CAFCO 300 and intumescent paint) were investigated, and both were found to provide satisfactory FRRs, where more than 60- and 120-min FRRs were achieved for most columns with CAFCO 300 and intumescent paint, respectively. The modeling and design methods presented in this paper can be used to conduct fire safety designs of CFRP-strengthened and insulated steel columns.