Fire resistance of concrete-filled high strength steel tubular columns

• Nonlinear finite element model has been developed.
• Fire resistance of composite columns using high strength steel has been studied.
• The effects of high strength steel and concrete grade have been investigated.
• The concrete moisture and types of concrete aggregate have been examined.
• The concrete–steel interface has been carefully considered in finite element model.

The main objective of this study is to investigate the effects of high strength structural steel on the fire resistance of concrete-filled steel tubular (CFST) columns under constant axial load using finite element analysis. A 3-D finite element model was developed to carry out both the numerical heat transfer and nonlinear stress analyses. The concrete–steel interface model was carefully considered in the finite element model. The initial geometric imperfections of the columns were also considered in the finite element model. The results obtained from the finite element analysis have been verified against experimental results, and showed that the finite element model can accurately predict fire resistance of the CFST columns. Furthermore, an extensive parametric study was performed to investigate the behaviour and strength of CFST circular columns. The parameters included the column dimensions, steel strength, concrete strength, loading ratio, different types of aggregates and moisture contents of the concrete. The column time–temperature and time–axial shortening curves were evaluated. It is shown that the diameter and strength of concrete have a relatively larger influence than the strength of steel on the fire resistance time of the CFST columns. At the same load ratio, the fire resistance is generally decreased with higher steel strength, and increased with the lower concrete strength. However, under the same load, the fire resistance of the CFST columns with the tubes yield strength of 690 MPa showed significant improvement than those steel tubes having yield strength of 275 MPa.