| It is well know that composite-sectioned square concrete filled steel tube(CS-CFST)is advanced in high-strength,durability,high residual strength and high fire resistance etc.When square CFST columns reinforced by circular steel tube under fire,the inner circular steel tube still bear part of the loads due to the protection of the outer concrete,thus the building integrity is kept better than normal steel columns(or CFST columns).So it is a well worthy work to investigate the fire resistance of CS-CFST columns.Experimental research and finite element analysis were carried out on square CFST columns reinforced by circular steel tube under four-side fire exposure.Three components including with different axial load ratios and end restraint conditions were tested.Thermal field distribution of cross section and axial deformation were measured.The influence of different axial load ratios and end restraint conditons to fire resistance were analyzed.FEM model was developed using ABAQUS to illustrate the heat transfer procedure and fire resistance of CS-CFST columns and the predicted results were validated by the measured results.Then the mechanism of square CFST columns reinforced by circular steel tube under four-side fire exposure was studied.The laws of axial bearing capacity of the circular CFST section as well as the square CFST section were investigated when the CS-CFST columns exposed to fire.Typical deformation curves were detailly introduced in this paper.Finally,the fire resistance performance analysis of CS-CFST columns with different parameters was conducted,including the influence of thermal field including heated height,load ratio,section type,steel ratio,steel strength,compressive strength of concrete.The main factors affecting the temperature field and the fire resistance were obtained,and a simplified method for the prediction of the fire resistance of CS-CFST columns was also proposed which can provide reference for the application of engineering practice. |
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