Research on fire resistance of CFSTRC columns subjected to fire

In order to study the temperature distribution and mechanical characteristics of concrete filled steel tube reinforced concrete( CFSTRC) columns subjected to fire,four CFSTRC specimens subjected to ISO-834 standard fire were tested to investigate their temperature distribution,fire resistance,deformations and failure mechanism. Then,a finite element analysis model using ABAQUS software was established to simulate the temperature field and mechanisms of CFSTRC columns. The results calculated by the theoretical model were compared with testing results,and a good agreement was found. On the basis of that,the factors affecting the fire resistance of CFST columns were studied. This results indicate that the concrete outside the steel tube is a natural insulation to steel tube and inner concrete,what makes the loss of bearing capacity of inner concrete be less; due to the interaction of various constituent parts of CFSTRC columns,the inner concrete is protected,and no local buckling occurs in steel tube; the columns show good integrity even when the columns fail; axial load level,sectional dimension,sectional core area ratio and slenderness ratio are the main parameters influencing the fire resistance of CFSTRC columns. Based on these parameters,simplified formulas of fire resistance were put forward,and calculated results by the formulas showed well agreement with both theoretical model results and testing results. The achievements can be referred to the fire resistance design of practical engineering where CFSTRC columns are used.