Experiment And Numerical Analysis On Fire Performance Of Special-shaped Column Composed Of Concrete-filled Square Steel Tubes

Special-shaped column composed of concrete-filled square steel tubes(SCFST),such as L-shaped,T-shaped or Crisscross-shaped,consist of a number of concrete-filled square steel tubes connected by connecting plate and ribbed slab,which have good development prospect in the steel residential building system.As the research on the resistance performance of composite column is rare,the ambiguity of fire-proof material meeting the request of the assemblage residential building has been the most urgent problem to be solved in the popularization of steel residential building.Based on the experimental research and numerical analysis for fire performance of SCFST column,the main contents of this paper are as follows:(1)Fire experiments were carried out on three full scale L-shaped SCFST columns.Through the type selection of fire-proof materials,calcium silicate board and ceramic fibre felt are selected as the fire-proof materials for the cover of composite column with two different fire-proof construction method.The experiments are performed under constant axial load and fire according to ISO 834 standard curve with the experimental variable of load level along which the failure modes,temperature-time curves of sectional measure points,axial displacement-time curves and fire resistances of tested columns were recorded.It is indicated that load level is the main factor affecting fire resistance.The heavier load is,the lower fire resistance is.As for ways of fire protection,the combination of board and felt was superior to double layers of board under the same level of load.(2)Finite element analysis(FEA)on fire performance and temperature field of concrete-filled steel tube(CFST)columns and L-shaped SCFST columns was accomplished with sequentially-coupled thermal-mechanical analysis method based on ABAQUS software.The FEA model includes temperature analysis module and thermal-mechanical analysis module.According to the theory of heat transfer,temperature filed FEA was carried out which considered the thermal performance of steel,concrete and fire-proof materials.Then thermal-mechanical FEA model was built which considered the thermal-mechanical performance of steel and concrete,surface contact and boundary condition,etc.Both modules were verified by test results from relevant literature and the author.It can be concluded that the way of numerical analysis can be well used to simulate the fire-resistance of single columns and SCFST columns and the temperature field value of calculation is less than true value with 8.2%-13.5% deviation in fire resistance calculation.Both of the deviation are in reasonable range.(3)Parametric analysis of the mechanical behavior of SCFST columns has been accomplished at high temperature.In order to research the influence of load level on mechanical of SCFST columns and differences of mechanical performance of CFST columns with differernt cross section under high temperature,typical examples were built which considering the load level and cross-sectional form as a parameter respectively,and the distribution and development of the axial and lateral deformation,stress and strain of each example were analyzed.It is indicated the heavier load is,the lower fire resistance is.The connecting plates and ribbed slabs of SCFST column are the weakness of fire protection,but the mechanical performance of SCFST columns will be better than CFST under reasonable fire protection.