Fire And Post-fire Behaviours Of Square Concrete-filled Steel Tubular

With the wide application of concrete-filled steel tube(CFST)in high-rise building structures,fire accident happened frequently in such structures have been caught the attention of the society.Therefore scholars both at home and abroad have studied the fire resistance,the post-fire behaviours and the repair methods after fire of CFST more and more deeply.Experiments indicated that even though the quantity of vent holes were set up according to the standard,the tube still emerged weld cracking or local buckling.A preliminary judgment was that the internal water vapor has not been released which caused the vapor pressure too big for the specimen to bear.The author suggested that scholars should increase the number of vent holes to avoid weld cracking of the tube under high temperatures.In order to investigate the influence of vent holes on fire exposure and post-fire behaviours of square CFST columns,this thesis has carried out the following work:(1)The tests of twelve square CFST columns subjected to axial loads under high temperature were conducted.In order to impose the load on specimens,an electro-hydraulic servo control system have been used.And in order to let the furnace temperature curves approach to the ISO-834 standard heating up curve,a recombination heating up method has been used.The influence of axial compression stress ratio,number of vent holes and steel ratio on exposure time-axial deformation curves and fire resistance time of the square CFST column were studied.The damage mechanism of concrete under high temperature was obtained to study the number of vent holes which have influence on fire resistance of square CFST.(2)By using 1000t pressure testing machine,the test of residual capacity of ten square CFST columns after fire were studied.The parameters of the test were the number of vent holes,axial compression stress ratio and heating time.And this thesis also discussed the influence of such parameters on the failure mode,the axial compression stiffness reduction factor and the residual capacity of the specimens.(3)Established the temperature field analysis model of square CFST column by using the ABAQUS finite element analysis software.According to the material constitutive model of steel and concrete after high temperature,an ABAQUS finite element model was developed to analyze the post-fire behaviours of square CFST columns.The finite element simulation results and the experimental results were compared and ananlyzed.