Research On Fire Resistance Of Concrete-filled Steel Tubular Columns With Different Seismic Damage

Fire is prone to occur after the earthquake,causing a large number of casualties and property losses.Concrete-filled steel tubular(CFST)columns are widely used in engineering filed due to their excellent mechanical properties.However,there were few tests,analysis and calculation methods of the fire resistance of CFST columns with seismic damage.Therefore,the tests of CFST columns with seismic damage have been conducted in this paper.Research and theoretical analysis mainly include the following:(1)Four square and circular section CFST columns subjected to constant compression and cyclic bending were tested respectively,where the horizontal load-displacement curves were measured and the different degrees of damage was generated.Then,the fire resistance tests of the 8 CFST columns with different degrees of seismic damage were carried out,where the temperature-time relationship,axial deformation-time relationship,fire resistance and failure mode were also obtained.(2)Based on ABAQUS software,the reasonable constitutive model of steel tube,constitutive model and the damage model of concrete under reciprocating load are determined,and the model of CFST column specimens were established.Comparing with experimental results,the modeling method is verified to be reliable.(3)Based on ABAQUS software,the reasonable thermal parameters and the thermal constitutive relation under high temperature of steel and concrete are determined,and the temperature field model and fire resistance model of CFST column specimens with different degrees of seismic damage were established.Comparing with experimental results,the modeling method is verified to be reliable.(4)The concept of damage factor is introduced,and the influence of steel tube thickness,steel tube yield strength,axial compression ratio and damage degrees on the fire resistance of CFST columns are analyzed.Combined with the fire-resistance formula proposed by Han Linhai,the damage reduction coefficient is proposed,the calculation formula of which was obtained by regression analysis on the basis of a large number of parameter analysis.As a result,the practical calculation method of fire resistance of CFST columns with different degrees of seismic damage is obtained.