Study On Fire Resistance Of Axially Restrained High Strength Q690 Steel Columns

Steel has poor fire resistance.When the temperature reaches 500?,the yield strength of steel reduce to half of the normal temperature strength.When the temperature reaches 600?,the steel lose most of the strength and stiffness.Therefore,it is necessary to study the fire resistance of steel structures.At present,most of code for fire resistance design of steel structures in various countries adopt the fire resistance design method,which are based on calculation to calculate the high-temperature bearing capacity of a isolated steel member under different sizes and load conditions to obtain the fire resistance design method of the structures.However,in order to get the actual situation of structural in fire,it is necessary to consider the integrity of the structure,that is,the restraint of other components.Therefore,many scholars consider the restraint of other steel members when studying the fire resistance of steel members,which provides a theoretical basis for engineering practice.In recent years,more and more building structures have adopted high-strength steel,which is characterized by high strength and small impact of residual stress.High-strength steel can lighten the weight of the structure,improve the seismic performance of the structure and bring considerable economic and social benefits.Q690 steel is a kind of domestic high strength steel,which has been applied in building structures.It has great significance to study the fire resistance of high strength Q690 steel columns.The fire resistance of high strength Q690 steel columns are analyzed in this paper.The main contents are as follows:(1)Fire resistance test of axially restrained high strength Q690 steel columns: The fire resistance of 6 H-shaped welded axially restrained high strength Q690 steel columns was tested.According to the ISO-834 standard curve,the influence of axial restraint stiffness ratio,slenderness ratio and load ratio on the fire resistance of steel columns were considered.The furnace temperature,steel column temperature,axial deformation,axial force and dispalcement of mid-hight of steel columns were measured with time.According to the test data,the buckling temperature,failure temperature,failure mode and post-buckling behaviour of the Q690 steel columns are obtained.(2)Finite element analysis of fire resistance of axially restrained high strength Q690 steel columns: The finite element model of high strength Q690 steel columns was established by ABAQUS finite element analysis software to carry out numerical analysis and displacement-temperature curves,axial force-temperature curves and failure mode were obtained.By comparing the analysis results with the test data,it is found that the analysis results of the numerical analysis are in good agreement.(3)Parametric analysis of fire resistance of axially restrained high strength Q690 steel columns: The verified finite element model was used to carry out parametric analysis of fire resistance of the axially restrained Q690 steel columns.The influence of five parameters,including temperature rise rate,slenderness ratio,axial restraint stiffness ratio,load ratio and initial bending were considered.Parametric analysis shows that: The buckling temperature of restrained Q690 steel columns decreases obviously with the increase of load ratio,slenderness ratio and axial restraint stiffness ratio.The load ratio and the slenderness ratio have great influence on the failure temperature,while the axial restraint stiffness ratio has little influence on the failure temperature,and the buckling temperature and failure temperature are less affected by initial bending and heating rate.(4)The fire resistance design method of axially restrained Q690 steel column: by analyzing the structure response and deformation characteristics of axially restrained Q690 steel columns before buckling under high temperature,the design method of axial restraint Q690 steel columns buckling temperature was put forward,which considered Q690 steel high-temperature material reduction.On the basis of the parametric analysis and the axial force amplification factor method,the design method of axially restrained Q690 steel columns failure temperature was proposed,which considered high-temperature material reduction of Q690 steel.Finite element software was used to verify the reliability of the design method.The verified formula was used to compare the fire resistance of the restrained Q690 and Q345 steel columns.