Fire Resistance Study On High Strength Q460 Steel Columns Considering Creep Effect And Residual Stress

The study of the fire resistance of steel columns is very important to the design of steel structures.The premature failure of the steel column under fire will directly affect the safety of the structure.Q460 steel has better mechanical properties compared with mild steel which is widely promoted and used at present in China.Q460 steel can reduce the weight of the structure and the size of the cross-section effectively,and bring the structure design more possibilities and greater economic benefits.The temperature rise of the unprotected steel component is rapid in fire,and steel's yield strength and elastic modulus decrease drastically as the temperature increases,which cause structural damage of losing bearing capacity.Research shows that the design method based on common steel components is not suitable for high-strength steel structures,so the study of the fire resistance of high-strength Q460 steel columns is of great significance.Under high temperature,the creep effect is obvious,which increases the deformation of the steel column at high temperatures,accelerates its destruction,and reduces the bearing capacity under fire.However,the residual stress is reduced under high temperature,and the impact of this change and creep has not been considered in the fire-resistant design codes in China.This paper analyzes the creep buckling performance and fire resistance of Q460 steel columns at high temperature.The main contents are as follows:(1)High-temperature creep buckling test of steel columns: The high-temperature creep bucking of six high-strength Q460 welded H-shaped steel columns were experimentally studied,considering the influence of slenderness ratio,load ratio,and temperature.The evolutions of the furnace temperature,column temperature,lateral displacement and axial displacement with time were measured.The creep buckling failure time of the specimen under constant temperature and load was obtained.(2)Fire resistance test of steel columns: The fire tests on two Q460 columns under ISO-834 standard heating curve were carried out.The changes in furnace temperature,column temperature,lateral displacement,and axial displacement with time were measured.The fire resistance and critical temperature of the steel columns under different load ratios were obtained.(3)Creep buckling and fire resistance performance analysis of high-strength Q460 steel columns: Mechanical parameters,creep parameters,and residual stress parameters of Q460 steels at high temperature were introduced.ANSYS finite element program was used to establish the mechanical analysis model of Q460 steel column considering high temperature creep and residual stress.The finite element was validated by results of creep buckling test and fire resistance test of Q460 steel columns.The parameters of the steel columns subjected to high temperature creep buckling were analyzed using the validated finite element model.The effects of slenderness ratio,load ratio,temperature and initial bending on the creep buckling performance of the steel columns at high temperature were considered.The parameters of the fire resistance performance of steel columns were also analyzed and the effect of slenderness ratio,load ratio,heating rate and initial bending on the fire performance of the steel column was considered.(4)Design method: Based on the results of parametric analysis,a simplified design method for fire resistance of Q460 welded H-shaped steel columns under axial load considering high temperature creep and residual stress was proposed.