Study On Local Stability Of High-strength Q960 Steel Compression Member At Elevated Temperature

With the improvement of steel smelting and welding technology,high-strength steel has been widely used in high-rise buildings,bridges,and large stadiums in recent years.Compared with ordinary low carbon steel,high-strength steel has great economic,social,and environmental benefits.Using high-strength steel can effectively reduce the crosssection size,the structure weight,and the project cost.It has a large space for building use,aligning with the green development strategy and energy conservation and environmental protection society.Although steel structure has many advantages,poor high-temperature resistance is one of its apparent shortcomings.In daily life,the fire caused by nonstandard electricity consumption is common,which brings a serious threat to steel structure buildings.It is vital to evaluate the mechanical properties of steel structures under fire.The current fire resistance design code of steel structure at home and abroad is mainly for ordinary low carbon steel,which is not suitable for high-strength steel.The mechanical properties of steel are degraded at elevated temperature,and the creep will increase the deformation,which will force the steel to fail in advance.The limit value of width thickness ratio to prevent local buckling of steel members at high temperature has not been put forward in the code of fire resistance design of steel structures in China,and the calculation method of bearing capacity of the members after the width thickness ratio exceeds the limit has not been given.In order to supplement and perfect the appropriate fire resistance design methods of high-strength steel,this paper carries out the test and finite element analysis on the local buckling of high-strength Q960 compression members,and the main contents are as follows:(1)Elevated-temperature tensile test: The high temperature tensile test of domestic high strength Q960 steel was carried out by constant temperature loading test method.The temperature range was 20℃～900℃.A total of 23 specimens were tested.The mechanical properties at high temperature,such as yield strength,ultimate strength,elastic modulus and stress-strain curve,were obtained.The mechanical property reduction coefficient and elevated temperature constitutive model of high-strength Q960 steel were fitted based on the test results.It provides necessary high-temperature mechanical properties data for the subsequent analysis of fire resistance of high-strength Q960 steel members.Simultaneously,the mechanical properties of Q960 steel at elevated temperatures are compared with other high-strength steels of different strength grades.(2)Creep test at elevated temperature: The creep tensile test of domestic Q960 highstrength steel was carried out by constant temperature loading method.The temperature range was 450℃～900℃.A total of 22 specimens were tested.The effects of different temperatures and stress levels were investigated,and the high temperature creep strain time curve of Q960 steel was obtained.According to the test data and Fields and Fields creep model,the high temperature creep model of Q960 steel was obtained by fitting.(3)Local buckling test at elevated temperature: Two groups of eight specimens were designed to study the local stability of high-strength Q960 welded H-shaped steel columns.The test included two ambient temperature specimens and six elevated temperature specimens.The effects of different cross-section forms,temperature,and heating methods on steel columns buckling capacity were studied.The heating curves,axial deformation,lateral deflection,and local buckling bearing capacity of steel columns were measured and recorded.(4)Local buckling analysis at elevated temperatures: The ABAQUS software was used to simulate the local stability test of high-strength Q960 steel compression members at high temperature,and the results were compared with the test results,which proved that the finite element modeling method was accurate and reliable.By using the above modeling method,a large number of parameter analysis were carried out on the local stability of high-strength Q960 steel compression members at high temperature.The effect of width-to-thickness ratio of flange,height-to-thickness ratio of web,temperatures,slenderness ratio,initial geometric imperfection and welding residual stress were investigated.(5)Simplified design method: Based on the above parameter analysis results,a simplified design method for local buckling bearing capacity of Q960 welded H-section steel compression members under axial load was proposed.