Study On The Bearing Capacity Of Q355 Hot Rolled Square And Rectangular Steel Tube Members Under Axial Compression And Combined Axial Forces And Moments At Elevated Temperatures

Although the steel is non combustible material,but it is not fire resistant.When the steel structure building is on fire,the temperature of steel members rises sharply within a short period,and the steel will lose most of its strength and stiffness.If the steel members are damaged,it will seriously endanger the safety of people and property.Therefore,it is necessary to study the fire resistance of steel structure.With the development of steel structure production technology,steel members with different cross-section shapes are used more and more in building structures.Thanks to the good aesthetic characteristics and installation convenience,square steel tube is often used as the main component of building structure.Under high temperature,the bearing capacity of steel members is closely related to section parameters.At present,there are some deficiencies in the bearing capacity design of most domestic and foreign steel structure fire resistance research.For example,the European steel structure fire resistance code is based on the width and thickness ratio of the section divided into one to four types of sections.In different section classification of bearing capacity design,there is a discontinuous point;Norms in the bearing capacity design in China,and also according to the generous than the cross section is divided into class a to d class section,have appeared in the discontinuous points.So in the discontinuous points,bearing capacity value of discontinuity,the calculation accuracy is poor.And specification ignores the interaction between panel,also does not take into account the strain strengthening on the bearing capacity of strengthening,makes the prediction accuracy is greatly reduced.Continuous strength method(CSM for short)is a design method based on the deformation capacity of the section.The design value of the bearing capacity is always continuous,and the interaction between the plates is taken into account,making full use of the steel strain strengthening performance,so that the prediction accuracy is better.In all kinds of steel structure buildings,Q355 ordinary steel is widely used.In this paper,the bearing capacity of Q355 hot-rolled square and rectangular steel tube members under axial compression and combined axial forces and moments is studied:Firstly,the finite element analysis(FEA)models of Q355 hot-rolled square and rectangular steel tube members under axial compression and combined axial forces and moments at high temperature was established by MATLAB program.The load displacement curves were obtained by numerical simulation.Compared with the ETH test,the numerical simulation results are in good agreement with the experimental results,which indicates that the load bearing capacity of Q355 hot-rolled square and rectangular steel tube members under axial compression and combined axial forces and moments at high temperature can be accurately simulated by using the FEA models.Secondly,the bearing capacity analysis of Q355 hot rolled square and rectangular steel tube members under axial compression:A large number of parametric analyes were carried out by using the verified FEA models,and then the primary and secondary coefficients of regularized slenderness ratio?_?in Eurocode_?=0.5(1+?_?+?_?~2)were corrected after finding the deficiencies of Eurocode,American code and Chinese code in predicting the bearing capacity of members under axial compression.The original formula was modified to_?=0.5(1+?_?+?_?~2),EC3?Modified design formula is proposed to predict the bearing capacity of axial compression members under high temperature.Compared with the accuracy of Eurocode,American code and Chinese code in predicting the bearing capacity of axial compression members at high temperature,it is concluded that the Eurocode with correction coefficient is more accurate.Third,the bearing capacity analysis of Q355 hot-rolled square and rectangular steel tube members under combined axial forces and moments:A large number of parametric analyses were carried out by using the verified FEA models,and then after finding the shortcomings of Eurocode,American code and Chinese code in predicting the bearing capacity of members under axial forces and moments,combinined with the accuracy advantages of Eurocode with correction coefficient in predicting the bearing capacity of axial compression members at high temperature and CSM in predicting the bearing capacity of bending members at high temperature,CSM-EC3?Modified was proposed to predict the bearing capacity of members under axial forces and moments at high temperature.Compared with the accuracy of Eurocode,American code and Chinese code to predict the bearing capacity of members under combined axial forces and moments at high temperature,it is concluded that the proposed design formula is more accurate.Then by changing the section thickness t,the comparative analysis of class II section was conducted.It is found that the prediction accuracy of the proposed design formula for class II section is still higher than that of Eurocode,American code and Chinese code.