| The material strength and elastic modulus of steel used in common building structure will decrease significantly under fire.At 600℃,the strength and elastic modulus of ordinary structural steel will be reduced to less than 1/2 of room temperature.In order to solve this problem,refractory steel has been developed in domestic and foreign steel mills.When the temperature reaches 600℃,the yield strength can still reach more than 2/3 of the yield strength at normal temperature,which has better fire resistance than ordinary steel.At present,most of the research on refractory steel at home and abroad focuses on the research and development of materials and the mechanical properties of the material itself,but the research on the mechanical properties of the basic members of refractory steel structure is less,and the research on the ultimate bearing capacity of refractory steel box section column and refractory concrete-filled steel tube column is lacking.There is no specific design method for refractory steel compression members in the current "Steel Structure design Standard" GB50017-2017 and "Technical Specification for Rectangular concrete filled Steel Tube Structures" CECS159-2004.The mechanical properties of refractory steel at high temperature and after high temperature are significantly different from those of ordinary structural steel,which can not be ignored to affect the welding residual stress and welding deformation,and then affect the ultimate bearing capacity of its compression members.Therefore,it is urgent to study the mechanical properties of refractory steel compression members,so as to provide test results and theoretical basis for refractory steel design and engineering application.Based on compound refractory steel independently developed by Nanjing Iron and Steel,this paper mainly studies the ultimate bearing performance and calculation method of refractory steel box section column and refractory concrete-filled steel tube column under eccentric compression at room temperature.The main contents and conclusions are as follows:(1)The bias tests of Q345 FR and Q460 FR fire-resistant box section columns with three different section sizes were carried out at normal temperature,and the test results were compared with the calculation results of Chinese Standard for Steel Structure Design GB50017-2017 and European specification EC3.The results show that the calculation results of the two existing codes are conservative for the refractory steel box section flexural members.Among them,the calculation result according to GB50017-2017 specification is about 19% lower than the test result;The calculated results in accordance with the EC3 specification are about 14% lower than the test results.(2)A numerical model of the box-section flexural member with geometrical initial defects and residual stresses was established by using ABAQUS general finite element analysis software.The accuracy of the prediction results was verified by comparison test results.On the basis of verifying the model,parameters such as residual stress,slenderness ratio,section width-thickness ratio,eccentricity ratio and steel strength were analyzed,and the influence law of different parameters on the ultimate bearing capacity of refractory steel box-section flexural members was summarized.The results of parameter analysis are compared with the calculation results of GB50017-2017 and European steel structure standard EC3.The results show that the calculation results of the bearing capacity of refractory steel box section flexural members are conservative according to the two codes.According to the research results of the ultimate bearing capacity of the refractory steel box flexural members,the two formulas are revised respectively.(3)Three kinds of Q345 FR and Q460 FR fire-resistant steel square steel tubes with different section sizes were tested for filling C50 concrete columns at normal temperature,and the test results were compared with the calculation results of current CECS159-2004 and European code EC4.The results show that the calculation results of the current CECS159-2004 code are in good agreement with the experimental results for the refractory-concrete-filled steel tube with box section.The calculation results of EC4 are in good agreement with the experimental results of refractory concrete-filled steel tube members with nominal yield strength of 345 MPa,but the prediction results of the ultimate bearing capacity of refractory concrete-filled steel tube members with nominal yield strength of 460 MPa are conservative.(4)The finite element analysis model of refractory steel concrete-filled square column was verified by the test results,and parameters such as residual stress,slenderness ratio,section width-thickness ratio,eccentricity ratio and steel strength were analyzed.The influences of different parameters on the ultimate bearing capacity of refractory concrete-filled square box section flexural members were summarized.The results of parameter analysis are compared with those of current CECS159-2004 and EC4.The results show that CECS159-2004 code can accurately predict the actual bearing capacity of refractory concrete-filled steel tube members.However,with the increase of slenderness ratio,the EC4 specification tends to overestimate the ultimate bearing capacity of refractory steel flexural members.Therefore,this paper puts forward some suggestions for revising the formula of European specification EC4. |
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