Overall Buckling Behavior And Design Method Of Fire-resistant High Performance Steel Welded I-section Members

Strength and elastic modulus of structural steel decrease rapidly under high temperature caused by fire disaster,which leads to collapse.A new type of high performance steel,designated as WGJ steel,with high strength as well as improved fire and corrosion resistance,was recently developed by Wuhan Iron and Steel(Group)Company.Based on this new type of steel,this paper studied the overall buckling behavior and design method of fire-resistant high performance steel welded I-section members,including columns and beams,under ambient temperature and elevated temperature.The major job of this paper includes the following parts:(1)The material properties of fire-resistant high performance steel are the most important basis of this study and have impact on the overall buckling behavior of steel structures.Standard tension coupons were prepared and tested under ambient temperature and elevated temperature,in order to obtain mechanical properties.After that,this paper suggested an equation to determine the stress-strain relations of WGJ steel under different temperatures.Besides,this paper also gave the reduction factors of 0.2% offset yield strength and initial elatic modulus,which could be applied to characterize the strength and stiffness of WGJ fire-resistant high performance steel under elevated temperature.(2)According to the investigations on high strength steel and high performance steel,residual stress plays an important role on the overall stability of steel members.This paper presented an experimental program to investigate the residual stress distribution of 3 welded I sections fabricated of fire-resistant high performance steel.The sectioning method was employed to quantify longitudinal residual stress.Based on the experimental results,the influence of width-to-thickness ratio,stress equilibrium of flanges and webs and fire-resistance of steel were discussed.Then a model to identify the magnitude and distribution of residual stresses was proposed and validated for fire-resistant high performance steel welded I-section members.This model provides supportive information to the design of welded I-section columns and beams fabricated of fire-resistant high performance steel.(3)7 welded I-section columns and 6 welded I-section beams fabricated of fire-resistant high performance steel with different sectional dimensions and slenderness were tested in order to obtain the failure modes and ultimate capacities.(4)A finite element model was established and validated by the experimental results of this paper and domestic or foreign reference under ambient temperature and elevated temperature.Python language was applied to conduct parametric modeling.Parametric analyses were conducted to further understand the effect of initial imperfection,residual stress,mechanical properties of steel and temperature on the overall buckling capacity of fire-resistant high performance steel welded I-section columns and beams.(5)The overall buckling capacities of welded I-section members fabricated of flame-cut fire-resistant steel plates were obtained by numerous numerical analyses.The numerical results were compared with design values obtained from the clauses in GB 50017-2003,Eurocode 3,ANSI/AISC 360-16 and CECS 200:2006.After that,modified design equations and curves were suggested for GB50017-2003 and CECS 200:2006,which could be used to design the overall buckling behavior of fire-resistant high performance steel welded I-section members under ambient temperature and elevated temperature.The modified design methods will promote the application of fire-resistant steel in our country and abroad.