考虑蠕变和残余应力释放的Q460钢柱抗火设计方法

承受荷载的钢结构在火灾下可发生明显的蠕变变形，钢结构中的焊接残余应力在火灾下也会一定程度地释放，因而高温蠕变变形和残余应力会对钢柱的耐火性能产生影响。为了准确地对高强度Q460钢柱进行抗火设计，有必要定量分析高温蠕变和残余应力释放对钢柱承载力的影响。采用电炉对2根焊接H形Q460钢柱进行耐火试验，得到无保护Q460钢柱在不同荷载水平下轴向位移、跨中侧向位移及温度随时间的变化曲线，并得到破坏时的临界温度。引入高温蠕变和残余应力，采用ANSYS有限元软件建立Q460钢柱耐火分析模型并对其火灾响应进行分析，通过试验数据验证模型的可靠性。利用有限元模型分析了ISO-834标准火灾下Q460钢柱在不同长细比、荷载比、初弯曲和升温速率下临界温度的变化。结果表明，荷载比的增大、初弯曲的增大以及升温速率的降低会降低Q460钢柱的临界温度。根据参数分析结果提出考虑蠕变影响的高强度Q460钢柱临界温度计算方法，可供结构抗火设计参考。

Fire resistance design approach of Q460 steel column considering creep and release of residual stress

Obvious creep deformations under fire can occur to a loaded steel structure,and the welding residual stress in the steel structure will be released to a certain extent under fire,thus the creep deformations and residual stress will affect the fire resistance of steel columns.In order to design high strength Q460 steel columns accurately,it is necessary to quantitatively consider the influence of high temperature creep and residual stress releasing on the bearing capacity of the columns.Fire tests on two H-shaped welded Q460 steel columns were carried out in an electric furnace.The variations of axial deformation,mid-height deflection,and temperatures of the two columns subjected to different load ratios were obtained,and the corresponding critical temperatures were determined.By incorporating the effects of creep and residual stress distribution at elevated temperatures,a model of Q460 steel column was established by ANSYS,and its fire response was analyzed.The reliability of the model was verified through comparisons against the test data.The influence of the key factors such as slenderness ratio,load ratio,initial imperfection and heating rate on the critical temperature of Q460 steel columns under ISO-834 standard fire was analyzed by employing the verified finite element model.It is found that increasing the load ratio and initial imperfection or decreasing the heating rate would decrease the critical temperature of Q460 steel columns.Based on the parametric analysis results,a design method considering the creep effect for determining the critical temperature of Q460 steel column was proposed,which can be used as a reference for structural fire resistance design.