高温作用后高强Q690钢焊接截面残余应力试验研究

焊接中的不均匀受热和冷却使钢材内部产生残余应力，残余应力会降低钢构件的刚度、稳定承载力和疲劳性能。钢构件在高温下的强度退化、塑性和蠕变变形会引起截面残余应力改变，从而影响其火灾下及火灾后承载力。为此，采用高强Q690钢材制作了6个焊接构件，包括H形、箱形两种截面形式。利用切条法测量其在常温（20℃）下、600℃和800℃高温作用后的截面残余应力，得到不同温度作用后残余应力的大小与分布。结果表明：高温作用后，残余应力有不同程度的释放；经历600℃作用后，箱形与H形截面残余应力幅值均下降至常温下的约35%；经历800℃作用后，箱形与H形截面残余应力幅值均下降至常温下的15%以下。基于试验结果，提出Q690焊接截面残余应力分布模型及残余应力幅值随受火温度变化的折减系数。

Experimental study on residual stress in high strength Q690 welded steel sections after high temperature exposure

Residual stress in steel section induced by non-uniform heating and cooling during welding process could reduce stiffness and deteriorate the stability capacity and fatigue life of steel members. Under fire conditions, the residual stresses in steel member could change due to steel strength degradation, plastic and creep deformation of steel at elevated temperature, and hence influence fire resistance and post-fire behavior of steel members. Six specimens, including H-section and box-section, were welded by using Q690 high strength steel. Residual stresses at ambient condition and after 600℃, 800℃ exposure were measured by employing cutting strips method. The magnitude and distribution of residual stresses in welded sections after various temperature exposure were obtained. The results show that residual stresses after fire exposure decrease significantly. For specimens heated to 600℃, the residual stresses decrease to 35% of that at ambient temperature for both box-section and H-section. For the specimens heated to 800℃, the residual stresses decrease to 15% for both box-section and H-section. Based on the test data, the distribution pattern and reduction factors of residual stresses for Q690 welded section after exposure were proposed.