Study On The Residual Stress Of Hot Bending Steel Circular Tube

The steel arch is a perfect structure form with efficient geometry and superior mechanical properties.It has been widely used in building construction and bridge engineering.The residual stress always exists in the steel structure.Although the residual stress will not cause the decrease of the strength of the steel,it may cause premature plasticity,which will seriously affect the stiffness,stability capacity,and fatigue resistance of the steel members or joints.In this paper,longitudinal residual stresses are measured via the cutting method.The hot bending process of the steel circular tube is simulated by numerical method.A parametric study of 54 numerical models is then conducted to investigate the influence factors on the residual stress including the bending ratio,the diameter-to-thickness ratio and the steel yield strength.According to the results of parametric analysis,the simplified residual stress model of the hot bending circular tube is proposed.The numerical simulation and experimental verification of the cold bending process of the steel circular tube are carried out.The simplified cold bending residual stress model is proposed and the difference between the two distributions is compared.The simplified hot bending residual stress model is used to study its influence on in-plane stable bearing capacity of the steel arch structure.(1)The residual stress distribution is symmetric for both extrados and intrados of the hot bending circular tube.The maximum tensile or compressive residual stress occur at the extrados or intrados near the neutral axis of the steel tube.(2)The bending ratio as the most important factor has a significant effect on the residual stress distribution and magnitude.There is no obvious correlation between the residual stress and the diameter-to-thickness ratio.The hot bending circular tubes with a higher steel yield stress have greater residual stress.The effects of the yield strength f_y can be simplified as residual stress multiplied by the value f_y/345.(3)The residual stress model of the hot bending circular tube is proposed as polyline formation.It fits the actual residual stress distribution well taking into account of the self-equilibrium characteristics.(4)The cold bending residual stress is also symmetrically distributed in both extrados and intrados.In extrados,the peak of the compressive residual stress of cold bending is 1.6times that of hot bending,and the peak of the tensile residual stress is 1.3 times that of hot bending.In intrados,the peak of residual compressive stress is close,and the tensile residual stress of hot bending is 1.3 times that of cold bending.(5)When the arch is elastically supported or hinged,the residual stress distribution model proposed in this paper will cause the steel arch to enter the elastoplastic stage in advance,but the ultimate bearing capacity is not significantly reduced.When the arch is rigidly connected,the residual stress distribution model proposed in this paper has little effect on the development of the steel arch elastoplastic stage.When the slenderness ratio is small,the steel arch is mainly characterized by strength failure,and the influence of residual stress of hot bending is small.With the increase of the slenderness ratio,the steel arch is mainly characterized by elastic-plastic stability failure,And the residual stress proposed in this paper will reduce the stable bearing capacity of the steel arch.When the slenderness ratio is large,the steel arch is mainly characterized by elastic instability failure,and the influence of residual stress is reduced.