Study On The Influence Of Welding Temperature On The Mechanical Properties Of Shield Tunnel Composite Pipe

The whole implementation of shield tunnels are mainly composed of three phases: design,construction and operation phase.The construction phase is the key to achieve the expected design requirements and reasonable function in the operation.As a result,the overall quality of the shield tunnel is directly determined by the quality during the construction phase.CoMPared with the traditional engineering problems,in recent years,the high temperature effect during construction phase has become the key factor restricting the cost,quality and service life of shield tunnel.In the manufacturing process of rectangular thin-walled steel pipe used for composite segments,the local steel plate will be subjected to welding high temperature.The uneven temperature field caused by high temperature will aggravate the stress redistribution in the rectangular steel pipe structure than in the ordinary steel structure,which leads to greater residual stress and deformation.These residual stresses and deformation can degrade the mechanical properties and also reduce the machining accuracy of rectangular steel tube,therefore,the composite segment of shield tunnel will be affected in terms of the bearing capacity and deformation,dimensional accuracy,assembly accuracy,waterproof performance as well as its cost.The above effects will turn more significant when the width and arc length of the monomer composite segment are increased,the number of welds is larger,or the welding position becomes asymmetrical.Therefore,it's an urgent problem to find out the harmful response caused by welding high temperature in the construction phase of composite segment and the characteristics of high temperature effect.The multi-field coupling analysis was adopted in this paper through the software ABAQUS and the concept of welding layout was put forward.The influence of welding layout on residual stress of structure was analyzed from three aspects: welding mode,welding sequence and welding interval time.Combined with engineering practice,the distribution characteristics of residual stresses in different plate thickness and welding temperature are analyzed.The effect of welding high temperature on the temperature,stress and deformation of rectangular steel pipe used for composite segment was revealed.The difference of influence of welding layout on residual stress of structure is explored,on this basis,the optimization scheme of simultaneous welding of large welds is put forward.The weakening effect of welding residual stress on structure was analyzed,and it is pointed out that the main truss beam is the weakest plate of the structure.