Numerical Simulation Of Typical Welded Joints' Residual Stress In Construction Steel Structure

Mutual restriction of population, and land resources and the pushing of urbanization make the urban buildings taller. In addition, because of the depletion of natural resources, it is imperative to develop green building and renewable materials. All these propose higher requirements to construction materials. Steel structures have many advantages such as: small specific gravity, high strength, superior mechanical properties, good earthquake resistance, high manufacture efficiency, ease of application and renewable. Therefore, steel structures are widely used in architecture and the proportion is increasing. The development of large-span and high-raise steel structure requires steel to have better properties. High strength steel gets wide application for its superiority in behavior of members under loading, structure security, durability and sustainable development.Welding is a frequently-used fabrication and process method. Welding structure has better connection behavior and higher rigidity, and welding process has preferable adaptability. Whereas, welding is a process of local heating and cooling which causes uneven temperature field and residual stresses as well as welding deformation. The magnitudes of welding residual stress in a steel structure are often as high as or even higher than the yield stresses of base metal and weld metal. Tensile transient or residual stress is an important factor causing hot crack and cold crack in the course of welding process. In addition, tensile residual stress is one of the major factors resulting in stress corrosion cracking, fatigue damage and brittle fracture during service. Moreover, welding distortion has negative effects on the accuracy of assembly and external appearance of the welded structures. In many cases, additional costs and schedule delays are incurred from straightening welding distortion. Therefore, it is very important and necessary to effective by control welding residual stress and distortion in a welded structure. Measuring the residual stresses with experiments is an expensive and low efficient method. With the development of computational technology, the FEM method is applied to predict welding stresses and distortion.Based on ABAQUS code, a thermo-elastic-plastic finite element method was developed to simulate welding process of multi-pass welding. The temperature field, residual stress and welding deformation of Q345 butt joint was simulated with the proposed method and the experimental method was implement to verify its accuracy. Moreover, the advantages and disadvantages of moving heat source and instantaneous heat source are compared. Then, the influence of welding sequence to residual stress of H section steel butt joint was studied with numerical and experimental method. Three different joint type, T shape joint, box column, longitudinal seam welded pipe, were computed with the proposed method to learn the stress distribution in different joints. Four butt joints fabricated with various materials, Q345, Q460, Q690, Q960, were also simulated to investigate the effect of yield stress to residual stress distribution.The results show that stress computed by moving heat source and instantaneous heat source are very close but the moving heat source gets more accurate welding deformation and the instantaneous heat source saves computational time. In H section steel butt joints, the welding sequence has distinct effect in stress distribution of web plate, and even the plus-minus of stress can be changed. The influence on flange plate is change the magnitude of stress but share similar trend. There is large tensile longitudinal residual stress in welding zone of T shape joint. The four corners of box column show tensile stress and the middle part of plate shows compressive stress. There is large tensile axial residual stress in welding zone while the stress in other area is small. The yield stress does not change the character of stress distribution, but the magnitude of stress increases with the increase of yield stress.The computational approach developed in the current study is helpful in predicting welding temperature field, residual stress and welding deformation of welded steel structures. The results obtained by the current work are also helpful in the production and manufacture.