Research On Welding Residual Stresses And Distortions In Steel Bridge Decks Stiffened With U-Shaped Ribs

Orthotropic steel bridge deck has been extensively used in bridge deck structure for modern steel bridges whose longitudinal stiffener usually adopt steel plate stiffened with U-shaped ribs. The welding residual stresses and distortions induced by the welding processes of U-shaped ribs not only reduce the structural manufacturing precision, increase the cost of correction, but also degrade the service performance. However, there is relatively little research, particularly measurement research, which has been conducted on welding residual stresses and distortions in steel bridge deck stiffened with U-shaped rib. Therefore, it is highly necessary to carry out a systematic and comprehensive research on this topic. In this paper, a series of fundamental researches were carried out first, including parameters determination of welding heat source model, residual stress measurement with blind-hole method, prediction of welding distortion, etc. Subsequently, these research results were verified by both of numerical simulation and experimental measurement. Finally, the research achievements were applied to the prediction and measurement of welding residual stresses and distortion in a steel bridge deck stiffened with U-shaped rib. The main content of this paper could be summarized as follows:(1) Both of overseas and domestic researches were reviewed and analyzed, including welding numerical simulation, parameter determination of welding heat source model, measurement method for welding residual stress, as well as research on welding residual stress and distortion in a steel bridge deck stiffened with U-shaped ribs. Meanwhile, the problems in the current research were pointed out. Furthermore, the objects and contents of this paper were established to solve these problems.(2) Depending on the finite element method (FEM) and computer graphics related theory, an automatic extraction technology of molten pool was put forward based on the isothermal curves. Subsequently, a new method to determine the parameters of double ellipsoidal heat source model (DEHSM) was proposed using the extraction technology and ANSYS optimizer. Meanwhile, a program was developed in Visual Basic in order to solve the DEHSM parameters. Based on the proposed method and program, the DEHSM parameters can be modeled parametrically and solved programmatically for those weld joints which have been commonly used in bridges. On this basis, the DEHSM parameters of four different welding processes were solved, and the discrepancies between calculated values and measured values of welding pool shape were compared. The results show that the proposed method and the program can solve the DEHSM parameters effectively and precisely.(3) In order to overcome the problems in the existing methods, including computational complexity and unsuitability for the stress over 90% of the material yield strength, a simplified iteration method was presented to eliminate the influences of plastic strain on the measurement precision of the blind-hole method. The proposed approach is simple in calculation, fast in convergence, and without limitation of the stress level. Whereafter, the existence, uniqueness, and convergence of the stress state calculated by the proposed method were investigated and verified. The results suggest that the proposed method can effectively eliminate the measuring error induced by plastic strain for the blind-hole method, and can also ensure the uniqueness of the calculation results.(4) With the purpose of investigating the magnitude and distribution of the welding residual stress in a steel bridge deck stiffened with U-shaped ribs, according to the research achievements about the determination of welding heat source parameters and the measurement of residual stress by the blind-hole method, the welding residual stresses were analyzed and measured utilizing the thermal elastic-plastic FEM and blind-hole method respectively. Subsequently, the calculation results were compared with the experimental results. Finally, the reasons of the welding residual stress exceeding 345MPa for Q345 steel were further explored.(5) For the sake of convenience in structural checking which considered the influences of welding residual stress on structural behaviors, two simplified graphics of welding residual stress were established for global analysis and local analysis on steel bridge decks stiffened with U-shaped ribs. Furthermore, the parameter values in the graphics were given out, and also the application notices were specified.(6) For the convenience of applying the inherent strain in the prediction of welding distortion, resorted to the initial strain/stress load in ANSYS, a simplified method, namely initial strain load method, was proposed to apply inherent stain, and a technique was introduced to calculate the equivalent load of inherent strain. Meanwhile, both of these two methods were verified.(7) For a welding procedure with grooves or filler materials, the underestimation problem of welding distortion in predictions based on the residual plastic strain was pointed out and the reasons for the underestimation were determined as well. In order to solve this problem, a prediction approach, namely welding distortion source (WDS) method, was proposed to estimate the welding distortion accordingly. Here, the WDS refers to the local displacement in the weld plastic zone upon cooling, which can be acquired by thermal elastic-plastic FEM. After obtaining the WDS, the overall welding distortions could be extrapolated. Simultaneously, the proposed method was verified utilizing numerical simulation and experimental measurement, employed to predict the welding distortions in a steel bridge deck stiffened with U-shaped ribs, and analyzed the influences of geometric parameters on the welding transverse bending deformation. Based on these researches, a procedure was established to estimate the welding transverse bending for steel bridge decks stiffened with U-shaped ribs. Besides, the key parameters were provided accordingly.