Anti-fatigue Optimization Design Of Steel Box Girder Diaphragm Based On Response Surface Method

With the rapid development of economy,steel box girder is one of the most commonly used main beam forms of modem long-span bridges.It is also a concentrated expression of new materials,new technologies and new design concepts in bridge engineering.Orthotropic steel bridge panels are used as steel.The preferred structure of the box girder bridge deck has the advantages of light weight structure,remarkable economy,strong carrying capacity and short construction period.However,while it has outstanding advantages,the fatigue problem of this type of structure is also prominent.Many typical cases of fatigue skin damage of orthotropic steel bridges at home and abroad show that once fatigue disease occurs,it will directly affect the operational quality and carrying capacity of the structure,and the disease.The emergence of the not only increases the cost of repair,but also the ideal repair effect.Therefore,the research on anti-fatigue design of orthotropic steel bridge deck is of great theoretical and practical significance.The specific work of this paper is as follows1.Briefly expound the historical development and research status of orthotropic steel bridge decks,summarize the fatigue diseases of orthotropic steel bridge decks and the defects and shortcomings of current research on fatigue performance of orthotropic plates.2.According to the engineering case,the finite element model of the orthotropic steel bridge deck segment is established,and the stress characteristics of the longitudinal rib and transverse diaphragm joint welds of the orthotropic steel bridge deck and the curved gap of the transverse diaphragm are analyzed.Determine the most unfavorable loading position of the fatigue analysis of the steel box girder,study the fatigue detail stress under the wheel load,and verify the correctness of the finite element simulation analysis method by comparing with the results of the laboratory model test.3.Analyze the fatigue causes of the transverse baffle fatigue details(including the longitudinal rib-transverse baffle weld joint and the arc-shaped opening of the transverse baffle),determine the fatigue performance control index of the common diaphragm,and adopt the orthogonal test design method.Investigate the influence of the elastic modulus of the pavement layer,the thickness of the diaphragm,the radius of the curved notch of the diaphragm,the height of the curved notch of the diaphragm on the control index,and the significant order of the factors.The arc notch radius,the notch height and the thickness of the diaphragm are the significant influence factors of the maximum main tensile stress of the longitudinal rib-transverse diaphragm,and the influence of the arc-shaped notch height of the diaphragm is the most significant.For the evaluation index of the maximum principal compressive stress of the arc-shaped notch of the transverse diaphragm,the thickness of the diaphragm is a significant influence factor,but the height of the arc-shaped notch of the diaphragm is extremely small and negligible.4.It is proposed that the maximum tensile stress a at the joint of the longitudinal rib-transverse baffle weld and the maximum compressive stress a3 at the arc-shaped opening of the transverse baffle are used as two optimization targets,and the transverse plane of the orthotropic steel bridge is separated based on the response surface method.After the anti-fatigue optimization design of the plate details,the maximum tensile stress at the joint of the longitudinal rib-transverse baffle is reduced by 27.85%compared with the original design,and the maximum compressive stress at the arc-shaped opening of the transverse baffle is reduced by 0.23%compared with the original design.The results are consistent with the predicted values calculated by the response surface method,and the optimized values obtained by the response surface method are satisfactory.