Hot Spot Stress Fatigue Analysis And Reinforcement Of Key Details In Orthotropic Steel Deck

Because of the complex structure details,large stress concentration,short stress influence line,fatigue problem of orthotropic bridge deck plate is serious under large bridge service pressure.Fatigue assessment of complex structure by nominal stress method,not only the nominal stress is difficult to determine,but also determining the S-N fatigue strength curve through a large variety of structural fatigue test is tough.Hot spot stress method is adaptable to the complex welding structure fatigue assessment,the various details can share a common Sh-N fatigue strength curve.To some extent,it reveals the essence of the welding structure fatigue cracking.In this paper,taking a suspension bridge of orthotropic steel box girder as the engineering background,based on the hot-spot stress method,fatigue stress analysis and life prediction of orthotropic deck key details under vehicle loads were conducted,researches on the fatigue crack and retrofit method were conducted.The main work completed is as follows:(1)The distribution of the fatigue cracks of OSD were analyzed,and process of the progressive improvement of the design of the fatigue damage was expounded;The S-N curve method,fracture mechanics method,damage mechanics method and reliability theory fatigue evaluation method for the fatigue assessment of orthotropic deck bridge are also described.(2)Research on hot spot stress finite element calculation method of orthotropic bridge deck was conducted.The element type,mesh size and surface extrapolation method are systematically studied,in calculation of welded structure hot spot stress finite element.(3)The fatigue stress analysis and life prediction of orthotropic bridge deck under vehicle load were conducted.A finite element model of the steel box girder was established by the finite element software ABAQUS,adopting the sub model method,to analyze the fatigue stress characteristics of plate-U rib,plate-diaphragm and diaphragm-U rib welded joints under the action of wheel load,and the fatigue life prediction was conduct.The influence of the equivalent hot spot stress on the fatigue life is discussed,and it considered of the influence of the stress gradient.(4)Studies on the cause of fatigue crack and strengthening method of cross diaphragm plate of orthotropic bridge deck were conducted.The fatigue stress characteristics of the curved notch of the transverse partition plate were analyzed,and it reveals the causes of the fatigue cracks.Three retrofit schemes for the arc notch fatigue cracks in the transverse diaphragm were analyzed and compared of.It suggested the best scheme of strengthening the diaphragm plate and the reinforcing effect is significant and the two fatigue source is not introduced.A comparative study on the fatigue performance of 7 kinds of diaphragm gap is carried out at home and abroad,the optimized shape of the cross hole of the rigid diaphragm was suggested.