Numerical Simulation And Repair Methods Of Fatigue Cracks On Steel Orthotropic Highway Bridge Deck

The orthotropic steel bridge deck is welded together with longitudinal ribs,beams and the bridge decks which are perpendicular to each other. With larger bearingcapacity, lighter weight, faster construction and more beautiful structure, thecontradiction between weight, bearing capacity and span are well solved. So theorthotropic steel bridge deck has become the first choice for a long-span steel bridgedeck. As the steel bridge deck is not only under the reciprocal action of wheel loaddirectly, but also participating in force as part of the main girder, the local deck isunder too much stress cycles. Coupled with the influence of weld defects and stressconcentration of the welded joint, fatigue cracks are produced easily. Once fatiguecracks appear in long-span steel bridges, it is very difficult and expensive to maintainthem. Moreover, they will lead to sudden catastrophic accidents. Fatigue cracks causeoutstanding demand of the maintenance, but the methods of maintenance are not veryeffective at present, which is mainly because that the study of fatigue failuremechanism is not yet deep.In order to investigate the fatigue crack growth process of the orthotropic steelbridge deck, and provide theoretical guidance for the anti-fatigue design andreinforcement, the finite element model based method for tracking the fatigue crackgrowth of orthotropic steel bridge deck is proposed. Based on the existed researchachievements, the repairing methods of the fatigue cracks are summarized. In thisthesis, the following aspects are investigated:1. Finite element method is used to simulate the fatigue crack growth; theinfluence of vehicle axle transverse position, average daily traffic volume, trafficgrowth and impact factor are considered by the method of modifying stress amplitudeat fatigue details, and then the revised equivalent stress amplitude is obtained.2. A method for numerical simulation on fatigue crack growth of steelorthotropic highway bridge deck based on general-purpose finite element software isproposed. Firstly, the critical locations that are apt to suffer fatigue failure of thewhole bridge are ascertained by the field survey results and the analysis of the wholestructure under the dead load and the live load. Then, the refined finite element modelwith typical welded details for the locations is established to analyze the stress amplitude. According to the vehicle-bridge vibration based analysis method, theinfluence of the stress impact factor on the stress amplitude is taken into account.Determine the fatigue crack propagation direction, path, and fatigue life, and thenanalysis the total process of fatigue crack propagation.3. Take the fatigue crack propagation analysis of an existing long-span cablestayed bridge with steel orthotropic bridge deck as an example, which indicates thefeasibility and accuracy of the method and calculation process. Study the effect ofpavement thickness, road surface, overload, road surface traffic growth rate to thecrack propagation life, and provides a theoretical basis for the bridge fatigue failurerepair and reinforcement in operation period.4. The repairing methods of the fatigue cracks are summarized, which could givereferences for retrofit of the fatigue cracks.