| Orthotropic steel bridge deck has the advantages of lighter weight, higher rigidity and shorter project time than the others. It also has the characteristics of better entirety, lower noise and better driving comfort than longitudinal-cross beam system deck. So orthotropic deck is more and more used in railway bridges recently, but the problem of fatigue crack of orthotropic deck has been paid much attention to all through the ages for the reason that it has complex structure and numerous weld joints. Deck-truss system structure is more used in railway bridges than other structures with orthotropic deck at present. Yongjiang railway cable-stayed bridge of Ningbo north-ring line, which uses composite girder with steel box girder and concrete box girder, is the first application of steel box girder in long span cable-stayed railway bridge in China. Based on the orthotropic steel bridge deck of steel box girder for Yongjiang bridge, this thesis investigates the following contents.1. Study on load transfer mechanism and fatigue sensitive locations of the orthotropic deck of steel box girder is made through finite element method and static section model tests. The research shows that:1) Effects of deck system and top plate system, which can be induced as bending-shearing effect, supporting effect, rigid frame effect and out-plane effect, play a major role in orthotropic deck, while effect of girder system, which can be ignored when fatigue problem is studied, play a weak role in orthotropic deck.2) Fatigue sensitive locations of orthotropic deck usually locate at the weld joints of steel plates and the edge of cutouts.3) Details associated with diaphragm of the orthotropic deck of box girder for railway bridges are affected by unsymmetrical loading effect weakly, that is to say that they are affected by out-plane effect weakly.4) Double-line effect should be considered when details are mainly affected by bending-shearing effect, while it can be ignored when details are mainly affected by supporting effect and rigid frame effect.5) Weakening role of railway bridge flooring on stresses of orthotropic deck is strong.2. Fatigue loading spectrum for newly-built railway bridges is established through Monte Carlo method according to theory study and data investigation. The program to generate the loading spectrum is realized based on Fortran language. The statistical characteristics of the loading spectrum obtained from the program have good correspondence with the investigated results. Both the properties of the typical grouping of trains and the random characteristics, including the type of locomotives and vehicles, the load and the sequence of the vehicles, are considered in the loading spectrum established in this thesis.3. In order to validate the fatigue sensitive locations of the orthotropic deck of steel box girder for Yongjiang bridge, the fatigue model tests are designed based on the equivalence principle of Miner damage degree. The experimental results show that each detail of the orthotropic deck by using trapezoidal ribs and V ribs satisfies the design life span, which is100years. But the one using V ribs performances much better. The fatigue categories of details based on hot spot stress are proposed by means of fatigue tests and the exist studies. The computational process for fatigue assessment and life-cycle evaluation is also provided. The orthotropic deck of Yongjiang bridge is served as a case study. The calculations of the damage degrees of validation fatigue tests and the fatigue assessment are accomplished by Fortran language.4. In order to investigate the respective structural behavior characteristics of the orthotropic deck of steel box girder for railway bridges and highway bridges, comparison study of stresses of the orthotropic deck of steel box girder for Yongjiang bridge is made among three situations, which are installing railway bridge flooring on the deck, installing highway bridge flooring on the deck and installing no flooring on the deck. The research contents are comparison study of longitudinal influence lines of stresses, transverse influence lines of stresses, stresses under representative vehicle and load transferring mechanism of flooring. Results of the research show that railway bridge flooring, the dispersal role of which is strong, weakens the stresses of orthotropic deck more, and highway bridge flooring, the dispersal role of which is weak, weakens the stresses of orthotropic deck less.5. Study on affecting laws of design parameters to static structural behavior is made through appropriate structure. Design parameters involved are height of crossbeam, thickness of top plate, thickness of web, thickness of rib web and shape of web cutout. Affecting laws of design parameters to static structural behavior of orthotropic deck are studied from the points of shearing effect, supporting effect, rigid frame effect and out-plane effect. |
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