| In China, super steel railway bridges are increasing quickly with the rapid development of high speed railway construction; now there are about 10 super steel bridges built-up or under construction or under design. Nanjing Dashengguan Yangtze River Bridge (NDB) on Beijing-Shanghai high speed railway is the earliest and the most influential one among the steel bridges mentioned above, and is the first railway bridge with 6 lines in the world. The main bridge of NDB is a continuous three main truss arch structure with span arrangement as (108+192+336+336+192+108) m. Among the 6 railway lines of NDB, there are 2 high speed ones with 300km/h designed speed and 350km/h reserved speed.On base of extensive collection and study of relevant information from home and abroad, combing theoretical analysis and experimental research, systematic research aiming at NDB was carried out in the thesis, including deck structural forms, mechanical characteristics, design and calculation methods, fatigue performance of U rib-to-diaphragm connection in orthotropic steel bridge deck and the anticorrosion problem of steel deck. The research of this thesis is supported by three key projects founded by Ministry of Railways. The innovative results are as follows:1. Aiming to the characteristics of multi-line, great span, high speed of NDB, after comprehensive comparison and study, orthotropic monolithic steel deck system with dense transverse girder (OSDTS) was recommended (and adopted) for NDB. OSDTS not only has good wholeness, big stiffness, but also decreases the whole deformation of bridge and improves the mechanical behavior of deck with the bottom chord and tie beam heightened.2. The transmission paths were studied for the deck loads on truss-girder composite structures with OSDTS, so was the load ratio through the paths and influence factors. The ratio of deck loads transferred through the two paths was given quantitatively for the first time. There is over 50% deck loads transferred from panel transverse girders to bottom chords or tie beam and then to bottom chord joints, which will cause vertical bending of the bottom chords and tie beam.3. Deck loads allocation among the three main trusses or arches were researched in the thesis. A concept of two steps allocation, ratio of the two allocations and its influence factors were put forward for the deck load on the three main trusses or arches. With the action of deck loads, load models of the three main trusses were put forward for truss-girder composite structures with OSDTS, which can be used for the design of the three main trusses or arches.4. According to the mechanical characteristics of truss-girder composite structures with monolithic steel deck, Two Step Analysis Method combing global analysis and local analysis of key parts, and three practical FEA methods for global analysis, namely, SPBM, SSM and SFM were summarized. SPBM is applicable for the middle and later design periods, for overall checking the stiffness, strength and stability of the bridges in construction or in service. SSM is good for the beginning design period, in which the bridge structure and member dimensions will be changed frequently. SFM is applicable for checking bridge stiffness, strength and stability of the main truss and deck frameworks, it is also effective for the construction procedure optimization calculation, tension order and forces of cable tension optimization calculation of cable stayed bridges and arch bridges.5. Experimental research was carried out on the fatigue performance of the U rib-to-diaphragm connection in orthotropic steel bridge deck. Referring to the orthotropic monolithic steel deck system of NDB, two full scale monolithic models of U rib-to-diaphragm connection were fabricated, refined finite element analysis and fatigue experiments were carried out on the two models. Results show that the U rib-to-diaphragm connection has good fatigue performance, which is neither influenced by hole shape in the diaphragm web under U rib, no matter it is apple shaped or flat bottom shaped nor by holes at the upper rib-diaphragm web-flange connections. The steel rails should be avoided to be located on the deck right above U ribs. The fatigue life of U rib-to-diaphragm connection was evaluated and the hole edge of diaphragm web under U rib was categorized into I fatigue type, corresponding to basic metal.6. A kind of compound preservation system with flexible waterproof layer for ballast orthotropic monolithic steel deck was presented and relevant tests were done. The results show that the antiseptic property, waterproofness, abrasion resistance and anti-skidding performance of this preservation system are good and the construction technology is simply. The long-term effectiveness of antiseptic property is still under observation. The environmental request of in-site operating should be reduced further more.7. The 321-Q370q stainless composite steel plate preservation system with the thickness (3+16) mm was presented and relevant tests were done. The results show that the 321-Q370q stainless composite steel plate hardly increases the deck load of the bridge while the material resources is wide and the plate size is large, the explode weld technique is mature, the antiseptic property and anti-skidding performance are good. The long-term effectiveness of antiseptic property is still under test. The price should be reduced further more.The above research achievements from 1-5 have been applied in the design of many a great steel bridge, such as Nanjing Dashengguan Yantze River Bridge, Jinan Yellow River Bridge, Anqing Railway Yantze River Bridge, Dongping River Bridge. The last two researches still need further improvement and long time observation.
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