Study On Construction Technology Of Long-span And Variable Crosssection Continuous Steel Box Girder Bridge

The research subject is related to the construction technology of large span and variable crosssection continuous steel box girder bridge.This subject study was based on the project of ChongQi highway bridge acrossing the Yangtze River.This project was located at the estuary of Yangtze River in Qidong Jiangsu province.In this research, mainly focusing on the technical difficulties appeared on the overall erection of the large span and variable crosssection continuous steel box girder segments.The difficulties include how to make the overall scheme for the all the steel box girder segments,how to lift the segments of the box girder integrally,how to adjust the position precisely and how to make the joint connects smoothly.I will use a variety of methods like engineering research, theoretical analysis, numerical simulation and field test to solve above-mentioned difficulties and carrying out my research on following three aspects.Through analysis with compare,the project adopted the construction proposal of prefabricating the steel box girder segments in the factory and lifting them integrally at the construction job site. In order to make the project being carried out smoothly,we made researches for the installation of the steel box girder in different orders and the pros and cons in different closure schemes. Finally we chose the construction craft of making the closure at the side span to eliminate the internal force on the benefit of the structure and easy to adjust the position of the segments for the bridge. After the investigations of the domestic floating cranes, we established rapid selection system to find the suitable floating cranes and made a combination scheme for the lifting of the segments under the condition of satisfying the height and weight.Also to ensure the safty of the lifting,we created special lifting sling system to match the heavy box girder segements.This system with its flexural structure and reasonable stress could be self-consistent equilibrium and it set up a new calculation method and design principles for these kinds of bridegs. Based on the analysis of historical hydrology data and field test data at the bridge site, we decided to place the floating crane at the upstream of the bridge.And Taking into account of the characteristics of the proposal that many vessels will work together and the anchor system is complicated,we made a reasonable layout scheme for all the vessels.According to structure type and the space at the top of the pier,we carried out the research of position adjustment system and local reinforcement method at the top of the pier.And we proposed a three dimensioned position adjustment system with the help of the permanent support saddle.This system make it possible that the segments position could be adjusted in three dimensions.For the box girder joint connection adjustment and reinforcement of the steel box girder,we proposed a corbel structure design combining with structure connection and position adjustment system.Due to the accumulative errors during installing process,at the joint there will cause a bigger error.To eliminate the errors and ensure the joint could be connected smoothly,we carried out several controlling methods like pressure weights,temporally pulling at the baseplate,and support saddle promotion and demotion.And because the steel box girder segments was connected by weld and bolt,to ensure the quality we made a research on the process and craft of the bolted girder and welding girder.This paper systematically studied the key technical problems appeared on the lifting and position adjustment of the large span steel box girder segments which is 185m long and 2690tons weight..And the research result gave a guiding and demonstration effects to the construction of the large span continuous steel box girder bridge at the severe environment of the inshore areas in our country.