Research On The Key Technologies And Safety Monitoring Of Prestressed Concrete Box Shaped Girder Bridge Across Railway By Incremental Launching Construction

Based on a real incremental launching construction project of the upgrade bridge on the 320 national road crossing the Hu-Kun railway in Kunming, the process was simulated step by step according to the designed proposal. The stress state of girder, launching nose and pier was investigated. Meanwhile, several key problems such as too large down-warping displacement of the launching nose, excessive reaction force and local stress were also studied. Moreover, the relative factors have been studied, which included the parameter of launching nose, section temperature gradient and depression of supports. In order to avoid that the internal force of the girder is too large, the front end of launching nose is able to successfully reach the temporary pier and controlling the girder stress in a safety level, several research have been done as follows:(1) According to the construction experience, the key problems during the incremental launching procedure have been summarized.(2) A finite element modal of simulating the incremental launching construction process step by step has been developed. The stress state as well as stability of girder, launching nose and pier during the construction stages has been studied. The methods of closed loop and maximum tolerance were adopted to monitor the bridge safety, respectively. Then, the comparison between testing and analytical results shows that there is a good achievement for this construction method applied in real project.(3) The internal forces of girder, the deformation of launching nose influenced by the stiffness, weight and length of launching nose were studied, respectively. The results could provide a guideline for design and optimization of launching nose.(4) Several sensitive parameters to incremental launching construction method were investigated, which included section temperature gradient, depression of supports and boundary condition varies and so on. After researching on the reaction force, girder internal force and launching nose displacement, a proposal for incremental launching construction was carried out.(5) Based on the 3D finite element modal of whole bridge, the varies of reaction force and local stress concentration influenced by the unequalizing support effect have been investigated.The results could be referred to design, construction and maintenance of related bridge.