为避免对铁路运营的干扰,上跨既有铁路桥梁常用的施工方法有转体法及顶推法,转体法要点时间短,施工过程无体系转换,在条件不受限的情况下应是首选方案；当桥位处受既有建筑物影响无法转体时,可考虑采用项推法.考虑到后期养护维修需要,一般不宜采用钢结构跨越既有线.采用顶推法施工的预应力混凝土梁,设计时需考虑顶推临时束配置、导梁与混凝土梁连接、永久墩及临时墩刚度、梁底合理线形等；顶推施工时易出现顶推力过大、滑道变形、滑块无法塞入、墩顶位移过大、墩底开裂、导梁与混凝土连接处梁体开裂等问题,均提出了相应解决方案.%The bridge crossing over an existing line are commonly erected by swing method and incremental launching method to avoid the interference on railway traffic. Swing method should be the preferred method when the construction conditions are not limited, with which the construction period is short and without system conversion. Incremental launching method may be adopted when the bridge is located near by the existing buildings and can not be swung. Steel bridge should not be adopted in the case of crossing over the existing line because of the maintenance needs in the future. Aiming at the prestressed concrete box girder by incremental launching method, the paper puts forward relevant solutions about the undermentioned problems; when design, the problems are the configuration of temporary steel tendon, connection between guide beam and concrete girder, rigidity of permanent pier and temporary pier, the alignment of girder bottom, etc; when construction, the problems are the excessive launching force, deformation of slide way, trouble on slider inserting, excessive deformation on pier top, cracking at the pier bottom and at the joint between guide beam and concrete girder, etc.
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