Girder-exchange construction method for existing railway bridge by successively incremeantal launching framework process

The invention relates to a girder replacement construction method of the existing railway line bridges, which applies a method of incremental launching framework. The girder replacement construction method is fulfilled according to seven steps: (1) A split slideway is respectively arranged on one side of the existing line and a framework is respectively prefabricated on the split type slideway; (2) Temporary rest piers are arranged under the existing line bridge and used to upbear a track skeleton, and the locking of seamless lines and the installation of a crossarm track are carried out on the two sections of a grider-replaced section; (3) The temporary rest piers are used to upbear the girder body of the existing line, and the bearings under the existing girder are disassembled; (4) the prefabricated framework is connected with the existing girder by a steel stranded wire; (5) A continuous jack is utilized to tow the steel stranded wire to haul the cascaded framework and the existing girder to the position required by the design; (6) The bearing side under the bottom plate of the prefabricated framework is grouted and reinforced; (7) After dropping the track and replenishing ballast, the line is resumed. The present invention has the advantages that the construction is safe and stable, the cost is reduced, the construction procedures are simplified, the construction period is shortened and the engineering cost is saved.