Project introduction 2.1 * * Double track railway bridge is one of the key control projects of Zhejiang Jiangxi railway electrification speed increase reconstruction project. The project site is located in Dingjiafang Village, Liling City, across the * * River. There are 17 holes in the whole bridge, of which: 0 # abutment and 5 # pier are located behind the Lujiang Porcelain Factory on the east bank of * * River; The main piers 6 #, 7 # and 8 # are underwater piers. They cross the river 190m along the bridge axis. The normal construction water level is 48.8m and the water depth is about 4m; 9 # pier - 17 # abutment is located in the vegetable field on the west bank of * * River. 2.2 The line on the bridge is designed as Grade I double track electrified railway with a design speed of 200km/h** The span of the double track railway bridge is arranged as 5 × 32m simply supported beam+(42m+2 × 64m+42m) prestressed continuous box girder+8 × 32m simply supported beam. The total length of the bridge is 663.07m. The design starting mileage of the bridge is D1K896+019.93, the ending mileage is D1K896+683, and the center mileage is D1K896+300.00. Among them, 0 # abutment - 3 # pier are located on the transition curve and flat slope, and the rest piers are located on the straight line and flat slope. 2.3 The main bridge is designed as a single box, single cell, variable height, variable cross-section continuous box girder, which adopts full prestressed design. The top plate of box girder is 9.2m wide, and the bottom plate is 6.4m wide. A two-way drainage slope of 2% is set on the top of box girder. C30 concrete circular piers with a diameter of 6.5m and a height of 11m are used for the main piers 6 #, 7 # and 8 # of continuous box girders; C30 concrete round ended piers are used for 5 # and 9 # side piers, with pier heights of 10m and 8.5m, pier neck width of 3m along the bridge and 9.8m across the bridge, and other pier shafts of 2.2m along the bridge and 8.8m across the bridge. The box girder is a three-way prestressed concrete structure: the longitudinal prestressed top, bottom and web steel strands of the beam body are 9-7 φ 5 high-strength low relaxation steel strands, which are tensioned at both ends by YCW250B jack, anchored by HVM15-9 group anchors, and the prestressed pipe is a metal corrugated pipe with an inner diameter of φ 80mm; The transverse prestressed tendon of the beam body is 3-7 φ 5 high-strength low relaxation steel strand, the fixed end is anchored with HVM15-3PB anchorage, the tensioning end is tensioned with a single YDC24Q jack, and the HVM15-3B flat anchorage is used for anchoring. The prestressed pipe is a flat metal corrugated pipe with an inner diameter of 60 × 19mm; The vertical prestressed reinforcement is φ 32 finish rolled thread cold drawn Ⅳ reinforcement, which is tensioned at the single end of the beam top with YG-70 jack, anchored with YGM-32 anchorage device, and the prestressed pipe has an inner diameter of φ 45mm. 2.4 Main materials require that ordinary reinforcement used for continuous box girder is divided into Grade I (Q235) and Grade II (HRB335) reinforcement, and the elastic modulus of reinforcement Es=210Gpa. The ordinary steel bars must comply with the provisions of the national standards Hot Rolled Steel Bars for Reinforced Concrete (GB1499) and Hot Rolled Plain Steel Bars for Reinforced Concrete (GB13013). The standard values of tensile strength are: Grade I steel bars fsk ＝ 235Mpa, and Grade II steel bars fsk ＝ 335Mpa. φ 15.2mm270 grade steel strand is used for longitudinal and transverse prestressed tendons of roof, with standard value of tensile strength fpk ＝ 1860Mpa, and elastic modulus Ep=1.95 × 105 Mpa; The vertical prestressed reinforcement adopts φ 32 finish rolled thread cold drawn Ⅳ reinforcement, with the standard value of tensile strength fpk ＝ 835Mpa, and the elastic modulus Ep=1.8 × 105 Mpa. Prestressed steel must comply with the national standards Hot Rolled Ribbed Steel Bars for Reinforced Concrete (GB1499) and Steel Strand for Prestressed Concrete (GB5224). The pre-stressed anchorage shall be HVM series, which must comply with the national provisions of Anchorage, Clamp and Connector for Prestressing (GB14370). The cement used for superstructure concrete is Shaofeng cement produced by Xiangxiang Shaofeng Cement Plant. 2.5 Continuous box girder shall be poured with light hanging basket cantilever. First, T-shaped bars and I-beams shall be used to erect falsework at 6 #, 7 # and 8 # piers. Pour section 0, and then symmetrically pour 1 # - 7 #, 1 '# - 7' #, 1 "# - 7" # beam sections to cantilever at both sides to form three T-structures. First close the middle span, and then erect falsework beside 5 # and 9 # piers to construct side span 9 and 10 beam sections, Close the side span to form a continuous beam. The simply supported beams of approach bridges from 0 # abutment to 5 # pier and 9 # pier to 17 # pier shall be prefabricated in the factory and laid by the bridge erecting machine.
