迫龙沟特大桥主桥为主跨430m的混合梁双塔双索面斜拉桥,边跨采用预应力混凝土主梁、中跨采用钢—混结合梁.该桥主梁采用不对称双悬臂方案施工,即边跨预应力混凝土梁采用牵索挂篮悬臂浇筑施工,中跨钢—混结合梁采用架梁吊机悬臂拼装施工.在该桥主梁施工中,采用不同步双悬臂施工,中跨钢梁安装超前边跨1个节段,以取消中跨约3 000 t的均布压重;在边跨距离桥塔中心27.5 m处设置施工辅助墩,以提高中跨结合梁的大悬臂状态稳定性;在中跨钢—混结合段处设置反拉压重装置,以提高塔梁锚固性能;设置塔梁临时固结和纵向限位装置,以抵抗墩顶处梁体的不平衡力矩;将边跨侧靠近桥台的3个节段合并成1个边跨现浇段,以减少双悬臂施工的节段数.该桥已于2016年完工,成桥线形及结构受力均满足设计和规范要求.%The main bridge of the Polong Gully Bridge is a hybrid girder cable-stayed bridge with double pylons,double cable planes and with the main span of 430 m.The main girder of the side span of the bridge on the one side is the prestressed concrete girder while that of the central span is the steel and concrete composite girder.The main girders of the bridge were constructed,using the asymmetric two-side cantilever scheme,that was,the prestressed concrete girder of the side span was cantileveredly cast on the one side of a pylon,using the guyed form traveler while the composite girder of the central span was cantilevedly assembled on the other side,using the deck crane.In the construction of the main girders,the two-side cantilever construction was carried out asynchronously.At the time the girder of the side span was cast,one more segment of the steel girder of the central span was assembled in advance so as to cancel the uniform counterweight of about 3 000 t to be arranged on the central span.At the 27.5 m of the side span to the center of the pylon,the auxiliary pier for the construction purpose was arranged to improve the cantilever state stability of the composite girder of the central span.At the joint section of the steel and concrete girders at the central span,the counter tension counterweight device was arranged to enhance that anchoring capacity of the pylon and main girder.The temporary rigid fixity and the longitudinal limit device for the pylon and main girder was arranged to resist the unbalanced moment of the girder atop the pier.The 3 segments of the girder of the side span close to the abutment were merged into the 1 cast-in-situ segment so as to reduce the numbers of the segments of the two-side cantilever construction.The construction of the bridge was completed in 2016 and the geometric shapes and structural forces of the bridge could all meet the relevant requirements in the design and codes.
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