大跨度混凝土斜拉桥拆除方案设计

上海泖港大桥老桥为(85+200+85)m双塔双索面预应力混凝土斜拉桥,采用塔梁固结、塔墩分离的结构体系。随着航道等级提升,该桥桥下净空无法满足通航需求,且原结构损伤较为严重,对其进行拆除。考虑紧邻新建主桥、老桥斜拉索损伤等不利影响,提出一套以“先上后下、逆序拆除”为原则的拆除方案,依次对桥面系、主梁、斜拉索、桥塔和下部结构进行拆除,并利用新建主桥后拼挑臂、斜拉索专用放张索夹设备等措施保障了拆桥的安全性。采用MIDAS Civil软件建立老桥空间杆系有限元模型,对老桥拆除过程中的结构受力进行分析,结果显示主梁、桥塔和斜拉索等主要受力构件的应力均满足规范要求,该拆除方案安全、合理。

Demolition Design for Long-Span Concrete Cable-Stayed Bridge

The Maogang Old Bridge was a two-pylon prestressed concrete cable-stayed bridge with three spans of 85,200 and 85 m.The stay cables were fanned out in double cable planes.The pylons were fixed with the main girder,but connected with the underneath piers via bearings.The upgrading of the navigation channel presented critical demands for the navigation clearance below the bridge,and the bridge itself had been in severe deterioration.Finally,a demolition decision was made.Considering the neighboring new bridge and the damage of the stay cables of the old bridge,the demolition of the old bridge was planned to be conducted in a top-down and backward manner,namely following the sequence of from deck system through main girder,stay cables and pylons to the substructure.The outriggers supporting the cantilever flanges of the new bridge and the specialist detensioning clamps of stay cables were taken over for use to ensure the demolition safety.The load bearing behavior of the old bridge during demolition was simulated by link elements in the library of MIDAS Civil.The results of the finite element analysis show that the stresses in the main girder,pylons and stay cables were within the range suggested in the codes,and the proposed demolition scheme was safe and rational.