大岳高速洞庭湖大桥桥塔异形下横梁施工技术

Construction Techniques for Asymmetrical Lower Tower Cross Beam of Dongting Lake Bridge on Linxiang-Yueyang Expressway

大岳高速洞庭湖大桥主桥为（1 480＋453.6）m双塔双跨钢桁架悬索桥,桥塔采用门式框架结构,君山侧桥塔下横梁采用单箱单室预应力混凝土结构,高7.0~17.0m,顶面宽10.793m。针对该桥桥塔下横梁结构特点和施工难点,从施工可行性、安全性、经济性以及工期等方面,对塔梁同步、异步施工方案进行比选,确定采用塔梁异步施工方案。塔柱正常爬模施工,待施工塔柱至5号节段,在下横梁与塔柱相交截面位置预埋下横梁钢筋及预应力系统,同时搭设下横梁落地施工支架,塔柱施工过下横梁位置后,进行下横梁异步施工。下横梁施工支架由钢管桩落地支撑、型钢拱形桁架及底模三部分组成。下横梁与塔柱结合面连接钢筋采用Ⅰ级接头质量标准全断面接头。施工中还采取了预应力线形控制、塔柱稳定性及塔柱根部应力控制、混凝土裂纹控制等关键技术措施。

The main bridge of Dongting Lake Bridge on Linxiang-Yueyang Expressway is a two-tower two-span steel truss girder suspension bridge with span arrangement of（1 480＋453.6）m.The towers are the portal frame structures,the lower cross beam of which on the Junshan side adopts the single cell single box pretressed concrete structure,7.0~17.0min depth and 10.793 m wide measured from the top surface.In light of the characteristics of the lower cross beam of the tower and the complexities of construction,the two schemes of tower-girder parallel construction and unsynchronized construction were compared from aspects of construction feasibility,safety,economic performance and construction schedule,and the tower-girder unsynchronized construction scheme was finally chosen.The tower columns were constructed by normal formwork climbing,when the construction of the columns reached the section No.5,at the intersectional cross section of the lower cross beam and tower columns,reinforcement and prestressing system for the lower cross beam were embedded,and the ground scaffoldings for the lower cross beam was erected at the same time.When the construction of the tower columns passed the location of lower cross section,the construction of the lower cross beam began to be carried out independently.The scaffolding system for the lower cross beam was composed of grounded steel supporting pipes,section steel arch-shaped truss and base formwork.The connecting reinforcement at the interface of the lower cross beam and tower columns adopts the full-section connection with GradeⅠ connecting joint quality standard.In the process of construction,a series of key construction techniques,like prestressing geometry control,tower column stability and tower root stress control and concrete oblique crack control,were adopted.