赤壁长江公路大桥主桥4号桥塔墩结合梁墩顶节段施工技术

Erection Techniques for Composite Girder Segments on Top of Pylon Pier No.4 of Main Bridge of Chibi Changjiang River Highway Bridge

赤壁长江公路大桥主桥为(90+240+720+240+90)m钢-混结合梁斜拉桥,主梁分为121个节段,由双边箱截面钢主梁、横梁、小纵梁等组成,4号桥塔墩墩顶钢梁共3个节段,考虑枯水期施工边跨侧滩地外露,采用浮吊拼装+墩顶拖拉法施工。桥塔墩设置墩旁支架辅助钢梁架设,墩旁支架采用简易支架,设计为分离直立柱结构,避免了传统斜立柱支架体系结构复杂且受限于围堰尺寸的影响;墩旁支架设置钢梁拖拉系统及钢梁姿态调节装置,以实现钢梁的拼装、纵移和姿态调整。墩顶钢梁利用浮吊在中跨侧依次拼装单节段钢梁杆件后向边跨侧分次拖拉,墩顶钢梁全部就位后,采用竖向调节装置通过“顶落梁”工艺精调钢梁高程和横向调节装置对钢梁横向偏位进行纠偏,保证墩顶节段姿态满足设计要求。借助主梁永久结构简化塔区临时约束设计,抵抗风荷载、施工不平衡荷载和不平衡索力造成的钢梁平动和转动,确保主梁悬臂节段施工安全。

The main bridge of Chibi Changjiang River Highway Bridge is a steel-concrete composite girder cable-stayed bridge with a main span of 720 m,two side spans of 240 m and two end spans of 90 m.The superstructure,divided into 121 segments for the ease-of-construction,consists of two edge longitudinal steel box girders,crossbeams and stringers.There are three segments on the top of pylon pier No.4 that were hoisted and erected by floating crane and pulled into position,given that the shoal under the side spans would be exposed during the dry season of the river.Scaffolds were installed besides the pylon pier No.4 to assist the steel girder erection.The scaffolds consisted of vertical posts,instead of the conventional diagonal posts,to simplify the structure and be free to accommodate the dimension of the cofferdam.Pulling system and position adjusting system were installed on the pier-side scaffolds to achieve the assembly,longitudinal manoeuvre and position adjustment of the steel girders.During the assembly of the pier-top steel girder segments,the floating crane stood on the central span side to assemble the members of an individual girder segment,and the segment completed was pulled towards the side span step by step.When all the steel girder segments over the pier were installed into position,vertical adjusting devices were employed to accurately adjust the elevation of the steel girders and transverse adjusting devices were used to tune the transverse geometry bias of the girder segments,ensuring that the position of the pier-top girder segments could meet the design requirements.The permanent structures of the superstructure were effectively relied upon to simplify the design of temporary constraints and combat swing and rotation of the steel girders caused by wind loads,eccentric loads and stay cable tensions,ensuring the safety of cantilever construction of the superstructure.