重庆白居寺长江大桥主梁合龙施工控制关键技术

Construction Control Techniques for Closure of Main Girder of Baijusi Changjiang River Bridge in Chongqing

重庆白居寺长江大桥为主跨660 m公轨两用钢桁梁斜拉桥,钢桁梁采用散件全悬拼方案安装。针对该桥合龙口两侧主梁梁长易受温度影响、两侧标高相差较大导致合龙口姿态调整难等问题,进行合龙施工控制技术研究。通过优化外侧3对斜拉索张拉索力的方式完成对合龙口姿态的调整,使合龙前的线形满足合龙施工要求;对合龙口空间坐标和温度进行48 h连续观测,确定合龙段杆件在设计基准温度下的配切长度,按该长度配切后的杆件保证主梁在设计基准温度下的无应力总长度不变;计算主梁在不同顶推量下所需的顶推力,在7号塔处设置纵向顶推装置;待配切后的杆件以及拼接板栓孔按施工图制孔后,顶推主梁使合龙段杆件满足安装精度后,现场打入冲钉和安装临时螺栓完成主梁合龙施工,合龙后主梁的轴线偏差为12 mm,标高偏差为17 mm,满足施工控制精度要求。

The Baijusi Changjiang River Bridge in Chongqing is a steel truss girder cable-stayed bridge with a main span of 660 m.The bridge has two levels of decks,where the upper deck carries roadway traffic and the lower deck accommodates light rail traffic.The steel trusses in the superstructure were cantilever-assembled to take shape from individual members at bridge site.Due to that the lengths of girder cantilevers at the closure gap are sensitive to thermal effect and there exists great elevation differece between the girder cantilevers,the closure attitude adjustment becomes a challenging work,thus carrying out closing construction control was quite necessary.The tensioning way of the three outermost pairs of stay cables were modified to achieve the synchronized adjustment of attitude of the closure gap,to make sure that the alignment of the under-construction bridge could meet the requirements of the closure construction.The spatial coordinates and temperatures of the closure gap were continuously monitored for 48 hours to determine the cutting and matching lengths of the members of the closure segment at the design reference temperatures.As per computed lengths,the members were matched and cut to ensure that the stress-free length of the main girder would not change at the design reference temperature.The pushing forces to the main girder were computed in accordance with the stipulated pushing lengths,and at the pylon No.7,longitudinal pushing devices were installed.Once the matching and cutting of the members was finished and the bolt holes in the splice plates were made in accordance with the construction drawings,the main girder was pushed to allow the members in the closure segment to meet the installation precision requirements,then the punch pins were driven in and temporary bolts were installed to complete the closure construction of the main girder.After closure,the axial alignment and elevation bias of the main girder were 12 mm and 17 mm,respectively,reaching the construction control precision requirements.