复杂海域49.2m混凝土箱梁海上造桥机抗风施工技术

平潭海峡公铁大桥长乐岸共计38孔49.2m跨铁路简支箱梁,采用单箱单室等高直腹板预应力混凝土结构,单孔自重1 560t。桥址海域环境复杂、大风频繁、作业环境恶劣、安全风险高,经综合比选,混凝土箱梁采用上行式海上造桥机现浇施工。采用MIDAS Civil软件建立造桥机模型,计算显示极端工况下造桥机抗风稳定性不满足要求,需采取防风、抗台措施。施工过程中,通过在造桥机两侧设置防风网,在其主梁或支腿处设置刚性拉压杆连接和对拉锚固体系,以及在中支腿侧向设置抗滑移系统等措施,提高了造桥机的抗风稳定性及混凝土箱梁现浇施工工效(最快达21d/孔)。

In-Situ Casting Technique for 49.2 m Concrete Box Beam in Complicated Sea Area Using Offshore Bridge Building Machine

The part of Pingtan Straits Rail-cum-Road Bridge on Changle-side bank consists of 38 spans of simply-support box beams,each 49.2 m long.The box beam is the mono-cell constant prestressed concrete box beam with straight webs,and the beams in a single span weigh 1560 t.The complicated marine environment at the bridge site and the frequently-visiting heavy winds pose great challenges to the construction and increase the safety risk of the project.Based on the comparison of construction schemes,the upward-walking offshore bridge building machine was selected for the in-situ casting of the concrete box beams.The software MIDAS Civil was used to establish the model of the bridge building machine.The analysis reflects that the wind resistant capacity of the bridge building machine under extreme loading conditions could not meet the requirements,thus,wind protection and typhoon resistant measures should be considered.During the construction process,a series of measures were taken to improve the wind resistant stability of the bridge building machine,like installing wind resistant screens on the two sides of the bridge building machine,adding rigid tensile rods and tie-back anchor system on the main beam or main legs,and installing anti-slippage system laterally on the central leg of the bridge building machine.The successful implementation of wind protection and typhoon resistant measures enhanced the in-situ casting of the concrete box beams(the maximum casting cycle reached up to 21 d per span).Although attacked by strong typhoons,the bridge building machine was safe and reliable,which greatly guaranteed the quality of the project.