超大尺寸承台预制混凝土围堰施工与计算分析

Construction of Prefabricated Concrete Cofferdam for Casting of Very Large Pile Cap and Computation Analysis

马来西亚石晶咖大桥主桥为(200+400+200)m预应力混凝土双塔斜拉桥,主墩承台采用八边形结构,长42.5 m、宽30 m、高5 m。该桥主墩承台采用预制混凝土围堰施工,围堰主要由围堰壁板系统(包括预制混凝土壁板、现浇湿接缝、安装支撑)和围堰底板系统(包括预制混凝土底板、底板梁、现浇湿接缝、局部现浇混凝土层)组成。为缩短建设工期,提高施工便捷性和安全性,结合马来西亚水上建设条件,围堰采用分块设计、分块施工方案,即壁板及底板分块工厂预制,现场拼装后焊接连接钢筋,而后浇筑混凝土形成整体。为验证施工方案的安全性,采用MIDAS Civil软件建立围堰有限元模型,分析高水位和低水位2种最不利工况下围堰结构的弯矩。计算结果表明:2种工况下结构的受力均满足规范要求,该桥采用的预制混凝土围堰施工方案可以满足结构安全性要求。该桥承台围堰底板已完工,底板各部位受力状况与设计基本一致。

The main bridge of Shijingka Bridge in Malaysia is a prestressed concrete girder cable-stayed bridge with two pylons that create a main span of 400 m and two side spans of 200 m.The pylon pier stands on an octagonal pile cap that measures 42.5 m×30 m,5 m high.The pile cap was cast with the assistance of a prestressed concrete cofferdam.The cofferdam consists of a wall system(including the precast concrete walls,cast-in-situ stitches and supports)and a bottom slab system(containing precast concrete bottom slabs,beam supporting slabs,cast-in-situ stitches,and local cast-in-situ concrete layers).To shorten the construction schedule,facilitate the construction and improve construction safety,the cofferdam was designed and constructed in blocks,namely to precast the walls and bottom slabs in the factory,then the walls and bottom slabs were spliced at the bridge site,the connecting reinforcing bars were welded,and finally the joints were filled with concrete to form an integral cofferdam structure.To verify the safety of the construction scheme,a finite element model of the cofferdam was developed using MIDAS Civil to analyze the bending moment of the cofferdam at the highest and lowest water levels of the river.The simulation results show that the load bearing performance of the cofferdam structure at the highest and lowest water levels can meet the code requirements.The prefabricated concrete cofferdam solution can satisfy the structural safety requirements.The installation of the bottom slabs had finished,and the loading conditions of bottom slabs in different zones were basically in agreement with the design.