宽幅短线预制混凝土箱梁横向预应力分次张拉研究

Study of Multiple Times of Transverse Prestress Tensioning in Wide Concrete Box Girder Fabricated by Short-Line Match Method

大跨径混合梁斜拉桥边跨混凝土梁常采用短线预制拼装法施工,施工过程中有多次体系转换。为确保施工过程中的安全和节段间的顺利拼接,以石首长江公路大桥主桥北边跨(75+75+75)m混凝土梁为对象,分析宽幅短线预制混凝土箱梁施工阶段以及成桥恒载状态下横向受力与变形,确定横向预应力分次张拉时机和控制目标,采用MIDAS Civil建立梁段有限元模型,根据施工阶段应力和位移结果确定合理的横向预应力张拉方案。研究结果表明,宽幅短线预制混凝土箱梁施工过程中以横向受力为主,且多次体系转换,横向预应力须分次张拉到位;横向预应力分次张拉方案由位移和应力双控,横向预应力分次张拉的次数和时机在保证安全和顺利拼接的基础上可根据施工特点进行优化,预应力张拉束数和张拉力百分比可结合工期要求和预应力施工的便利性来进行考虑。

The side-span concrete girder in the long-span hybrid girder cable-stayed bridge is commonly fabricated by the short-line match method,and the structure often experiences multiple systematic transformations in the construction process.To ensure security and the smooth assembly of the sections over construction,the(75+75+75)m north side-span concrete girder was taken as the study object,to analyze the transverse loading condition and deformation of the wide concrete box girder fabricated by the short-line match method in the construction process and under the dead loads in the completed bridge state,and to determine the timing of multiple times of transverse prestress tensioning and the control targets.MIDAS Civil was used to establish the finite element model of girder sections,to determine the rational transverse prestress tensioning scheme in accordance with the stresses and displacement in the construction stage.The results of the study show that transverse load-carrying condition played a dominant role in the construction process of the wide concrete box girder fabricated by the short-line match method,the structure went through multiple times of systematic transformation,hence,the transverse prestress must be tensioned by multiple times accordingly.Displacement and stress are the two control parameters in the scheme of multiple times of transverse prestress tensioning.The times and timing of transverse prestress tensioning can be optimized according to the characteristics of the construction,on the premise that secure and smooth assembly are assured.The amount of prestressing tendons and the tensioning force percentage should be designed taking account of the construction schedule and ease of construction.