四线铁路斜拉桥索塔锚固区环向预应力设计研究

椒江特大桥主桥为主跨480m的四线铁路连续钢桁梁斜拉桥,采用H形混凝土塔,索塔锚固采用环向预应力锚固。为确定索塔锚固区环向预应力的合理布置方式,采用MIDAS FEA建立桥塔实体模型,对U形束、井字形直束2种布束方式进行比选,在此基础上,分析施工、运营及断索工况下锚固区的受力性能,并进行预应力合理张拉顺序研究。结果表明:环向预应力采用U形束布置是经济、合理的;锚固区混凝土在预应力切向基本处于受压状态,在预应力法线方向出现1 MPa以内的拉应力,斜拉索张拉会增加侧壁内侧、外索孔处水平拉应力,运营期寒潮效应使塔壁外侧产生较大拉应力,断索时前、后壁齿块横桥向拉应力增加;上塔柱应设置外表面钢筋网片并加强竖向、环向配筋;环向预应力施工时,宜同时张拉内、外侧预应力。

Design of Hoop Prestress in Cable-Pylon Anchorage Zone of Cable-Stayed Bridge Accommodating Four Rail Tracks

The main bridge of Jiaojiang Bridge is a continuous steel truss girder cable-stayed bridge accommodating four railway tracks.The bridge has a main span of 480 m.The pylons are H-shaped concrete pylons,to which the stay cables are anchored via hoop prestressing tendons.To determine the rational layout of prestressing tendons in the cable-pylon anchorage zone,the software MIDAS FEA was used to build the solid model of the pylon.The prestressing tendons were bundled in U and " 井" shapes,and the characteristics of the two arrangements were compared,based on which the load bearing behavior of anchorage zone in the construction and operation stages as well as the state with broken cables was analyzed.The rational way of prestressing tendons tensioning was studied.The results show that the U-shaped way of prestressing tendons layout is economical and rational,the concrete in the anchorage zone is basically in compression in the tangential direction,an internal tensile stress of 1 MPa occurs in the normal direction of prestress,and the tensioning of stay cables increases the horizontal tensile stress at the inner and outer cable holes.In the operation stage,cold air will induce greater tensile stress in the outer surface of pylon walls,and when there are cables broken,the tensile stress in longitudinal direction in the concrete anchor wedges attached to both front and rear walls will increase.For the upper pylon columns,reinforcement mesh should be installed on the outer surface of pylon walls,and additional prestressing tendons should be installed in the vertical and hoop directions.During the construction of hoop prestressing tendons,the inner and outer tendons should be tensioned simultaneously.