50 m U形UHPC-NC简支梁桥设计研究

Design of Bridge with 50 m-Long Simply-Supported Spans of U-Shaped UHPC-NC Composite Girders

为简化混凝土U形梁施工和提升结构耐久性,以广西贺巴高速茶花山天桥为背景,提出一种可实现快速化施工、结构性能优异并兼具经济性的新型U形超高性能混凝土-普通混凝土(UHPC-NC)组合梁结构。该U形UHPC-NC组合梁桥主跨50 m,纵梁采用UHPC,为弧形立面,跨中处梁高3.2 m,支点处梁高1.95 m,跨中区域腹板厚10 cm,近支点处腹板加厚至25 cm,支点区域腹板厚60 cm;每片纵梁分3段预制,相邻节段间设置齿键,采用胶接缝连接;2片UHPC纵梁由12道宽40 cm、高65 cm预制预应力混凝土横梁通过UHPC现浇接缝连接,纵梁与横梁均为预应力构件;桥面板由7.5 cm厚预制桥面板底模与16.5 cm厚现浇NC桥面板构成。结构分析结果表明:纵梁和横梁剪扭耦合效应明显,跨中区域以受弯为主,支点附近以剪扭耦合作用为主,且剪力和扭矩呈反对称分布;该桥各构件承载力、稳定性、抗裂性能和刚度均满足规范要求;与钢-混凝土组合梁和钢箱梁相比,新型U形UHPC-NC组合梁结构每平米造价分别低约32%和44%,具有良好的经济性。

This paper presents a new type of U-shaped ultra-high performance concrete-normal concrete(UHPC-NC)composite girder,which can be rapidly erected and exhibits sound structural performance and economy,leading to simplified construction and improved durability of U-shaped concrete girders.In the Chahuashan Overpass of Hezhou-Bama Expressway in Guangxi Province,the 50 m-long main span consists of U-shaped UHPC-NC composite girders,the UHPC stringers measure 3.2 m deep at midspan and grow thinner to 1.95 m at the supports,with webs of 10 cm thick in the midspan zone and localized web thickness of 25 cm,and the thickness at supports reaches 60 cm.Each stringer was divided into three sections to facilitate the girder fabrication,each and every two sections were connected by shear studs and epoxy pouring.Two UHPC stringers are composed of 12 prestressed concrete floor beams that measure 40 cm wide and 65 cm deep,and connected via cast-in-situ UHPC stitches.The deck panels consist of 7.7 cm-thick steel-NC prefabricated formwork and 16.5 cm-thick NC slabs.The structural analysis demonstrates that the shear-torsion coupling effect of the stringers and floor beams is significant,with bending dominating the midspan zone and the shear-torsion coupling effect governing the support zones,and the shear forces and torsional moments reveal an asymmetric distribution.The load bearing capacity,stability,anti-cracking performance of all the components meet the code requirements.Compared to the steel-concrete composite girder and steel box girder,the costs per unit of the U-shaped UHPC-NC composite girder were reduced by 32%and 44%,respectively,indicating sound economy.