重庆凤来特大桥总体设计

Overall Design of Fenglai Bridge in Chongqing

重庆凤来特大桥主桥为计算跨径580 m的上承式钢桁拱桥。该桥设计过程中,选取主跨710 m单跨悬索桥、主跨600 m斜拉桥和计算跨径580 m的上承式钢桁拱桥3个方案,从结构特点、施工技术和经济性3个方面进行分析比选。由于计算跨径580 m的上承式钢桁拱桥方案具有结构简洁、整体刚度大、对V形河谷地形适应性好、上部结构施工难度低和造价最低的优势,因此最终采用该桥型方案。主拱拱轴线采用悬链线,计算矢高116 m,计算矢跨比1/5,拱轴系数2.0,拱肋采用双片主桁,上、下游两榀主桁平行布置,横向中心间距20.2 m;主桁上、下弦杆采用箱形截面,截面内宽1.8 m,内高1.8 m。结合原位试验和基坑有限元计算结果,拱座采用重力式拱座,扩大基础,自然山体两侧基坑边坡开挖后,采用预应力锚索和喷锚支护。拱上立柱采用等截面钢箱排架结构。拱上主梁采用工字形钢板梁+预应力混凝土桥面板的组合梁。通过结构计算,拱肋、平联和斜撑等各钢结构杆件强度和整体刚度、稳定性均满足要求。采用斜拉扣挂、缆索吊装方案进行主拱节段、立柱单元以及主梁构件安装。

The main bridge of Fenglai Bridge in Chongqing is a deck-type steel truss arch bridge that spans 580 m.At the preliminary design stage,three types of bridges were considered,including the suspension bridge with a main span of 710 m and with hanger cables only in main span,the cable-stayed bridge with a main span of 600 m and the deck-type steel truss arch bridge spanning 580 m,and the 580 m-span arch bridge was finally selected due to the advantages of structural configuration,construction techniques and economy.In general,the deck type steel truss arch bridge looks slender and elegant,has superior stiffness and suits the V-shaped valley well,at the same time,the construction challenges and costs are also competing factors.With a catenary alignment,the arch consists of two parallel arch ribs spaced at 20.2 m centers along bridge width,rising 116 m(calculated)with a rise-to-span ratio of 1/5(calculated)and arch-axis coefficient of 2.0.The upper and lower chords of the arch rib are of box cross-section measuring 1.8 m wide and 1.8 m deep inside.Based on the field tests and numerical simulation of foundation pits,the arch seats are designed to be gravity structures mounted on spread foundations.After excavation,the slopes of the foundation pits(natural hill body)were strengthened using prestressing anchor cables and shotcreting.The spandrel columns are steel bents made up of steel tubes of box cross-section.The deck system consists of I steel plate girders overlaid with prestressed concrete slabs.Through structural analysis,the strength,overall stiffness and stability of the arch ribs,lateral bracings and diagonals could meet the requirements.The arch ribs were erected by the cable-stayed cantilever assembly method,and the spandrel columns and deck system were erected by the cableway crane.