700 m级中承式缆拱桥设计

随着拱桥跨径的增加，拱肋稳定性问题突出，且巨大的推力需通过系杆或基础平衡，大跨度悬索桥的庞大锚碇耗资巨大. 针对这两个问题，结合拱和缆索的受力特点，提出一种新的桥梁结构体系——中承式缆拱桥. 首先，在主跨和边跨均加入拱圈；其次，去掉悬索桥锚碇，将主缆锚固于边拱拱脚；最后，通过选取适宜的垂跨比、矢跨比及拱轴系数，保证结构在恒载作用下主缆张力、主拱推力、边拱推力在数值上基本相等，从而使结构处于无推力状态并达到改善结构力学性能的目的. 给出了新型桥的具体结构形式和受力机理，并以700 m跨径为例对其进行设计研究，对其施工过程提出了设想. 有限元计算分析表明:中承式缆拱桥的拱与缆索共同承担桥面荷载，与同条件下的连续拱桥相比，其强度承载力提高约25%，稳定承载力提高约70%，同时恒载作用下结构产生的水平力基本为0，为突破拱桥跨径奠定了坚实的基础. 

Design of Half-Through Cable-Arch Bridge with 700 m Main Span

As the span of arch bridges increases, the stability problem of the arch rib is becoming severe and the huge horizontal thrust needs to be balanced with tie rods or foundation; meanwhile, large anchors of a long-span suspension bridge costs a lot. Aiming at the two problems above, a new type of bridge structure, half-through cable-arch bridge, was proposed based on mechanical properties of arches and cables. The specific structure and force mechanism of this new type bridge are elaborated. First, arch rings are added to both the main span and side span of a suspension bridge. Then, its anchors are removed and main cables are anchored to the side arch feet. Finally, by choosing appropriate parameters such as sag-to-span ratio, rise-to-span ratio and arch-axis coefficient, the tension of main cable, the thrust of main arch and the thrust of side arch can be basically equal in value under dead load, so that the structure is in a state of no thrust and thus structural mechanical properties can be improved. Taking a half-through cable-arch bridge with a 700 m main span as an example, the design of its structural layout and components are described in details and a sequence of construction steps is suggested. Finite element analysis shows that the arch and cable of half-through cable-arch bridge share the load of bridge deck; compared with the continuous arch bridge under the same conditions, the half-through cable-arch bridge can increase the strength bearing by nearly 25% and increase the stable bearing capacity nearly by 70%. In addition, the horizontal force generated by the structure is nearly zero under dead load, which lays a solid foundation for breaking through the span limit of arch bridges.