500 m口径球面射电望远镜索网结构形态和受力分析

500m口径球面射电望远镜(Five-hundred-meter Aperture Spherical radio Telescope，FAST)是国家重大科技基础设施项目。口径500m、半径300.4m的球冠形索网是FAST反射面的主体支承结构。通过促动器的主动控制，索网可以在标准球面和不同抛物面之间转换，即索网为可主动变位的结构。针对FAST索网结构设计中由主动变位引起的形态分析和轻量化需求等问题开展研究，提出了目标位形应变补偿法，统一了球面基准态和抛物面态的形态分析方法，解决了多目标位形索网结构的形态分析问题；提出预应力优化方法，将球面基准态最大索力降低了29%；研究了索网球面基准态和抛物面态的受力性能，并与实测结果进行对比，索力吻合较好,50%以上钢索索力相对误差在5%以内。

Form-finding and structural behavior of cable net of Five-hundred-meter Aperture Spherical radio Telescope

The Five-hundred-meter Aperture Spherical radio Telescope (FAST) is one of China’s major science and technology infrastructure. A spherical-crown-shaped cable net, of which the aperture and radius are 500 m and 300.4 m, respectively, is adopted as the primary supporting structure of FAST’s reflector. The shape of the cable net switches between datum sphere and various paraboloids under active control of the actuators, endowing the structure with a feature of active shape changing. Various issues caused by active shape changing, including the form finding and the structurally lightweight requirement, in the design of FAST’s cable net are investigated in this paper. A Strain Compensation Method for Objective Shape, which is capable of unifying the form-findings of the datum sphere state and the paraboloid states of the cable net, is proposed to realize the form-finding of multi-target-geometry cable net. A scheme for the pretension optimization of the cable net is put forward, by which the maximum cable force under the datum sphere state is reduced by 29%. The structural behavior of the cable net under the datum sphere state and the paraboloid states are studied. The theoretical cable forces are compared with the test results, and the deviations of more than 50% cable forces are within 5%.