Analysis Of Tensioning Process And Adjustment Of Cable Force For FAST Cable-Net Structure

The Five-hundred-meter Aperture Spherical radio Telescope (FAST) is the largest diameter radio telescope in the word. It belongs to the China’s Eleventh Five-Year Plan. FAST is supported by a long-span spatial statically indeterminate cable-net structure with significantly non-linear characteristics. The shape-changing of cable-net structure is controlled by the control cables. According to the different stress states, there are three states of cable-net such as zero state, initial state and load state. The cable-net structure is in zero state after the installation. To make the structure change into the initial state a tension process is required. The tension process is an important step of cable-net structure construction. In order to provide guidance for practical construction and ensure safety and reliability of tension scheme, it is necessary to simulate the tension process. There are inevitably some errors during the construction process, an adjustment of the marginal cables is used to ensure the state of cable-net to meet the requirement.Firstly, the finite element method for cable structures is introduced in detail. The tension process could be divided into three stages. According to the practical structure form and construction method of the FAST, a back-running method is taken to simulate the tension process. The displacement and internal force of cable-net structure have been obtained. The change of internal force is stable during the tension process. According the analysis some cable force of control cables are larger than the initial state, the reliability of temporary anchorage of control cables should be noticed. The influence of temperature on tension process has been analyzed by design temperature load. The results show that the effect of temperature on cable force is larger, and some corresponding measures should be taken.In order to guarantee the safety, the adjustment of cable force is carried out after the first tension stage. In order to avoid the influence of environment temperature, the elongation of marginal cables is chosen to be the instruction of the adjustment of cable force. Considering the obvious geometric nonlinear character of Cable-net structure, a nonlinear iterative method of the adjustment of cable force is proposed through a combination of the influence matrix method and modified Newton-Raphson method. In the end, the adjustment of cable force has carried out by the calculated results, and good effects are obtained.