The Anchorage System And Its Ultimate And Fatigue Performance For A Super Large Cable Net Structure

With the further exploration of the unknown world,human beings are eager to build more and larger astronomical telescopes,and the super cable net structure is the key part of the construction of the giant astronomical telescope.The cable net of FAST(Five-hundred-meter aperture spherical radio telescope),with the self-weight of approximate 1200 tons and 2,000 tons of supported panels,is a typical structural system for supporting reflector surface.FAST is the largest cable structure in the world and has the highest observation precision.The FAST reflector is used for tracking celestial bodies by adjusting the position,which causes cable relative position of cable net frequent change.Consequently,the cable anchorage system is bearing the cyclic load,ultimately leading to fatigue failure after long term service.How to ensure the safety of cable net structure under huge static and dynamic loads is one of the most important problems in the design and construction of FAST.The National Observatory requires that the stress amplitude of main cable of FAST cable is at least 500 MPa,which is not only beyond current relevant national standards(China),but also unprecedented in the world.Aiming at FAST project,the cable anchor structure analysis is taken as the main line to carry out the research.By theoretical analysis and numerical simulation,the anchorage system components are designed and optimized;and through the test and engineering application,the anchorage system is verified to achieve the desired goal that fatigue stress amplitude up to 500 MPa,cable force accurate measured and cable length error within ±1.0mm.Main contents include:(1)The stress and loading condition of the cable net anchorage system has been characterized under environmental temperature change and different working condition.The correlation equation of force between the main cables and the Boom Vang is derived.It is found that the temperature has little influence on cable stress,and the fatigue load is mainly caused by the position change of the cable net.The stress amplitude and loading cycles of the main cable in the middle zone of the cable net are larger,where the type of S3,S4 and S6 cables bear the highest.(2)The formula of the stress distribution of radial compression and the axial tensile is derived in terms of partially symmetric analysis of the anchorage structure.Meanwhile,the equation of the anchorage efficiency coefficient is derived,which provides a theoretical guidance for the reasonable adjustment of the stress distribution in the anchorage structure.The concept of anchoring efficiency index and the design principle of anchorage structure parameter selection according to the same anchoager efficiency index are put forward.On this basis,a new type of double cone anchorage structure is proposed.(3)Through the elastic-plastic contact numerical analysis method,the axisymmetric model of the double cone anchorage structure of S3 specifications is established.The optimum parameters are as follows: the inclination angle of the main anchor cup is 4.1°,the inclination angle of the auxiliary anchor cup is 3°,the internal friction coefficient of the inner cone is 0.1,and the elastic modulus of the cold casting body is 36 GPa.Then,the three-dimensional fine model of anchorage structure is established,and the ultimate strength and fatigue performance are studied,and the specific size parameters are determined.On this basis,the reference and optimization method are established for the design of anchorage structure series.(4)Based on the fatigue test,the single epoxy resin spraying strand and galvanized wire made from super 82 B steel are selected as the cable tendon.According to the failure criterion of maximum Von-mises stress,the anchor cup,fork ear,pin and joint plate are optimized and designed.(5)The monitoring method is put forward that a fiber strain gauge is attached to the strain sensitive position of the outer wall of the anchoring cup and the cable force is measured by calibration,which measurment error is less than 5% and can meet the engineering requirements.A cable length constant temperature load regulation control method is put forward and the cable length measurement and control process is established,which test shows that the measurement error of cable length can meet the requirement of high-precision control of ±1.0mm.The construction strategy of the FAST cable net is proposed that cable net simultaneous installed in 5 adjacent symmetrical zones after cables layed out in the central zone,so that the splicing of the cable net can be completed smoothly and rapidly.The cable net adjustment strategy is proposed that adjusting the length of edge cables symmetrically afer 1/4 Boom Vang positioned is proposed,which can make the cable net structure formation precisely.