Research on Catenary Characteristics of FAST Tie-Down Cable and its Effect on Actuator and Joint

To study catenary characteristics of FAST (Five-hundred-meter Aperture Spherical radio Telescope) tie-down cable, this paper establishes tie-down cable equilibrium differential equation and cable length formula based on catenary theory, analyzes numerical simulation of multi-segment bar element method, and designs an experimental scheme. Taking 1×7 Ø12.7steel cable and Ø10 CFRP (Carbon Fiber Reinforced Polymer) cable for example, we can obtain three results respectively through manners mentioned above, and the agreement among them is excellent. Meanwhile, difference between results and elastic deformation of no-weight cable is not so big that catenary of two cables can be negligible. Further research shows that cable length is more sensitive to catenary than horizontal angle; cable longer deformation will benefit actuator to meet position precision effortlessly, however, stroke and velocity of actuator will increase and initial tension displacement of tie-down cable decrease correspondingly, this alteration should be compensated during reflector surface measuring and controlling; due to chord-tangent angle and tangential force is less than 1.28°and 241.4N, catenary effect on joint pose is weaker; generally speaking, CFRP cable has less catenary problem than steel cable, better mechanics characteristics, but bigger stroke and velocity for actuator and smaller initial tension displacement for tie-down cable. The research will provide references for design of tie-down cable, actuator, joint, and reflector measurement and control.

ELASTIC RESTRAINED DISTORTIONAL BUCKLING OF STEEL-CONCRETE COMPOSITE BEAMS BASED ON ELASTICALLY SUPPORTED COLUMN METHOD

Restrained distortional buckling (RDB) is different from overall buckling and distortional buckling, and it usually occurs in the hogging moment region of composite beams. It may govern the member design for some cases, and should be taken into consideration. The present paper investigates the elastic RDB of composite beams based on elastically supported column method. First, Svensson's elastically supported column model is improved by including the participation of the web as part of the buckling column. The corresponding theoretical expressions for the improved elastically support column subjected to a varying axial force are derived by the potential energy expression and equilibrium differential equation, respectively. Then, the precision of several elastically supported column methods for the RDB problem is discussed, based on the finite element method (FEM). The results show that elastically supported columns subjected to a negative uniform moment or a triangular moment have a good agreement with FEM results, but they are not valid for the cases of nonlinear moment distributions. In order to consider the complicated load conditions of composite beams, the equivalent moment assumption is introduced and proved to be suitable for the RDB problem. However, there is an applicable range of the length of the hogging moment region. Thus, a critical length formula of equivalent moment assumption of RDB is put forward and verified by FEM. Furthermore, a three-step simplified method is presented which can solve the elastic RDB problem of continuous composite beams. The proposed method, in which values of elastically supported column methods can be tabulated previously, is simple and suitable for design purposes.

Solid-Liquid Coupling Mechanism Research in Seepage Field and Stress Field of Fractured Rock Mass

In this article, we use the porosity to express the effective stress of rock mass, and get the equilibrium differential equation. on this basis, using equivalent continuum model and the finite element method to simulate the degree of coupling. In full consideration the interaction between groundwater and the rock framework and referring to the underground water solid coupling seepage flow mathematic model, based on finite element theory, we obtain the calculation method and the coupling method. These methods can real simulate groundwater seepage condition and have a great significance.