Research On Stability Of Double Column Suspension Cable Guyed Tower

The double column suspension cable guyed tower is a tensegrity structural system that consists of tower column,guy,suspension cable,insulator string,conductor and ground line,of which the high-rise flexible structrual character makes wind load to be its dominant load.The tension force of windward guys will increase under wind load,thus lead to the increase of the corresponding guyed mast's axial force,but the tower column's critical load of static instability won't increase when the guy tension force reaches a critical value.Although the decrease of the leeside guys' s tension force will make the axial force of corresponding tower column reduce,the lateral stiffness of tower column along transmission line direction will reduce too,which leads to the tower column's critical load of static instability reducing.The design of tower line system is based on static load,but it is usually influenced by the dynamic wind load in practice,under which tower column will bear larger dynamic load along its axial direction,and the tower column will occur parametric resonance when the frequency of the dynamic load is twice as much as the fundamental frequency of the tower column's lateral vibration.Because the double column suspension cable guyed tower covers vast floor area,the system is commonly used in desert and gobi,where the wind speed may be much stronger than the design wind speed,in other words,it exists the possibility of collapse about the tower line system.In this paper,the static and dynamic stability of double column suspension cable guyed tower are studied,and the main research works are as follows:(1)The equivalent section property of lattice tower column is attained according to strain energy equivalence,this equivalent method which is verified from static response and the modal can be used in the static and dynamic simplified analysis of lattice tower column.(2)The simplified static stability analysis model is attained according to mechanical character of tower column,which is a uniform cross section compression bar with hinged at bottom and linear elastic support at top.In order to get the stiffness of elastic support,firstly,the calcutaion formula of inclined guy's equivalent elasticity modulus is deduced based on generalized varitaional principle,in this formula,it considers guy's geometric nonlinear casuing by sag under selfweight.Secondly,the calculation formula of elastic support's stiffness in static simplified analysis model is attained according to the definition of stiffness,and the stiffness value is attained according to the finite element analysis results of tower line system under static wind load.The calculation formula of guyed mast's static calculation length coefficient is derived based on stability theory of compression bar,and the influence of inclined guy's initial pretension and wind speed are studied.Finally,the correctness of this theory research is verfied by eigenvalue buckling analysis function offered by ANSYS.(3)The simplified model of tower column parametric resonance research is mainly in accordance with its static simplified model except the accessor method of the elastic support's stiffness value.Firstly,in order to get the stiffness values of the elastic support,the equivalent dynamic stiffness is calculated according to the new method that S.Ali Ghafari Oskoei proposed.Secondly,the calculation formula of elastic support's dynamic stiffness is elicited according to the definition of stiffness,and the stiffness value is calculated by combing with the finite element analysis results of tower line system under dynamic wind load.Finally,the partial differential equation of the simplified analysis model is attained based on Hamilton principle,which can be disassociated into ordinary differential equation througth Galerkin method.Thus the dynamic stability domain and unstability domain of tower column is attained according to the critical frequency equation that Bolotin proposed.(4)The wind speed time-histories of simulation points in tower line system are composed based on harmonic synthesis method,which are transferred to wind load and applied to tower line system.The finite element analysis of tower line system is built in ANSYS,shape-finding analysis and static solution are accomplished,and then the stress initialation and dynamic analysis of tower line system is accomplished by the implicit-explicit order solution function that ANSYS/LS_DYNA provides;on this basis,appling B_R criterion to research nonlinear dynamic stability of tower line system,and the parmetric analyses are accomplished in regard to guy's initial pretension,wind direction and span,which main purpose is to research these parmetrics influence on the tower line system's critical load of nonlinear dynamic statiblity.In the end,a further outlook of the research work on static and dynamic stability of double column suspension cable guyed tower is proposed in the summary part of this paper.