Dynamic Stability Analysis Of The Guyed Masts

The guyed mast is consist of a slender tall mast and inclined pretensioned guys, being supported by pretensioned guys, the guyed mast is more economical than general upright mast, so it is attended in the engineering field. Because its complicated principle is not fully known, the catastrophic failure probability of guyed masts is very high under normal designing and constructing in civil engineering field. According to the data about near upon one hundred collapsed cases of guyed masts, the 50 percent of them were damaged by wind load, hail load and ice load, and few of them was caused by very large wind load, such as cyclone, most of them were damaged because of instability of guyed masts owing to large amplitude vibration when wind velocity is not very large. There are many factors which can induce instability of guyed masts, of which the internal resonance and ice coated galloping are primary factors according to theory analysis and data of damaged guyed masts case, so the dissertation emphases on the theory analysis and sample analysis about the two factor which induced instability. The dissertation present the stability criteria of elastic structure system under arbitrary dynamic loads by using the first Lyapunov theory, and build the nonlinear dynamic model of guyed masts, and use the change of energy to show the stability criteria. It can be seen that the criteria is reliable and simple through the stability analysis of classic examples and actual guyed mast structures, it is of advantage for big structures with many elements and nodes. The dissertation present more simple displacement criteria for evaluating the dynamic stability of guyed masts on the basis of summarizing the stability characters and law of guyed masts. The dissertation separated the guyed masts'motion into two parts for parametric vibration, the total motions and local motions. The total motions are 3-D motions of the structure regarding the guys as tension bars, the local motions are the motions of guys with two fixed ends. By using lagrange's formula to combine the two motions, then we can obtain the motion equations in which global-local interaction appears as linear, quadratic and cubic coupling. It is obtained that the large amplitude vibration of guys which is caused by internal resonance can result in the large displacement of guyed mast through coupling interaction, even result in the instability of guyed masts. In the very moist areas, the aerial cables, guys and masts are very easy to be coated with ice when the temperature descend sharply. The ice coated guys may cause galloping owing to negative air dynamic damping, which can cause the catastrophic failure of structures. The dissertation deduced the correlate formula between critical velocity and attack angle on the basis of Glauert-Den hartog formula, the galloping critical velocity can be calculated accurately using this formula, at the same time, it is the critical condition to judge whether the iced coated guyed masts is stable. The wind tunnel test of two guyed masts models on the stability was made inTJ-2 wind tunnel laboratory, some dynamic and instability characters are obtained, and the theory analysis for two models were carried out, so that the theory analysis and experiment results can be verified reciprocally.