Research On Wind Induced Vibration Of±800kV DC Cross-rope Suspension Tower-line

A cross-rope suspension (CRS) tower is mainly composed of two pressurizedlattice angle-steel columns and a tensioned guy suspension cable system. Such a tower,if comparing with the other free-standing power-transmission towers, features for itsvarious advantages such as clear stress, little steel quantity, and easy installation. Windload is the main controlling load factors due to its structural property of large span andhigh flexibility. However, such type of tower is seldom used in projects because of itslarge floor space and maintenance workload. With the successive projects of powertransmission from the western to the eastern region in China, some power lines will passGobi and desert areas where the cost of space occupation is quite low, thus highlightingthe economic advantages of cross-rope suspension towers. Therefore the research andanalysis of wind-induced vibration concerning such type of towers are becoming evenmore important. In this thesis, effort has been made in various aspects with themethodology of the combination of wind-tunnel test, finite-element modeling and thetheoretical analysis.①A rigid double-mast model is made with the high-frequency balance techniquein the wind-tunnel test for the research and study on the wind characteristics of asingle-mast and double-mast system in Type-B landform turbulent flow and uniformflow field. The basal bending moment power spectrum is obtained at various directionsof along wind, cross wind and torsional wind for a single mast and double mastrespectively under different shielding effect in turbulent flow field. Then a dynamicwind-load analytical model is established based on the result of the above-mentionedtest. The drag coefficientsare measured in the uniform flow field, and the along-windresistance coefficient is compared with the corresponding standards made by variouscountries. The result shows that the value based on the standard of China tends to beunsafe.②The aero-elastic model of cross-rope suspension tower and the tower-linesystem are designed and fabricated. The foundation unit of the entire tower isthoroughly processed for mast bottom hinge connection and initial pretension oflines. Also the wind-tunnel test is conducted for the research of its wind-inducedresponses. The wind load transferring mechanism of tower-line system wasrevealed. The results show that the leeward guys tend to be slack and compression on leeward mast decreases when the wind speed increases. Oppositely, the tensionin windward guys and compression on windward mast increases with the windspeed enhancement.The results also show that the changes of guy initial tensionhave a significant influence on mechanical properties of tower-line system underwind load condition.Thus the guy initial tension should be selected optimally.③A finite-element model of cross-rope suspension tower system is established,and the dynamic time-history analysis with harmonic wave superposition method isconducted. The two key structural parameters such as cross-rope sag-to-span ratio andguy pretension are studied, and their influences to the three wind-induced vibrationresponses such as guy tension, the counter-acting force of mast support, and thealong-wind displacement of the mast top, the results show that the value of cross-ropesag-to-span ratio should be greater than1/9and the value of guy pretension should lessthan30%of its design bearing capacity. On this occasion, the tension in guys andcompression in masts would maintain in smaller values, which can lead to a much morereasonable structure.④In consideration of the nonlinear characteristic of cross-rope suspension tower,its wind-induced responses are further studied and discussed. Under the action of windload, the guys would be in tension and the masts would be in compression.So theconcept of peak factors based on the conventional static equivalent wind load isdeveloped, so as to conduct wind-resisting design for the pressurized tower masts andthe tensioned line components.⑤A simplified mechanical model of a cross-rope suspension tower on the basisof the test result is established. Modeling on kinetic equation with the application ofHamilton principle has been conducted, and thus the partial differential equations ofmotion is obtained, and then the above-mentioned partial differential equationsaredisassociated into ordinary differential equations through Galerkin method. Based onthe nonlinear vibration, the main resonance pattern within the system range is furtherstudied, and the steady solution is obtained by dissolving the ordinary differentialequations with approximate analytical methods, and finally the stable range of thesystem through Lyapunov’s stability theorem is obtained.Finally, on the summarizing of this thesis, further study of the problems is proposed.