Analysis Of Wind-induced Response And Fatigue Life Of High-rise Tower

Wind load is one of the sensitive loads for high-rise towers, which randomly varies over time. In the windy coastal areas of China, Fatigue damage or even failure of high-rise towers is likely caused by long-term wind-induced vibration or extremely strong wind at the time of frequent typhoons landing. In recently years, the related enterprises also suffers great economic loses due to the accidents of wind-induced fatigue problems of high-rise towers. To ensure safe use of high-rise towers in windy areas, How to estimate their wind-induced fatigue lives and analyze their laws of fatigue damage, has become an urgent requirement. However, the dynamic responses and random fatigue life of high-rise towers couldn’t be analyzed by the theory applied in current domestic and international standards or rules, in which wind load is equivalent to static load. Aiming at these problems, the main research work and achievements are as follows.(1) The along-wind and cross-wind time-history samples and wind-induced responses for a typical coastal high-rise tower were simulated at various wind speeds by using MATLAB and ANSYS software, based on random vibration theory, harmony superposition method and frequency characteristic of wind and wind load. Furthermore, the accuracy of simulation was verified through the target values or the theoretical solutions in frequency domain.(2) The wind-induced vibration responses in the empty and operating conditions of this high-rise tower were analyzed. It indicated that, in the range of resonant wind velocities, the tower’s vibration was mainly caused by the cross-wind vibration, induced by vortex shedding, and the empty tower’s resonant response was more violent than that in the operating condition. But when away from the resonant wind velocities, the tower’s vibration was mainly due to the components of the turbulent flow, the response values exponentially increased with increasing wind speeds, and these response values in the operating condition were greater than those in the empty condition at the same wind speeds.(3) The wind-induced fatigue life of this high-rise tower was estimated and analyzed, including considering the changes of wind speed and direction, typhoons, and resonant vibration of the empty tower, based on rain-flow method, Miner fatigue cumulative damage theory and fatigue design S-N curves on BS5500. It was concluded that, in the supercritical range where the vortexes were shedding randomly, the deterministic cross-wind resonant response values might be conservative for fatigue life estimation of this tower, computed by Rumman’s theory in JB/T4710. Cross-wind resonance was the decisive factor of wind-induced fatigue for this empty tower, while the along-wind vibration was the mainly reason leading to fatigue damage of this operating tower, caused by the strong gale and stronger wind. If this tower contained defects or high stress concentration in operating condition, several strong typhoon loads might cause it significant fatigue damage and even failure.The analysis methods of wind-induced vibration response and wind-induced fatigue supplied by this dissertation can also be applied to the related analysis of other high-rise vessels in windy areas. Therefore, it provides some insight into vibration control design, Safety assessment and so on for high-rise vessels.