| With the rapid development of the cable-stayed bridges,as its number increases,the span is growing and more sea-crossing bridges are emerging.The cable is an important part of the cable-stayed bridge,because of its flexibility,light weight,small damping;it is very easy to vibrate seriously under the rain-wind load,causing fatigue damage,reduce its service life.In this paper,the study on fatigue damage of stay-cables in offshore and the MR damper on the vibration control of stay-cables include the following aspects :(1)Using harmonic superposition method and linear filtering method to simulate the fluctuating wind speed.The simulation results show that the horizontal and vertical wind velocity time history curves have good randomness,and the deviation between the simulated power spectrum and the target power spectrum is small.The harmonic superposition method is based on the discrete spectrum simulation of the stochastic process,the algorithm is simple and practical.If the number of simulation points are very big,the Fourier algorithm is used to improve the calculation speed.(2)In this paper,the buffeting response of the stay-cables under fluctuating wind load is studied by using the time domain analysis method,and the fatigue life of the staycables is predicted by the S-N curve,the Miner linear fatigue damage criterion and the rain flow counting method.Calculating and analyzing the factors of the stay-cables on affecting the fatigue damage.The influence of stay-cables diameter,length,damping ratio,inclination angle and wind load on the stay-cables fatigue life is obtained.The bigger the diameter and the inclination angle of the stay-cables,the shorter the fatigue life;with the increase of damping ratio of stay-cables,the service life is increased;the greater the wind speed,the shorter the life of the stay-cables;The change of the length of stay-cables has a significant effect on the fatigue life.Based on the dimensionless analysis of the staycables,concluding that the damping ratio,length and the wind load are important to fatigue life of stay-cables.Then the fatigue reliability index of the stay-cables is calculated.Its value is far less than the target reliability index,so the reliability of the stay-cables needs to be improved,especially in the extreme catastrophic climate environment.(3)Through the comparison of pulsating wind power spectrum codes,considering the average wind along the height change and change effect of fluctuating wind turbulence intensity and turbulence integral scale of stay-cables fatigue life,different specification wind spectrum on fatigue life of the stay-cables has a certain influence,considering the influence of different wind velocity spectrum to the national standard in some multinational in engineering.With the increase of the ground roughness and the height of the ground,the life of the stay stay-cables is getting smaller and smaller.(4)Firstly,the influence of the type of MR damper,the installation position and the voltage on the fatigue life of the stay-cables is studied.The fatigue life of the stay-cables increases with the increase of the damper type,installation position and voltage.The larger the damper model is,the better the damping effect of the stay stay-cables is.The higher the installation position,the greater the voltage,the better the damping effect.Secondly,the semi-active control algorithm is studied,and the results show that the semiactive control algorithm based on the displacement and velocity direction and the semiactive control algorithm based on the optimal control force is ideal,and the effect is stable.When the type of the damper,the installation position and the applied voltage change in a certain range,the life of the stay-cables has been effectively improved,which ensures the stable working state of the stay-cables in the service period.Thirdly the fatigue damage of damper is studied.According to the analysis,it can be seen that the steel will not be damaged.However,in the long-term use of the damper,there may be oil leakage at the piston,the rubber material will also occur under the action of the damper output fatigue failure.Finally,in the engineering example,the comparison between the damper and without damper is carried out to verify the effect of damper control.(5)Building finite element model of the Hangzhou Bay Bridge south bridge and studying on fatigue life of stay cables under buffeting.The number of fatigue damage on the Z15~Z20 cable analysis available in the full bridge state,response of tower and the main beam under the action of wind load on the cable has a great effect,and that the cable length is the key factor influencing the fatigue life.According to the calculated fatigue reliability,the fatigue failure of stay cables under the average wind speed of 100 years in 50m/s will not have enough reliability. |
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