Research On The Control Of Wind Cable For Long-span Suspension Bridge Aerostatic Instabilityand Buffeting Vibration

With the increase of the cable structure bridges’ span, their stiffness and damping aredeclining, and the bridges are more sensitive to wind loads. In most cases, wind resistance ofthebridges become the primary problem in bridge design.This paper choose the Aizhai bridge asthe engineering background. It studies the static instable velocity, the changing process of thedisplacement of the midspan nodes with different wind speed and buffeting response under thenatural wind after applying wind cable for bridge. It provides reference for similar bridgedesign.Firstly, finite element model of the original bridge and applying wind cable on the bridgeare built, study the law of four kinds of wind cable parameters’ effect on the dynamiccharacteristic of bridge by changing the angle about pull rod of wind cable and bridge deck, thelength of pull rod, the cross sectional area of wind cable and pull rod and the initial strain ofwind cable and pull rod. The optimal parameters of wind cable are determined by comparingkey frequency of bridge. The calculations show that: applying the wind cable makes eachfrequency of bridge increase and showing the stiffness of bridge increase. The vertical schemeof90degree works well for the angle of pull rod of wind cable and bridge deck; changing pullrod’s length has an inconspicuous effect on dynamic characteristics of the bridge; The crosssectional area ofwind cable and pull rod is the bigger, the increasing ofthe frequency of bridgeis more obvious. The increasing initial strain of wind cable and pull rod has a obviousincreasing effect the order frequencyofbridge.Secondly, the linear method is used to calculatethe instable criticalwind velocityofbridgebefore and after, three dimensional nonlinear method is used to calculate the displacement ofthe midspan node and the change of axial force of main cables with the different wind velocitybefore and after applying wind cable wind. It can be obtained, after applying the wind cable,the instable wind velocity of transverse heeling is improved10.1%, the instable critical windvelocity of static force torsion It can be found by the changing of axial force of main cables: isimproved8.9%and the displacement of the midspan nodes reduce clearly. The instable windvelocity is120m/s before applying the wind cable,however, axial force ofmain cable changesgently after applying the wind cable, axial force has no mutational distribute until the wind velocity is180m/s. It shows that the stiffness and stability of structural are improved afterapplying wind cable.Finally, according to the random vibration theory, MATLAB software is used to simulatehorizontal pulsation wind and vertical pulsation wind of the midspan.Random wind istranslated to random buffeting force by Davenport buffeting force model. It is show bycalculating the time-history response of structure that: amplitude of bridge is decrease, and theeffect ofresisting wind is clear after applyingwind cable.By calculating the aerostatic instable critical wind velocity, the changing process of themidspan node with different wind speed and random buffeting response, results show thataerostatic critical wind velocity is increased, after applying the wind cable,It makes the verticalaverage amplitude has a increase.It has a strong restrain effect to the lateral, torsion amplitudeof bridge and the amplitude is more stable, show that the wind cable has a good effect on windresistance.