Research And Development Of A Wireless Monitoring System For Stay Cable Vibration Control

The cable-stayed bridges are widely used because of their simple structure,beautiful appearance and low cost.However,as the main force structures of cable-stayed bridge,the stay cables are so light,small and flexible that in particular,it's easy to vibrate by a large margin with the action of transverse wind.So it's obvious to find that the quality of stay cables may influence the driving safety and also shorten the working life of bridges.Therefore,in order to ensure the driving safety and prolong bridge life-span,it is necessary to take effective measures to reduce the vibration of the cable.In recent years,particularly with the enlargement of the span and the elongate cables,it becomes more and more difficult to control the cable vibration.Of the two vibration,the control mode of passive vibration is limited,while the cost of active vibration is high but low security.Besides,recent studies have shown that the semi-active control method based on adjustable magnetorheological damper(MR damper)can make up the imperfection of passive and active vibration,and in the meantime this method may has an excellent control effect.In this paper,a new development system based on MR damper aims at closed loop control and wireless monitoring of cable vibration.The research contents are as follows,(1)A closed loop system is designed to control the vibration of stay cable by using the DSP chip as the control core,and combining with the MR damper and acceleration sensor.This system can accomplish the real-time acquisition of the acceleration signal,the extraction of frequency information,the output control voltage and the voltage conversion current MR damper and other functions.At the same time,the system employs ZigBee wireless module to communicate and combine with the monitoring system developed by LabView software thus it makes the signal transmission and monitoring of the cable vibration control system true.(2)In the case of reliable RS485 communication,compare the RS485 and ZigBee communication data transmission results;in addition,in the lower position machine set fixed transmission signal,realize the wireless communication between the host computer and the next bit machine;through the two experiments,verify the feasibility of ZigBee wireless module in the near distance communication.On the basis of reliable ZigBee wireless communication,the FFT algorithm and output control voltage of the vibration control wireless monitoring system are verified.The experimental results show that the vibration control of the whole system and thewireless transmission parameters are correct.(3)In order to realize the wireless transmission of long-distance and large-data-quantity signal,this paper conducted the design and and performance tests of different application-layer communication protocols between superodinate and subordinate computers and of different antenna orientations for the coordinator and terminal node.The tests verified that the communication protocol using with-identifier-data packet had more stable performance than that using without-identifier-data packet,and that the vertical antenna direction for both terminal node and coordinator showed best communication performance for the near-ground communication.The studied wireless communication module realized 90% or above data-receiving-rate within 350 m communication distance.The designed system can be used in the wireless communication of long distance and large data quantity of civil engineering structure(especially long span bridge)for health monitoring.(4)The vibration control of wireless monitoring system applied in Taizhou Jiaojiang bridge cable,and the whole system is field vibration function debugging and wireless data transmission effect analysis.The wireless communication results show that the data transmission is correct,and the data receiving rate in more than 90%,which basically meet the design requirements.At the same time,the vibration control effect of the vibration control system installed on the bridge under the influence of typhoon is analyzed,and the existing problems of the system are found out and the solution is put forward.