Monitoring Sensor And Mechanism Of Scour Depth Of Brdge Foundation Based On Optical Fiber Vibrating Wire

With the rapid development of society and economy in China,the progress of public infrastructure construction is also accelerating.Among them,as an important part of modern infrastructure construction,the safety and durability of bridge construction project are more and more concerned.Among the reasons that threaten the safety of bridge use,the scour effect of water flow on the bridge foundation is one of the most important factors.Therefore,it is very important to develop an effective monitoring technology for scour depth of bridge foundation.Based on FBG sensing technology,a new type of bridge foundation scour depth monitoring device is designed.The device obtains the change of riverbed scour depth by monitoring the change of fiber chord natural vibration frequency.The main research contents are as follows:(1)The design scheme of bridge foundation scour depth sensor based on optical fiber vibrating string is proposed.On the basis of analyzing the characteristics of bridge foundation scouring process,a design scheme of bridge foundation scouring sensor based on optical fiber vibrating string is proposed.Based on the fact that foundation scouring will change the embedded length of the riverbed sediment to the optical fiber vibrating string,thus changing the natural frequency of the optical fiber vibrating string,the frequency of the optical fiber vibrating string is measured by the FBG sensor in the optical fiber vibrating string,and then the scouring depth of the bridge foundation is inversed.(2)The dynamic model of bridge foundation scour monitoring sensor based on optical fiber vibrating string is established.On the basis of considering the effect of sediment embedment and fluid solid coupling,the Rayleigh Ritz method is used to establish the dynamic model of optical fiber vibrating string under sediment constraint,and the model of inversion of sediment embedment length by vibrating string frequency is established.Through parameter analysis,the influence of various parameters of scour sensor on the above inversion model is obtained.(3)The scour experiment of bridge foundation scour depth monitoring sensor is carried out.The fabrication process and packaging method of optical fiber vibrating string in the monitoring sensor are studied.The flushing depth monitoring sensor model based on optical fiber vibrating string is made,and the flushing water tank device for flushing experiment is designed and manufactured.The experimental results verify the feasibility of the scour depth inversion based on the natural frequency of optical fiber vibrating wire scour monitoring sensor.