Fiber Optic Sensor And Its Applications In Strain And Deformation Monitoring Of Cable-supported Grid Structures

Cable-supported grid structure has become one of the standards for one nation’s architectural technology.However,along with the development of novel structures there now exist many risks and challenges during the construction period.Therefore it is urgent and significant to conduct effective,real-time and long-term structural health monitoring(SHM)system to prevent cable-supported grid structures from engineering accidents.Generally speaking,the basic unit of a complete structural health monitoring system,fiber optic sensors(FOS)can be divided into two categories:quasi distributed fiber optic sensors and distributed fiber optic sensors(DFOS),based on their measurement ranges.In this article a series of researches has been performed as follows.(1)Among the quasi distributed fiber optic sensors,the most representative sensor is fiber Bragg grating(FBG)sensor which has been fully developed and commercialized by far.However,limited by the intrinsic property of optic fiber,FBG sensors are sensitive to both strain and temperature.But the construction period of a cable-supported grid structure would usually last for years when the temperature effect cannot be ignored.In order to solve this problem,a new method to package a FBG sensor is brought up based on the working principle of FBG sensors.This package structure utilizes negative thermal expansion material to neutralize the fiber wavelength changes caused by temperature.In this way,FBG sensor is insensitive to temperature.Experiment tests and application in real engineering have proved the effectiveness of the FBG sensor insensitive to temperature.(2)The advantage of DFOS mainly lies in the long range of sensing distance which can cover most area of a complete structure.In this article,the strain measurement result of DFOS is used to reconstruct structural deformation.For rod elements,deformation reconstruction algorithm in space is derived on the basis of plane deformation reconstruction theory.Through experiment tests,it has been proven to be effective.For plate elements,a new sensor layout is designed based on the principle of strain rosette.With the aid of inverse finite element method,the deformation of plate structures is reconstructed.(3)The structural characteristics of cable-supported grid structures request numerous and different types of sensors to evaluate the safety status of the structure.A data acquisition device is very crucial in data collection system.In order to demodulate signals of different sensors synchronously,the Distributed Complex Multi-Sensor system is introduced from the hardware level and software level.It has realized signal demodulation of different types of sensors in just one device and all sensors can work collaboratively.Therefore real-time structural health monitoring is possible which is very important due to the fact that the structural safety need to be determined within the shortest time.The DAQ device and FBG sensor insensitive to temperature have been applied in SHM system of Olympic Sports Center Stadium in Zhengzhou.Monitoring result are analyzed to explain structural behaviour in different construction stages.