| Strain is one of the most important parameter of stress loading and health of engineering structure.And it is an important item in scientific management and calamity early warning of key infrastructure utilities.In engineering field,a lot of parameters can be converted into strain amount.Currently,traditional strain detection equipments mainly use electrical strain gages,however,due to the zero drift,strain gages are difficult to implement long-term on-line measurement,and difficult to immune from electromagnetic interference,and also difficult to perform well at harsh detecting site with humidity and pollution environment.Fiber Bragg grating(FBG)strain detection technology is a new detection technology.It is of high sensitivity,and can be converted the strain into measurable optic wavelength signal.It has the advantage of long life detection,high precision,electromagnetic interference immune,and corrosion resistance.Its light signal avoids the problem of zero drift.It can also do networking and do remote detecting.Comparing with the strain gauges,its advantages are much better.Based on FBG strain measurement technology,and based on its theory,method and application,and according to the main line of study on strain detection theory,strain sensing device,and strain detection system,this thesis takes a variety of methods,such as theoretical analysis,numerical simulation and experimental test,to study and to research.The main research contents are as follows:(1)Research on FBG strain sensing characteristics and its strain transfer law.Based on the elaboration of the characteristics of FBG strain sensors,the strain transfer rules of three encapsulation styles are analysed: surface gluing,embedding,and suspended gluing.The influence of average strain transfer efficiency from the interlayer structure parameters and material parameters are simulated and analyzed,that suspended gluing style of an FBG could avoid the loss of strain transfer.So,it is a correct encapsulating method.The principle of strain increasing/decreasing of above three encapsulation methods is researched,and an FBG holding method of clamping type is an advantageous way of reducing strain transfer loss.The principle of eliminating temperature influence in strain sensing is also discussed,and shows that double-grating method of temperature compensation is a better way in engineering application.(2)Development of FBG strain sensing device.According to the requirement of structure strain measurement and considering in aspects of structure design,material selection,strain increment and temperature compensation,various strain sensing devices are designed.There are:(a)By means of theoretical analysis and according to the demand of structural strain detection,a ring type FBG strain gauge is designed.Its FBG is suspended glued.This gauge avoids strain transfer loss,and is of sensibility increasing,and and its sensitivity coefficient is adjustable.Convenient in assembly is also its advantage.(b)According to the demand of weigh-in-motion(WIM),FBG stress cells with twin-bore parallel beam are designed.Repeated experiments between two diffent material,steel alloy 40 CrNiMo and aluminium alloy LY12 show that the repeatability accuracy of 40 CrNiMo is 4.45 times high as LY12.(c)According to the requirements of strain test of high rigid structure,An FBG strain sensor with sensitivity increasing function is designed.Its advantages are 7 times higher of sensibility increasing than detecting directly and damage free in installation.(d)According to the requirements of displacement mearsurement,An FBG displacement sensor with double FBG is designed.By means of a spring,strain signal can be changed into displacement signal.It has therefore an effect of sensitivity decreasing.Temperature compensation methods of above four kinds of sensors are also studied.The results are good.(3)Research and development on WIM method of commodities in bulk by FBG strain sensing device on a belt conveyor.According to the demand of research project,its basic principle of WIM is introduced.A dynamic measurement algorithm of FBG strain measurement system was established.Weighing cells with traditional Wheatstone bridge strain gauges were replaced by FBG strain cells,and an FBG weighing system was built on a belt conveyor.In this system,double scale frames were used,conveyor belt speed was obtained by the method of time delay estimation.The electric belt speed meter was therefore eliminated.Belt conveyor weighing without electricity was achieved.The works of measured data simulation and weighing accuracy test were also discussed.Application in SINOPEC shows that in harsh working environment,the system works stably for a long time,weighs more than 30,000 tons coal,and its accuracy is 0.5%.This result shows that this application is successful.(4)Research on dynamic monitoring method of conversion resistance of railway switch by FBG strain sensors.Based on analyzing the principle and structure characteristics of the switch,FBG strain sensors of switch action bar and their nondestructive installation way,and the monitoring method of switch conversion state were developed.In the engineering application of Hankoubei station of Wuhan Metro Line 1,dynamic resistance curves of various states of switches were obtained.The monitoring results showed that for a Siemens S700 K switch machine,its pole pressured stroke took 5s,maximum load:-5.9kN,average load:-3.3kN.After the stroke,the locking force was kept at-0.6kN.In tensile stroke,it also took 5s.Maximum load: 6.8kN,average load: 5.5kN,locking force: 0.2 kN.At present,there is no report to mention this monitoring way,neither at home nor abroad.(5)Research on remote online monitoring method of multi-parameter of ballastless track on high-speed railway bridges with long span beam.The necessity of long-term monitoring in track stress and deformation on high-speed railway bridges is discussed.According to different monitoring requirements,monitoring methods and FBG strain sensing devices were developed,such as track strain sensors,track displacement sensors,track plate displacement sensors,convex table displacement sensors,and crevice displacement sensors between two longe beams of a long span bridge.In this thesis,respectively taking the applications of remote monitoring of ballastless track plates CRTS I of high-speed railway bridges with long span beam as examples,a curve of track strain in three months shows that the strain changes in a period from spring to summer or in a period of a day,and it meets the low of expanding when heated and contracting when cooled.A curve of track displacement in 18-month,further shows an annually periodic variation of displacement.These examples also show the superiority of long term monitoring of FBG.This monitoring of ballastless track on long span bridge is a creative work.The positive effects in this paper,hope to be able to promote FBG engineering application and to promote the transformation of research achievements. |
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