Damage Monitoring And Health Diagnosis For Arch Bridge Suspender

Suspenders are arguably the most crucial elements of the arch bridge structure. However, they are often suffered from damage due to corrosion, fatigue and anchor head abrasion, what is more, these damages will perhaps cause arch bridge collapse, engendered severe casualties and economic loss, brought great bad social effect. It is very important to develop a series of methods that are monitored and assessed suspender damage.In this dissertation, the suspender tension, fatigue corrosion and anticorrosion cement mortar damage were monitored, and a systemic monitoring and corrosion fatigue life evaluating method was introduced and developed. A field application was examined through these methods.The main contributions of the thesis are given as follows:Firstly, the measurement of suspender tension using vibration menthod is mostly considered that the suspender is idealized as taut strings.This idealization simplifies the analysis may introduce unacceptable errors in many applications. The neural network intelligent methodology was proposed to compute suspenders tension, and design steps and optimization methods of neural network were given. In order to get correct neural network predictive model, 200 data of 20 bridges was used to train the neural network. The applicability of the proposed intelligent methodology was verified by comprasion with the others method through a case study.Secondly, the application of fiber Bragg gratting (FBG) sensors monitored arch bridge suspender stress was inventigated. The bare FBG sensors were directly installed in in-service arch bridge suspender by opening window. Its wavelength shift due to strain and temperature change has been studied theoretically, and theirs sensitivity coefficient was gotten through calibrating experiment. Techniques of installation of FBG sensors, suspender windows repairing and sensors temperature compensation have been explored in-service arch bridge. A new kind of smart glass fiber reinforced polymer optical fiber Bragg gratting (GFRP-OFBG) composite bar was developed to monitor the new constructing arch bridge suspender strain. The GFRP-OFBG sensors installation technology, number, strain and temperature sensitivity coefficient and how to setup transmission line were systemically studied. The different diameter GFRP-OFBG sensor's limit strain was compared. It was verified that diameter 7mm GFRP-OFBG sensor was suit for the application of suspender strain monitoring. Based on these methods and technology, adhere intelligent suspender and replaceable intelligent suspender have been exploited. It was found that the two intelligent suspenders could well monitor the whole tensile process.Thirdly, the suspender tensile damage was monitored using acoustic emission (AE) technique, and AE characteristic parameters of tensile damage were investigated by the new and old steel strand, single suspender tensile experiment. Multiparameter analysis method based on correlation figure was proposed to recognize steel strand break and localization. According to the correlation figure of AE accumulative energy, the steel strand damage evolution process and law can be dynamically analyzed and broken strand numbers and time are judged. Based on the monitoring data, the relationship between AE parameter and damage variables was derived, and the steel strand tensile damage evolution equation is defined with AE accumulative energy relative change. The steel strand damage evolution law was studied applying the AE characteristic parameter time series fractal theory. In the initial stage of loading,the fractal value of steel strand is unsteady. When the cable crack begins its fast propagation, the fractal dimension appears the"increase-decrease"pattern, which could be used to identify the steel strand critical failure.Fourthly, AE monitoring systems for anticorrosion cement motar damage were established. AE characteristics of anticorrosion cement mortar were studied with three-point bending test. Compared with AE counts embraceable curve and load curve, it was found they had a good corresponding connection. Three damage evaluation methods were proposed: 1) Rate process analysis, its statistic model can correctly predict the AE event number and judge anticorrosion cement mortar damage state. 2) AE signal amplitude versus hits correlation figure analysis, in the different stress state embraceable curve of AE signal amplitude versus hits correlation figure can express anticorrosion cement mortar damage evolution process. 3) Fractal theory, the fractal dimension change of the whole damage process can be predicted the anticorrosion cement mortar critical failure. Based on the experiment, analyzed AE mechanics, damage factors were ?defined as variation of AE energy, the equation of damage evolution and the constitutive equations presented by AE parameters were derived. The evolution equation has been verified through experiments. ?Fifthly, the arch bridge suspender fatigue accumulative damage life assessment method was proposed using monitored data. The fatigue stress spectrum of different state arch bridge suspender was otained using different computing method. According to the data of arch bridge suspender monitoring and fatigue model experiment, the computing formulas and steps of suspender corrosion fatigue accumulative damage were given. The fatigue life of corrosive and noncorrosive steel wires was compared, the estimating results were well coincided with the practical case.Lastly, the above monitoring method and assessment criterion were applied in Sichuan E Bian Dadu river arch bridge suspenders and tie cables. The suspender tension and damage was successfully monitored. The different length suspender and different steel strand of the same suspender stress was analysed based on the monitoring data. The tie cables tensile process was successfully monitored utilizing GFRP-OFBG intelligent sensors, which supplied a great reference meaning to construction.