Research On Health Monitoring System And Condition Assessment Of Large-Scale High-Speed Railway Bridge Structure

Due to the high-speed train running, and the interaction of the long-term environment corrosion, material aging, fatigue effect of vehicle loads and other factors, damage cumulation and resistance attenuation of high-speed railway bridge structures inevitably occurred, which necessarily affects the normal use of structures, and will lead the decline of capability of resisting nature disaster and the function of normal environment, furthermore some components’damnification perhaps expand fast, and in extreme cases, catastrophic accident will suddenly happen. In order to ensure structure security, suitability and durability, the research work is taken health monitoring system which met large-scale high-speed railway bridge characteristics, and condition elevation based on large-scale high-speed railway bridge monitoring data as center. The main research results are as below:1. The research results in related field at home and abroad have been collected; then the health monitoring process, the developing situation of high-speed railway, and the existed bridge status elevation theories are systemically expatiated.2. The construction situation of large-scale high-speed railway bridge at home and abroad has been summarized. Then "Health Index"of high-speed railway bridge structure had been defined; For different bridge types, there are some differences between structure characteristics and health index, which shows the difference of the index system of different bridge types. Afterwards, the developing trend of large-scale high-speed railway bridge structure has been predicted. Finally, in the health monitoring process, vulnerability of the large-scale high-speed railway bridge should be fully understood, and the vulnerable parts should be identified. Nanjing Da-sheng-guan Yangtze River Bridge (the representative large-scale bridge in Beijing-Shanghai High-speed Railway) was taken as an engineering analytic example to make static and dynamic force analysis on the basis of existed research methods&theories. On the one hand the vulnerable parts can be easily found, on the other the hand health indexes of high-speed railway bridge structure, such as natural frequency, amplitude, acceleration ratio of deflection to span and so on, can be understood quantitatively.3. Health monitoring system of high-speed railway bridge structure should be mainly focused on dynamic monitoring, especially superstructure’s down deflection and substructure foundation’s settlement. Due to the low natural frequency of high-speed railway bridge(usually less than1Hz), sensors with high sensitivity, low-frequency response and wide dynamic measurement range are chosen to test low-frequency vibration, whose low-frequency response can reach0.1Hz even0.01Hz. Otherwise, when high-speed trains pass through the bridge, high-frequency vibration may be caused, so the sensors should also have high sampling frequency. After making comparison, sensors suitable for health monitoring system of high-speed railway bridge structure are given, and the specific requirements of each sensor’s main technical indexes are also proposed, combined with high-speed railway bridge characteristics.4. A systematic study has been carried out on the problem about optimal sensor placement. Firstly, the two optimal sensor placement methods, which based on modal observability (denoted by "Method A") and damage identification (denoted by "Method B"), are separately applied. And each fisher information matrix can be denoted as QΦ and Qs. Then the double criterions’ objective function (fisher information matrix’s trace value reaches max, simultaneously coefficient matrix’ condition number reaches min) was established, according to the matrixes’ own characteristics and suitable criterion. Finally, due to the inconsistent results of the two methods, in this paper "Method A" was given weight coefficient of0.4, and "Method B" was given weight coefficient of0.6. So the role of each method’s degrees of freedom remaining to be selected is expressed as a percentage multiplied by corresponding weight coefficient. In this way, the final optimized result is the superposition of the two types of information, not only considering each degree of freedom’s modal information in undamaged structure, but also considering each degree of freedom’s damage sensitivity information. The whole optimization process can be called "Weighted Information of Degree of Freedom Method". Take Nanjing Da-sheng-guan Yangtze River Bridge as an engineering example, using "Weighted Information of Degree of Freedom Method" to optimize its acceleration sensor. The optimization result was agreed with the numerical results, so the proposed method in this paper was verified correct. At last, sensors satisfied the accuracy requirements were selected to conduct the overall layout of monitoring points.5. Combined with "Fundamental code for design on railway bridge and culvert"(TB10002.1-2005),"Railway Bridge Verification Standard"(2004),"Code for Design of High Speed Railway"(TB10621-2009) in China,"Railway Structure Design Standard" in Japan, and "EUROCODE" in Europe and so on, dynamic index limit standards at home and abroad about high-speed railway bridge were introduced firstly. Afterwards, this paper compared each dynamic index limit between normal-speed railway bridge and high-speed railway bridge, and analyzed the differences between them in detail. Certainly, dynamic index limits about high-speed railway bridge structure at home and abroad also have a comparison, and the result shows that the type and corresponding dimension of dynamic index are similar, which reflects the connection of the specifications at home and abroad. Finally, summarized the dynamic parameters of large-scale high-speed railway bridge structure which has been built, and done some preliminary study on bridge transverse&vertical stiffness and vehicle parameters’limit standards.6. The condition assessment contents of highway bridge, normal-speed and high-speed railway bridge had a comparative analysis. Then the index system of condition assessment was established on the basis of large-scale high-speed railway bridge characteristics. Since some indexes’normal/ordinary value or safety limit are unknown, it’s difficult to evaluate structure condition by using dynamic parameters directly. So dynamic parameters change was chosen as a benchmark to evaluate structure condition. Supposed on stationary random process and approximate a normal distribution, and according to this statistical regularity and the concept of confidence level and confidence interval, status levels of large-scale high-speed railway bridge can be divided into different parts. Each level was quantitatively controlled by confidence interval, and qualitatively described the usage of various levels, which unify the qualitative and quantitative methods. The weight of each evaluation index was solved by using the Uncertain AHP (analytical hierarchy process), Set-valued Statistics and Barycenter Decision Theory. Evaluation model of large-scale high-speed railway bridge was established by Internal Extension Evaluation Theory, and specific evaluation process was given followed by. Finally, take Caiyuanba Yangtze River Bridge as an engineering example to assess its operating conditions.