| Fatigue cracking problems in the orthotropic steel deck of bridges have been extensively reported in many countries, which have become a predicament during the bridge design, construction and maintenance. Facing great challenges, many scholars have carried out studies on fatigue problems of orthotropic steel deck, published numerous articles and acquired certain achievements. However, there is still a great space left for the further in-depth study. The problem of how to scientifically assess the fatigue life of a steel bridge deck in its operation stage so as to timely make corresponding inspection and preventive maintenance is of great theoretical significance in aspects of improving the durability of steel bridge deck and saving high maintenance cost, and also has practical values.In recent years, with the rapid development and wide application of the bridge health monitoring technique, vast numbers of useful data are obtained in the operating process via the sensors installed in the bridge. Based on the health monitoring system for Balinghe River Bridge in Guizhou Province, the study of how to make rational application of the measured data got from the health monitoring system to assess the fatigue life of structural details of orthotropic steel bridge deck is presented in this paper. The fatigue life evaluation of Balinghe River Bridge is intensively carried out based on the nominal stress method, hot spot stress method, the vehicle load spectrum method and the new fatigue life gauge method. At last, the time-dependent fatigue reliability method is adopted to decide on the orthotropic steel deck inspection strategy with the purpose of reducing inspection costs and enhancing inspection efficiency. The main work and obtained results are as follows:1. The history of the development of orthotropic steel deck is reviewed; the common cracking locations are summarized and analyzed. The evolution of the structural details are described in detail, including the evolution of the longitudinal rib type, a reasonable evolution of the stiffness and the evolution of the connection details. The latest techniques of orthotropic steel deck fatigue monitoring, including WIM system, FBG monitoring technique and fatigue life gauge technique are summed up.2. The analysis and process of the dynamic stress monitoring data for the bridge health monitoring system is studied. A systematic study is carried out for the layout of nominal stress monitoring testing points, the choice of the fatigue strength, the analysis of stress monitoring data and the fatigue life evaluation based on nominal stress. Based on the nominal stress method and the measured data from the monitoring system, the fatigue life evaluation of Balinghe River Bridge is realized. The results show that the fatigue life of Balinghe River Bridge meets the design requirements under the action of current traffic loads.3. Fatigue life evaluation technique based on the hot spot stress method is studied. The hot spot stress concentration factor of each and every fatigue details of steel bridge deck is analyzed. And a systematic study and summarization for the layout of the hot spot stress testing points, the derivation of the hot spot stress fatigue strength, the analysis of hot spot stress monitoring data and the fatigue life evaluation based on hot spot stress is conducted, upon which fatigue life evaluation procedures based on hot spot stress monitoring are established. By means of the measured data from the monitoring system, the fatigue life evaluation of the orthotropic steel bridge deck of Balinghe River Bridge is realized. The results indicate that the hot spot stress evaluation method simplifies the form of welding, reduces the dispersion of the results, and is superior to the nominal stress method.4. Fatigue life evaluation technique based on the vehicle load monitoring is studied. Based on WIM systems, the bridge vehicle traffic flow and vehicle weight are statistically analyzed and the vehicle weight probability model is established. The probability model of vehicle spacing is established based on Poisson process and the random team load as a fatigue design load is simulated by the Monte Carlo theory. The standard fatigue truck and the random fatigue load are selected for highway bridges in the western mountainous areas in China, the axle frequency value spectrum and random axle frequency value spectrum are derived for orthotropic bridge deck. The fatigue life of conventional fatigue details of the orthotropic steel deck of Balinghe bridge is evaluated. The results basically agree with the results based on the stress monitoring, under the current traffic condition, the actual service life is longer than the design life.5. Fatigue life evaluation technique based on the new fatigue life gauge is studied and the fatigue life evaluation method based on the new fatigue life gauge is proposed. Combined with the deduced standard fatigue truck, the relation of the change in resistance value and the cumulative damage is derived and established. And then, the fatigue life can be calculated based on the change of resistance value. The new fatigue life gauges installed in Balinghe River Bridge and the analysis of the measured data indicate that the fatigue life gauge is a sensor which has the capacity of fatigue load accumulation and memory, its irreversible resistance changes record alternating strain history of monitoring points, which is suitable for long-term fatigue damage monitoring of long-span bridges.6. One of the major purposes of fatigue monitoring and life evaluation is to provide references for the inspection and maintenance of steel bridge deck. Thereby, the inspection strategy based on fatigue dynamic reliability is proposed accordingly. The fatigue limit state equation is established, meanwhile, the formula of fatigue dynamic reliable indicator is proposed to calculate the time-dependent reliability index of steel bridge deck. The relation between the inspection strategy and fatigue reliability is built, so as to provide references for making scientific inspection strategy. Compared with the traditional regular inspections, the inspection method based on fatigue reliability has significant advantages. |
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