Fatigue Reliability Analysis Methods And Application For Slab Track Structure

Based on foreign advanced technology and design methods, a large number of test section and engineering construction practice are conducted during these years. China’s ballastless track technology with independent intellectual property rights and systematic ballastless track design theory are gradually developed. Ballastless track with its high smoothness, high stability and low maintenance features are widely used in high-speed railway and passenger railway line. However, owing to the load, structural and environmental parameters in ballastless track exists evident stochastic characteristics during the service, the current ballastless track design theory and methods does not reflect the real needs in structure fatigue resistant design and also difficult to accurately analyse the fatigue performances of the structures. In this dissertation, based on the structural reliability theory and the practical demand of the ballastless track, a fatigue reliability analysis model and methods is proposed to analyze the fatigue performance of the slab ballastless track(SBT). The studies have been carried out in this dissertation as follows:(1) According to the literature review and the practical demand of ballastless track structure during long-term service, a mathematics model is developed to describe the stochastic load, structure and environment parameters in ballastless track. Then a vehicle-track-foundation coupling system dynamic simulation finite element model is established to analyze the distribution characteristics and statistical parameter of the train loads acting on the rail of SBT under the excitation of track longitudinal irregularity. Finally, the Monte Carlo simulation method is proposed in generating sample of the stochastic load, structure and environment parameters.(2) The elastic foundation multi-composite beam model is corrected in computing the lateral moment of structures in SBT. Based on the corrected model, a methodological framework of analyzing the distribution characteristics of train loading effect (moment) of the structure in SBT with stochastic parameters is proposed. The train load, fastener stiffness and foundation coefficient are selected as stochastic parameters, and generated as a stochastic sample by Monte Carlo simulation method. In this way, the distribution characteristics and statistical parameter of the moment of track slab and base plate in SBT with the selected stochastic parameters are presented.(3)According to the heat transfer theory, a temperature field equation for the SBT is derived. Based on this equation and the city’s historical meteorological data, the gradient temperature action (includes common values and daily maximum values) and axial uniform temperature action (includes common values and daily average, amplitude and maximum values) of the track slab and base plate in SBT for the city are figured out. And a statistical analysis is carried out to analyze the distribution characteristics and distribution parameters of the temperature action of the track slab and base plate in SBT. Based on the probability model and distribution characteristics of the temperature action, a method is proposed to determine the representative probability values of the daily maximum temperature action for the SBT. Take into account the requirements of related criteria and SBT’s feature, this dissertation proposed the suggested values of the daily maximum gradient temperature action and axial uniform temperature action for some cities in China.(4) The potential fatigue failure mode and its characterization index of the track slab and base plate in SBT is developed based on the potential damage patterns and structural feature. Take into account the fatigue performance of the concrete and rebar in reinforced concrete structure, this dissertation is presented the reliability analysis model and limit state equation of the potential fatigue failure mode for track slab and base plate of SBT in non-environmental condition. An attenuation function φ(t) is introduced to reflect the environmental effect of carbonation in atmospheric conditions or freeze-thaw cycle in cold environment on the fatigue performance of the concrete and rebar materials. Based on laboratory test and theoretical analysis, the reliability analysis model and limit state equation of the potential fatigue failure mode is derived to evaluate the fatigue resistant for track slab and base plate of SBT in environmental condition.(5) Based on the reliability analysis model and limit state equation of the potential fatigue failure mode for track slab and base plate of SBT in non-environmental condition and environmental condition, this dissertation analyzed and evaluated the reliability index and failure probability of the fatigue resistant of each potential fatigue failure mode for track slab and base plate of CRTS-Ⅱ (CRTS is an abbreviation of the China Rail Transit Summit) and CRTS-Ⅲ slab track in different regions and different environments.A series of studies on the fatigue reliability analysis model of SBT are carried out in this dissertation, such as theoretical analysis, laboratory tests and numerical simulation. These researches will promote the development of fatigue reliability analysis methods of SBT, and will provide a new way to improve the fatigue resistant design and fatigue performance evaluation for SBT.