Research On The Life Cycle Reliability Analysis Method For Steel Railway Bridge

The basic task of bridge structures design is to meet the needs of structural function with requirement reliability at the most economical way and life cycle is the establishment of reliability. The whole life cycle of structure is the time history which is from design, fabrication and construction to use and insufficiency performance of structural after some years used. The different stages of the whole structural life are the process of interaction and mutual influence and complementary and an organic whole is formed. Therefore, research on the life cycle based on reliability theory has an important practical meaning for the economical efficiency and durability and scientific management of bridge structures.Based on the evolution history of design methods and applied conditions of limit states design codes from home and abroad, the paper gives system study on the design reliability indexes and process of manufacturing operation and reliability of whole life cycle for steel railway bridges. The main research achievements are read as follows:(1) All kinds of calculated methods for the reliability index with their serviceable range, merits and drawbacks are arranged and analyzed. The first order second moment method (JC method) is found to be suitable for the bridge structures.(2) Material properties uncertainty of different materials like Q345qD,Q370qE and Q420qE are derived from the analysis. With the geometric uncertainty and calculation mode uncertainty, the statistical parameters for the resistance of structural member are obtained.(3) The target reliability indexes of ultimate limit states are proposed according to the calibration. For the steel railway bridges with ductile fracture, the target reliability index of the first-level, second-level, third-level of safety classes are separately 4.7,4.2 and 3.7. At the meantime, the partial factors of dead load and live load and resistance are suggested as 1.35,1.2 and 1.4.(4) Based on analogism, 2.3,2.0 and 1.7 are proposed to be the target reliability indexes of serviceability limit states for first-level, second-level, third-level of safety classes. According to analysis of serviceability limit states, vehicle ride comfort and stability are the governing factors under the condition of increasing train load and running speed. Whether the lateral resonance occurs or not has something with the wavelength of hunting motion and running speed of locomotive.(5) Manufacture quality reliability of steel bridge is depended on the reliability of workmanship and human's operation. At the moment, the cumulative function of manufacturing quality in our country is lognormal distribution, of which the mean is 1.12 and the standard deviation is 0.56, the larger of the mean value, the better of the fabrication quality. Most of all, quality impact factor Z w is proposed. According to sensitivity analysis, it is found that time and disposition and management are the main impact factors on human error. As a result, the general function of human error is deduced. Meanwhile, risk levels provoked by accidents from manufacturing are classified. At last, the paper combines human error and its loss, constitutes risk matrix and supplies countermeasures in the face of risk.(6) The equivalent stress range of steel railway bridges can be analyzed by Weibull distribution. During the fatigue reliability analysis with S-N curve and linear elastic fracture mechanics, the relation between manufacture and serviceability is established with the quality impact factor Z w.(7) Lifetime variation curve of the time-dependent reliability is completed in the paper and Weibull distribution function and the Markov chain model can be used to realize the reliability analysis of life cycle for bridge structures.