Research On Safety Evaluation Of Heavy Haul Railway Steel Bridge

With China’s rapid economic development in recent years, the railway bridges are carrying increasingly heavier traffic. At present, one of the development trends of domestic and foreign railway is by the way of increasing the train axle weight to increase traffic capacity and improve transport efficiency. Moreover, the manufacturing technology of railway freight cars in our country has been close to or reached the international advanced level, we have already had the ability to produce the large axle load freight cars. In this case, the problem that whether the existing steel railway bridges have the abilities to carry the heavy haul transportation, that is to say,if the existing bridges can meet the safety requirements in bearing capacity and fatigue performance etc, these problems need to study deeply. In addition, with the continuous progress of the construction technology of bridge in our country, the span of the steel is increasing constantly, and the structure is also in constant innovation, so a large number of new structural details are emerged. The problem that whether fatigue properties of a new type of structure details can meet the requirements of heavy haul transportation, also need to be concerned.In order to solve the problems that may occur after existing bridges carrying heavy haul traffic, from the point of view of the bearing capacity, fatigue loading characteristics and fatigue life evaluation etc, by the means of calculation and analysis, fatigue tests of the key structure details, the following aspects are studied.The minimum load incremental method of the failure tree theory is used for calculating the ultimate bearing capacity. Two typical steel trusses are selected, calculation and analysis of their ultimate bearing capacity under the design load, 27 tons,30 tons axle load of heavy haul trains are performed. The failure mode, the failure member and the ultimate bearing capacity are obtained, and the safety reserve of the steel truss girder are grasped.According to the most unfavorable equivalent load effect, considering the reserves of dynamic coefficients, the adaptability of the bridges designed of China-live load to 27 tons,30 tons axle load of heavy haul train are analyzed. The spans that can carry the heavy haul traffic are obtained.The methods of different fatigue life evaluation, including S-N curve evaluation method, linear elastic fracture mechanics method, and fatigue life reliability assessment method based on S-N curve are summarized and analyzed. The three methods of fatigue assessment are used for evaluation of fatigue life of two the typical steel truss after the operation of 30 tons axle load of heavy haul train. The residual fatigue life of different members and the members that need to be reinforced are obtained.The difference of the loading waveform between the actual bridge and laboratory is studied. Several key structure details in the steel bridges are selected to carry out the fatigue experiment under the rectangular wave (trapezoidal) and sine waveform load conditions. The influence degree to the fatigue performance of different waveforms are studied, the result is analyzed to judge that if the fatigue performance is changed under extreme heavy transport conditions, and to verify that if the allowable value need to be reduction and confirm the reduction coefficient value when performs fatigue calculation.The various types of new steel bridge structure details are summed up. The three major categories of 17 kinds of structural details includes main truss structure details, deck structure details and main truss and deck system connection details are classified and analyzed. The adaptability of the details to heavy haul transportation condition are studied, for the details that cannot meet the requirement,the suggestion of the improvement measures are put forward.