The Application of Fatigue Models to Railway Bridges

摘要

This paper describes work that is being carried out to develop an approach forrnassessing the effects of dynamic loading on ageing metal bridges. The overallrnproject involves work in a number of different areas: the development of bridge andrnrolling stock models and their interaction; the development of loading data to modelrnvariable track alignment and wheel profiles; the measurement of bridge responses tornrolling loads; the calculation of cumulative fatigue damage and the evaluation ofrnremaining fatigue life.rnThis paper illustrates the approach taken in assessing the fatigue loading appliedrnto the bridge. It discusses the methodology and mechanisms of fatigue analysisrnwhen applied. The procedure presented involves the implementation of the rain-flowrnalgorithm. This method involves decomposing the stress history of each location onrnthe structure into a series of stress cycles. This approach enables the application ofrntraditional methods such as the Palmgren-Miner hypothesis. The method and itsrnimplementation are described in detail. Considerations such as material properties,rnstress concentrations and previous loading history are also considered andrnaddressed.rnThe importance of the dynamic interaction between the rolling stock, track andrnbridge systems, when considering fatigue, is dealt with in depth. Distinctions arernmade between different forms of structure and the difference in the response of shortrnand long span bridges. The paper also addresses the different methods ofrnapproaching fatigue problems including: allowable stresses, the calculation of safernworking life, or the calculation of safe working loads. The paper also discusses thernideas of low and high cycle fatigue.