Fatigue and dynamics of secondary beams in steel railway bridges

Abstract: Many steel railway bridges in Europe are older than 50 years whilethey are subjected to higher loads than they were originally designedfor. As many of these bridges are approaching the end of their designlife it is crucial to carry out accurate fatigue assessments in order toensure their safety and keep them in service. Usually the influence ofdynamics on fatigue damage is taken into account using dynamicamplification factors from design codes whereas the actual influenceof dynamics has not been thoroughly studied.   During this study the importance of dynamics on fatigue damage isexamined on two specific examples, namely the Söderstöm Bridgeand the Åby älv bridge, which are good examples of open deckbridges that are common among steel railway bridge population.   Different train speeds, the cross beam effect and load distributionwere studied in order to assess the importance of dynamics on fatiguedamage. Three dimensional finite element models were created andlater modified to perform dynamic analysis. Moving point loads wereused to simulate the loading of moving trains. Fatigue damages werecalculated at the various locations to evaluate the influence ofdynamics on fatigue damage.   The results show that the dynamics has small influence on fatiguedamage at studied speeds and damage is not dependent on speed.Assessed cross beam effect was not detected on studied bridges interms of dynamics, but has great influence in terms of statics.