Advanced Assessment of Welded Bridges for Fatigue and Brittle Fracture

Around 50% of steel and steel—concrete composite bridges owned by Trafikverkethave been built before 1970, when there was limited knowledge about fatigue and brittlefracture of structural steel products. This was the case in particular for the usage of theseproducts in construction of welded bridges. At the same time, fatigue deterioration inthese structures is undergoing due to the escalation of freight volume as well as theincreased axle loads of modern trains and lorries. Realistic assessment of residualservice life of these structures is crucial in more efficient planning of repairs andavoiding unnecessary replacement costs. Therefore, more accurate conditionassessment methods are important from both economic and sustainability aspects.While the improved assessment methods for existing structures have been subject ofextensive research since 1990\u27s, their use in regular engineering practice is still limited.This study is an attempt to review the recent advances in structural assessment ofwelded steel bridges and to present them in a structured manner for the use of practicingengineer. In this report, a multi-step assessment methodology for fatigue and brittlefracture of welded bridges is presented, mainly based on the past research in Europe.The assessment steps are comprised of preliminary assessment (phase I), detailedinvestigation (phase II), and expert investigation (part III). Detailed information isgiven in the report for the corresponding input data (resistance-side and action-side)and modelling options for each of these assessment steps. As expected, the moreadvanced method is used, the more extensive set of input data and analytical effort isrequired. When applicable, the assessment method has been adapted to the relevanttechnical requirements stipulated by Trafikverket.Finally, the application of the presented multi-step assessment is examined on a casestudy bridge (G\uf6ta river bridge). Phase II assessment of the bridge based on historicalloading data shows insufficient fatigue life for a critical detail that has been replicatedin many locations over the bridge. The results of phase III assessment suggest thatintensified inspections of vulnerable details in regular time intervals are sufficient forensuring the safe service of the structure until the end of its planned service life