Utmattningsjämförelse mellan Eurokod och verkligheten: A Fatigue Stress Comparison with Eurocode
Independent thesis Advanced level (professional degree), 20 credits / 30 HE creditsStudent thesis
Fatigue is a phenomenon that can occur when a structure is exposed for repeated loads dur-ing a long time. This is what has happened in the Vårby Bridge south of Stockholm. The bridge, which was erected in 1996, was just after ten years during an inspection detected to have cracks in the weld between the stiffener and the flanges. This lead to an extensive inves-tigation to be able to describe what was the cause. Because of the great measurement a lot of data about the traffic flow and their effect on the bridge was obtained. That raised an idea of comparing the fatigue models in Eurocode against a real case. The question that was of in-terest was how well the Eurocode models actually were compare to the real measurements, how they relate to each other and how they relate to a fictitious real vehicle.The intermediate values for Nobs is showing that there is quite large differences. Therefore they should be used. The model should be a straight line instead of the “stair model” that is used today so the fatigue is designed on the safe side rather than the unsafe side which it is today in the upper part of the span.The results show that the bridge is able to handle the free flowing traffic that it is exposed for. At the simulation of FLM 3 together with DEM the result shows a life length that is satisfactory with the recommendations in Eurocode. The ratio between the equivalent stress range for FLM 3 and the free flowing traffic was 89 percent. The ratio between FLM 4 and the free flowing traffic gave that the traffic was 22 percent higher when the equivalent stress ranges was compared.The comparison between FLM 3 and FLM 4 was made with ÅDTt from the free flowing traffic. This gave a ratio of 73 percent between the models, with FLM 4 as the lower one.The fictitious real vehicle of 25,25 meters didn’t give any critical results, but was higher than the fatigue limit. What could be seen was that the actual contribution from vehicles of the same amplitude that the simulations gave is very low in the free flowing measurements. This means that they are no danger for the bridge.Another conclusion is that measurements should be done on other bridges to see how the stress range of the traffic actually is compared to Eurocode. One should also review the FLM 4 and see if it could be modified to fit the Swedish conditions of vehicle design and distribu-tion. Another thing that might be overlooked is if there could be some sort of collective pa-rameter, taking the fact that not all vehicles are fully loaded in to account. For future struc-tures maybe it would be in place to start cooperate between the designing sector and the truck manufactures to make both the trucks and the bridges as optimized as there can be, and to avoid unnecessary fatigue contribution.
Place, publisher, year, edition, pages
2013. , 92 p.
Teknik, Bro, utmattning, Vårby, spänningar, examensarbete, Bridge, Fatigue, Stresses, Master Thesis
IdentifiersURN: urn:nbn:se:ltu:diva-55154Local ID: c0c16cfd-2e5a-45f8-b53c-dfb42421b597OAI: oai:DiVA.org:ltu-55154DiVA: diva2:1028535
Subject / course
Student thesis, at least 30 credits
Civil Engineering, master's level
Validerat; 20140214 (global_studentproject_submitter)2016-10-042016-10-04Bibliographically approved