Change search
ReferencesLink to record
Permanent link

Direct link
Strengthening of I-girder bridges: Fatigue endurance
Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering.
2016 (English)Independent thesis Advanced level (professional degree), 20 credits / 30 HE creditsStudent thesis
Abstract [en]

Structures have always been subjected to the detrimental consequences of the fatigue phenomenon. The consequences due to this damaging effects leads to crack initiation and the ultimate result being complete failure. Fatigue appears on structures that has to endure fluctuating loads over a long period. The crack initiation occurs irregular geometries such as in the vicinity of welds and bolts. A structure that suffers a lot due to fatigue are road bridges. In this thesis the structure under investigation is a composite bridge with a concrete slab on top of two I-girders. The recommended lifetime of road bridges in the Eurocode is 100 years.Bridges are exposed to daily and yearly traffic loads. Also the amount of traffic and therefore the total weight shows a continuously increasing trend over the years. This tendency is under no circumstances expected to stagnate. Eurocode has based its approach to verification of fatigue on applying adversely combined traffic loads, in both directions, on the bridge. In the procedure of double I-girder composite bridges verification there is an uneven distribution of the vehicle loads and the stresses, as the bridge is behaving as an open cross-section. The concrete slab is the only apparent part that is transferring the vehicle loads to the other girder and gives therefore an unequal distribution of the loads.Because of this uneven load distribution there appears to exist some potential in finding a means to strengthen the bridge by ways of making it work as a semi-closed cross-section. This will enhance the load distribution over to the non-stressed girder. In this thesis the focus was set on the stress relation between the center web stiffener to the lower flange, with and without the strengthening, for a real case section. Assessment were done for case studies where the Rokån bridge as well as four arbitrary cross-sections were investigated in search of retrieving an increased understanding of the mechanism of stress distribution.The strengthening approach is to introduce a truss assembly, in shape of a K, in the plane between the two I-girders bottom flanges. This approach reduced the stresses in the middle position of the Rokån bridge by approximately 8.3 %. In addition, the parametric study of the arbitrary cross-sections, with the same truss system, where made. Reductions there showed stress values in the interval of 5.9 % and 16.6 %. Based on this study it was found that it is possible to establish a relation between the length on the bridge and the distance, w, between the girders. With regards to this study in applying this K-bracing, indicates that given stress reductions can prolong the bridges technical life to about 2.5 times.In comparison to strengthening ways available on the market, such as CFRP sheets and an additional concrete slab, there are advantages and disadvantages, such as self-weight, total cost, new fatigue details and the most important stress reduction.While the reductions tends to be quite high, there still exists a FE-model uncertainty regarding the coupling between the K-bracing junctions and the bottom flanges where the fusion of the elements was done with a node to node attachment. In a reality attaching the K-bracing onto the flange will be done by means of a bolted, welded or friction connection, which may lead to another fatigue category and increased/decreased stress concentrations at the new joints.

Place, publisher, year, edition, pages
2016. , 83 p.
National Category
Engineering and Technology
Identifiers
URN: urn:nbn:se:ltu:diva-60092OAI: oai:DiVA.org:ltu-60092DiVA: diva2:1044060
Educational program
Civil Engineering, master's level
Supervisors
Examiners
Available from: 2016-11-10 Created: 2016-11-01 Last updated: 2016-11-10Bibliographically approved

Open Access in DiVA

fulltext(5602 kB)15 downloads
File information
File name FULLTEXT01.pdfFile size 5602 kBChecksum SHA-512
f2aaa890c7c9302bf5661ab25b33cdff58942b0ebc4e64aa883f9ce6cb5fc022a9b20e3e5558a6c24372d169223786a0f7908e0fcb632f82f6c350172dffc24d
Type fulltextMimetype application/pdf

By organisation
Department of Civil, Environmental and Natural Resources Engineering
Engineering and Technology

Search outside of DiVA

GoogleGoogle Scholar
Total: 15 downloads
The number of downloads is the sum of all downloads of full texts. It may include eg previous versions that are now no longer available

Total: 8 hits
ReferencesLink to record
Permanent link

Direct link