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Innovative structural details using high strength steel for steel bridges
KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Structural Engineering and Bridges.ORCID iD: 0000-0002-3699-0814
2019 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

The use of high strength steel has the potential to reduce the amount of steel used in bridge structures and thereby facilitate a more sustainable construction. The amount of steel and what steel grade that can be used in bridge structures and other cyclic loaded structures are often limited by a material degradation process called fatigue. The fatigue resistance of steel bridges are to a large extent depending on the design of structural details and connections. The design engineer is limited by a few pre-existing structural details and connections – with rather poor fatigue resistance – to choose from when designing steel bridges, and is therefore often forced to increase the overall dimensions of the structure in order to cope with the design requirements of fatigue. This licentiate thesis aims at increasing the fatigue resistance of fatigue prone structural details and connections by implementing new and innovative structural solutions to the already pre-existing details given in the design standards. A typical fatigue prone detail is the vertical stiffener at an intermediate cross-beam, which will be in focus. By improving the fatigue resistance, less steel material will be required for the construction of new steel bridges and composite bridges of steel and concrete. It is shown in this thesis and the appended papers that the use of high strength steel for bridge structures can considerably reduce the amount of steel used, the steel cost and the harmful emissions. However, this is only true if the fatigue strength of critical details can be substantially improved. Furthermore, a few new and innovative structural details and modifications to already existing details are proposed in this thesis and in the appended papers, that have the potential to increase the fatigue resistance of steel bridges and composite bridges of steel and concrete. However, further analyses are required in order to make these structural details viable for construction.

Abstract [sv]

Genom användandet av höghållfast stål så kan en mindre mängd material användas som i sin tur leder till ett mer hållbart byggande. Mängden stål och vilken stålkvalité som kan användas vid byggandet av stålbroar och andra cykliskt belastade konstruktioner avgörs ofta av nedbrytningsprocessen utmattning. Utmatningskapaciteten hos stålbroar är till stor del beroende av brons anslutningsdetaljer. Brokonstruktören har vid designstadiet ett begränsat antal beprövade anslutningsdetaljer att välja bland – vilka ofta har relativt låg utmattningskapacitet – och konstruktören är därmed ofta tvungen att öka konstruktionens dimensioner för att klara av kraven gällande utmattning. Den har licentiatuppsatsen har till syfte att förbättra utmattningskapaciteten för utmattningsbenägna anslutningsdetaljer i stål genom att införa nya och innovativa anslutningsdetaljer, bland de redan existerande detaljerna som finns i de olika standarderna. En utmattningskritisk detalj som kommer att ligga i fokus är anslutningen mellan livavstyvningen och tvärförbanden hos en I-balk. Genom att förbättra utmattningskapaciteten så kan en mindre mängd stålmaterial användas vid byggandet av stålbroar och samverkansbroar i betong och stål. I denna uppsatsen kunde det påvisas att höghallfast stål for broar kan betydligt sänka mängden stålmaterial, stålkostnaden och koldioxidutsläppen. Dock så gäller detta enbart om utmattningskapaciteten for kritiska anslutningsdetaljer kan ökas avsevärt. Dessutom, som en del av den har uppsatsen så har ett par nya och innovativa anslutningsdetaljer föreslagits som har potential att forbättra utmattningskapaciteten. Dock, så krävs ytterligare studier for att dessa förslag skall kunna användas i byggnation av nya stålbroar.

Place, publisher, year, edition, pages
Stockholm: Kungliga Tekniska högskolan, 2019. , p. 54
Series
TRITA-ABE-DLT ; 1933
Keywords [en]
High strength steel, fatigue, steel bridges, steel and concrete composite bridges, innovative steel details
National Category
Infrastructure Engineering
Research subject
Civil and Architectural Engineering, Structural Engineering and Bridges
Identifiers
URN: urn:nbn:se:kth:diva-259949ISBN: 978-91-7873-274-6 (print)OAI: oai:DiVA.org:kth-259949DiVA, id: diva2:1353864
Presentation
2019-10-24, M108, Brinellvägen 23, Stockholm, 13:00 (English)
Opponent
Supervisors
Note

QC 20190925

Available from: 2019-09-25 Created: 2019-09-24 Last updated: 2019-09-26Bibliographically approved
List of papers
1. Overview of steel bridges containing high strength steel material
Open this publication in new window or tab >>Overview of steel bridges containing high strength steel material
(English)In: International Journal of Steel Structures, ISSN 1598-2351, E-ISSN 2093-6311Article in journal (Refereed) Submitted
Abstract [en]

 The use of high strength steel has the potential to reduce the amount of steel used in bridges and thereby, facilitate a more sustainable construction. A survey of existing bridges built using high strength steel is presented in this paper with emphasis on the Swedish bridge stock. The survey aimed at identifying the steel grades that were used and where in the cross-section they have been used. A case study on the inuence of fatigue shows that today's regulations make it more dicult to use high strength steel in comparison to previous regulations.

Keywords
High strength steel, Steel bridges, Composite bridges, Fatigue assessment, Hybrid girders
National Category
Infrastructure Engineering
Identifiers
urn:nbn:se:kth:diva-259929 (URN)
Available from: 2019-09-24 Created: 2019-09-24 Last updated: 2019-09-24
2. Optimizing the steel girders in a high strength steel composite bridge
Open this publication in new window or tab >>Optimizing the steel girders in a high strength steel composite bridge
(English)In: International Journal of Steel Structures, ISSN 1598-2351, E-ISSN 2093-6311Article in journal (Refereed) Submitted
Abstract [en]

The use of high strength steel has the potential to reduce the amount of steel used in bridges and thereby, facilitate a more sustainable construction. In this study, an optimization of a composite steel and concrete bridge is presented. The study aimed at identifying the potential benets of using high strength steel, compared to conventional steel, in terms of weight, material cost and environmental impact. The optimization routine followed what is outlined in the Eurocode and satised both ultimate and serviceability limit state conditions, with exception of fatigue. To study the inuence of fatigue a separate verication was performed on the solutions found from the optimization. The study showed that substantial savings in weight, environmental impact and material cost could be made by implementing high strength steel. However, when the fatigue verication according to Eurocode was considered, the potential benets of using steels of higher grade vanished completely.

Keywords
High strength steel, Composite steel and concrete bridge, Optimization, Hybrid girder, Fatigue
National Category
Infrastructure Engineering
Identifiers
urn:nbn:se:kth:diva-259933 (URN)
Available from: 2019-09-24 Created: 2019-09-24 Last updated: 2019-09-24
3. The impact of local geometry on the fatigue life of a welded structural detail
Open this publication in new window or tab >>The impact of local geometry on the fatigue life of a welded structural detail
2019 (English)In: Proceeding of Nordic Steel 2019, 2019Conference paper, Published paper (Refereed)
Abstract [en]

Fatigue often limits the capacity of welded steel bridges, and thus often governs the amount of steel required. The fatigue life is, to a large extent, governed by stress concentrations and the magnitude is controlled by local as well as global geometry; by improving the local geometry the stress raising effects can be lowered and by increasing the global dimensions the nominal stress can be reduced. The fatigue assessment format presented in the Eurocode gives little or no room for the designer to control the local geometry of the structural detail, and is often left with increasing the overall dimensions in order to improve the fatigue life of the structure. This paper aims at investigating the possible impact on the fatigue life of welded steel structures by different weld geometries. In this paper a vertical stiffener will be studied by fracture mechanics. The study showed that significant improvements in fatigue life can be made by small changes to the weld geometry and the most pronounced effect was by changing the weld toe radius, and

Keywords
Fatigue; Steel bridges, Vertical stiffener, Weld geometry
National Category
Infrastructure Engineering
Identifiers
urn:nbn:se:kth:diva-259936 (URN)
Conference
The 14th Nordic Steel Construction Conference (NSCC)
Available from: 2019-09-24 Created: 2019-09-24 Last updated: 2019-09-24

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