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Resistance of Cold-Formed L-Columns Made of High Strength Steel
2014 (English)Independent thesis Advanced level (professional degree), 20 credits / 30 HE creditsStudent thesis
Abstract [en]

Steel is a material with constant development and recent years showed, that by changing the initial mixture of minerals and alloys, the strength of the material can be significantlyimproved. New generation is called high-strength steel (HSS) and in many cases the value ofyield or ultimate strength is nearly doubled compared to the steel products used nowadays.Designers across Europe can therefore design less massive or much bigger structures thanever before. Great help for every designer is Eurocode and for steel structures it is namelypart 3 (EN-1993-1-x). Unfortunately the majority of formulas, buckling curves, tables and all other recommendations were created according to the tests on steel with strength ranging from 235-460 MPa.Higher strength classes (till 700 MPa) were briefly described in Eurocode EN1993-1-12 fromFebruary 2007 and in most of the cases it is recommended to use similar procedure as for steel S460, which is a part of traditional Eurocode. Question of designing high-strength steelsaccording seems to be understood, however it isn’t.It is year 2013 and six years in development means a lot of time to improve or totally changethe behaviour of high-strength steels. It can be assumed, that using traditional parts ofEurocode in combination with EN1993-1-12 is safe and the designed structure will sustain alldesign loads.Yet, designers are no more focused just on reliability of structure, but also on its economic and environmental part. Usage of current Eurocode, which is more than 6 years old and doesn’t reflect improvements of modern steel, can easily lead to very conservative design,which can increase the price of final structure and also use of more material, than it isactually necessary.This thesis is focused on high strength steel cold-formed equal-leg angles with different angles of folding. This topic includes combination of research questions connected with highstrength steel and cold-forming.Peculiarities of this type of cross-sections will be studied through investigation of its resistance. Due to the press-braking it is expected that the corner area has changed its material properties. Moreover, changes of design resistance will differ according to change of angle of folding. Therefore, the optimum angle will be searched for economical design.Furthermore, the influence of material thickness will also be investigated as the fact whichinfluences on resistance.It is expected that the current design according to Eurocode is conservative in terms ofpredicting the design resistance for high strength steel. Moreover, it is expected that classification of considered specimens might not be fully applicable.First part of this thesis is dedicated to theoretical background and evaluating geometrical properties of cross-section, followed by calculation of critical forces for each element.To check results of mathematical evaluation of this thesis, in next part finite element analysis is used, both linear and nonlinear. Each specimen will be modelled and its behaviour estimated during compression. The influence of initial imperfections and boundary conditions on the model will be studied.Next step will include laboratory test, where all specimens will be tested in compression.After performed procedures comparison of obtained results will be held. Therefore, therewill be three steps of research: design according EN, FEM analysis and experimentalinvestigation. This type of research method gives possibility to obtain validated results andto make conclusions which will be safe.As the outcome of the research it is expected to find answer if current Eurocode produceseconomical predictions, or there is a need for further testing and change of current designrules and recommendations.

Place, publisher, year, edition, pages
2014. , 231 p.
Keyword [en]
Technology, High-strength steels, Compression, Buckling, Local buckling, Cold-forming
Keyword [sv]
URN: urn:nbn:se:ltu:diva-52820Local ID: 9e94c94b-de14-414c-b1af-9996272f57cdOAI: diva2:1026192
Subject / course
Student thesis, at least 30 credits
Educational program
Environmental Engineering, master's level
Validerat; 20140213 (cani)Available from: 2016-10-04 Created: 2016-10-04Bibliographically approved

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