Projects / Programmes
Members with box cross-section subject to compression and bending
| Code |
Science |
Field |
Subfield |
| 2.01.00 |
Engineering sciences and technologies |
Civil engineering |
|
| Code |
Science |
Field |
| T230 |
Technological sciences |
Building construction |
Steel members, thin-walled box profiles, element stability, column buckling, plate buckling, initial geometric imperfections, residual stresses, compression-bending interaction, tests, numerical simulations
Researchers (1)
| no. |
Code |
Name and surname |
Research area |
Role |
Period |
No. of publicationsNo. of publications |
| 1. |
20205 |
PhD Luka Pavlovčič |
Civil engineering |
Head |
2008 - 2010 |
0 |
Organisations (1)
Abstract
For the construction of an attractive and light weight steel structures, slender thin-walled profiles are often used, built-up of slender plates that may additionally be made from high strength steel. Capacity of such members is governed by two types of instabilities: local instability, such as local buckling of plates, and global buckling instability of the element when it is slender as a whole. Columns with slender webs can be subjected to coupled local and global instability and the problem may be even more complex when column is subjected to combined compression and bending. Some recent researches have shown that the procedures for the desgn of thin-walled slender members in compression and bending, given in the European standards Eurocodes which are fully accepted also in Slovenia, are either too conservative or for some types of profiles even unsafe. The intention of the proposed project is to be actively involved in research activities on the presented instability phenomena, which are nowadays very topical at different European research organizations, aiming at improving the Eurocode procedures in order to obtain efficient and throughout safe methods for different types of profiles at various loading conditions.
In the partnership with the University of Stuttgart the performance of seven full-scale tests is planned on welded and cold formed slender box columns in compression as well as in combined compression and bending. Different types of instabilities will be analysed. The test results will serve for the verification of numerical models, which would account for measured material properties and initial imperfections of specimens. On these models the numerical study of initial geometric imperfections and residual stresses (due to welding and cold-forming) will be carried out. In the next step an extensive numerical parametric study will be performed, covering the wide area of local and global member slendernesses. The influence of high strength steel will also be investigated. Based on test and all numerical results a new proposal for the design of slender box members in compression and bending will be developed. This procedure should take into account the principles of Eurocodes and also be harmonized with other procedures for other types of profiles, which are at present in the development phase at other research institutions.
Significance for science
Scientific contributions are the following:
- 8 performed full-scale tests expand the base of available tests with the results for different specimen geometry, manufacturing procedure and load introduction, serving as a useful data base for different researches. Based on fully documented and published test results further calibration or verification of any other calculation or numerical model is possible as well as the development of a method concerning the considered problem.
- The successful performance of accompanying tests and measurements is very important as a basis for numerical simulations and the analysis of different imperfections. Results of executed tests and measurements are fully documented and can serve for general use.
- The successful measurement of residual stresses on welded as well as comparable cold-formed profile offers the direct comparison of the influence of different manufacturing procedures to the development of residual stresses and consequently to the column capacity. The measured level of compression residual stresses in the welded profile appeared to be very high (40% of fy) due to large weld-to-plate thickness ratio. The cold-forming contributes to the stress gradient though the plate thickness rather than to the level of membrane residual stresses.
- The important contribution represents also the successful numerical simulation especially in the respect of large sensitivity of column capacity to any kind of imperfections. For the demanding measurements of residual stresses and geometric imperfections as well as large sensitivity of columns to imperfections, the difference in column capacities within 6 % proves the accuracy of FE simulations.
- The verified FE models together with the available data on imperfections offered also the quantitative influence analysis of different imperfections (residual stresses, global and local geometric imperfections, column inclination) and their arbitrary combinations. It was proven that for advanced engineering practice implication of different imperfections could be replaced by proper equivalent geometric imperfections also in the case of considered columns.
- Numerical parametric study has covered a wider range of global and local slenderness parameters. In several cases columns were additionally loaded in bending by variation of load eccentricity. Two steel grades were taken into account and all the calculations were carried out for two classes of initial imperfections – for relatively light welds and relatively heavy welds. From the results of calculations a broad data base of »virtual tests« was created, which is available also for any other researchers.
- Based on obtained data base the present design procedure for column capacity according to Eurocode 3 was analysed into detail, together with two recent proposals of modifications – (Detzel, 2006) and (Brune, 2000). The slenderness regions where each method gives unsafe results were diagnosed. Due to remarkable uncertainty and scatter of the inputted initial imperfections, instead of fine calibration or corrections of existing methods research finally proposes more accurate definition of imperfection classes with the introduction of steel grade parameter into the definition of limits between these classes.
- The research opens some new questions and gives two suggestions for necessary further research activities: to experimentally investigate columns with small global slenderness (around 0.2) and large local slenderness (at least 1.0) since the results in this slenderness range – no matter the design procedure - are up to 8 % unsafe for the light weld situation and even up to 15 % overestimated for heavy welds. The second research direction may be an experimental study of the influence of different welding procedures and weld thicknesses to the development of residual stresses and consequently to the column capacity. In this way different imperfection classes could be accurately systemized and defined.
Significance for the country
The importance for the development of Slovenia may be found in the international cooperation and the involvement of posdoc project in the actual international research carried out at the acknowledge European institutions. This frame offers the possibility of free exchange of knowledge and research experiences between different research environments and countries. In this way Slovenia proves to be one of the agile and relevant members of the European community on the field of research as well as in professional matters. These objectives are proved by the following:
- 10 month of the research stay at the University of Stuttgart, Institute of Structural Design (Prof. Ulrike Kuhlmann), where the experimental part of the research was carried out.
- The partnership with the Technical University of Dortmund (Prof. Dieter Ungermann, Assoc. Prof. Betina Brune), where at the same time the similar investigation on open C profiles is carried out.
- As the active researcher on the field of stability problems I helped at giving lectures at the University of Stuttgart for the elective course K4a: Steel plated structures (Stahlflächentragwerke).
- Membership of the scientific committee of the relevant international conference from the field of steel structures: Eurosteel 2008, taking place on 3rd to 5th of September 2008 in Graz, Austria.
- Attending of different meetings in the project framework as well as other workshops necessary for the improvement of knowledge from the same field: Stahlbau-Kalender-Tag on 20th of June 2008 in Stuttgartu, Deutscher Stahlbautag on 9th – 10th of October 2008 in Mainz and COMBRI Workshop »Stahl- und Verbundbrücken« on 7th of November 2008 in Düsseldorf.
- Involvement in bridge design of the third bridge over Orinoco in Venezuela, within the Kuhlmann-Gerold-Krauss-Eisele design office from Ostfildern-Nellingen nearby Stuttgart, with Prof. Ulrike Kuhlmann as one of the partners. Both chords of truss girders are welded in box profile subjected to the compression and bending – the application of this research in the design practice.
- Invitation to present research results to the important meeting of european working group ECCS TWG 8.3, which is competent for actualisation of Eurocodes from the field of stability of steel structures.
- The participation and presentation of the results at different international and national conferences (Civil-Comp 2009, Funchalu, Madeiri; Stability and Ductility of Structures, Vilnius, Litva; ZGKS, Rogaška Slatina) and meetings of different project working teams (Köln, Stuttgart, Hirschberg, Hamburg).
- As a competent researcher in the field of stability problems I was additionally included in smaller research project on stability problem of king-profiles of steel sheet quay walls in elastic soil embedment (during Stuttgart working period). I participated also at some result presentations and publications (in acknowledge germain journal Stahlbau - 5th input under chapter 6, contribution in proceeding of »Spundwände« workshop in Hamburg).
Most important scientific results
Final report,
complete report on dLib.si
Most important socioeconomically and culturally relevant results
Annual report
2008,
final report,
complete report on dLib.si
