Keywords: steel space-truss, plastic buckling, rectangular hollow members, numerical analysis, verification of experimental results, ABAQUS finite element program.

The steel space-truss systems are applicable to a very wide range of applications in the practice of structural engineering. The Hungarian TOP-SYSTEM space-truss system, which was developed by the DUNAFERR Iron Work Company, contains rectangular hollow members. The edges of these members are formed with the help of excessive plastic deformations into the special flattened shape to set up the connections.

This paper is concerned with the behaviour of the rectangular hollow members during the formation procedure and during the compressing experiment. At first the deformation of the plate elements of the members and the development of the plate buckling state are analyzed. The special "flattening" process is described using an appropriate finite element model and analysis, thus the results are compared to the results of the manufacturing process.

In the numerical analysis the shaping load is applied as displacement of the pressing tool. The numerical analysis followed the pressing stage of the real manufacturing process, and we obtain the maximum pressing force within good tolerance.

Furthermore the experimental and numerical analysis of the buckling modes of these flattened end members, as compressed bars was undertaken. We applied the resulting shape of the quarter bar model of the "flattening" process and we modelled the whole flattened cross section instead of the quarter of the hollow section because of the unsymmetrical experimental buckling shape of the compressed bar. The numerical analyses was performed assuming perfectly centrally loaded bars, thus the deformation state remained symmetrical during the collapse. The numerical analysis shows good correlation with the experimental results.

Further calculations will be done for the analyses of other loading cases, such as pure bending, compressing-bending, torsional moment. The refinement and evaluation of the different load cases will be included in future work. We would like to create a 3D failure surface for this type of hollow sections.

1

"TOP-SYSTEM DUNAFERR. Space-Truss Roof- and Structure System" (in Hungarian), Design Manual S-45, Budapest: Gyorsjelentés Kiadó Kft. 1997.

2

Fülöp A., Iványi M. "Experimentally Analyzed Stability and Ductility Behaviour of a Space-Truss Roof System". International Journal of Thin-Walled Structures, Vol. 42, Issue 2, Elsevier Science Ltd, pp. 309-320, 2004. doi:10.1016/S0263-8231(03)00062-4

3

Hibbitt, Karlsson & Sorensen, Inc. ABAQUS/Standard User's Manual Version 6.3

4

DUNAFERR Sheet-forming Ltd. (DLA Ltd.), Cold bent steel sections, (in Hungarian), Dunaújváros, Hungary, 1996.

5

Euripides S. Mistakidis and Sokrates V. Tsiogas, "Failure modes of circular hollow members with flattened edges", Journal of Constructional Research 59, pp. 1573-1592, 2003. doi:10.1016/S0143-974X(03)00101-9

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