Keywords: cold formed steel joints, back-to-back lipped channel sections, full scale tests, finite element analysis, parametric study, virtual testing.

Previous studies reported the results of a large experimental and numerical program carried out at the "Politehnica" University of Timisoara and Technical University of Cluj in order to evaluate the performance of three different configurations of ridge (apex) and eaves knee joints of pitched roof cold-formed steel portal frames of back-to-back lipped channel sections and bolted joints under monotonic and cyclic loading. The behaviour and failure mechanisms of the joints were observed in order to evaluate their rigidity, strength and ductility. In a second phase, considering the poor performance of joints with web bolts only, joint configurations with both web and flange bolts were used to test two full-scale double frame units under: (1) horizontal load, and (2) horizontal and gravity loadings. The objective of the full-scale tests was to assess performance of pitched-roof cold-formed portal frames with moment-resisting joints subject to lateral loading, with particular emphasis on earthquake loading. The experimental program is described in the first section of the paper, with further details in [1,2].

In section two the numerical analysis results are given. The numerical analysis of the tested joints in the experimental programs was performed, obtaining calibrated finite element models. Later, a parametric study consisting of fourteen joint configurations of the ridge (apex) joints was conducted using the calibrated numerical model. The failure modes of material yielding and local and distortional buckling of the joint components as a result of stress concentrations were found in this study.

The experimental joint strengths and numerical results predicted by the parametric study were compared with the design strengths calculated using the principles of the component method proposed by current European specifications for steel joints. The results also provide further interpretation of the experimental results and give potential for optimization for the joints analysed. Details about the component method application are included in section three.

The paper summarizes the experimental work, the numerical results of the tested joints and the results of the parametric study on the developed joint typologies, giving the variation of the mechanical characteristics of the analyzed connections with the joint geometry changes. The calibrated knee and ridge models are able to reproduce the same failure mechanism as obtained experimentally, offering a fair force-displacement and moment-rotation agreement between test and the finite element results. The methodology based on the component method fits very well with experimental and finite element results and is relatively simple to apply. The results generated can be used as input for linear elastic analysis of portal frames with such kind of joints.

1

D. Dubina, A. Stratan, A. Ciutina, L. Fulop, Zs. Nagy, "Performance of ridge and eaves joints in cold-formed steel portal frames", Proc. of the 17th International Specialty Conference, Orlando, Florida, USA, 727-742, 2004.

2

D. Dubina, A. Stratan, Zs. Nagy, "Full-scale testing of cold-formed steel pitched-roof portal frames of back-to-back channel sections and bolted joints", Proceedings of the Sixth International Conference on Steel and Aluminum Structures, Oxford, UK, 931-939, 2007.

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