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Cold-formed steel (CFS) structural members retain their positions in the lightweight construction industry. This is due to the significant advantages of CFS. The optimization of these CFS elements will allow the construction of economical buildings with increased load capacities and solutions for stable and economical construction will be obtained. The main aim of this research was to evaluate the effectiveness of these new CFS sections with the estimation of remarkable instabilities and failure modes. This article deals with an experimental study on the behavior of CFS beams of open delta and bi-delta form stressed by four-point bending loads. These cross section shapes are often used in floors as main and secondary beams. The section properties are based on the effective width method designated by the Eurocode 3 standard. A nonlinear finite element (FE) analysis using the ABAQUS program is performed and the comparison between the experimental, numerical and theoretical results is done. Finally, the results showed above all that the breaking loads of the delta and bi-delta beams corresponded to the modes of local buckling and crushing of the web.

Currently, cellular steel beams are widely used by structural engineers and major companies due to their useful structural applications and serviceable performance. However, these types of steel beams are susceptible to different states of instability and failure mechanisms such as web post-buckling. The aim of this paper is to investigate the effectiveness of using externally bonded pultruded carbon fiber (CFRP) profiles for the strengthening of web post-buckling in thin webbed cellular beams as an alternative to the typical welding technique of reinforcement. A proposed numerical model created with the finite element software ABAQUS capable of capturing the de-bonding and fracture along the adhesive layer between steel and CFRP has been validated using published experimental results. The suggested numerical model is then used to simulate the parametric analysis of using pultruded CFRP T and U sections to strengthen six cellular beams of various sizes. It was found that this novel technique was able to prevent the web post-buckling failure mode or delay it to a grater load with a considerable strength enhancement comparable to control beams.

Le procédé de soudage présente une modélisation très complexe car il implique des couplages entre des phénomènes mécaniques, thermiques et métallurgiques qui conduisent à la création des contraintes et des déformations résiduelles irrégulièrement distribuées au niveau de la section soudée. Cet article porte sur une étude expérimentale du comportement thermomécanique d’une poutre isostatique en profilé laminé renforcée par des éléments métalliques, assemblés au moyen de cordons de soudures et sollicitée par une charge concentrée (essai de flexion trois points). L’impact de la technique de soudure employée (cordons continus et discontinus) sur le comportement de l’élément est analysé. Des modèles numériques sont étudiés en utilisant un code de calcul basé sur la méthode des éléments finis où l’effet thermique dû à l’opération de soudage est pris en considération. Les résultats obtenus sont en très bon accord avec ceux expérimentaux.Mots clés: Soudage, Modélisation, Déformations résiduelles, Eléments finisEnglish Title: A section reinforcement of a metal structure element by weldingEnglish AbstractThe welding process presents a very complex modelling because it involves couplings between the mechanical, thermal and metallurgical phenomena which lead to the creation of stresses and residual strains irregularly distributed at the welded section level. This paper relates to a thermomechanical behavior's experimental study of an isostatic beam in reinforced rolled section of metallic elements by means of weld seams and solicited by a concentrated load (three-point bending test). The welding technique impact used (continuous and discontinuous weld seams) on the element behaviour is analysed. Numerical models are studied using a calculation code based on the finite element method, and the thermal effect due to the welding operation is taken into consideration. The obtained results are compared with those obtained experimentally. The results obtained are in very good agreement with the experimental ones.Keywords: Welding, Modeling, Residual deformations, Finite elements