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Direct Strength Method in Built-Up Cold-Formed Steel Beams: Reliability Analysis Under Different Code-Specified Load Combinations
DOI:
https://doi.org/10.5216/reec.v21i1.81740Keywords:
Cold formed profiles, direct strength method, Structural reliability, Built-up beams, BendingAbstract
In cold-formed steel structures, the use of built-up beams, particularly U-sections, has been increasing. The growing demand for cost-effective solutions has led to the development of built-up members with enhanced load-carrying capacity. This paper proposes a reliability assessment of built-up members by applying the Direct Strength Method (DSM). A comprehensive database was established, including both open and closed cross-sections. Using this database, a statistical analysis of the "model error" variable was performed, followed by reliability index (β) evaluations to assess the safety levels of DSM. The approach considered a finite strip model that emphasizes the composite action of the elements forming the section. In the reliability analysis, the load combinations prescribed by the AISI S100 (AISI, 2016) and NBR 14762 (ABNT, 2010) standards were applied. Furthermore, a calibration of the resistance factors, Ø (AISI, 2016) and γ (ABNT, 2010), was conducted for each target reliability index specified in the codes. The results highlighted the need for adjustments to the currently adopted resistance factors. Based on the conducted analysis, more appropriate values would be approximately: ØLRFD ≈ 0.85, ØLSD ≈ 0.70, and γNBR ≈ 1.25. These adjustments can contribute to a more accurate design approach, better aligned with safety and structural performance requirements.
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