Experimental and numerical assessment of reinforced SHS T-joints with doubler plate

The use of hollow sections in civil construction has gained recognition due to their efficient structural behaviour, aesthetic appeal, and effective incorporation into composite structures. Recent progress in design codes has facilitated the increased adoption of hollow sections in various countries. However, Brazilian design rules are relatively new. This paper investigates the structural behaviour of reinforced T-joints, focusing on the influence of doubler plate thickness. Current codes, such as EN1993-1-8 and NBR 16239, disregard the contribution of the reinforcement thickness below the recommended minimum value. Therefore, an experimental program was conducted, involving five tests on square tubular profiles (SHS) varying both geometry and doubler plate thickness. Additionally, a parametric study based on a validated numerical model was carried out in order to enlarge the database, examining the impacts of some joint parameters in the joints' structural response. The results reveal that increasing the doubler plate thickness enhances the joint capacity by up to three times, particularly for values below the code-specified threshold, with this improvement being nonlinear and closely correlated to the observed failure modes. A comparative analysis with existing formulae reveals a substantial divergence of up to 50 %, leading to the proposal of a new formulation. This new method, which carefully assesses two different failure modes, provides a more reliable approach for reinforced T-joints' ultimate capacity.