Experimental investigations of N‐joints made of high‐strength hollow sections

This article presents experimental investigations of the structural behaviour of welded N-joints made of high-strength hollow sections. A total of 13 large-scale tests were carried out on joints made from five different steel grades (S500MH, S620QH, S700MH, S770QH and S890QH) using both circular (CHS) and square (SHS) hollow sections. All specimens have been produced with full penetration butt welds to avoid weld failure and isolate punching shear failure (PSF) and chord face failure (CFF). Welding parameters were optimised based on dilatometer results and thermal cycle limits (t$_{8.5}$ ≤ 12 s). Measurement techniques included strain gauges and digital image correlation (DIC) to quantify joint deformation by chord indentation. The force–indentation relationship was used to determine the ultimate strength of the joints. The results demonstrate the effects of steel grade, β-ratio, chord slenderness and preload on the load-bearing behaviour of the joints and provide a reliable basis for numerical modelling and future design recommendations for N-joints made of high-strength steel.