Welding simulation of tubular K-joints in steel S690QH

Residual stress state in planar tubular K-joints, in the chord within the gap region between the two braces, is studied using numerical weld modelling. The motivation comes from past full-scale fatigue tests on tubular trusses made of various steel grades with sizes typical of bridge trusses, which shows that the cracking occurs at the hot spots located in this region. Residual stress field characterization is needed in order to assess its role in fatigue cracking, especially for the case of cracks occurring on the compression brace side. Comparison between residual stress field in a Y-joint and a K-joint is made to assess the significance of restraining effect in the gap region. Phase transformations during welding and cooling down are determined and their impact on the final residual stress state is evaluated. Computed residual stresses are compared to the neutron diffraction measurements. Transient thermal field and cooling times substantially affect phase transformations. Therefore, their accurate reproduction in the analysis is important.