Assessment of Subzero Fracture of Welded Tubular K-Joint

The deformation, ultimate load capacity, and fracture behavior of full-scale welded K-joints fabricated from cold-formed rectangular hollow sections have been studied both numerically and experimentally. An extensive experimental program of welded K-joints tested to failure at temperatures between 23 and $-60°\mathrm{C}$ revealed that the primary failure mode was ductile tearing of the chord flange at the toe of the tension brace-to-chord weld. For some joints tested at $-40$ and $-60°\mathrm{C}$ , initial ductile tearing led to brittle fracture. Finite-element based $J$ -integral assessment of an advancing crack for one K-joint geometry was combined with $J–\Delta a$ material curves measured at $-40°\mathrm{C}$ . Assessment revealed that crack advance, once initiated, would be expected to continue at a nearly constant load. The assumed shape and size of the initial crack in the finite-element model were considered to be conservative and the estimated maximum load capacity and joint ductility were conservatively predicted with respect to the experimental results. This procedure was found to be promising for assessing the ultimate ductility of tubular joints at low temperatures.