Modeling the effects of residual stresses on defects in welds of steel frame connections

This work describes an eigenstrain approach to impose realistic residual stress fields on 3-D finite element models for the lower-flange welds of the type found in large, beam-column connections. The 3-D models incorporate the full geometry of a pull-plate specimen designed to reduce the cost of testing full connections while retaining essential features of the fracture prone, weld region. The 3-D analyses examine pull-plate configurations with a variety of geometric parameters for both through-width and semi-elliptical cracks in the weld root pass. The numerical results include tables of values for the non-dimensional “geometry” factors (Y) needed to compute stress intensity factors. The residual stress fields generated by the proposed eigenstrain functions closely match those computed using 2-D, thermo-mechanical simulation of the welding process. Stress intensity factors, obtained from corresponding J-integral computations, show clearly the significant fracture toughness demand from residual stresses prior to application of the structural loads. An alternative design for a grooved backup bar shows considerable promise to reduce fracture toughness demands by re-positioning the weld root pass below the beam flange and thus outside the primary load path. Analyses here indicate approximately a 65% reduction in KI-values for tension loading in the flange.