AbstractRecent studies investigating lateral torsional buckling suggest that North American steel design provisions may overestimate the bending resistance of welded girders that buckle laterally in the inelastic range. Furthermore, these provisions do not distinguish between rolled and welded members, but welded girders are widely suspected of possessing unfavorable residual stress distributions that may cause them to be more susceptible to lateral torsional buckling than their rolled counterparts. However, lack of sufficient supporting experimental test data may render existing analytically based assessments of the design equations inadequate. To address the paucity of physical testing, an experimental program was developed to determine the lateral torsional buckling resistance of full-scale I-shaped welded three-plate steel girders fabricated with current shop processes. This paper describes the development of the test program and a unique girder-stability test bed. Test results for seven girders, including measured initial geometric imperfections, load–displacement responses, and moment capacities, are then presented. A finite-element model of the test specimens, validated against the test data, is finally used to investigate the adequacy of the beam design provisions specified in the Canadian and US steel design standards. The results confirm that the current design equations can accurately predict the moment resistance of compact welded steel girders that fail in either the elastic or inelastic lateral torsional buckling mode.