Residual stresses must be taken into account when evaluating the stability of a steel bridge girder. Residual stresses are unavoidable, as manufacturing processes for steel plates introduce thermal residual stresses in the material. For welded built-up sections, such as those commonly used in large steel plate girders, these thermal residual stresses are due to 1) cooling after rolling, 2) flame cutting of the flanges, and 3) welding between the web and the flange. Residual stresses can influence the lateral torsional buckling resistance of structural steel members and need to be considered in design. This paper experimentally investigates residual stresses due to flame cutting using the sectioning method. In this study, residual stresses are measured after flame cutting and welding 60 mm thick steel (S355N) flanges, a typical size used in the fabrication of bridge girders. Results from flame cutting confirm the findings of previous studies which reveal that residual stress distributions have a high tensile component at the flame cut edge. Procedures and testing of welding residual stresses are also presented. Residual stress measurements from this study could be used to develop a longitudinal and through-thickness residual stress model for thick flame-cut plates and welded plates used in bridge I-girder construction. Such a model could serve as an initial state in non-linear finite element analyses to predict the residual stress influence on the LTB of steel bridge girders.