A metal construction with welded joints often fails under repeated loads by fatigue. Fatigue cracks at welded joints occur because real stress-strain behavior of welded joints is not taken into consideration by standard design. The article is devoted to the stress behavior determination of welded joints in railway girders under external loads and residual stresses. Design deficiencies and technological features of welded girders were identified. These features may increase stresses at welded joints and decrease fatigue life. As a result of studying the existing methods for determining stresses in welded joints, authors used a method, that takes into account the residual welding stresses and design features of welded girder. In this study, the stresses were determined in a cracking area of a girder with the help of finite element modeling. It was shown the correspondence of the stresses in the finite element model and the real girder, tested under the moving load. Retrofitting of stiffeners in welded girders with fatigue cracks was carried out using corner plate connected tightly stiffener and beam flange. Strain measurements under the moving load before and after the retrofitting near cut ribs were taken. The dependence of the stresses at the beam webs was demonstrated near the upper welded ends of stiffeners on the stiffness of rib connections to beam flanges. These findings can be useful at the fatigue life design of the welded elements at building constructions.