Flange thickness transitions in welded girders - design recommendation for the complex additional local stress state

Additional local stresses are present at flange thickness transitions of welded girders, caused by the necessary equalization of the different total flange forces, as well as by the - often present - eccentricity between the smaller and larger flange plates. On one hand, these additional stresses are present in the flange plates themselves, especially in the case of eccentric configurations. In this case, local bending in longitudinal direction also causes secondary bending in transversal direction of the flange plates, leading to high normal stresses in vertical direction in the attached web plate. On the other hand, the equalization of the flange forces leads to high local shear stresses in the web and fillet welds - between web and flange plates. In the study presented in this paper, extensive numerical calculations (using the finite element method), within the practically relevant geometric parameter range, were carried out in order to quantify the mentioned stress effects. These results were used as the basis for the development of a design recommendation for use in practice. After a brief discussion of the general load-carrying behaviour at thickness transitions, this paper explains the use and background of the recommendation.