This thesis deals with the behavior of plated girders, composed of compact flanges and slender webs, which are usually stiffened with longitudinal and transversal stiffeners. The main goal was to analyze transversal stiffeners, which have to provide a rigid support for the base plate. The first part of the thesis overviews the design rules for plate girders, which are included in the standard EN 1993-1-5. Numerical results from the finite element analysis are shown in the second part. Numerical simulations were performed to confirm or disprove the existing equation for the evaluation of stiffness. For longitudinally stiffened and unstiffened plates in compression the expressions from standard EN-1993-1-5 were used. It was shown, that the deflection criterion is not satisfied in all cases. A new design rule, which ensure the
proper stiffness of the transversal stiffeners, was suggested. For longitudinally stiffened plates in shear solutions developed for unstiffened plates in shear were used. These equations yield a good approximation.