[en] The paper summarizes the investigations on shear resistance of I-girders longitudinally stiffened by closed trapezoidal stiffeners, performed in the frame of a European RFCS project (RFS-CR-03018) designated as “ComBri” (Competitive Steel and Composite Bridges by improved Steel Plated Structures), with configurations typical of what may be expected in the design of modern steel
bridges. It first reports on four full-scale tests performed at RWTH Aachen, on stiffened panels with strong closed stiffeners where the deformations have been measured with photogrammetric devices. As expected, failure in the subpanels has been governing. A devoted FEA shell model is then described and validated towards these results and other experimental sources. The numerical simulations demonstrate a very good agreement with the test-results. Parametric studies performed with a sophisticated numerical tool help pointing out several aspects where the recommendations of EN 1993-1-5  on stiffened panels in bending and shear may be improved.