<p>Curved steel panels are widely used in structures such as ships, aircrafts and bridges. During the last decades, plates with an out-of-plane curvature in the cross-section of the bridge are being used, partly to increase the aesthetics. The elastic buckling behaviour of curved plates is not covered by standards of codes for bridge design, resulting in rather conservative solutions. In the current research, there is investigated how curved steel panels used as a web panel in a closed box girder interacts with shear and bending stresses. Therefore, a double symmetric box is numerical simulated in a three point bending test. The first mode shape found by a LBA is used as an initial geometric imperfection, in order to trigger buckling of the webs. It is proven that when increasing the curvature while keeping a similar slenderness ratio, the buckling mode of a plate can change from elastic to inelastic and even plastic buckling. This behaviour is found back in the webs of the closed steel sections. Slender curved plates have an equal load-deflection path as their straight variant. Inelastic and plastic buckling of the webs results yield zones in the web, eventually combined with geometric deformations. The girders with curved webs are sensitive to imperfections in such a way that slender curved panels have a large reduction in initial stiffness with increasing amplitude. On the other hand, moderate or thick curved panels remain their initial stiffness but have a reduction in their ultimate load capacity.</p>