Ductile behaviour of steel structures depends on mechanical properties of steel materials and steel structures are designed so that plastic deformations occur on beams particularly in beam-to-column connections under cyclic loads. Details on moment-resisting beam-to-column connections are given only for I-profiles in the Turkish Earthquake Code (TEC, 2007) and no details about beam-to-column connections consisting of box or circular hollow sections is available in the relevant code. That is why there is an uncertainty in the definition of the ductility level of the structural system consisting of box and circular hollow sections. The purpose of this study is to prevent local buckling effects to occur under bending in welded connections of circular hollow sections. In this context, the contribution of cover stiffness plates of different sizes to the behaviour and the effect of plate sizes on the capacity were investigated numerically and experimentally. Results obtained from experimental analysis are given comparatively supported by ANSYS program. (C) 2016 Elsevier Ltd. All rights reserved.