The present paper aims to analyze the mechanical behavior of bolted steel beam-to-column joints with extended endplate and different stiffeners subjected to bending moment. These connections are a widely used in steel structures and are generally considered as semi-rigid. This study is based on a finite element model that takes into account the geometrical, material and contact non-linearities between the basic components in the connection. The numerical model is validated on the basis of the experimental results available in the literature. Endplate stiffening provides additional rigidity and strength that can be quantified. In addition to the global behavior of the connections, the numerical model is used to analyze in detail the evolution of the bolt forces and the prying forces that can arise between the endplate and the column flange.