When it comes to bolted connections, the most used cross-sections for columns and beams are without a doubt the I-profile family. There is sufficient research and theoretical knowledge in the literature to determine the stiffness characteristics of moment connections of this category. The moment connection analysis methodology for this family of sections is known as the Method of Components, developed by Zoetemeiier [6], and which is also adopted in EN 1993-1-8 [2]. This method provides a theoretical evaluation of the three of the most important properties of connections, namely: Strength, stiffness and ductility, and is based on a mechanical model.

On the other hand, cases are not rare when square or circular sections, welded with I- beams, are used for columns, instead of open sections. For this configuration, according to the knowledge of the authors, there is no unified analytical formulation (adopted in the form of a code/rulebook) that would describe the three most important properties of the connections. For these reasons, in design practice, it is often the case for welded connections between square columns and I-beams that the connection is modeled as a fully rigid connection.

In this paper, an approximate method for determining the rotational stiffness for this category of welded connections is proposed, using FEM software, Ideas StatiCA 21.1.

The moment at the joint from an external load, generated by this rotational stiffness, is calculated. The effect resulting from the action of this moment including the deformation of the front face of the column is also considered.

The same deformable effects are calculated when the joint is treated as fully rigid. Finally, a comparative analysis at the level of a frame with a semi-rigid connection and a frame with an ideally rigid connection is conducted. The results and effects of these assumptions are interpreted.