Semi-rigid portal frame finite element modelling including the axial versus bending moment interaction in the structural joints

Beam-to-column joints are often subjected to bending and axial forces. Although, the axial force coming from the beam is usually low, it can reach significant values that may significantly reduce the joint flexural capacity. Typical examples of these structures are vierendeel girder systems with semirigid joints. These systems, widely used in building construction, can take advantage of the member flexural and compression resistances eliminating/avoiding the need for extra diagonal members. The main aim of this paper is to demonstrate by means of four vierendeel beam examples the influence of the moment versus axial force interaction over the overall portal frame response. This paper also fully describes the proposed finite element formulation to consider the force/moment interaction by directly modifying the semi-rigid joint stiffness and ultimate bending capacity. The proposed procedure was also calibrated against test and analytical data to accurately model the semi-rigid joint response.