An effective component-based method to model semi-rigid connections for the global analysis of steel and composite structures

A substantial effort has been made in recent years to characterise the behaviour of semi-rigid connections. Recent studies and modern codes, in particular EC3 and EC4, not only include methods and formulas to define both their resistance and stiffness, but also emphasise the importance of a correct modelling of the panel zone under shear and compressive forces. The traditional approach of modelling the connection by means of springs attached to the end of the beams at both sides of the joint implies the use of an interaction parameter, called the ββ factor in EC3 and EC4, that depends on the moments and shear forces acting on the panel zone. Both the stiffness and strength of the springs depend on this parameter. However, the definition of the ββ factor implies an approximation of the internal forces at the joint, and therefore its use requires an iterative process at the time of performing the global analysis of the structure.This paper deals with a new component-based approach to model internal and external semi-rigid connections for the global analysis of steel and composite frames. The method is based on a finite dimensioned elastic–plastic four-node joint element that takes into consideration, in a congruent and complete way, its deformation characteristics (components in Eurocode  ), including those of the panel zone, and all the internal forces that concur at the joint. As a consequence, this new element avoids the use of the ββ factor and the inherent iterative process that it requires. In addition, the eccentricities of the internal forces coming from the beams and columns that meet at the joint are also considered. Examples are solved that validate the new approach and demonstrate its efficiency. In addition, it is shown that when using the ββ factor the iterative process may not converge for elastic–plastic analysis. Moreover, the limitations imposed on ββ by EC3 and EC4 may lead to substantial errors in the internal forces and moments.