Mechanical model for the analysis of steel frames with semi rigid joints

The rigidity of joints is known to affect the structural behaviour of steel frames. Accurate determination of such rigidity may require the use of laborious numerical modeling (such as Finite Element) of the joint. The main objective of this paper is to present a mechanical model in order to take into account the influence of the joints on the behaviour of steel frames. This mechanical model is based on the analogy of three springs, and a non deformable element of nodes describing relative displacements and rotations between the nodes and the elements of the structure. For this model, a stiffness matrix and a nodal load vector of a beam element in bending are obtained. Examples are provided to illustrate the simplicity and efficiency of the method.