Investigating how to model panel zone in steel frames with end plate connections

Abstract:
In most steel frame designs the beam to column connections are assumed to be rigid or pinned but in many steel frames we have beam to column connections with semi-rigid behavior. The structures with semi-rigid connections include systems with the connections in joints which are not completely rigid, but allow, usually, some relative movements in directions of generalized displacements.
Early experimental studies showed the importance of panel shear deformations for stable energy dissipation under cyclic loading. Modeling of the panel is very important for the avoidance of local failure of columns under ultimate limit state.
A substantial effort has been made in recent years to characterize the behavior of semi rigid connections. Recent studies and modern codes, in especially EC3 and EC4, include methods and formulas to resistance and stiffness of panel zone. EC3 proposes a mechanical model for the semi-rigid joint in which each component is modeled by an equivalent linear spring.In these model we have some components that show with springs. These springs are assembled to form a single bilinear (elastic–plastic) rotational spring that models the connection, and is attached at the intersection between beam and column for the global analysis.
Both the stiffness and strength of the springs in EC3 and EC4 depend on β factor that definition of this parameter 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. So E.Bayo proposed a new component-based method (or cruciform element method) to model internal and external semi-rigid connections that revived and modified EC methods. So a cruciform element (a four-node element) is proposed to avoid β factor, and the inherent initial guessing and iterative process that it requires, and includes the finite size and deformation modes of the joint.
One of main problems that structural engineer deal with is considering End Length Offset in conventional softwares. Extended end plate connection is one of beam-column semi rigid connection that we want to evaluate this behavios by using cruciform connection model and other panel zone models.
In this paper three 2 dimensional frames with extended end plate connections are modeld in MATLAB using Cruciform element method and these result are compared with SAP2000 results in eight cases that in four cases panel zone are modeld and four cases are without panel zone modeling. In which of this End Length Offset considering are once just for beams and the other for beams and columns (in two case of Rigid Zone Factor : 0.5 and 1). The results show that modeling panel zones according to EC method and considering Rigid Zone Factor equal to 1 in columns and beams are best assumption to analysis of 2D frames with extend end plate connections, but if we don’t model panel zones, we must considering Rigid Zone Factor equal to 0.5 in columns and beams to give nearby actual results.

Keywords: semi rigid connections, extended end plate, Rigid Zone Factor, End Length Offset