Inelastic behavior and design of steel panel zones

The effect of panel zone yielding on the potential for fracture of welded-bolted steel connections is investigated, with the objective of gaining a better understanding of the inelastic behavior of the panel zone region and of critically assessing current seismic provisions for steel panel zone design. The research objectives are addressed through detailed, three-dimensional, nonlinear, finite-element analyses of connection subassemblies. The characteristics of the analysis configurations used in this research are derived from the geometry of a typical pre-Northridge fully restrained beam-colum steel connection. Important geometric parameters are varied over the practical range of interest in order to evaluate their effect on connection behavior. To assess the influence of the parameters of interest, a number of different stress, strain, and combined stress/strain indices are employed. These quantities are sampled at connection plastic rotations ranging from 0.0025 to 0.03 rad. Results from the finite-element analyses show that, although beam plastic rotation demands are smaller in connections with weak panel zones, the stress conditions at the beam-column interface are more critical at higher connection plastic rotations. Therefore, although the panel zone can effectively contribute to overall connection ductility, a weak panel zone can also lead to a greater potential for brittle and/or ductile fracture at higher connection plastic rotations. The finite-element analyses also suggest that current design provisions may not be appropriate when applied to panel zones in exterior joints.