Enhancement of panel zone (PZ) contribution to the ductility of post-northridge welded connections

Abstract

In welded connections, beam-end and panel zone (PZ) are the only sources to dissipate the seismic energy released during an earthquake. Energy dissipation at the PZ is accompanied by the inelastic shear deformation at PZ. In seismic codes, in order to reach to the maximum plastic rotation capacity of connection, the inelastic shear deformation is controlled by a balance condition with respect to the initiation of flexural yielding of beam flanges. Hence, connections are classified as weak, balance and strong panel zone connections. In the case of weak PZ, balance condition can be obtained by increasing the thickness of the column's PZ or using doubler plates. This study was aimed to obtain balance condition for connections with strong panel zones. Therefore, a circular hole was opened at the column web in the PZ region. A pre-tested post-Northridge connection which has a strong panel zone was modeled using finite element analysis. Then the effects of different diameter holes on the behavior of this type of connection were investigated. Further, a function was proposed to determine the PZ shear yielding resistance in the presence of a circular hole in PZ. Analytical results showed that the column with a PZ hole ratio (hole diameter divided by PZ height) of 18% associated with a PZ hole of 50 mm, radius and balance ratio of 0.81 appears to be the best configuration for increasing the PZ plastic rotation from 0.05% to 0.2%. This increase in plastic rotation capacity of PZ would only increase the total plastic rotation capacity of the connection by 10%. This indicates that a connection of this type also require modifications at the beam-end to increase both the total plastic rotation capacity and contribution of panel zone to the inelastic behavior of connection.