Seismic Panel Zone Design Effect on Elastic Story Drift in Steel Frames

A substantial change in seismic design requirements for column panel zones (PZs) in steel moment-resisting frames (MRFs) for buildings was implemented recently in several codes for building construction. Previously, it was implied that PZs had to develop the full flexural plastic strength of the beams framing a joint without yielding. In the newer seismic steel codes the concept of allowing panel zones to yield prior to or simultaneously with beams has been adopted. This change is based on increasing evidence that PZs can safely sustain cyclic strain reversals and thereby provide some of the needed ductility for a frame. After discussing the basis and the nature of these new provisions, their effect on elastic story drift is illustrated in two examples. A simple approximate method is developed for determining elastic story drift due to PZ deformations. This method can be conveniently used with conventional computer frame-analysis programs without introducing additional degrees of freedom into the system.