Seismic performance of PR frames in areas of infrequent seismicity

The Wind Moment Frame (WMF) method has been and continues to be widely utilized in the Central and Eastern U.S., resulting in a very large population of structures having been designed without a rigorous analysis with respect to lateral loads. The WMF method assumes that the beams can be designed as pinned for gravity loads and that the structure can be analyzed as rigid for lateral loads. The primary objective of this research is to determine whether moment-resisting frames designed by the WMF method are adequate to handle the increased demand on lateral resistance made by modern seismic codes, and to evaluate and compare the seismic performance of existing and new moment-resisting steel frames with partial strength and partially restrained (PS/PR) connections. Prototype frames---labeled the Older, Intermediate, and Modern frames---were designed and analyzed using appropriate seismic design codes and a modified version of the DRAIN-2DX program. Nonlinear analyses utilizing synthetic ground motions for the Mid-America region were performed. The seismic performance of these PS/PR frames was evaluated in accordance with FEMA 273/356 criteria. In addition, probabilistic verification of their seismic performance, considering the effects of the uncertainties and randomness, were conducted. The results show that all PR frames designed in this study satisfied the selected performance objective with a 99% confidence level for the global performance limit state. Thus, the seismic performance of the PR frames in the Mid-America region will be satisfactory even under large ground motions.