Seismic Performance of PR Frames in Mid-America Earthquake Region

The wind moment frame (WMF) method has been and continues to be widely utilized in the central and eastern United States, resulting in a very large population of structures having been designed without a rigorous analysis with respect to lateral loads. The primary objectives of this paper are 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 partially restrained (PR) connections. Three prototype frames were designed and analyzed utilizing synthetic ground motions for the Mid-America region. The seismic performance of these PR frames was evaluated in accordance with FEMA 273/356 criteria. In addition, studies were conducted on the confidence level of the performance results to take into account the uncertainties and randomness inevitably involved. This analysis and evaluation found that all PR frames designed in this study satisfied the selected performance objective with 99% confidence level for the global performance limit. Thus, the seismic performance of the PR frames in the Mid-America region will be satisfactory even under large ground motions.