Seismic Performance Comparison of Ordinary Concentrically Braced Frames in the Western and Central United States

Ordinary concentrically braced frames (OCBFs) are intended to be moderately ductile steel seismic-force-resisting systems and are permitted in low-rise buildings in regions with high seismic hazards. There has been relatively little research to quantify the seismic performance of OCBFs, with most of the previous work emphasizing the role of reserve capacity on performance. To improve the understanding of seismic performance and validate current design provisions, a series of nonlinear response-history analyses were conducted. Two, three-story OCBF study buildings were designed in accordance with ASCE/SEI 7-16 for sites in Seattle, WA and Memphis, TN; the sites have relatively high seismic hazards (Seismic Design Category D) but different tectonic settings. Well-established nonlinear modeling approaches for concentrically braced frames were utilized to analyze suites of ground motions scaled to hazard levels corresponding to 475- and 2,475-year return periods. The results of these new analyses and previous special concentrically braced frame (SCBF) studies were employed to compare OCBF seismic performance with different building locations (Seattle or Memphis), braced-frame classifications (OCBF or SCBF), and braced-frame configurations (chevron or paired single diagonal). The SCBFs do meet collapse performance standards, but the OCBFs analyzed in the present work do not meet collapse performance standards due to early onset of brace and gusset-plate connection fractures that led to large inter-story drifts. The collapse probabilities were higher for the chevron configuration OCBFs, as well as for the OCBFs designed for the Memphis site. These results suggest a need for future OCBF research and modifications to current provisions to ensure OCBFs achieve safe but economical designs