Collapse Risk of Steel Special Moment Frames per FEMA P695
Matthew S. Speicher, Jazalyn D. Dukes, Kevin K. Wong
The American Society of Civil Engineers (ASCE) performance-based seismic design standard, ASCE 41, contains methodologies used by practicing engineers to assess existing buildings and to design new buildings. In 2015, the National Institute of Standards and Technology completed a study of the relationship between the methodologies used in ASCE 41 and those used in traditional prescriptive design standards; e.g., ASCE 7 and American Institute of Steel Construction (AISC) specification 341. The study showed inconsistencies between the two approaches, with some potentially unwarranted conservatism in ASCE 41. To further investigate the relationship between performance-based and prescriptive methodologies, this report presents the results of a collapse assessment of six steel special moment frames. The goal is to verify that the buildings have a no greater than 10 % probability of collapse given a risk-targeted maximum considered earthquake, which is the design intent of ASCE 7. The influence of modeling assumptions, such as using default ASCE 41 backbone curves versus experimentally-derived backbone curves, is discussed. Furthermore, the impacts of other choices in the analyses such as damping, composite slab action, and P-delta column modeling are explored. The results are used to scrutinize the performance indicated by the ASCE 41 assessment. In general, the performance indicated by the ASCE 41 assessment is shown to be conservative relative to the collapse performance indicated by using the methodologies within the Federal Emergency Management Agency (FEMA) publication P695. Based on the findings in this report, the authors recommend that the approach used in ASCE 41 assessments be reviewed to reduce overly-conservative results.