Project 07—Reassessment of Seismic Design Procedures

This paper describes work by the Seismic Design Procedures Reassessment Group (SDPRG) of Project 07 to update the seismic design maps and procedures of the 2009 NEHRP Recommended Provisions. Project 07 was a joint effort of the Building Seismic Safety Council (BSSC), the Federal Emergency Management Agency (FEMA and the United States Geological Survey (USGS). As part of Project 07, the SDPRG worked with the USGS to incorporate new (2008) hazard data and improved earthquake ground motion criteria in the 2009 Provisions. Work by SDPRG resulted in three significant changes to design ground motions: (1) "probabilistic" ground motions are now defined in terms of uniform risk, rather than uniform hazard, (2) ground motion intensity is now defined in terms of the maximum spectral response in the horizontal plane, and (3) "deterministic" ground motions are now defined by 84th percentile spectral response (rather than 1.5 times median spectral response).