Conditional Mean Spectrum: Tool for Ground-Motion Selection
Publication: Journal of Structural Engineering
Volume 137, Issue 3
Abstract
A common goal of dynamic structural analysis is to predict the response of a structure subjected to ground motions having a specified spectral acceleration at a given period. This is important, for example, when coupling ground-motion hazard curves from probabilistic seismic hazard analysis (PSHA) with results from dynamic structural analysis. The prediction is often obtained by selecting ground motions that match a target response spectrum and using those ground motions as input to dynamic analysis. The commonly used uniform hazard spectrum (UHS) is shown here to be an unsuitable target for this purpose, as it conservatively implies that large-amplitude spectral values will occur at all periods within a single ground motion. An alternative, termed a conditional mean spectrum (CMS), is presented here. The CMS provides the expected (i.e., mean) response spectrum, conditioned on occurrence of a target spectral acceleration value at the period of interest. It is argued that this is the appropriate target response spectrum for the goal described above and is thus a useful tool for selecting ground motions as input to dynamic analysis. The CMS is described, its advantages relative to the UHS are explained, and practical guidelines for use in ground-motion selection are presented. Recent work illustrating the impact of this change in target spectrum on resulting structural response is briefly summarized.
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Acknowledgments
Thanks to Curt Haselton for identifying the example Riverside site used to illustrate the CMS calculations. Thanks to Eduardo Miranda and Curt Haselton for insightful comments that improved the quality of this paper. Thanks to the many members of the Pacific Earthquake Engineering Research Center and other colleagues who have raised intelligent questions and comments that motivated this paper. The writing of this paper was supported by the U.S. Geological Survey, under award number USGS08HQAGO115.
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Information & Authors
Information
Published In
Journal of Structural Engineering
Volume 137 • Issue 3 • March 2011
Pages: 322 - 331
Copyright
© 2011 American Society of Civil Engineers.
History
Received: Jul 23, 2008
Accepted: Feb 21, 2010
Published online: Feb 26, 2010
Published in print: Mar 1, 2011
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