Date on Master's Thesis/Doctoral Dissertation

5-2009

Document Type

Doctoral Dissertation

Degree Name

Ph. D.

Department

Civil and Environmental Engineering

Committee Chair

Hagerty, Donald J.

Author's Keywords

Synthetic time histories; Central eastern U.S. attenuation; Synthetic ground motions; Synthetic earthquakes; Attenuation models; Variation in structural response

Subject

Earthquakes; Seismology--Research

Abstract

This study focuses on the variation in structural response to synthetic ground motions derived from the latest attenuation models developed for the Central Eastern United States (CEUS) and used by the USGS to develop the latest edition (2008) of the National Seismic Hazard Maps. Specifically, it compares the ductility demands induced by these synthetic earthquake records via nonlinear time history analysis conducted on single degree of freedom systems of various natural frequencies. The synthetic ground motions generated for the study are compatible with target response spectra from these eight CEUS attenuation models and representative of various magnitude and distance combinations. The goal was to investigate the amount of variation in the structural response due to ground motions described by these differing attenuation models. In particular, the study determines whether these discrepancies are too great to permit this approach for developing synthetic records to be used as input in time history analysis for the seismic design of structures in the CEUS. Results from the study do indeed show that the variation is great with many scenarios indicating conflicting predictions of ductility demand. In many cases there are contradictory results indicating whether damage would or would not occur (i.e., if the structure would reach yielding or not). Prime examples include the earthquake scenarios of magnitude 5.5 at 10 km, 6.5 at 25 km, and 7.5 at 50 km. The synthetic time histories compatible with nearly half of the attenuation models representing these scenarios produced ductility demands that indicate significant yielding will occur in most structures while time histories compatible with the remaining attenuation models for these same scenarios indicate that no yielding will occur in any type of structure. In those cases where there is agreement that the structure will yield, there are discrepancies in the level of ductility demand that will be required. Also, a procedure is introduced which uses time history analysis to estimate the magnitude of the synthetic ground motions. This procedure is then applied to the results obtained from this study to infer the over prediction or under prediction of structural response to synthetic motions derived from the eight CEUS attenuation models.

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