Dynamic Stiffness and Damping of a Shallow Foundation from Forced Vibration of a Field Test Structure
Publication: Journal of Geotechnical and Geoenvironmental Engineering
Volume 137, Issue 4
Abstract
Foundation impedance ordinates are identified from forced vibration tests conducted on a large-scale model test structure in Garner Valley, California. The structure is a steel moment frame with removable cross-bracing, a reinforced concrete roof, and a nonembedded square slab resting on Holocene silty sands. Low-amplitude vibration is applied across the frequency range of 5–15 Hz with a uniaxial shaker mounted on the roof slab. We describe procedures for calculating frequency-dependent foundation stiffness and damping for horizontal translational and rotational vibration modes. We apply the procedures to test data obtained with the structure in its braced and unbraced configurations. Experimental stiffness ordinates exhibit negligible frequency dependence in translation but significant reductions with frequency in rotation. Damping increases strongly with frequency, is stronger in translation than in rocking, and demonstrates contributions from both radiation and hysteretic sources. The impedance ordinates are generally consistent with numerical models for a surface foundation on a half-space, providing that soil moduli are modestly increased from free-field values to account for structural weight, and hysteretic soil damping is considered.
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Acknowledgments
This work was partially supported by the Center for Embedded Network Sensing (CENS) at UCLA and also by fellowship funding from UCLA. This research made use of the testing facilities of NEES and NEES at UCSB. NEES Site PI Dr. Jamison Steidl is thanked for his assistance with site operation and data collection, as are NEES at UCSB staff Hank Ratzesberger and Paul Hegarty. We thank Timothy Ancheta, Dennis Hiltunen, George Mylonakis, and Dimitris Pitilakis for helpful discussions over the course of this research. We thank Lisa Star for independently checking the test results. Two anonymous reviewers are thanked for their helpful comments. We thank Dr. Atsushi Mikami for performing the SASSI runs for the test structure.
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Information & Authors
Information
Published In
Journal of Geotechnical and Geoenvironmental Engineering
Volume 137 • Issue 4 • April 2011
Pages: 344 - 353
Copyright
© 2011 American Society of Civil Engineers.
History
Received: Oct 2, 2009
Published online: Aug 18, 2010
Accepted: Oct 7, 2010
Published in print: Apr 1, 2011
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