Effects of Moment-to-Shear Ratio on Combined Cyclic Load-Displacement Behavior of Shallow Foundations from Centrifuge Experiments
Publication: Journal of Geotechnical and Geoenvironmental Engineering
Volume 135, Issue 8
Abstract
Current design guidelines for shallow foundations supporting building and bridge structures discourage footing rocking or sliding during seismic loading. Recent research indicates that footing rocking has the potential to reduce ductility demands on structures by dissipating earthquake energy at the footing-soil interface. Concerns over cyclic and permanent displacements of the foundation during rocking and sliding along with the dependence of foundation capacity on uncertain soil properties hinder the use of footing rocking in practice. This paper presents the findings of a series of centrifuge experiments conducted on shear wall-footing structures supported by dry dense to medium dense sand foundations that are subjected to lateral cyclic loading. Two key parameters, static vertical factor of safety , and the applied normalized moment-to-shear ratio at the footing-soil interface, along with other parameters, were varied systematically and the effects of these parameters on footing-soil system behavior are presented. As expected, the ratio of moment to the horizontal load affects the relative magnitude of rotational and sliding displacement of the footing. Results also show that, for a particular , footings with a large moment to shear ratio dissipate considerably more energy through rocking and suffer less permanent settlement than footings with a low moment to shear ratio. The ratio of actual footing area to the area required to support the vertical and shear loads , called the critical contact area ratio , is used to correlate results from tests with different moment to shear ratio. It is found that footings with similar display similar relationships between cyclic moment-rotation and cumulative settlement, irrespective of the moment-to-shear ratio. It is suggested that shallow foundations with a sufficiently large suffer small permanent settlements and have a well defined moment capacity; hence they may be used as effective energy dissipation devices that limit loads transmitted to the superstructure.
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Acknowledgments
This research work was supported by the Pacific Earthquake Engineering Research (PEER) Centers Program of the National Science Foundation (NSF) under Award No. NSFEEC-9701568 and PEER Project No. NSF2262001. Any opinions, findings and conclusions or recommendations expressed in this paper are those of the writers and do not necessarily reflect those of the NSF. This work could not have been accomplished without the extensive assistance of Chad Justice, Tom Coker, and Tom Kohnke, and the entire staff of the UC Davis Center for Geotechnical Modeling. The writers would like to acknowledge the suggestions and contributions of Geoff Martin, Tara Hutchinson, Jonathan Stewart, Ross Boulanger, Boris Jeremic, Dan Wilson, Key Rosebrook, Justin Phalen, Jeremy Thomas, and Jose Ugalde.
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Information & Authors
Information
Published In
Journal of Geotechnical and Geoenvironmental Engineering
Volume 135 • Issue 8 • August 2009
Pages: 1044 - 1055
Copyright
© 2009 ASCE.
History
Received: Jan 3, 2008
Accepted: Dec 6, 2008
Published online: Feb 23, 2009
Published in print: Aug 2009
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