foundation flexibility and damping from forced vibration testing of field structure lisa m. star...
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Foundation Flexibility and Damping from Forced Vibration Testing of Field Structure
Lisa M. StarMichael J. GivensGeorge MylonakisJonathan P. Stewart7-11-2012
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What is Soil-Structure Interaction (SSI)?
SSI is the collection of effects that soil behavior has on a structure and structural behavior has on the soil
Two Important SSI effects:Altered Ground Motions (Kinematic
Interaction Effects)Foundation Stiffness and Damping
(Inertial Interaction Effects)
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What is SSI? – Inertial Effects
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What is SSI? – Inertial Effects
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What is SSI? – Inertial Effects
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What is SSI? – Inertial Effects
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What is SSI? – Inertial Effects
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The SSI Problem Small
Stiff/Strong Foundation
Small displacements protect frame from damage
High forces cause wall damage
Large
Flexible/Weak Foundation
Large displacements cause frame damage
Foundation yield and rocking protects wall
Small
Stiff/Strong Foundation
Small displacements protect frame from damage
High forces cause wall damage
Large
Flexible/Weak Foundation
Large displacements cause frame damage
Foundation yield and rocking protects wall
Foundation flexibility changes structure behavior and the failure mode
Conservative or unconservative?
from ATC 40
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UCLA SSI Test Structure2.13 m x 4.26
m foundation2.13 m tall
HSS 12”x12”x1/2” steel columns
0.25 m thick reinforced concrete upper deck
Removable bracing
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Field Test Sites - WLA
NEES@UCSB Wildlife Refuge Liquefaction Field Site
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Field Test Sites - GVDANEES@UCSB Garner Valley Field Site
Test structure-soil-structure interaction
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Foundation Stiffness and Damping
Adapted from Tileylioglu et al. (2011)
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Existing SSI ModelsFunction of G, , and foundation
dimensions
Baseline Knowledge Report, Stewart et al. 2010
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Foundation Impedance - Theory
Translation and Rotation:
2 2sh s ff f s ff ff
xf
F m u h u m u hk
u
*
2 2 2sh s ff f s ff ff ff f
yyf
hF m h u h u I m h u hk
*
*j
jj
Imaginary(k )( * k ) 2
j jk real k *( )
Adapted from Tileylioglu et al. (2011)
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Foundation Impedances
Longitudinal
Transverse
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WL - Foundation Impedance - Shaking in Longitudinal Direction
Compared to Pais and Kausel (1988)Model 1: Vs=108 m/sModel 2: Vs=98 m/s
Max Strain: 0.00045% G/Gmax: >0.985
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WL - Foundation Impedance - Shaking in Transverse Direction
Compared to Pais and Kausel (1988)
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GVDA - Foundation Impedance - Shaking in Transverse Direction
Compared to Pais and Kausel (1988)Model 3: Vs=207 m/s
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Large Amplitude Shaking in Longitudinal Direction
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Large Amplitude - Shaking in Longitudinal Direction
Compared to Pais and Kausel (1988)
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Large Amplitude - Shaking in Longitudinal Direction
Compared to Pais and Kausel (1988)
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Compared to Pais and Kausel (1988)
Large Amplitude - Shaking in Transverse Direction
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Summary and Conclusionso There were a very small number of field
scale tests available. The experiment provides high quality data that is freely available to other researchers.
o Soil-Foundation Impedances:oWe find that kx weakly decreases with f and kyy
strongly decreases with foWe find that is strongly dependant on f
o Nonlinear Soil-Foundation Impedance:oFoundation stiffness decreases as strain
increasesoDamping increases as strain increases
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AcknowledgementsNEES@UCLANEES@UCSBNEES@UtexasSalih Tileylioglu, Ph.D.NSF CMMI 0618804, PI Jack
MoehleNSF CMMI 0927178 (NEES
Operations, PI Julio Ramirez)
Thank You