Foundation Flexibility and Damping from Forced Vibration Testing of Field Structure
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Transcript of Foundation Flexibility and Damping from Forced Vibration Testing of Field Structure
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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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 - GVDANEES@UCSB Garner Valley Field Site
Test structure-soil-structure interaction
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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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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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GVDA - Foundation Impedance - Shaking in Transverse Direction
Compared to Pais and Kausel (1988)Model 3: Vs=207 m/s
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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)